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Appendix A: Typical

This appendix contains descriptions and images of a dozen spacecraft selected from the many that are currently operating in interplanetary space or have successfully completed their missions, plus one that is now preparing for launch. Included is at least one representative of each of the eight spacecraft classifications described in Chapter 7 (see page 243). The scheme of limiting coverage of each spacecraft to a two-page spread in this appendix allows the reader to easily compare the various craft, their specifications, their missions, and their classifications, but it does not allow room to list all of a spacecraft’s activities, discoveries and questions raised; indeed entire books can and have been written on each. Complete profiles of these and other spacecraft are, how- ever, readily available at a single web site: http://nssdc.gsfc.nasa.gov/planetary. Contents:

Spacecraft Classification Page

Voyager 294 Flyby 296 Spitzer 298 Chandra Observatory 300 Orbiter 302 Cassini Orbiter 304 Messenger Orbiter 306 Atmospheric 308 310 Laboratory Rover (launch: 2009) 312 Penetrator 314 Engineering 316 294 Appendix A: Typical Spacecraft The Voyager Spacecraft

Fig. A.1. Each Voyager spacecraft measures about 8.5 meters from the end of the science boom across the spacecraft to the end of the RTG boom. The boom is 13 meters long. Courtesy NASA/JPL.

Classification: Flyby spacecraft Mission: Encounter giant outer and explore Named: For their journeys

Summary: The two similar spacecraft flew by and . continued on to encounter and . Both are on -system escape trajectories, and have penetrated the solar- termination shock. In 1998, became the distant human-made object.

Payload: Imaging science wide-angle and narrow-angle cameras, UV , IR spectrometer-radiometer, photopolarimeter, on scan platform. Low-energy charged parti- cle detector, spectrometer, detector, (4), plasma wave detector, planetary receiver, audio and video messages from en- coded on gold record.

Nation(s): USA at Launch: 800 kg Radio : S- and X-band Stabilization: 3-Axis, thrusters Propulsion: Electrical power: RTG Launch date: 1977 : -IIIE/ The Voyager Spacecraft 295

Fig. A.2. One of the Voyager spacecraft during vibration testing at JPL on 25 1977. Mission module is attached atop the injection propulsion unit (IPU) which was later jettisoned. Science boom (right) and radioisotope thermoelectric generator (RTG) boom (left) are folded down in launch configuration. The 13-meter long magnetometer boom is stowed within canister above middle left. White cylinders are RTG mass simulators; actual RTGs were installed just prior to launch. Thermal control louvers were placed differently prior to flight; the golden record of messages from Earth was placed on the bay seen near the center of the . Courtesy NASA/JPL-Caltech. 296 Appendix A: Typical Spacecraft The New Horizons Spacecraft

Fig. A.3. The New Horizons Spacecraft measures about 3 meters overall at its widest dimension. Courtesy NASA/JPL.

Classification: Flyby spacecraft Mission: Encounter and then explore Named: For its journey

Summary: New Horizons took a -assist from Jupiter in 2007 and will fly by dwarf Pluto and its Charon in 2015. It is expected to encounter one or more additional objects in the Kuiper Belt. Image courtesy Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).

Payload: Seven instruments: , a 6-centimeter aperture to feed its Mul- tispectral Visible Imaging Camera and Linear Etalon Imaging Spectral Array. Alice, an . LORRI, the Long Range Reconnaissance Imager, which consists of a 20.8-centimeter aperture telescope with a CCD imager. SWAP, the Analyzer around Pluto, which measures charged particles from the solar wind. PEPSSI, the Pluto Energetic Particle Spectrometer Investigation, which characterizes neutral atoms. SDC, the Student Dust Counter. REX, the Radio Science Experiment, which functions as a . It also records the received spectrum of the DSN’s uplink during experiments.

Nation(s): USA Mass at Launch: 478 kg Radio Link: X-band Stabilization: 3-Axis thrusters or spin Propulsion: Hydrazine Electrical power: RTG Launch date: January 19, 2006 Launch vehicle: -V/Centaur The New Horizons Spacecraft 297

Fig. A.4. Artist’s conception of the New Horizons spacecraft encountering a Kuiper Belt object. The , about 45 AU away, appears in the glow of the zodiacal dust. The many objects in the Kuiper Belt, normally not visible because they are so far apart, are shown here to give an impression of the large number of icy worlds beyond Neptune. Image cour- tesy Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI). 298 Appendix A: Typical Spacecraft The Spitzer

Fig. A.5. The measures about 5 meters in length overall. Tele- scope shell cut away to reveal cooled telescope assembly within. Adapted from images courtesy NASA/JPL-Caltech.

Classification: Observatory spacecraft Mission: Observe objects deep in the universe, , and Named: In honor of American astrophysicist , Jr. (1914–1997). Originally Space Telescope Facility (SIRTF), renamed after launch.

Summary: One of the four NASA Great including Hubble, Compton, and Chandra. the Sun in an Earth-trailing at about 1 AU, keeping its facing the Sun to shield the entire spacecraft from infrared radiation. The telescope has an 85-centimeter diameter primary mirror cooled to 5.5 K by boiling off liquid from an onboard 50.4- supply. This cools the telescope’s optics via a vapor-cooled shell and also cools the instruments near the plane. Cooling permits Spitzer to observe deep into the infrared region of the spectrum without interference from warm optics. Upon exaustion of coolant in 2009, sunshade keeps telescope at 34 K (instruments 4 K cooler due to additional passive cooling).

Payload: Spitzer’s Infrared Array Camera operates simultaneously at 3.6 μm, 4.5 μmm, 5.8 μmm and 8 μmm . The Infrared Spectrograph observes from 5.3 μmto 37 μm. The Multiband Imaging Photometer works from 24 μm to 160 μm.

Nation(s): USA Mass at Launch: 950 kg Radio Link: X-band Stabilization: 3-Axis reaction wheels Propulsion: Cold Electrical power: Solar Launch date: , 2003 Launch vehicle: -II The Spitzer Space Telescope 299

Fig. A.6. Spitzer releases its aperture dust cover in this artist’s conception. Thermal blanketing on the warm spacecraft bus is not shown. The vapor-cooled shell which sur- rounds the whole telescope has an upper surface (facing the solar panel shield) of polished metal to reject heat. The lower half of the shell is painted black to best radiate heat (which can be better seen by searching online for image ID: sirtf0410 04). The parabolic high-gain antenna is affixed to the lower left end of the spacecraft bus and cannot be seen in this view. Image courtesy NASA/JPL-Caltech. 300 Appendix A: Typical Spacecraft The Chandra X-Ray Observatory

Fig. A.7. The Chandra spacecraft measures 13.8 meters in length. Its solar arrays span a width of 19.5 meters end-to-end across the spacecraft. Courtesy NASA/CXC/.

Classification: Observatory spacecraft Mission: Capture images and spectra of high-energy events in the universe Named: In honor of Indian-American astrophysicist Subrahmanyan Chandrasekhar (1910–1995) (Not to be confused with lunar orbiter Chandra-yaan)

Summary: One of the four NASA Great Observatories (including Hubble, Spitzer, and Compton). Its mirrors’ high angular resolution give Chandra one hundred times greater sensitivity than previous x-ray . Known as the Advanced X-ray Facility (AXAF) prior to launch. Operates in a 64.2-hour, 10,000-kilometer x 140,000- kilometer Earth orbit above the x-ray absorbing . Data from Chandra has been greatly advancing the field of x-ray astronomy since August 1999.

Payload: The Advanced CCD Imaging Spectrometer (0.2–10 keV) and the High Reso- lution Camera (0.1–10 keV), both within the Science Instrument Module. Either of two spectroscopic gratings may be swung into the optical path downstream of the mirrors: the High Energy Transmission Grating (0.4–10 keV) or the Low Energy Transmission Grating (0.09–3 keV).

Nation(s): USA Mass at Launch: 4,620 kg Radio Link: S-band Stabilization: 3-Axis, reaction wheels Propulsion: Hydrazine Electrical power: Photovoltaic Launch date: July 23, 1999 Launch vehicle: STS Columbia/IUS The Chandra X-Ray Observatory 301

Fig. A.8. Artist’s conception of the Chandra spacecraft. Concentric rings below the open aperture cover are the leading-edge rims of the 1.2-meter and smaller diameter nested high-resolution modified-cylindrical mirrors of Chandra’s Wolter grazing-incidence (see page 197) 10-meter focal length telescope, which extends toward the science instrument module at right. Courtesy NASA/CXC/SAO. 302 Appendix A: Typical Spacecraft The Galileo Spacecraft

Fig. A.9. Galileo spacecraft in flight configuration. Spacecraft height is 5.3 meters. Com- ponents below the Spin Bearing Assembly are de-spun to permit pointing while upper part spins. From image courtesy NASA/JPL.

Classification: Orbiter spacecraft Mission: Explore Jupiter, its , and its Named: In honor of (1564–1642), who observed Jupiter and discovered its four largest moons in 1610

Summary: Observed , Earth, and two en route; deployed Jupiter atmo- sphere probe; orbited Jupiter 1995–2003 and observed Jupiter and Galilean at high resolution. Observed planet’s magnetosphere and its interaction with Sun, Jupiter, and its moons. Observed Shoemaker-Levy 9 fragments impacting Jupiter in 1994. Deorbited to destruction in Jupiter September, 2003.

Payload: CCD imager, UV and extreme-UV , near-IR mapping spectrome- ter, photopolarimeter-radiometer, energetic particle detector, dust detector, plasma spec- trometer, heavy counter, magnetometers (2), plasma wave receiver.

Nation(s): USA, Mass at Launch: 2,380 kg Radio Link: S-band* Stabilization: Spin Propulsion: Biprop Electrical power: RTG Launch date: October 18, 1989 Launch vehicle: STS Atlantis/IUS

*X-band unusable due to failure of HGA to deploy, as illustrated in Figure A.9. The Galileo Spacecraft 303

Fig. A.10. Galileo spacecraft. Science boom, folded downward, is left of center with end of stowed MAG boom just left of the NASA emblem. Low-gain antenna No. 1 is atop the stowed central mesh high-gain antenna. Large black circular component is bus sunshade. The heavy ion counter with its two circular apertures, obscured in the drawing on the previous page, is visible atop the bus to the right of center. Three of four hoist attach- ments, removed before flight, are visible protruding through sunshade. Image courtesy NASA/JSC. 304 Appendix A: Typical Spacecraft The Cassini Spacecraft

Fig. A.11. The Cassini spacecraft measures 6.3 meters in length. Not shown: RTGs, thermal blanketing, main engine cover, MAG boom, RPWS antennas, Huygens Probe. Covers on instruments and louvers placarded “REMOVE BEFORE FLIGHT.” Optical instrument apertures face out of page toward you; their radiators and scanner apertures point toward top of page. The spacecraft’s 6.8-meter length is largely due to the size of the bipropellant tanks inside. Image courtesy NASA/JPL.

Classification: Orbiter spacecraft Mission: Explore Saturn, its moons and magnetosphere Named: In honor of Italian-French astronomer G. D. Cassini (1625–1712)

Summary: Observed Venus, Earth, and Jupiter during gravity-assist flybys en route. Entered Saturn orbit July 2004, deployed Huygens probe (see page 308) December 2004 on a three-week free-fall to Titan. Currently orbiting Saturn, observing rings, moons, atmosphere, and magnetosphere.

Payload: CCD imagers (2), UV imaging spectrograph, visual and near-IR mapping spec- trometer, composite IR spectrometer, analyzer, magnetometers (2), radio and plasma wave receiver, magnetospheric imager, plasma spectrometer, mass spectrometer, and radio-frequency instrumentation for radio science experiments.

Nation(s): USA, ESA, ASI + Mass at Launch: 5,712 kg with Huygens Radio Link: S- X- and Ka band Stabilization: 3-axis, reaction wheels Propulsion: Biprop, monoprop Electrical power: RTG Launch date: October 15, 1997 Launch vehicle: Titan-IVB/Centaur The Cassini Spacecraft 305

Fig. A.12. Artist’s rendering of Cassini spacecraft in flight configuration, shown without blanketing. Three Radio and Plasma Wave (RPWS) antennas extend 10 meters, magne- tometer (MAG) boom extends 11 meters. Note the complex of feed horns in the middle of the 4-meter diameter High-Gain Antenna (HGA), which permits the synthetic aperture radar to acquire five parallel image swaths. RTGs are equipped with shades to avoid IR glare in the optical instruments. The Huygens Probe is attached at left, and the optical instrument apertures point toward the upper right. Cosmic Dust Analyzer instrument is the drum near the image’s center, and a helium tank for bipropellant pressurization is visible to its lower right. See also: www.jpl..gov/basics/cassini. Image © Gordon Morrison, reproduced by permission. 306 Appendix A: Typical Spacecraft The Messenger Spacecraft

Fig. A.13. Messenger spacecraft in flight configuration measures 6 meters across the solar panels. Image courtesy NASA/Johns Hopkins University Applied Physics Labora- tory/Carnegie Institution of Washington.

Classification: Orbiter spacecraft Mission: Orbit and observe the planet and its environs Named: For the Roman of the gods, and as acronym for: MErcury Surface, , , and Ranging

Summary: Messenger observed Earth, Venus, and Mercury during gravity-assist flybys, and will enter orbit around Mercury on March 18, 2011, after two more Mercury gravity- assist flybys while in solar orbit. Planned mission in Mercury orbit is one Earth year (about four Mercury years).

Payload: CCD imagers (2), -ray and neutron spectrometer, x-ray spectrometer, UV visible and IR spectrometer, altimeter, magnetometer, and energetic particle and plasma spectrometer. All but the latter instrument (see EPPS in Figure A.13) are mounted on a nadir-facing panel inside the conical launch adapter.

Nation(s): USA Mass at Launch: 1,100 kg Radio Link: X-band Stabilization: 3-Axis, reaction wheels Propulsion: Biprop, monoprop Electrical power: Photovoltaic Launch date: August 3, 2004 Launch vehicle: Delta-II/Star-48 The Messenger Spacecraft 307

Fig. A.14. Artist’s impression of the Messenger spacecraft orbiting Mercury. keeps the entire spacecraft, except for the solar panels, constantly in the shadow of its ceramic-cloth sunshade. Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. 308 Appendix A: Typical Spacecraft The Huygens Spacecraft

Fig. A.15. The Huygens spacecraft’s atmospheric measures 2.7 meters in diameter. Image courtesy .

Classification: Orbiter spacecraft Mission: Investigate the atmosphere and surface of Saturn’s moon Titan Named: For Dutch astronomer (1629–1695) who discovered Titan

Summary: Huygens separated from Cassini in Saturn orbit 2004, its bat- teries having remained inactive for over seven years. Then a timer turned on the Probe’s electronics for a 2.5-hour investigation. The heat shield decelerated the probe from 22,000 to 1,400 kilometers/hour, reaching a peak of 14 g. At an altitude of 160 kilometers, a pilot parachute pulled off the back cover and deployed the 8.3-meter diameter main parachute, slowing the probe to 80 meters/second and releasing the heat shield. The instruments then deployed and began taking data. At 110 kilometers altitude and 40 meters/second the main parachute separated and a 3-meter diameter chute deployed to achieve descent to the surface within 2.5 hours. At a few hundred meters altitude a lamp switched on to illuminate the surface and help acquire images and spectra. The probe landed at 5 meter/second on soggy sand as a -measuring penetrometer rod first bumped off a pebble and then entered the sand. Surface instruments characterized the , while the atmospheric instruments detected an abundance of vapor, presumably boiling away from the comparatively warm probe resting on the cold damp surface. At the 90 K surface temperature, rocks and sand are made of , and the liquid is methane.

Payload: Aerosol collector and pyrolyser, gas chromatograph and mass spectrometer, descent imager/spectral radiometer, atmosphere structure instrument, Doppler wind ex- periment, and a surface science package containing multiple instruments to sample and characterize the surface.

Nation(s): European Mass at Launch: 319 kg Radio Link: S-band to Cassini Stabilization: Spin Propulsion: None Electrical power: Battery Launch date: October 15, 1997 Launch vehicle: See Cassini (pg 304) The Huygens Spacecraft 309

Fig. A.16. Huygens spacecraft during installation of the back cover. The top of the atmospheric probe itself is visible over the rim of the heat shield. In the inset above, the first pilot chute has already removed the back cover, and the 8.3-meter diameter main parachute slows the probe while the spent heat shield is released. Images courtesy ESA. 310 Appendix A: Typical Spacecraft The Phoenix Spacecraft

Fig. A.17. The Phoenix Mars Lander spacecraft measures 5.5 meters overall with solar arrays deployed. From image courtesy NASA/JPL.

Classification: Lander spacecraft Mission: Study history of Mars’s H2O and habitability potential in arctic Named: After the mythological that is reborn from its own ashes

Summary: Created from hardware and plans remaining from the failed 1998 Mars Lander and the cancelled , Phoenix landed within the arctic circle on May 25, 2008. Imaging systems help identify targets, and a digs through soil to water ice below and delivers samples to experiments, including miniature ovens, a mass spectrometer, and a chemistry lab-in-a-box, to characterize soil and ice chemistry.

Payload: Surface stereographic imager, thermal and evolved gas analyzer, microscopy, electrochemistry, and conductivity analyzer, meteorological station, robotic arm with cam- era, scoop, and thermal and electrical conductivity probe.

Nation(s): USA Mass at Launch: 350 kg Radio Link: UHF Stabilization: 3-Axis to landing Propulsion: Monoprop Electrical power: Photovoltaic Launch date: August 4, 2007 Launch vehicle: Delta II The Phoenix Spacecraft 311

Fig. A.18. Artist’s conception of the Phoenix lander spacecraft. Having completed a ten-month journey, the spacecraft’s cruise stage was jettisoned five minutes prior to atmo- spheric entry, then the heat shield was released after parachute deployment. When on-board radar sensed it was down to 570 meters above the surface, the parachute was released and hydrazine thrusters carried it to a soft landing as seen here. Loss of sun- in the winter, extreme cold, and frost will prevent further operations by January 2009, and there is little chance Phoenix will survive the winter. See also page 269. Image courtesy NASA/JSC. 312 Appendix A: Typical Spacecraft Spacecraft

Fig. A.19. Mars Science Laboratory measures 2.8 meters overall. Adapted from artist’s conception, image courtesy NASA/JPL-Caltech.

Classification: Rover spacecraft Mission: Investigate past and present potential to support microbial life Named: Descriptively (may be changed in or prior to flight)

Summary: Mars Science Laboratory plans to bring more than ten times the mass of previous rovers into the Martian atmosphere in late 2012, and will be the first at Mars to execute energy-dissipating S-turns before heat shield jettison. After parachute descent, a -powered “sky crane” hovers and lowers the rover on cables to a soft touchdown. Rover itself is almost four times the mass of each 2003 ( or ).

Payload: Descent imager, gas chromatograph, mass spectrometer, tunable laser spec- trometer, x-ray diffraction, and fluorescence instrument, “geologist’s hand lens” imager, APXS, mast camera, ChemCam (see pg 325; laser pulses vaporize target material up to 10 meters away; telescope with spectrometer identifies excited atoms), radiation assess- ment detector, environmental monitoring station, dynamic of neutrons instrument, mast-mounted navigation cameras, low-mounted stereo hazard-avoidance cameras, sample acquisition/sample preparation & handling system.

Nation(s): USA Mass at Launch: 3,400 kg* Radio Link: Ka-, X-band, UHF Stabilization: Mars gravity Propulsion: Electric motors Electrical power: RTG Launch date: Planned Oct-Dec 2011 Launch vehicle: Atlas-V

* Launch mass includes cruise and descent hardware. Mars Science Laboratory Spacecraft 313

Fig. A.20. Artist’s conception showing the Mars Science Laboratory spacecraft being let down to a soft landing by its sky-crane after aerodynamic entry with S-turns, parachute descent, and retro-stage activation. Image courtesy NASA/JPL-Caltech. 314 Appendix A: Typical Spacecraft The Deep Impact Spacecraft

Fig. A.21. Deep Impact spacecraft is 3.3 meters in height. Courtesy NASA/JPL.

Classification: Impactor spacecraft. Mission: Excavate material from comet 9P/Tempel for external observation Named: For its mission (and in deference to the popular 1998 film)

Summary: On July 3, 2005, the flyby spacecraft released an impactor which navigated itself (see pg 58) to impact the . Typically, impactor spacecraft are designed for on- site measurements using direct-sensing instruments, though to date no such spacecraft has succeeded. Deep Impact penetrated the comet’s surface purely to cause a crater and raise ejecta for the benefit of remote-sensing observations from the flyby spacecraft and from Earth. Now on an extended mission called Extrasolar Planet Observation and Extended Investigation to search for extrasolar planets via and transit methods en route to flyby of Comet Hartley 2 in October 2010.

Payload: Flyby spacecraft: 30-cm aperture telescope with high-resolution IR spectrom- eter and multi-spectral CCD camera, 12-cm aperture telescope for medium-res imaging. Self-navigating impactor: 12-cm aperture telescope for automatic targeting.

Nation(s): USA Mass at Launch: 650 kg + 370 kg impactor Radio Link: S-, X-band Stabilization: 3-Axis Propulsion: Monoprop Electrical power: /Battery Launch date: January 12, 2005 Launch vehicle: Delta II The Deep Impact Spacecraft 315

Fig. A.22. Deep Impact flyby spacecraft (above) being mated with the impactor space- craft (shoulder-level). The impactor operated on battery power after separation, obtaining images and navigating autonomously via built-in hydrazine thrusters, to an impact with the comet at 10.2 kilometers/second. The impact released about 19 gigajoules (equivalent to 4.8 tons of TNT). It returned images on approach via its S-band radio link with the flyby spacecraft. Image courtesy NASA/JSC. 316 Appendix A: Typical Spacecraft The Deep Space 1 Spacecraft

Fig. A.23. Deep Space 1 spacecraft in launch configuration measures 2.5 meters in height. Courtesy NASA/JPL.

Classification: Engineering Demonstration spacecraft Mission: Demonstrate twelve new for use on scientific missions Named: As first in a series of deep space testing missions Summary: Demonstrated solar electric propulsion, solar concentrator arrays, autonomous navigation, autonomous remote agent, small deep space transponder, Ka-band solid state amplifier, beacon monitor operations, low power electronics, power actuation and switch- ing module, and multifunctional structure. Miniature integrated camera/imaging spec- trometer, and single-package ion and spectrometer instruments. Upon comple- tion of technology testing objectives, acquired science data during flybys of in 1999 and Comet Borrelly in 2001. Payload: Twelve engineering experiments (including two science instruments). Nation(s): USA Mass at Launch: 489 kg Radio Link: X, Ka-band Stabilization: 3-Axis, thrusters Propulsion: Electric (ion) Electrical power: Photovoltaic Launch date: October 24, 1998 Launch vehicle: Delta II/Star-48 The Deep Space 1 Spacecraft 317

Fig. A.24. Artist’s conception of the Deep Space 1 spacecraft in flight configuration operating its solar-electric-powered ion engine. The solar arrays measure about 12 meters end-to-end across the spacecraft. Image courtesy NASA/JPL. Appendix B: Typical Instruments

A scan through Chapter 6 will show that there are perhaps as many different science instruments as there are scientists who have questions. Since this appendix can’t list them all, it shows one or more solid examples of each of the four instrument categories described in Chapter 6 (see page 183). Each entry lists the instrument’s capabilities and ranges of sensitivities. Also included are one spacecraft engineering appliance (stellar reference unit) and one ground-based facility (DSN station).

Instrument Classification Page

Galileo Solid-state imager Passive Remote 320 MRO HiRISE Passive Remote 321 Cassini Radar Active Remote 322 MGS Mars Laser Altimiter Active Remote 323 Spitzer IR Spectrograph Passive Remote 324 MSL ChemCam Active Remote 325 Voyager Magnetometer Passive Direct 326 Huygens ASI Passive Direct 327 APXS Active Direct 328 MER Mossbauer Spectrometer Active Direct 329 Cassini Stellar Reference Unit Engineering* 330 Deep Space Station 55 DSN Station„ 331

*Designed as spacecraft attitude-control input device rather than part of the scientific-instrument payload. „Earth-based facility. 320 Appendix B: Typical Instruments Solid-State Imager Abbreviated: SSI Spacecraft: Galileo

Classification: Passive remote-sensing instrument

Captures: High-resolution images of targets including Earth, Moon, and Venus -tops during gravity-assist flybys; asteroids Gaspra, Ida, and Dactyl; and the comet Shoemaker-Levy 9 impact with Jupiter en route; and from Jupiter orbit images of various levels in Jupiter’s atmosphere and vari- ations in color and albedo of Jovian satellite surfaces indicating differences in composition. Fig. B.1. Galileo Solid-State Imaging in- Basis of operation: Cassegrain re- strument. Telescope aperture is the dark ring flecting telescope focuses light onto a on left, with secondary mirror creating the radiation-shielded focal-plane detector central obstruction mounted on clear quartz aperture plate. Image courtesy NASA/JPL. through shutter and selected filter. De- tector is passively cooled to about 163 K by thermally conductive attachment to external radiator plate. Aperture cover was jettisoned after launch.

Specifications: Focal length: 1,500 millimeters; Fixed focal ratio f/8.5; tweny-eight selectable exposure times between 0.004 sec and 51.2 sec; Field of view 8.13 × 8.13 mrad. Sensitive to visible through near-infrared light; eight-position wheel has seven spectral filters from 400 to 1100 nm plus clear; CCD built by Texas Instruments and JPL; RCA 1802 microprocessors control the instrument; CCD radiation shield is 1-centimeter thick tantalum. Aperture: 176.5 mm Detector: 800 × 800 pixel CCD Power draw: 15W, 28 VDC Mass: 29.7 kg Assembled by: NASA/JPL Location: Despun scan platform Heritage: Voyager narrow-angle camera telescope, shutter, filters Operated: October 18, 1989 (launch), through September 21, 2003 High-Resolution Imaging Science Experiment 321 High-Resolution Imaging Science Experiment Abbreviated: HiRISE Spacecraft: Mars Reconnaissance Orbiter (MRO)

Classification: Passive remote-sensing instrument

Captures: High-resolution images of surface of Mars resolving 1-meter fea- tures, and stereoscopic images permit- ting vertical resolution to 30 centime- ters height. Three spectral filters allow color imaging.

Basis of operation: Cassegrain tele- scope with extraordinary focal length illuminates assembly of one-dimensional (line-of-pixels) CCDs. Spacecraft along- track motion supplies images’ second dimension (push-broom mode). Light reaches focal-plane assembly via cus- tomary two-mirror Cassegrain optics plus a tertiary mirror in a path with two beam-folding flat mirrors. Focal- plane assembly at end of twelve-meter path holds fourteen overlapping 2,048- pixel staggered CCDs. Data stored in Fig. B.2. MRO HiRISE. Cassegrain tele- camera memory. scope, with additional beam-folding op- tics in back, shown above enlargement of Specifications: 12-m focal length; f/24 focal-plane assembly with fourteen linear focal ratio; All CCDs are 2,048-pixel CCDs (housed in back, see arrow). Courtesy linear; ten with red filter total a 20,000- NASA/JPL-Caltech. pixel line, two have blue-green filters, two have IR filters, near red array center. Memory: 28 Gbit; Resolution: 1 μrad, 0.5 m at surface. Aperture: 50 cm Detector: Linear CCDs Power draw: 68 W, 28 VDC Mass: 65 kg Assembled by: Ball Aerospace Location: Nadir platform Heritage: Deep Impact, Operated: In science orbit* (post-aerobraking) September 29, 2006, to present. *Also took calibration images en route, and early-orbit demos prior to aero- braking. Imaged Earth and Moon from Mars (ID: PIA10244). 322 Appendix B: Typical Instruments Radar Abbreviated: RADAR Spacecraft: Cassini

Classification: Active remote-sensing instrument

Captures: Microwave radio energy scattering and reflecting from a tar- get which it has illuminated with its radar beam in active modes, and the microwave energy radiating naturally from a target in passive mode.

Basis of operation: RADAR is acronym for RAdio Detection And Ranging, but the technique has gone beyond these functions. Cassini’s radar oper- ates in three active modes and one pas- sive mode. Synthetic Aperture Radar (SAR) creates images from time delay and Doppler shift, measured in the re- turn signal, to create two-dimensional images (see pg 199); altimetry sends radio energy straight down to surface and times its return, to measure dis- tance; scatterometry measures strength Fig. B.3. Close-up of Cassini Radar mul- of backscattered energy; radiometry tiple feeds near center of HGA used to measures natural microwave emission acquire synthetic-aperture imaging data in from target in passive remote-sensing five distinct beams. Radar electronics box is mounted atop the bus beneath HGA. Image mode. courtesy NASA/JPL-Caltech. Specifications: Emits coded pulses at 13.78 GHz (Ku-band). Resolution is a function of distance from the target. SAR resolution, 0.35 to 1.7 kilometers; altime- ter, 24 to 27 kilometers horizontal, 90 to 150 meters vertical; radiometer, 7 to 310 kilometers. Aperture: 4m Detector: Microwave receiver Power draw: 108 W, 28 VDC Mass: 42 kg Assembled by: ASI, JPL Location: Atop bus and in HGA Heritage: Techniques developed for SIR-C and Operated: October 26, 2004, to present. Mars Orbiter Laser Altimeter 323 Mars Orbiter Laser Altimeter Abbreviated: MOLA Spacecraft:

Classification: Active remote-sensing instrument

Captures: Measurements of distance between instrument and Martian sur- face. Data reduces to topographical mapping, providing information for es- timating flow velocities and discharges in channels. After laser failure on June 30, 2001, the instrument acquired IR radiometry data from the surface as a passive remote-sensing in- strument.

Basis of operation: Pulses of laser light are aimed toward the surface. A por- tion of the output laser energy from each pulse is diverted to the detec- Fig. B.4. The Mars Global Surveyor Laser tor to start a clock counter. Energy Altimeter. The laser is the small cylinder returning at the of light from mounted on the left side of the large circular the surface is collected by a reflect- collector-mirror light shield. Telescope sec- ing Cassegrain telescope, which focuses ondary mirror is supported in the black cen- the light onto the detector. Precise tim- tral column. Image courtesy NASA/GSFC. ing of collected pulse backscatter, com- pared against the counter, yields dis- tance data. An 80C86 microprocessor controls the instrument’s operation.

Specifications: Neodymium-doped yttrium aluminum garnet (Nd:YAG) near-infra- red laser, wavelength 1,064 nm; Laser subtends 0.4 mrad, spreads to about 130 meters on Martian surface; 10 Hz pulse rate results in 330-meter spacing along ground track. Range resolution 37.5 centimeters; absolute accuracy depends on spacecraft orbital knowledge and is generally <10 meters. Aperture: 50 cm Detector: Silicon-avalanche photodiode Power draw: 34.2 W, 28 VDC Mass: 25.85 kg Assembled by: NASA/GSFC Location: Nadir platform Heritage: MOLA Operated: Orbit insertion (September 11, 1997) through spacecraft loss (November 2, 2006) 324 Appendix B: Typical Instruments Infrared Spectrograph Abbreviated: IRS Spacecraft: Spitzer Space Telescope

Classification: Passive remote-sensing instrument

Captures: Infrared light via the Spitzer telescope optics from , , so- lar system objects, interstellar gas and dust, intergalactic gas and dust, and other targets, and breaks it down into its constituent wavelengths for mea- surement.

Basis of operation: Each of four spec- trographs records spectra at a differ- Fig. B.5. Spitzer IRS includes four spec- ent level of detail and wavelength, λ, trographs aligned radially within the chilled chamber behind the telescope’s primary mir- by introducing a grating into its light ror. A: short-λ high-resolution, B: short-λ path and measuring the spatial distri- low-res, C: long-λ high res, D: long-λ low res. bution of the wavelengths dispersed by Courtesy NASA/JPL-Caltech, Spitzer Sci- the grating. Instrument is cooled by liq- ence Center. uid helium to about 1.4 K.

Specifications: The short-λ high-resolution spectrograph (A) covers 10–19.5 μ; the short-λ low-resolution spectrograph (B) covers 5.3–14 μ; the long-λ high-resolution spectrograph (C) covers 19–37 μ; the long-λ low-resolution spectrograph (D) covers 14–40 μ. Detectors are 128 x 128 arrays. The shorter-wavelength (Si) de- tectors are doped with arsenic (As); the longer-wavelength Si detectors are doped with antimony (Sb). Aperture: Spitzer’s 85 cm Detectors: Sb: Si and As: Si Assembled by: Ball Aerospace Location: Multi-instrument chamber Operated: September 12, 2003, to present. Chemistry and Camera 325 Chemistry and Camera

(Laser-Induced Remote Sensing for Chemistry and Micro-Imaging) Abbreviated: ChemCam Spacecraft: Mars Science Laboratory (MSL)

Classification: Active remote-sensing instrument

Captures: Close-up micro-images of targets at 2–9 meters distance, and then emission spectra of plasma gener- ated from a 1-millimeter diameter por- tion of a target when laser-heated to 10,000 ◦C (micro-imaging by itself can operate beyond 9 meters distance).

Basis of operation: CCD remote micro- imager provides telescopic close-up views of target from at least 2 meters distance through telescope on rover’s mast. Up to seventy-five laser pulses Fig. B.6. Artist depicts MSL ChemCam en- are then focused through the same tele- ergizing a pre-selected and micro-imaged tar- scope onto a target, causing of get 6 meters away. Note the infrared laser atoms in excited states. Three spectro- beam would not actually be visible. Im- graphs disperse light from the ablated age courtesy NASA/JPL-Caltech/LANL/J.- material into component wavelengths L. Lacour, CEA. via gratings, and resolve and measure emission lines on linear CCD detectors. Spectrographs are fed via fiber-optic cable from the telescope. In energizing a target, this Laser-Induced Breakdown Spectro- graph (LIBS) can remotely remove dust and weathering layers.

Specifications: Telescope: 10-centimeter aperture Schmidt-Cassegrain. Imager: field of view 30 centimeters at 10 meters; 80 μrad resolution. Laser: wavelength 1,067 nm (infrared); 30 mJ per 5-ns pulse, repeating at 15 Hz up to seventy-five pulses before recharging forty seconds; spectrographs sensitive to wavelengths from 240 to 800 nm with 0.09-0.3 nm resolution. Aperture: 10 cm Detector: CCDs Power draw: 7W Mass: 6kg Developed by: LANL, CESR Location: Mast and body Heritage: Earth-based Operated: Planned for 2012. 326 Appendix B: Typical Instruments Magnetometers Abbreviated: MAG Spacecraft: Voyager 1 and Voyager 2

Classification: Passive remote-sensing instruments

Captures: Magnetic field measure- ments in the plasma media in planetary vicinities, interplanetary space, the so- lar heliosheath, and, it is hoped, inter- stellar space.

Basis of operation: Two low-field- strength sensors were extended by un- furling a three-rib fiberglass boom af- ter launch (page 176 shows a similar boom in stowed configuration). Mag- netometer “C” in Figure B.7 is at the end of the 13-meter long boom, and magnetometer “D” is approxi- mately mid-boom. The boom removes the highly sensitive instruments from magnetic disturbances close to the Fig. B.7. Four magnetometers on a Voyager spacecraft metals and electric currents. spacecraft prior to HGA installation. Fiber- Two high-field-strength sensors (“A” glass boom stowed within cylinder behind and “B,”) are permanently mounted magnetometer “D” will untwist and extend to hold magnetometer “C” out at a distance near the spacecraft bus. Energizing a of 13 meters. High-field magnetometers “A” wire coil surrounding the HGA per- and “B” remain in positions shown. See also mits in-flight calibration of all four page 294 for deployed configuration. Image instruments. Fluxgate magnetometers courtesy NASA/JPL-Caltech. are discussed in Chapter 6 (see page 216).

Specifications: On each spacecraft: two low-field-strength instruments with eight selectable dynamic ranges from ±8.8 nT to ±50000 nT; two high-field-strength instruments with two selectable ranges, ±5× 104 nT and ±2 × 106 nT. Aperture: N/A Detector: Flux-gate Power draw: 3.2 W Mass: 5.5 kg (total of 4) Developed by: GSFC Location: On boom and near bus Operated: Continuously since autumn 1977. Atmospheric Structure Instrument 327 Atmospheric Structure Instrument Abbreviated: HASI Spacecraft: Huygens

Classification: Passive direct-sensing instruments (except impedence sensors)

Captures: Measurements of accelera- tion in three axes, atmospheric pres- sure and temperature, acoustic events, electrical impedance, , and waves. Also processes radar altimetry data.

Basis of operation: Coordinated by the HASI data processing unit are twin temperature sensors, each dual- element platinum resistance thermome- Fig. B.8. Huygens Probe with HASI sensors ters. A Kiel-type inlet tube exposes deployed. Inner cover (in place during flight atmosphere to temperature-calibrated operation) removed for clarity. “A” points silicon capacitive absolute pressure sen- out the pressure sensor inlet stub with two sors in which the pressure bends temperature sensors (microphone situated at a thin silicon diaphragm. Three or- its base), “B” shows one of 2 booms with thogonally mounted piezoresistive ac- electrical permittivity and wave sensors, “C” celerometers and one single-axis (spin) indicates one of four radar altimeter anten- servo- are situated near nas, and the are in the small the spacecraft’s center of mass. Two housing near the spacecraft center. Data pro- deployable booms measure the at- cessing unit is upper left of center. Image mosphere’s electrical properties. Each courtesy ESA. boom holds two ring-shaped elements, which are the transmit- and receive- mutual impedance sensors, and a disc-shaped relaxation sensor — these are ac- tive direct sensors.

Specifications: Temperature resolution 0.02 K; pressure resolution 1 Pa; accelera- tion 1–10 μg high-res, 0.9–9 mg low-res; acoustic threshold 10 mPa; AC electric wave strength threshold 2μV/m; mutual impedance 10−11 (Ωm)−1; relaxation in- tervals: 1 min, and 25 ms to 2 s, with 1 mV threshold. Aperture: Kiel-type pressure inlet Power draw: ≈ 5W Mass: 5.7 kg total Developed by: ASI Location: See Figure B.8 Operated: On January 14, 2005, from 09:15 to 13:30 UTC SCET. 328 Appendix B: Typical Instruments Alpha X-Ray Spectrometer Abbreviated: APXS Spacecraft: Sojourner

Classification: Active direct-sensing instrument

Captures: Back-scattered alpha par- ticles, , and X-Rays resulting from exposing a sample to a radioactive source in order to provide information on the chemical composition of Martian rocks and soil.

Basis of operation: Rover drives to a target of interest and deploys APXS into firm contact with the sample or soil. The radioisotope (244Cm) within the instrument emits alpha particles (APs), which are he- lium nuclei consisting of two protons and two neutrons, with known en- ergy. As these particles strike atoms Fig. B.9. The APXS on the back end of in the target, the instrument records Sojourner. Image ID JPL-25888BC courtesy energy spectra in 256 channels result- NASA/JPL-Caltech. ing from each of three interactions: al- pha particle elastic (Rutherford) scat- tering, alpha-proton nuclear reactions with certain light elements, and excitation of atoms in the target by alpha par- ticles that causes them to emit X-Rays of characteristic energies. These spectra provide indications of atomic species of most of the target’s elements, with the ex- ception of and helium. Some APXS instruments, such as those on MER, have an X-ray source as well as an AP source.

Specifications: Sensitivity to elemental composition approaching the parts-per- million range. Measured abundances of MgO, Al2O3, SiO2,K2O, CaO, TiO2, MnO, and FeO, with best sensitivity to the lighter elements. Sojourner rover mobile mass 11.5 kg; delivered to Vallis by the Mars Pathfinder lander. Aperture: N/A Power draw: 0.8 W Mass: 0.74 kg Developed by: MPI, U of Chicago Location: See Figure B.9 Heritage: Russian , and Mars, 1996 Operated: July 4 through September 27, 1997. Mini-M¨ossbauer Spectrometer 329 Mini-M¨ossbauerSpectrometer Abbreviated: MIMOS-II Spacecraft: Mars Exploration Rovers (2)

Classification: Active direct-sensing instrument

Captures: γ-ray (gamma-ray) spectra from , by sensor head on robotic arm. Control and processing electron- ics within rover body. Opportunity’s MIMOS-II detected seven iron-bearing at : , , , nanophase ferric oxides, kamacite, , . In Crater, Spirit found the first six of these plus ilmenite and .

Basis of operation: Instrument head re- mains in contact with target, cobalt (57Co) illuminates it with γ-rays to probe for iron. Per M¨ossbauereffect, Fig. B.10. M¨ossbauerspectrometer sensor a fraction of source γ rays do not lose head is one of four units at the end of robotic energy due to recoil, so they have al- arm. Inset: view from mast-mounted Nav- most the right energy to be absorbed Cam as arm extends toward target on Mars. by atoms in target. Sensor head accel- MIMOS-II is at center in close-up, its aper- erates source through a range of ve- ture represented by concentric discs (APXS locities, ±12 mm/s, via linear motor, is on right, micro-imager behind MIMOS-II, Doppler-shifting radiation to match RAT on left). image and instrument target absorption energies. Detector mockup on full-scale model courtesy NASA senses resulting γ-ray emission from ex- JPL-Caltech. cited target atoms during hours of in- tegration time.

Specifications: Sensitive to 14.4 kev γ-ray emission indicative of iron, including its phase and oxidation state. Target integration time originally eight hours; >48 hours as of May 2007, about five half-lives of the 57Co gamma-ray source since it was created. Aperture: 1-cm diameter aluminum window Power draw: 2W Mass: 0.5 kg Developed by: University of , Germany Location: See Figure B.10 Heritage: First developed for Russian Mars 1998 rover whose launch failed. Operated: January 2003 through present. 330 Appendix B: Typical Instruments Stellar Reference Unit Abbreviated: SRU Spacecraft: Cassini

Classification: Passive remote-sensing engineering appliance

Captures: Images of star fields. Auto- matically estimates spacecraft attitude based on the images.

Basis of operation: A small refract- ing telescope focuses wide-angle im- age of star field onto a CCD. SRU- internal JPL-developed code identifies up to five stars by referring to stored data and estimates space- craft’s attitude. Estimates are commu- nicated to AACS. SRU constitutes pri- mary source of Cassini’s attitude in- formation, either rotating with respect to the star background or stationary. SRUs are permanently mounted with fields of view perpendicular to those of the other optical instruments. Note in Fig. B.11. Two SRUs on Cassini remote Figure B.11 the SRU apertures point sensing pallet. Upper SRU is situated di- in the same direction in which the op- rectly left of imaging system narrow-angle tical science instrument radiators face camera, the boresight of which is orthogo- (white circle and other flat surfaces). nal to those of the SRUs. From image ID: This side of the spacecraft is con- 97pc1028, courtesy NASA/JPL-Caltech. strained by flight rules never to face the Sun.

Specifications: Limiting star visual magnitude, 5.6; number of stars in database, 5,000; field of view, 15◦×15◦; internal attitude knowledge resolution, 1 mrad. Field of view: 7.5◦× 7.5◦ Detector: 1,024×1,024 px CCD Power draw: 12 W Mass: 10 kg Assembled by: Officine Galileo Location: Remote sensing pallet Operated: October 1997 through present. Deep Space Station 55 331 Deep Space Station 55 Abbreviated: DSS 55 Facility: Deep

Classification: Transmitting & Receiving Station

Captures: Microwave energy from spacecraft at X- & Ka-band frequen- cies for extraction of , rang- ing, Doppler, and radio science data. Also participates in scientific observa- tions and engineering activities.

Basis of operation: Pointed by rotat- ing in azimuth on wheels and circu- lar steel track, in elevation on roller- bearings. Incoming radio intercepts parabolic main reflector, concentrates at quadrapod-supported subreflector, comes to focus at a mirror below cen- tral hole in main reflector. Radio beam, enclosed in a 2.5-meter diameter cylin- drical waveguide, then encounters four more mirrors on the way to receiving equipment below ground level. Trans- Fig. B.12. Deep Space Station 55, DSN’s mitter’s output is ducted via the same newest 34-meter aperture beam-waveguide mirrors and waveguides to the subre- deep space station. Located outside Madrid, Spain. Time-lapse video of construction: flector, from where it evenly illumi- deepspace.jpl.nasa.gov/dsn/gallery/video.html. nates the main reflector for propaga- Image courtesy NASA/JPL-Caltech. tion to spacecraft. Simultaneous uplink and downlink is standard practice. Ev- ery DSS connects with signal process- ing center via fiber optic cable.

Specifications: One of nine 34-meter diameter DSN stations. Physical location spec- ified in three dimensions to the millimeter. Downlink: 8.4–8.5 GHz X-band; 31.8– 32.3 GHz Ka-band. Uplink: 7.145–7.235 GHz X-band, 17.5 kW. Aperture: 34 m Detector: HEMT : Right- and/or left-circular Moving mass: 300,000 kg Developed by: NASA/JPL Location: Madrid, Spain Gain: X-band 70 dB uplink, 68 dB downlink, Ka 79 dB downlink Operated: Around-the-clock from October 2003 to present. Appendix C: Space

This appendix explains nomenclature for some regions and scales of space. It also provides some approximate values for distances, light-times, particle densities, and temperatures. A page is devoted to Jupiter’s atmospheric features, and one to Saturn’s elegant rings. Many of these features are easy to see when viewing Jupiter and Saturn from Earth.

Interplanetary Space is the space among the planets of our solar system and within the heliosphere, which is the Sun’s realm of practical magnetic influence. Besides the planets, most of the material in interplanetary space is from the Sun. Fast- moving plasma known as the solar wind flies out from the Sun in all directions, faster in the solar polar regions than in the equatorial. Occasional bursts of ion known as coronal mass ejections also fly outward from the Sun within the heliosphere. Magnetic fields surround most of the planets and interact with the solar wind and mass ejections. Planets with strong magnetic fields such as Earth and the gas giants have that largely divert the solar around them. Beginning beyond Neptune’s orbit, a band of cometary bodies, called the Kuiper Belt, may extend outside the heliosphere. Its population includes bodies orbiting at a large range of inclinations compared to the planets, which are more or less confined to the plane. The solar wind slows to subsonic velocity at a front called the termination shock, located just beyond the outer edge of the heliosphere. Voyager 1 and Voyager 2 have already penetrated the termination shock and confirmed that its location is constantly changing. Voyager 1 exited the shock at 94 AU toward the north and Voyager 2 exited at 86 AU toward the south, and today they are flying through the region between it and the heliopause, the point where the and solar wind pressures balance. This region is called the heliosheath. The distribution of mass in interplanetary space includes the Sun (99.85%) and the planets (0.135%). The remaining 0.015% makes up everything else: , planetary satellites, , and plasma.

Interstellar Space is the space outside the heliosphere, where the Sun’s magnetic in- fluence cannot redirect incoming charged particles. Since the Sun is moving among the local stars and through intervening clouds of gas and dust, the heliopause is associated with a curved “,” as illustrated in Figure C.1, along which interstellar material bunches up and flows around the heliosphere. The distance from the Sun to the heliopause and the bow shock is not known as of 2008, but 334 Appendix C: Space they are estimated to begin at about 200 AU. Interstellar space lies beyond the bow shock. Five spacecraft are bound for interstellar space: and , which are no longer communicating; Voyager 1 and Voyager 2, and New Horizons, which may still be measuring their environment and communicating, when they penetrate the heliopause, to report on interstellar conditions within our galaxy. A sphere of cometary bodies called the is thought to lie well outside the heliosphere in interstellar space, at an estimated one light-year or so from the Sun. While no bodies have been observed within the Oort cloud itself, it is believed to be the source of all long-period comets that have been observed closer to the Sun.

Intergalactic Space The Sun and planets, all the local stars, and all spacecraft, while moving along their proper trajectories, are also orbiting the central region of our galaxy which contains a super-massive black hole about twenty-six thousand light years distant. Outside the galaxy’s magnetic field are the vast reaches of space among the billions of galaxies in the universe.

Outer Space is a term used mostly in the popular literature to refer to any space that is outside most of the Earth’s atmosphere, typically more than a hundred kilometers above the surface. All of space is permeated by gravitation, electromag- netic radiation, and plasma in various amounts. There is no empty space; there is no escaping Earth’s gravity, or the Sun’s, because the gravitation of any physi- cal mass only diminishes with distance. In free-fall in orbit, however, a spacecraft experiences zero or near-zero .

Table C.1. Distances and Light-Times in Space.

Distance (approximate) Light-time Example 299,793 km 1 s 78% of the Earth–Moon average dist. 149,598,000 km (1 AU) 8.31 min Sun–Earth average dist. 624,150,000 km 34 min Earth–Jupiter at opposition. 16.2 x 109 km 15 hr Earth–Voyager 1 * 63,000 AU 1 year Light-year 4.2 LY 4.2 y Nearest star 8.6 LY 8.6 y Bright star 26,000 LY 26,000 y 2.53 x 106 LY 2.53 x 106 y Nearest galaxy 14 x 109 LY 14 x 109 y Farthest galaxies AU = (average Sun-Earth dist.), LY = light year. *As of December 2008. References 335

Table C.2. Particle temperatures and densities in space, modeled.

Region Temperature, K Density, atoms / cm3 Earth-vicinity 10,000 6 Neptune-vicinity 200,000 1.4 Termination shock 600,000 0.1 Heliopause 2x106 0.2 Bow shock 30,000 0.3 Interstellar cloud past heliopause 8,000 0.3 Local interstellar void 106 0.0001 Intergalactic medium 100 10−6 Best lab vacuum — 1000 Residence 2.7 x 1019 295 Sensitive instruments can detect particles’ temperatures, but physical , such as spacecraft and asteroids, are not affected by particles in such low densities, even though the particles may have temperatures in the hundreds of thousands of . They are mainly affected by exposure to incident sunlight and shadow.

References

[1] May-Britt Kallenrode. : An Introduction to Plasmas and Particles in the Heliosphere and Magnetospheres. Advanced Texts in Physics. Springer, 3 edition, 2004. [2] Priscilla C. Frisch, editor. Solar Journey: The Significance of Our Galactic Environ- ment for the Heliosphere and Earth. Astrophysics and Space Science Library. Springer, 2006. [3] W. Oegerle, M. Fitchett, and L. Danly, editors. Clusters of Galaxies. Space Telescope Science Institute Symposium Series. Cambridge University Press, 1990. [4] John W. McAnally. Jupiter: and How to Observe It. Astronomers’ Observing Guides. Springer, 2008. [5] Ellis D. Miner, Randii R. Wessen, and Jeffrey N. Cuzzi. Planetary Ring Systems. Springer-Praxis, 2007. 336 References

Table C.3. Some Temperature Examples.

Kelvin Degrees C Degrees F Example 0 –273.15 –459.67 Absolute zero 2.7 –270.5 –454.8 Cosmic microwave background 4.2 –268.95 –452.11 Liquid helium boils 20.28 –252.87 –423.16 Liquid hydrogen boils 35 –235 –390 Surface of Neptune’s moon 72 –201 –330 Neptune atmosphere, 1-bar level 76 –197 –323 Uranus atmosphere, 1-bar level 90 –180 –300 Surface of Saturn’s moon Titan 100 –175 –280 Night-side surface of Mercury 134 –129 –219 Saturn atmosphere, 1-bar level 153 –120 –184 Mars surface nighttime low 165 –108 –163 Jupiter atmosphere, 1-bar level 195 –78.15 –108.67 Carbon dioxide freezes 273.15 0.0 32.0 Water freezes 288 15 59 Mars surface, daytime high 288 15 59 International standard atmosphere 373.15 100 212 Water boils 635 362 683 Venus surface 700 425 800 Day-side of Mercury 1500 1200 2000 Yellow candle flame 3700 3400 6700 Sunspots 5700 5400 9800 Solar photosphere 7000 7000 12000 Plasma in neon sign 2x106 2x106 3.6x106 Solar corona 15x106 15x106 27x106 Solar core References 337 2008 Don Dixon / cosmographica.com, reproduced by permission. Panel (B) by T. Pyle, Spitzer Space Science measurements), where the heliosheath begins. Panel (C) is an actual image of a stellar bow shock, about half a © Voyager Rough approximations of scale of interplanetary space and the beginning of interstellar space. In order outward from the Sun Fig. C.1. are the terrestrial planets,solar the wind goes main subsonic, asteroidspace and belt, the beyond. the heliosheath The gas (not spheroid illustrated).panel giant Oort The (A) planets, heliopause cloud illustrates and marks of planets the theThe and comet beginning Kuiper Kuiper Kuiper nuclei of belt. Belt the belt, resides Next solarthe may showing in are bow actually parabolic Pluto’s interstellar shock, the extend highly bow space and termination elliptical much shock interstellar AU at shock, orbit, farther (average just over where the of than 50,000 outside the aphelion AU illustrated. the of from Artist’s heliopause. which the conception Termination is Sun. shock panel about Artist’s would (B) 49 conception be illustrates AU inside from how the the panel Sun. light-grey (A) area scales of with bow shock, at roughly 90 light-year across, where L.L.Sun. Panel Orionis’s (A) stellar artwork wind is colliding with gas and dust in the about 1,500 light-years from the Center, serves to generallymoves illustrate through solar its bow local shock, interstellar but medium. was Panel created (C) to image illustrate ID: Spitzer’s STScI-PRC02-05 actual courtesy view NASA of Hubble R Heritage Hya’s Team STScI/. bow shock as the star 338 References Identification of Jupiter’s major atmospheric belts and zones. These are the ones that persist over the years. Features which are image ID: PIA04866 courtesy JPL/NASA/Space Science Institute. not always visible are notprovides shown complete (e.g information “bands” onthe which all may west appear of as within these. indicatedgenerally zones, by Belts and on the are some the arrows. the higher order ZonesCassini darker of are belts regions 100 lighter and where meters/second. in zones), clouds The color. but rise, Great Their reference and Red clouds [4] their Spot descend, rotates and blow counterclockwise their within from winds the the blow west south east to tropical toward east. zone. Wind Adapted from are Fig. C.2. References 339 ), F Ring, and the densest part of the E Ring, whose diameter is greater than the average S was in Saturn’s shadow on September 15, 2006. Fine particles in the Cassini Division, transparent when viewed from Cassini Saturn’s rings identified. The broad A, B, and C Rings can be easily seen in a small telescope from Earth. Fine particles of the D, Earth-Moon distance. Explanations ofdistant the Earth many features is in visibleappears this just image in inside may the be theplanetary lower found G ring left at Ring www.jpl.nasa.gov/basics/saturn. systems. of on Forof Radial E example, the the myriad Ring, clouds upper particles which are left.Institute. of is artifacts Saturn’s widely created small of moon various and stray sizes , maintained light. imaged orbiting by Only more the the tens than moon’s planet. of once Adapted . meters in from Reference in the image [5] vertical mosaic, ID: thickness, provides Saturn’s full PIA08329, rings information courtesy are on JPL/NASA/Space made Science up Fig. C.3. E, F, and Gtaken Rings while (normally difficult to see from Earth) appear bright in forward-scattered light in this high-phase-angle mosaic of images Earth, also appear bright here,(south). backlit Distances in indicate sunlight. The Saturn dense radius B (R Ring appears dark because it blocks light from passing through from below Appendix D: The Electromagnetic Spectrum

Figure D.1 illustrates the nomenclature associated with the electromagnetic spec- trum that is generally applicable to interplanetary flight1. Electromagnetic radi- ation extends from the lowest energy and longest wavelength as radio waves up through infrared, visible and ultraviolet light, x-ray and finally , which is the highest energy and shortest wavelength radiation (note the term “cosmic ray” does not denote any sort of electromagnetic radiation, but rather particles such as the nuclei of hydrogen through iron moving through our galaxy at high speed). The spectrum in the figure appears as a vertical list. A line drawn horizontally across the list would show the same electromagnetic radiation expressed in wavelength, frequency, and energy; there is no spectral distinction along the horizontal axis, only nomenclature. Figure D.2 illustrates the effect on radiation in various parts of the spectrum of the Earth’s atmosphere and . The atmosphere’s complete absorption of gamma-rays, x-rays, and much of the ultraviolet wavelengths allows life as we know it to exist here. The absorption of many of the wavelengths of infrared is a hindrance to ground-based IR astronomy, although high mountaintop observatories can gain some advantage. The fact that the ionosphere reflects some wavelengths of radio is a boon to long-distance earthbound radio communications, as the signals can reflect between Earth’s surface and the ionosphere, propagating around the planet long beyond the line-of-sight horizon. It is worthwhile to consider that such a small part of the electromagnetic spec- trum — visible light, a mere sliver across Figure D.1 — has served humans for all of history and prehistory in the quest to know more of the universe. Around the beginning of the it became possible to capture the wealth of additional information contained in additional bands of wavelengths (or photon energies). Among the many varied technologies now in hand, radio telescopes on Earth’s sur- face are capable of capturing views of otherwise invisible phenomena deep across intergalactic space such as those shown in Figure D.3; infrared observato- ries operating high above the atmosphere show us otherwise hidden phenomena such as the places and processes of stellar birth; and orbiting x-ray telescopes and gamma-ray observatories provide glimpses into the most energetic of cosmic events. Figure D.4 shows the remnant of the 1602 (stellar explosion) named in honor of Johannes Kepler, who observed it in the . Pub- lished in observance of the explosion’s four-hundredth anniversary, the illustration comprises views in several parts of the electromagnetic spectrum separately and combined: two in X-ray, one in visible light, and one in the infrared. 342 Appendix D: The Electromagnetic Spectrum Notes

1Some of the powers of ten in Figure D.1 are not labeled because their associated values are not used in general practice. For example x-rays and gamma-rays are more often identified by their photon energies, not by their frequency or wavelength. Similarly radio waves are commonly identified by wavelength and frequency; infrared, visible, and in many cases the ultraviolet, are usually described in values of wavelength alone.

Fig. D.1. Wavelengths, frequencies and photon energy equivalencies. Commonly used electromagnetic spectrum nomenclature is shown. A=˚ Angstrom, which is one-tenth of a nanometer; μ = micro(-meter). Notes 343 Opacity of Earth’s atmosphere to various wavelengths. The Earth’s atmosphere is 100% opaque to x-ray wavelengths (and to gamma rays, whichultraviolet, but are lessens, not the illustratedVisible atmosphere in light becoming is this more only diagraminfrared transparent, but slightly and as absorbed, would millimeter-wavelength wavelengths radio beatmospheric but approach transparency. are further infrared violet Wavelengths longer blocked to is in than entirely,wavelength. the absorbed the about Adapted but left). variously visible 10 from longer at Opacity meters part image wavelengths are continues different courtesy of of blocked at NASA. wavelengths. the by radio, Large 100% the spectrum. down portions for ionosphere. to Figure most of D.1 about of the shows 10 the far frequency meters, as (right-side) well enjoy as perfect Fig. D.2. 344 Appendix D: The Electromagnetic Spectrum

Fig. D.3. Radio and visible light view of galaxy 0313-192. About a billion light years distant, this appears edge-on in this visible-light image by the Hubble Space Telescope. An energetic jet of high-speed particles can be seen in 20-centimeter wave- length radio “light” pouring out along the galaxy’s poles thousands of light years into the surrounding intergalactic space, presumably powered by an accretion disk around the galaxy’s central black hole. A closer view, made in 3-centimeter wavelength radio, is shown at right. The radio images, acquired by the of radio telescopes in Socorro, New Mexico, are shown in light grey superimposed on the visible-light im- age. The second spiral galaxy visible in the left-hand panel is about two hundred million light years closer to Earth than is 0313-192. View online in color by searching for im- age ID: STScI-PRC03-04. Courtesy NASA, NRAO/AUI/NSF and W. Keel (University of Alabama). Notes 345

Fig. D.4. Multi-spectral view of SN 1604. The last known supernova in our galaxy appeared in 1604 and was observed by Johannes Kepler. Four hundred years later the Chandra X-ray Observatory in Earth orbit, the Spitzer Infrared Space Telescope Facility in solar orbit trailing the Earth, and the Earth-orbiting Hubble Space Telescope made observations of SN 1604, “Kepler’s Supernova,” in four different parts of the electromag- netic spectrum. These views are shown separately and combined in this figure. Spectra obtained in these various wavelength bands reveal processes ongoing as the debris shell continues to evolve and expand into the surrounding interstellar space. View online in color using image ID: STScI-PRC04-29a. Courtesy NASA, ESA, R. Sankrit and W. Blair (Johns Hopkins University). Appendix E: Chronology

This time-ordered list of selected events of interest and importance to interplanetary flight includes not only a good number of spacecraft mission events,1 which begin on page 351, but also the dates of some milestones in the Deep Space Network’s history, as well as some historical breakthroughs in knowledge.

Circa 270 BCE The Greek astronomer and mathematician of Samos (ca. 310–230 BCE) estimates Sun and Moon sizes and distances and proposes that the Earth revolves around the Sun, a theory that does not gain acceptance.

Circa 140 The Greek/Egyptian astronomer Claudius Ptolemaeus (Ptolemy, ca. 85–165) writes Mathematike Syntaxis, later known as the Almagest, an Earth-centered cosmolog- ical treatise.

1543 The Polish scholar Nicholaus Copernicus (1473–1543) cautiously publishes his the- ory of the Sun-centered solar system.

1572 November 2 A “new star,” brighter in the sky than the planet Venus, is widely observed in the constellation Cassiopeia, and accurate observations of its location and brightness are recorded by the Danish astronomer Tycho Brahe (1546–1601), among others. It remained visible for two years. Located in our galaxy about ten thousand light years away, the remnant of this supernova, SN 1572, is a target of investigation today.

1600 The exact date of the invention of the telescope is not preserved in history, but it was in general use by this time, largely for Earth-bound applications.

1604 October 9 A star in our galaxy about twenty thousand light-years away explodes and produces a “new star” in the constellation Ophiuchus, appearing brighter in 348 Appendix E: Chronology the sky than the planet Jupiter. Johannes Kepler is among the astromomers to observe it, and today the supernova remnant is named for him. See Figure D.4 on page 345.

1610 January 7 The Tuscan scholar Galileo Galilei (1546–1642) first observes Jupiter and its companion moons with a homemade astronomical telescope. Later in the same year he observed Saturn and noted, “...to my very great amazement Saturn was seen to me to be not a single star, but three together, which almost touch each other.”

1612 December Galileo observes Saturn while the Earth was passing through its ring plane, viewing the thin rings edge-on. On the disappearance of Saturn’s companions he notes, “I do not know what to say in a case so surprising, so unlooked-for and so novel.”

1619 The German mathematician and astronomer Johannes Kepler (1571–1630), using the extensive stellar observations made by Tycho Brahe, completes formulation of his three laws of planetary motion.

1655 The Dutch mathematician and astronomer Christaan Huygens (1629–1695) pro- poses that Saturn was surrounded by “a thin, flat ring, nowhere touching, and inclined to the ecliptic.” He discovers Saturn’s largest moon Titan the same year.

1668 The English polymath Sir Isaac (1642-1727) builds the first telescope to successfully use reflecting optics, a type now widely known as the Newtonian re- flector.

1676 The Italian-French astronomer Giovanni Domenico (Jean-Dominique) Cassini (1625– 1712) discovers a gap in Saturn’s rings now named the Cassini Division in his honor.

1686 Newton publishes Philosophie Naturalis Principia Mathematica. Chronology 349

1704 Newton publishes Opticks, which includes his work with prisms and the spectrum of visible light.

1781 13 March The German-born astronomer (1738–1822) discovers the planet Uranus using a large homemade Newtonian reflector telescope.

1800 13 March Herschel discovers the infrared part of the electromagnetic spectrum.

1801 The German chemist and physicist Johann Ritter (1776–1810) discovers the ultra- violet part of the electromagnetic spectrum. January 1 The Italian astronomer Giuseppe Piazzi (1746–1826) discovers the first asteroid, . Initially regarded as a new planet, it is now recognized as one of millions of bodies orbiting the Sun in the main .

1842 The Austrian physicist Christian Doppler (1803–1853) describes the change of ob- served frequency when source or observer are approaching or receding.

1847 September 20 The American Association for the Advancement of Science (AAAS) is established and meets in Philadelphia, Pennsylvania, the following year. Publi- cation of its journal Science begins in 1880.

1856 The Scottish physicist and mathematician James Clerk Maxwell (1831–1879) shows that Saturn’s rings cannot be solid and must be made of “an indefinite number of unconnected particles”.

1864 Maxwell formulates equations of electromagnetism and shows that light is an elec- tromagnetic wave.

1869 August 18 A total of the Sun enables the English astronomer Norman Lockyer (1836–1920) and, independently, the French astronomer Pierre Janssen (1824–1907) to find a yellow spectral emission line at 587.49 nm in the solar corona spectrum and attribute it to an unknown element (later named helium). November 4 Lockyer publishes the first issue of the journal . 350 Appendix E: Chronology

1880 July 3 AAAS begins publishing the weekly journal Science.

1886 The German physicist Heinrich (1857–1894) demonstrates the reception of electromagnetic waves with an antenna.

1877 September the Italian astronomer Giovanni Schiaparelli (1835–1910) claims to see straight channels (Italian canali) on the surface of Mars. Confirmed by some later observers but not others, they were popularized by the American astronomer Per- cival Lowell (1855–1916) but were ultimately proven to be optical illusions.

1895 Italian inventor Guglielmo Marconi (1874–1937) sends and receives radio signals, demonstrating the feasibility of radio communications.

1900 October 19 The German physicist Max (1858–1947) proposes his black- body radiation law to describe the observed radiated spectra.

1903 December 17 First sustained, powered, and controlled flight of an airplane, piloted by the American inventor Orville Wright (1871–1948).

1905 March The German-born theoretical physicist Albert Einstein (1879–1955) shows that the photoelectric effect can be understood as light interacting with matter in discrete quanta of energy ().

1906 The American inventor Lee De Forest (1873–1961) creates the triode vacuum-tube amplifier.

1913 July The Danish physicist Niels Bohr (1885–1962) publishes a model of the atom involving orbiting a nucleus, and photon emission based on electrons changing orbits.

1925 The German engineer Walter Hohmann (1880–1945) describes the minimum-energy interplanetary transfer trajectory. Chronology 351

1926 March 16 First liquid-propellant launched, built by the American inventor Robert Goddard (1882–1945), using a DeLaval nozzle.

1930 The Hungarian-German-American engineer and physicist Theodore von K´arm´an (1881–1963) becomes director of the California Institute of Technology’s Guggen- heim Aeronautical Laboratory, later to help it become the Jet Propulsion Labora- tory.

February 18 The American astronomer (1906–1997) discovers Pluto. Initially regarded as a new planet, it is now recognized as one of many similar bodies, called plutoids, orbiting the Sun in the region beyond Neptune.

1939 January and March The German-American physicist Hans Bethe (1906–2005) pub- lishes two papers showing how nuclear fusion reactions produce energy in the stars.

1951 The American engineers Julian Allen (1910–1977) and A.J. Eggers (1922–2006) discover that the destructive frictional heating of atmospheric (re-)entry vehicles can be managed by using a high-drag, blunt-nose design.

1957 Begins the Space Age. October 4 The launches I, the world’s first artificial satellite, into Earth orbit.

Fig. E.1. Sputnik-I. 352 Appendix E: Chronology

1958 January 31 The United States launches its first satellite, Explorer I, into Earth orbit. Its subsequent identification of the Van Allen belts constitutes the first sci- entific discovery using a space-borne instrument.

29 July The US National Aeronautics and Space Administration (NASA) is es- tablished by act of Congress. It replaces the old National Advisory Committee on Aeronautics.

1959 January 4 The Soviet Union’s 1, launched January 2, passes by the Moon at a distance of 5,995 kilometers (launched 2 January) and enters , the first spacecraft to escape from Earth’s gravitational hold.

March 4 The U.S , launched the previous day, passes within 60,000 kilo- meters of the Moon.

September 14 The USSR’s , launched on September 12, impacts the Moon in the Palus Putredinus region.

October 7 The USSR’s , launched October 4, returns the first images from the lunar far side.

1961 August 23 The American mathematician Michael Minovitch describes “gravity propelled interplanetary space travel,” later to be known as the “” technique.

1962 April 26 The US , launched April 23, impacts the .

August 27 The US launches to Venus.

December 14 Mariner 2 Venus flyby at 34,773 kilometers.

1963 December 24 Deep Space Network (DSN) established by incorporating the world- wide facilities of JPL’s Deep Space Instrumentation Facility.

1964 July 31 US spacecraft , launched July 28, crashes on the Moon between Mare Nubium and Procellarum after returning 4,308 images.

November 28 The US launches to Mars. Chronology 353

1965 February 20 US spacecraft , launched February 17, impacts the Moon in Mare Tranquillitatis after returning 7,137 images.

March 24 The US , launched March 21, impacts in the lunar crater Alphonsus after returning 5,814 images.

July 15 Mariner 4 flies by Mars at 9,846 kilometers, executing the first radio occultation at Mars, and returning the first images from another planet.

July 20 The USSR’s , launched July 18, passes the Moon at 9,200 kilometers, returning twenty-five images from the lunar far side. The spacecraft continues to aphelion at the for a spacecraft test, re-transmitting the lunar images.

1966 February 3 The USSR’s , launched January 31, makes the first lunar soft landing using and . It returns panoramic images of the lunar surface and radiation measurements from through Febru- ary 6.

April 3 The USSR’s , launched March 31, enters .

June 2 US , launched May 30, lands on the Moon inside a 100 kilometer- diameter crater in Oceanus Procellarum by means of retrorockets. Surviving the lunar night, it returns 11,240 images through July 13.

August 14 US , launched August 10, enters lunar orbit. Scouting potential landing sites for Surveyor and , it returns 229 images and other data through October 29 when it impacts the far side on command.

August 28 The USSR’s , launched August 24, enters lunar orbit. It acquires data on X-ray and gamma-ray emissions characterizing the lunar surface and mea- sures the lunar gravity field and and radiation flux through October 1.

October 25 The USSR’s , launched October 22, enters lunar orbit. It re- turns images and other data through January 11 1967.

November 10 , launched November 6 (US), enters lunar orbit. It returns images and other data scouting potential landing sites for Surveyor and Apollo through October 11, 1967, when it impacted the surface on command.

December 24 , launched December 21 (USSR), soft-lands on the Moon near Oceanus Procellarum. It returns panoramas and soil data through about De- cember 31. 354 Appendix E: Chronology

1967 February 8 , launched February 5 (US), enters lunar orbit. It returns 626 images and other data scouting potential landing sites for Surveyor and Apollo through October 29, when it impacts the surface on command.

April 20 , launched April 17 (US), soft-lands on the Moon inside a 200- meter crater in southeast Oceanus Procellarum. It returns data on the and 6,326 images May 4.

May 7 , launched May 4 (US), enters lunar orbit. Its mission is similar to Lunar Orbiter 1 and Lunar Orbiter 2.

June 12 The USSR launches 4 toward Venus.

June 14 (US) lifts off toward Venus.

July 22 , launched July 19 (US), enters lunar orbit to acquire data on interplanetary plasma, magnetic fields, energetic particles, and solar X rays.

August 5 , launched August 1 (US), enters lunar orbit.

September 11 , launched September 8 (US), soft-lands on the Moon in Mare Tranquillitatis.

October 18 enters Venus atmosphere and deploys multiple instruments which return data while the spacecraft descends by parachute, the first successful controlled entry and descent of a spacecraft into the atmosphere of another planet.

October 19 Mariner 5 flies by Venus at 4,000 kilometers returning data.

November 10 , launched November 7 (US), soft-lands on the Moon in Sinus Medii.

1968 January 10 , launched January 7 (US), soft-lands on the Moon near Tycho crater in the lunar highlands.

April 10 , launched by the USSR on April 7, enters lunar orbit.

September 18 , launched September 14 (USSR), flies around the Moon. It returns to Earth on September 21 in a controlled re-entry, carrying living biological specimens.

November 14 Zond 6, launched November 10 (USSR), flies around the Moon and returns to Earth November 17 in a controlled re-entry. Chronology 355

1969 January 5 Venera 5 (USSR) launches on a mission to Venus.

January 10 (USSR) launches toward Venus.

February 24 Mariner 6 (US) launches toward Mars.

March 27 Mariner 7 (US) launches towards Mars.

May 16 Venera 5 (USSR) flies by Venus and deploys an instrumented atmospheric probe which enters Venus’ atmosphere and parachutes toward surface.

May 17 Venera 6 (USSR) executes a Venus mission similar to that of Venera 5.

July 20 Following a July 16 launch, ’s Lunar Module Eagle (US) touches down on the Moon, carrying the first humans to set foot on the lunar surface: Neil Armstrong (1930–) and Buzz Aldrin (1930–). Along with Command Module pilot Michael Collins, they return to Earth on July 24 in Command Module Columbia. After additional crewed landings by , 14, 15, 16, and 17, the last to set foot on the moon, Eugene Cernan, returned to Earth December 19, 1972.

July 31 Mariner 6 flies by Mars at a distance of 3,431 kilometers.

July 17 , launched July 13 (USSR), enters lunar orbit.

August 5 Mariner 7 flies by Mars at a distance of 3,430 kilometers.

August 11 Zond 7, launched by the USSR on August 7, flies around Moon. It returns to Earth August 14.

October Invention of CCD by the Canadian physicist Willard Boyle (1924–) and American scientist George Smith (1930–) at Bell Labs.

1970 August 17 Venera 7 (USSR) lifts off for Venus.

September 24 , launched September 12 (USSR), returns lunar samples to Earth from Mare Foecunditatis.

October 24 Zond 8, launched October 20 (USSR), flies around the Moon, It returns to Earth October 27 in a controlled re-entry.

November 15 , launched November 10 (USSR), soft-lands on the Moon in the Sea of , and deploys an instrumented rover, , which travels over 10 kilometers taking soil analysis data.

December 15 Venera 7 soft-lands on Venus, returning data via orbiter. 356 Appendix E: Chronology

1971 May 19 (USSR) launched toward Mars.

May 28 (USSR) launched toward Mars.

May 30 (US) launched towards Mars.

October 3 (USSR) enters lunar orbit (launched September 28).

November 14 Mariner 9 (US) enters Mars orbit, becoming the first spacecraft to orbit another planet. It returned data until 27 October 1972 but continues to orbit Mars.

November 27 Mars 2 enters Mars orbit and makes scientific observations through August 22, 1972.

December 2 Mars 3 (USSR) enters Mars orbit, and delivers a lander that achieves a soft landing. Although the lander then quits functioning after twenty seconds, its touch-down is the first controlled landing on another planet (, 1976, is the first which landed and succeeded in its mission).

1972 February 21 , launched February 14 (USSR), soft-lands on the Moon near Mare Foecunditatis. It returns samples to Earth on February 22.

March 3 Pioneer 10 (US) launches toward Jupiter.

March 27 (USSR) launches toward Venus.

July 22 Venera 8 enters Venus atmosphere, soft-lands, and returns data from the surface for 50 minutes, 11 seconds, via orbiter.

1973 January 15 and , launched January 8 (USSR), reach the lunar surface.

April 5 Pioneer 11 (US) launches toward Jupiter and Saturn.

June 15 -RAE-B, launched June 10 (US), enters lunar orbit to make radio astronomy observations.

July 25 (USSR) launched towards Mars.

November 3 (USA) launched on a gravity-assist trajectory toward Venus and Mercury.

December 3 Pioneer10 flies by Jupiter at 200,000 kilometers. Chronology 357

1974 February 5 Mariner 10 (USA) flies by Venus at 5,768 kilometers and obtains a gravity assist to Mercury.

February 12 Mars 5 (USSR) enters Mars orbit.

March 29 Mariner 10 makes its first flyby of Mercury at 704 kilometers.

June 2 , launched May 29 (USSR), enters lunar orbit.

September 21 Mariner 10 makes a second flyby of Mercury, at 48,069 kilometers.

December 4 Pioneer 11 flies by Jupiter.

1975 March 16 Mariner 10 makes a third and final flyby of Mercury at 327 kilometers.

June 8 (USSR) launches toward Venus.

June 14 Venera 10 (USSR) launches toward Venus.

August 20 Viking 1 (USA) launches towards Mars.

September 9 (USA) launches towards Mars.

October 22 Venera 9 soft-lands on Venus and operates 53 minutes on the surface, returning data via orbiter.

October 25 Venera 10 soft-lands on Venus and operates 65 minutes on surface, returning data via orbiter.

1976 June 19 Viking 1 enters Mars orbit.

July 20 Viking 1 soft-lands on Mars, the first landing on another planet to succeed with an operable spacecraft.

August 7 Viking 2 enters Mars orbit.

August 18 , launched August 9 (USSR), soft-lands on the Moon in and returns soil samples to Earth on August 22.

September 3 Viking 2 soft-lands on Mars.

1977 August 20 Voyager 2 (USA) lifts off for Jupiter and beyond.

September 5 Voyager 1 (USA) launches toward Jupiter and beyond.

December 15 Voyager 1 overtakes Voyager 2 in the main asteroid belt. 358 Appendix E: Chronology

1978 May 20 Pioneer-Venus Orbiter (USA) launches toward Venus.

August 8 Pioneer-Venus Multiprobe (USA) launches toward Venus.

August 12 Explorer 59 (USA), also known as International Cometary Explorer (ICE) and International Sun-Earth Explorer-C (ISEE-C), lifts off to acquire data in heliocentric orbit then encounter comet Giacobini-Zinner.

September 9 (USSR) launches toward Venus

September 14 (USSR) launches toward Venus

December DSN Mark-III Data System implementation completed. This is an up- grade to the tracking system that establishes and maintains the links between spacecraft and flight project teams using 26-, 34-, 64-, and 70-meter aperture sta- tions.

December 4 Pioneer-Venus Orbiter enters Venus orbit.

December 9 Pioneer-Venus Multiprobe’s probe (called Sounder) and three smaller probes enter the Venusian atmosphere.

December 21 Venera 12 (USSR) soft-lands on Venus and transmits data via orbiter for 110 minutes after landing.

December 25 Venera 11 (USSR) soft-lands on Venus and transmits data via orbiter for 95 minutes after landing.

1979 Voyager 1 flies by Jupiter and obtains gravity assist to Saturn.

July 9 Voyager 2 flies by Jupiter and obtains gravity assist to Saturn.

September 1 Pioneer 11 flies by Saturn.

1980 March DSN implements the ability to combine signals received from multiple an- tennas in real time to increase the effective aperture by arraying stations.

November 12 Voyager 1 flies by Saturn and enters a northerly interstellar trajec- tory.

1981 August 5 Voyager 2 flies by Saturn and obtains a gravity assist to Uranus.

October 30 (USSR) launches toward Venus.

November 4 (USSR) launches toward Venus. Chronology 359

1982 March 1 Venera 13 soft-lands on Venus and transmits data via orbiter for 127 minutes after landing.

March 5 Venera 14 soft-lands on Venus and transmits data via orbiter for 57 minutes after landing.

1983 June 2 (USSR) launches toward Venus.

June 7 Venera 16 (USSR) launches toward Venus.

October 10 Venera 15 enters Venus orbit and conducts SAR imaging of the planet’s surface.

October 14 Venera 16 enters Venus orbit and conducts SAR imaging of the planet’s surface.

1984 December 15 (USSR) launches for Venus and Comet Halley.

December 21 (USSR) launches for Venus and Comet Halley.

1985 January 8 launches toward Comet Halley and Earth encounters on Japan’s first interplanetary mission.

11 June Vega 1 deploys atmospheric balloon and lander probe at Venus.

June 15 Vega 2 deploys atmospheric balloon and lander probe at Venus.

July 2 , the first joint European interplanetary mission, launches toward Comet Halley.

August 18 (Japan) launches for Comet Halley.

September 11 Explorer 59 encounters plasma tail of comet Giacobini-Zinner.

1986 DSN implements the Mark-IV Data System, a computer-network-based system that manages the links between spacecraft and flight project teams using 34- and 70-meter aperture stations.

January 24 Voyager 2 flies by Uranus and obtains gravity assist to Neptune. 360 Appendix E: Chronology

January 28 STS Challenger (USA) and crew tragically lost during ascent.

March 6 Vega 1 flies by Comet Halley at 10,000 kilometers.

March 8 Suisei flies by Comet Halley at 151,000 kilometers.

March 9 Vega 2 flies by Comet Halley at 3,000 kilometers.

March 11 Sakigake flies by Comet Halley at 7 million kilometers.

March 13 Giotto flies by Comet Halley at 596 kilometers.

1987 April DSN implements three X-Band high-efficiency 34-meter aperture stations. Additional upgrades to these antennas followed.

1988 May 29 DSN completes upgrade from 64-meter apertures to 70-meter.

July 12 (USSR) launches toward Mars.

1989 January 29 Phobos 2 enters Mars orbit.

March 27 Phobos 2 contact lost prior to deploying landers on the Martian moon Phobos.

May 4 Magellan (USA) launches toward Venus.

August 25 Voyager 2 flies by Neptune and enters southerly interstellar trajectory.

October 18 Galileo (USA) launches toward Venus on a gravity-assist trajectory to Jupiter.

1990 January 24 (Japan) engineering test spacecraft launches into highly elliptical Earth orbit with apoapsis at lunar distance.

February 10 Galileo flies by Venus on a gravity-assist trajectory to Jupiter.

14 February Voyager 1 turns on cameras after they had been dormant for nine years and captures images of the Sun and six planets. Cameras were then shut off permanently.

April 25 Hubble Space Telescope (USA) launches into Earth orbit. Chronology 361

July 2 Giotto flies by Earth for science data acquisition and gravity assist, the first encounter with Earth by a spacecraft approaching from deep space. August 10 Magellan enters orbit at Venus. October 6 () solar-polar orbiter launches.

1991 April 11 Galileo HGA deployment attempts begin; antenna fails to open. October 29 Galileo flies by asteroid 951 Gaspara at 1,600 kilometers en route to Jupiter. December 8 Galileo flies by Earth on a gravity-assist trajectory to Jupiter.

1992 January 8 Sakigake flies by Earth. February 8 Ulysses Jupiter flyby changes the spacecraft’s inclination in solar orbit to about 80◦, an attitude from which it can observe the Sun’s polar regions. July 10 Giotto flies by Comet Grigg-Skjellerup at 200 kilometers. September 25 Mars Observer (USA) launches toward Mars. December 8 Galileo flies by Earth a second time on a gravity-assist trajectory to Jupiter and carries out an optical communications experiment by observing laser illumination from Earth using the imaging science instrument.

1993 May 24 Magellan begins to circularize its highly-elliptical orbit via aerobraking in Venus’ atmosphere, the first such operation at another planet. This results in the ability to acquire high-resolution gravity-field measurements. June 14 Sakigake flies by Earth, within its . August 21 Contact with Mars Observer lost prior to Mars orbit insertion.2 August 28 Galileo flies by asteroid at 2,400 kilometers en route to Jupiter and discovers Ida’s satellite, Dactyl. December 12 Hubble Space Telescope refurbishment, correcting optical focus and making additional upgrades, completed in orbit,.

1994 February 21 (USA), launched January 25, enters lunar orbit. July 16-22 Galileo observes the impact of fragments of comet Shoemaker-Levy 9 into Jupiter’s atmosphere south of the . 362 Appendix E: Chronology

October 13 Magellan impacts Venus in the termination experiment following ex- periments that used the solar panels as windmill blades to study the free molecular flow regime.

October 28 Sakigake flies by Earth at 7 million kilometers.

December DSN implements the first beam-waveguide 34-meter aperture stations. Additional upgrades to these antennas followed.

1995 July 13 Galileo releases its Jupiter atmospheric probe.

September 30 Pioneer 11 ’s last signal detected, from about 45 AU.

December 7 Galileo enters orbit at Jupiter and collects telemetry and tracking data from the atmospheric probe during its entry.

1996 February 14 NEAR Shoemaker (Near-Earth Asteroid Rendezvous, USA) launches toward asteroid .

November 7 Mars Global Surveyor (USA) launches toward Mars.

December 4 Mars Pathfinder (USA) launches toward Mars.

1997 February 21 Hubble Space Telescope’s second refurbishment completed in orbit.

June 27 NEAR Shoemaker flies by asteroid 253 Mathilde at 1,200 kilometers.

July 4 Mars Pathfinder lands in the Ares Vallis region on Mars.

July 6 Mars Pathfinder (USA) rover Sojourner rolls off the lander and onto the Martian surface.

September 12 Mars Global Surveyor enters Mars orbit.

October 15 Cassini-Huygens (USA-Europe) launches toward Venus on a gravity- assist trajectory to Saturn.

1998 January 11 Lunar (USA), launched January 7, enters lunar orbit.

January 23 NEAR Shoemaker flies by Earth at 540 kilometers for gravity-assist, putting it on course for asteroid . Chronology 363

February 17 Voyager 1 exceeds the length of Pioneer 10 ’s flightpath and becomes the most distant human-made object.

April 26 Cassini-Huygens flies by Venus on a gravity-assist trajectory to Saturn.

October 24 Deep Space 1 (USA) technology demonstration spacecraft launches toward asteroid 9969 Braille.

December 11 (USA) launches toward Mars.

1999 February 4 Mars Global Surveyor completes aerobraking maneuvers, circularizing its orbit in preparation for science data collection.

February 7 (USA) launches toward comet Wild 2.

June 24 Cassini-Huygens flies by Venus for the second time on a gravity-assist trajectory to Saturn.

July 29 Deep Space 1 flies by asteroid 9969 Braille at 26 kilometers.

August 18 Cassini-Huygens flies by Earth on a gravity-assist trajectory to Saturn.

September 23 Mars Climate Orbiter unintentionally enters Martian atmosphere and is lost.3

2000 February 17 NEAR Shoemaker enters orbit at asteroid 433 Eros.

December 30 Cassini-Huygens flies by Jupiter on a gravity-assist trajectory to Saturn.

2001 January 23 NEAR Shoemaker soft-lands on asteroid 433 Eros, becoming the first spacecraft to land on an asteroid. Operation continued until February 28.

April 7 (USA) launches toward Mars.

August 8 (USA) launches for the L1 Lagrangian Sun-Earth point to collect solar wind samples.

September 22 Deep Space 1 flies by comet Borrelly at 2171 kilometers.

October 24 2001 Mars Odyssey enters Mars orbit.

November 16 Genesis arrives at L1 and begins collecting solar wind samples until December 3, 2004, when collection ended and the sample collection canister was sealed. 364 Appendix E: Chronology

2002 January 11 2001 Mars Odyssey completes aerobraking maneuvers circularizing its orbit in preparation for science data collection.

2003 January 23 Pioneer 10 ’s last signal detected, from about 84 AU.

May 9 (Japan) launches toward asteroid 25143 Itokawa.

June 2 (USA) launches for Mars.

June 10 Spirit (USA) Mars Exploration Rover spacecraft launches toward Mars.

8 July Opportunity (USA) Mars Exploration Rover spacecraft launches toward Mars.

September 21 Galileo enters Jupiter’s atmosphere in a procedure to dispose of the spacecraft lest it collide with and introduce Earth microbes to its surface or to its sub-surface saltwater .

October 21 The American astronomers Mike Brown (1965–), Chad Trujillo (1973–), and Rabinowitz (1960–) discover an object later named in the Kuiper Belt beyond Pluto. Dispute follows among scientists over the definition of the word “planet.”

November 13 SMART 1 technology demonstration spacecraft (Europe), launched September 27, enters lunar orbit.

December 25 Mars Express enters Mars orbit.

2004 January 2 Stardust flies by comet Wild 2 at 250 kilometers, collecting samples of ejecta.

January 4 Spirit Mars Exploration Rover spacecraft arrives in Gusev Crater on Mars.

January 15 Spirit (USA) Mars Exploration Rover spacecraft drives onto .

January 25 Opportunity Mars Exploration Rover spacecraft arrives at Meridiani Planum on Mars.

January 31 Opportunity Mars Exploration Rover spacecraft drives onto Martian soil. Chronology 365

March 2 (Europe) carrying the lander, launches toward Mars on a gravity-assist trajectory to comet Churyumov-Gerasimenko.

May 19 Hayabusa flies by Earth at 3,725 kilometers for gravity assist to asteroid 25143 Itokawa.

July 1 Cassini-Huygens enters Saturn orbit.

August 3 Messenger (Europe) launches toward Venus on a gravity assist trajectory to Mercury.

September 8 Genesis returns to Earth. The parachute fails to deploy because an accelerometer had been installed upside down, and the sample capsule crashes into the Utah . The sample fragments are recovered for analysis nonetheless.

December 25 Huygens Titan probe separates from Cassini orbiter.

2005 January 12 Deep Impact (USA) launches toward comet .

January 14 Huygens executes parachuted descent through Titan’s atmosphere and survives landing.

March 4 Rosetta-Philae (Europe) flies by Earth for the first time on a gravity-assist trajectory to comet Churyumov-Gerasimenko.

May Voyager 1 penetrates the solar termination shock at 94 AU, where the solar wind goes subsonic, and enters the heliosheath behind the heliopause.

July 3 Deep Impact (USA) releases impactor in the path of oncoming comet Tempel 1 from a distance of 880,000 kilometers.

July 4 Deep Impact’s impactor strikes comet Tempel 1. Flyby spacecraft observes the event, also widely observed from Earth, while approaching from 10,000 kilome- ters.

July 4 Deep Impact begins an extended mission named EPOXI (for Extrasolar Planet Observation and Characterization Investigation) using its imager to ob- serve extrasolar planetary . A further extended mission Deep Impact Extended Investigation (DIXI), will fly by comet Hartley 2 on October 11, 2010, at 1000 kilometers.

August 2 Messenger flies by Earth at 2,347 kilometers on a gravity assist trajectory to Mercury.

August 12 Mars Reconnaissance Orbiter (USA) launches for Mars, circularizing its orbit in preparation for science data collection. 366 Appendix E: Chronology

November 9 (Europe) launches toward Venus.

November 19 Hayabusa settles onto asteroid 25143 Itokawa. On 24 November sam- ple collection was attempted, for a planned return to Earth in June of 2010.

2006 January 15 Stardust returns samples of comet and interplanetary material to Earth.

January 19 New Horizons (USA) launches toward Jupiter on a gravity assist tra- jectory to Pluto and other Kuiper belt objects.

March 10 Mars Reconnaissance Orbiter enters Mars orbit.

April 11 Venus Express enters Venus orbit.

August 24 The International Astronomical Union creates the first scientific defi- nition of the word “planet,” and decides that several objects in the solar system, including Pluto, are defined as “dwarf planets.”

September 11 Mars Reconnaissance Orbiter completes aerobraking maneuvers

October 24 Messenger flies by Venus at 2,990 kilometers on a gravity assist trajec- tory to Mercury.

2007 February 25 Rosetta-Philae flies by Mars at 250 kilometers on a gravity-assist trajectory to comet Churyumov-Gerasimenko.

February 28 New Horizons flies by Jupiter on a gravity assist trajectory to Pluto, Charon, and other Kuiper belt objects, to continue into the Kuiper belt and beyond.

June 5 Messenger flies by Venus for the second time at 337 kilometers on a gravity assist trajectory to Mercury.

August 4 Phoenix (USA) Mars Lander launches toward Mars.

September 27 (USA) launches toward Mars on a gravity-assist trajectory to main-belt asteroids and and Ceres.

October 3 Kaguya (Japan), launched September 14, enters lunar orbit.

October 9 Kaguya releases companion satellite Okina into lunar orbit to participate in radio science experiments.

October 12 Kaguya releases companion satellite Ouna into lunar orbit to partici- pate in radio science experiments. Chronology 367

November 5 Chang’e 1, the first Chinese deep-space mission, launched October 24, enters lunar orbit.

November 13 Rosetta-Philae flies by Earth a second time at 5,295 kilometers on a gravity-assist trajectory to comet Churyumov-Gerasimenko.

2008 May 25 Phoenix lander lands on Mars and begins observations.

June 5 Messenger flies by Mercury the first time at 200 kilometers on a gravity assist trajectory to return to Mercury on its next solar orbit.

July Voyager 2 penetrates the solar termination shock at 86 AU, where the solar wind goes subsonic, and enters the heliosheath behind the heliopause.

July 1 Cassini completes its primary tour of the Saturn system and begins an extended mission in Saturn orbit.

September 5 Rosetta-Philae flies by asteroid 2,867 Steins en route to comet Churyumov-Gerasimenko.

October 6 Messenger flies by Mercury a second time at 200 kilometers on a gravity assist trajectory to return to Mercury on its next solar orbit.

November 2 Last transmission received from Phoenix lander.

November 12 First direct observation of an — a planet of another star. The star is , 25 light-years away, and the planet was detected and con- firmed in HST visible-light images (see page 285).

2009 January Orbiting Carbon Observatory (USA) planned to launch into Earth orbit.

February Dawn to fly by Mars on a gravity-assist trajectory to Vesta and Ceres.

September 29 Messenger to fly by Mercury a third time at 200 kilometers on a gravity assist trajectory to return to Mercury on its next solar orbit.

November Rosetta-Philae to fly by asteroid 2867 Steins en route to comet Churyumov- Gerasimenko.

November 13 Rosetta-Philae to fly by Earth a third time on a gravity-assist tra- jectory to comet Churyumov-Gerasimenko.

2010 October Deep Impact (renamed EPOXI) expected to fly by and observe Comet Hartely 2. 368 Appendix E: Chronology

2011 March 18 Messenger expected to enter orbit at Mercury.

August Dawn expected to enter orbit at main-belt asteroid Vesta.

October Mars Science Laboratory (USA) earliest planned launch.

2012 May Dawn expected to leave orbit from Vesta and set off for Ceres.

2013 August BepiColombo (Europe) expected to launch on a six-year mission to orbit Mercury.

2014 May Rosetta-Philae expected to enter a slow orbit at comet Churyumov-Gerasimenko, descending and releasing the lander Philae, which is intended to fasten to the comet with harpoons, in November 2014,.

2015 February Dawn expected to enter orbit at main-belt asteroid Ceres.

14 July New Horizons expected to fly by to Pluto at 10,000 kilometers, and by its moon Charon at 27,000 kilometers.

Notes

1Spacecraft data selected largely from planetary mission data published online by Dr. David R. Williams of the NASA Goddard Space Flight Center. Complete technical details of any planetary spacecraft and its mission may be found at http://nssdc.gsfc.nasa.gov/planetary/chronology.html. 2Included here to support discussion in Chapter 4. Most other lost missions are not listed in this chronology. 3Included here to support discussion in Chapter 2. Most other lost missions are not listed. Appendix F: Units of Measure, Abbreviations, Greek Alphabet

Units of Measure bps Bits per second; a measure of data communications rate. There are seven base units in the Inter- ◦C Celsius temperature; derived from the national System of Units (SI). All other SI base unit K –273.15. SI units are derived from these base units. c Centi. A multiplier; x 10−2 from the Latin Many of the derived units have special names “centum” (hundred). and symbols. Most of the units of measure c in a vacuum; 299,792,458 listed here are either SI units — base or de- m/sec. rived — or units recognized by SI. The SI cd Candela; the SI base unit of luminous in- base unit definitions listed here are from the tensity. The candela is the luminous in- U.S. National Institute of Standards Guide tensity, in a given direction, of a source to the SI. that emits monochromatic radiation of 12 A ; the SI base unit of electric cur- frequency 540 ×10 hertz and that has rent. The ampere is that constant cur- a radiant intensity in that direction of rent which, if maintained in two straight 1/683 per steradian. parallel conductors of infinite length, Da Dalton; a unit of atomic mass approx- of negligible circular cross section, and imately equal to the mass of one pro- placed 1 meter apart in vacuum, would ton or one neutron (electrons have little produce between these conductors a force mass). equal to 2 × 10−7 newton per meter of dB Decibel; a base-10 logarithmic expres- length. sion of power or dimensionless ratio. A A˚ Angstrom;˚ an internationally recognized number of decibels represents the num- non-SI unit of length (typically wave- ber of tenths to which the power of ten 20 10 length or sizes of atoms) equal to 0.1 is raised: 20 dB = 10 / = 100. nanometer. dBm Decibel referenced to a milliwatt; 30 30 10 AU Astronomical Unit; a measure of dis- dBm = 10 / = 1000 mW (1 W). tance, based on the mean sun-Earth dBHz Decibel referenced to one hertz; 40 40 10 distance. The International Astronom- dBHz = 10 / = 10,000 Hz (10 kHz). ical Union defines the AU as the dis- dBi Decibel referenced to an isotropic radi- 50 10 tance from the Sun at which a particle ator to express gain; 50 dBi = 10 / of negligible mass, in an unperturbed = 100,000-fold increase (gain). ◦ orbit, would have an of degree of arc 1 of arc; 1/360 of a circle. 365.2568983 days (a Gaussian year). The eV Electron volt; a measure of the energy AU is thus defined as 1.4959787066 × of an electromagnetic wave or photon. 9 1011 m = 149,597,870.66 km. G Giga; a multiplier, x 10 from the Latin bel Unit of power ratio; most often ex- “gigas” (giant). Note: while Giga means pressed as the decibel, dB, 0.1 bel. 109 everywhere, in the U.S., a billion 370 Appendix F: Units of Measure, Abbreviations, Greek Alphabet

means 109, while in other countries us- substance. The mole is the amount of ing SI, a billion is equal to 1012. substance of a system which contains as G Gauss; a unit of magnetic flux density many elementary entities as there are equal to 1/10,000 tesla. atoms in 0.012 kilogram of carbon 12. g Gram; SI unit of mass. N Newton; the SI unit of force derived from Hz Hertz; the SI unit of frequency: the the SI base units m·kg·s−1. number of cycles per second, derived n Nano; a multiplier, x 10−9 from the Greek from the SI base unit s−1. “nanoz” (dwarf). J Joule; the SI unit for energy, work, or ohm (Symbol Ω) The SI unit of electrical quantity of heat, equal to N·m, derived resistance, equal to V/A, derived from from the base units m2·kg·s−2. the base units m2·kg·s−3·A−2. K ; the SI base unit of thermody- Pa Pascal; the SI unit of pressure or stress, namic temperature. The kelvin is the equal to N/m2, derived from the SI base fraction 1/273.16 of the thermodynamic units m−1·kg·s−2. temperature of the triple point of water rad Radian; the SI unit of plane angle, de- (273.16 K or 0.01 ◦C). rived from m·m−1 = 1. Equal to 180/π k Kilo; a multiplier, x 103 from the Greek degrees of arc, about 57.295◦. “khilioi” (thousand). s Second; the SI base unit of time. The sec- kg Kilogram; the SI base unit of mass. The ond is the duration of 9,192,631,770 pe- kilogram is equal to the mass of the in- riods of the radiation corresponding to ternational prototype of the kilogram. the transition between the two hyper- LY Light Year; a measure of distance, the fine levels of the ground state of the distance light travels in one year; about cesium-133 atom. 63,240 AU. second of arc 1” of arc = 1/60 of a minute M Mega; a multiplier, x 106 from the Greek of arc. “megas” (great). sr Steradian; the SI unit of solid angle, de- m Milli; a multiplier, x 10−3 from the Latin rived from m2·m−2 = 1. This is the “mille” (thousand). solid angle subtended at the center of m Meter; the SI base unit of length (U.S. a sphere of radius R by a portion of the spelling; elsewhere, ). The meter sphere’s surface having an area R2. The is the length of the path travelled by area of a sphere is 4π sr. light in vacuum during a time interval T Tesla; the SI unit of magnetic flux den- of 1/299,792,458 of a second. sity equal to 10,000 gauss. micro A multiplier; x 10−6 from the Greek V Volt; the SI unit of electrical potential “micros” (small). difference or electromotive force, equal μ Symbol for micron (micrometer); one mil- to W/A, derived from the base units: lionth of a meter. Also a multiplier pre- m2·kg·s−3·A−1. fix; see micro. W Watt; an SI unit of power equal to joules minute of arc 1’ of arc = 1/60 of a degree. per second, derived from the SI base mol Mole; the SI base unit for amount of units m2·kg·s−3. Conversions 371 Conversions

Table F.1. SI to English Unit Conversions Millimeters to inches: mm x 0.0393700787401575 = in Centimeters to inches: cm x 0.393700787401575 = in Meters to feet: m x 3.28083989501312 = ft Meters to yards: m x 1.09361329833771 = yd Kilometers to : km x 0.621371192237334 = mi Grams to ounces: g x 0.0352739907229404 = oz to pounds: kg x 2.20462262184878 = lb Newtons to pounds force: N x 0.224809024733489 = lbf Kelvin to Celsius: K – 273.15 = ◦C Celsius to : (◦C x 9/5) + 32.0 = ◦F 372 Appendix F: Units of Measure, Abbreviations, Greek Alphabet Abbreviations

3-D Three dimensional C3 Characteristic energy (intensive quan- Ae Exhaust area tity) At Throat area C3H8 Propane AAAS American Association for the Ad- C/A Closest approach vancement of Science Ca AACS Attitude and Articulation Control C&DH Command and Data Handling sub- System system AAS American Astronomical Society Caltech California Institute of Technol- AC Alternating current ogy ACP Aerosol collector and pyrolizer CAPS Cassini plasma spectrometer Ag Silver CCD Charge-coupled device AIAA American Institute of Aeronautics CCSDS Consultative Committee for Space and Astronautics Data Systems Al Aluminum CD Compact disc Al2O3 Alumina Cd Cadmium AMD Angular Desaturations CDA Cosmic dust analyzer Amp Amplifier (see also Units of Measure CDR Critical Design Review listed below) CDS Command and Data Subsystem AO Adaptive optics CEA Cambridge Electron Accelerator AO Announcement of opportunity CERR Critical Events Readiness Review APL Applied Physics Laboratory, Johns- CESR French Centre d’Etude Spatiale des Hopkins University Rayonnements APXS Alpha-particle X-ray spectrometer CH3N2H3 Mono-methyl hydrazine, MMH ARQ Automatic repeat-request CIRS Composite IR spectrometer As Arsenic Cl ASI Agenzia Spaziale Italiana (Italian Space CLT Command-loss timer Agency) CM ATK Alliant Techsystems, Inc. Previously Cm Curium , Inc., now known as ATK Launch CMC Center Management Council Systems Group. CMD Command data type (one of seven in ATLO Assembly, test, and launch opera- DSN) tions CME AUI Associated Universities, Inc. CMG Control-moment gyro BCE Before current era CNES French National Center of Space Re- Be search BER Bit error rate CNG Compressed natural gas Biprop Bi-propellant Co Cobalt BLF Best-lock frequency CO2 Carbon dioxide bps Bits per second CO2 Carbon dioxide BPSK Binary Phase Shift Keying modula- COBE COsmic Background Explorer tion CTS Command and Telemetry Subsystem BVR Block-V (Roman numeral five) Re- CXC Chandra X-Ray Center ceiver ΔDOR or DDOR Delta dfferenced one-way BWG Beam-waveguide DSN antenna range CCarbon ΔV Delta V; change in velocity C2H2 Acetylene DC Direct current C2H8N2 Unsymmetrical dimethyl - DDOR or ΔDOR Delta differenced one-way zine, UMDH range Abbreviations 373

DECIGO DECi-hertz Interferometer Grav- GMT Greenwich Mean Time itational wave Observatory GPMC Governing Program Management DN Data number in telemetry Council DOF Degree(s) of freedom GPS Global Positioning System Dop (Dopp) Doppler shift GR General relativity DOR Differenced one-way range GRNS Gamma-ray and neutron spectrom- DPS Division for of the eter American Astronomical GRS Gamma-ray spectrometer DR Decommissioning Review GSFC NASA Goddard Space Flight Center DS1 Deep Space 1 spacecraft H2 Molecular hydrogen DSCC Deep Space Communications Com- H2O Water plex H2O2 DSS Deep Space Station H2SO4 Sulphuric acid DSL Digital subscriber line HASI Huygens atmospheric structure in- DSM Deep Space Maneuver strument DSN Deep Space Network HCN DSS Deep space station HEF High-efficiency (at X-band) DSN an- DVD Digital versatile disc tenna ECC Error-control coding HEMT High-Electron Mobility Transistor EDAC Error detection and correction HF High Frequency EDL Entry, descent, and landing HGA High-Gain Antenna EDR Experiment Data Record HiRISE High-Resolution Imaging Science EDT Eastern daylight time Experiment EGA Engine gimbal assembly HRG Hemispherical-resonator gyro EHF Extremely High Frequency HST Hubble Space Telescope EIRP Effective isotropic radiated power HTPB Hydroxy-terminated polybutadiene ENA binder EOPM End of Prime Mission Isp Specific impulse (intensive quantity) EPPS Energetic particle and plasma spec- IBM International Business Machines trometer ICRF International Celestial Reference ERT Earth-receive time Frame ESA European Space Agency IEC International Electrotechnical Commis- ET Ephemeris time (see Glossary) sion EU Engineering unit in telemetry IEEE Institute of Electrical and Electron- F&P Fields and particles ics Engineers, Inc. originally (in its mod- F&T Frequency and timing data type (one ern expanded scope, the name is simply of seven in DSN) I-triple-E) FEC Forward error-correction IERS International Earth Rotation and Ref- Field-effect transistor erence Systems Service FFT Fast Fourier transform INCA Ion and neutral camera FM Frequency modulation (or modulated) INMS Ion and neutral mass spectrometer FRR Flight Readiness Review IPU Injection Propulsion Unit g Local IR Infrared G Universal gravitational constant IRS Infrared Spectrograph 2 g 0 Standard Earth gravity, 9.80665m/s IRU Inertial Reference Unit GaAs arsenide ISO Integrated Sequence of Events GC Gas chromatograph Isp Specific impulse GCMS Gas chromatograph mass spectrom- ISS Imaging science subsystem eter ISS International Space Station Ge IUS GEM -epoxy motor 374 Appendix F: Units of Measure, Abbreviations, Greek Alphabet

JAXA Japanese Aerospace Exploration MGA Medium gain antenna Agency MIL-STD Military standard JHU Johns-Hopkins University MIMI Magnetospheric imaging instrument JPL Jet Propulsion Laboratory (Caltech) MIMOS Mini-M¨ossbauerspectrometer JSC NASA MIT Massachusetts Institute of Technol- Ka Band of microwave radio frequencies ogy (see Appendix D) MLI Multi-layer insulation KDP Key decision point MMH Mono-methyl hydrazine KOH hydroxide MMU Mission module unit KSC NASA MOI Mars Orbit Insertion rocket burn Ku Band of microwave radio frequencies MOLA Mars Orbiter Laser Altimeter (see Appendix D) MON Mixed oxides of nitrogen LANL U.S. Los Alamos National Labora- MON Monitor data type (one of seven in tory DSN) LASCO Large angle spectrometric corona- Monoprop Mono-propellant graph MPD Magnetoplasmadynamic thruster LBS Linear Boom Actuator MPI German Max Planck Institute LCD Liquid-crystal display MP P Maximum power point LDPC Low-density parity-check MRB Mission Readiness Briefing LED Light-emitting diode MRO Mars Reconnaissance Orbiter LGA Low-Gain Antenna MRO Memory readout Li Lithium MS Mass spectrometer LIBS laser-induced breakdown MSL Mars Science Laboratory LIGO Laser Interferometer Gravitational N2 Molecular nitrogen Wave Observatory N2H4 Hydrazine LINEAR LIncoln Near-Earth Asteroid Re- N2O4 Nitrogen tetroxide (NTO) search NAIF Navigation and Ancillary Informa- LISA Laser-Interferometer Space Antenna tion Facility LNA Low-Noise Amplifier NASA U.S. National Aeronautics and Space LORRI Long-Range Reconnaissance Imager Administration LRC NASA Research Center Nd:YAG Neodymium-doped yttrium alu- LV FRR Launch Vehicle Flight Readiness minum garnet Review NEAR Near-Earth Asteroid Rendezvous LV LRR Launch Vehicle Launch Readiness spacecraft (renamed NEAR-Shoemaker) Review NEO Near-Earth object LY Light year NH3 MAG Magnetometer NH4CLO2 Ammonium MAG Magnetometer NiCd -cadmium MARCI Mars Color Imager instrument NIMS Near-IR mapping spectrometer MCD Maximum-likelihood Convolutional NIST National Institute of Standards and Decoder Technology MCO Mars Climate Orbiter spacecraft NO Nitric oxide MCR Mission Concept Review NRAO U.S. National astronomical radio ob- MDR Mission Definition Review servatory MEC Mass expulsion control NRC U.S. National Research Council MEMS Micro-Electro-Mechanical System NS Neutron spectrometer MEP NSF U.S. National Science Foundation MEPAG Mars Exploration Program Anal- NSSDC National Space Science Data Cen- ysis Group ter MER Mars Exploration Rover NTO Nitrogen tetroxide MGA Mars gravity assist O2 Molecular Abbreviations 375

OD Orbit determination RTG Radioisotope thermoelectric genera- OH Hydroxyl tor ORR Operations Readiness Review RWA assembly OSI Open Systems Interconnection S Band of microwave radio frequencies (see OSR Optical solar reflector Appendix D) OTM Orbit Trim Maneuver S33 Saturn-tour Command Sequence num- Pc Combustion chamber pressure ber 33 Pe Exhaust pressure SAF Spacecraft assembly facility P&W Pratt and Whitney SAO Smithsonian Astrophysical Observa- Pb Lead tory PDR Preliminary Design Review SAR Synthetic aperture radar PDS NASA Planetary Data System Sb Antimony PDT Pacific Daylight Time SBC Swing-By Calculator PEPSSI Pluto Energetic Particle Spectrom- SCET Spacecraft event time eter Science Investigation SDC Student Dust Counter PI Principal investigator SEP Sun-Earth-Probe (spacecraft) angle PICA Phenolic-impregnated carbon abla- SET Search for Extraterrestrial Intelligence tor SHF Super High Frequency PIR Proposal Implementation Review SI International System of Units PLAR Post Launch Assessment Review Si Silicon PLL Phase-locked-loop SiO2 , silica PMC Program Management Council SIR System Integration Review PMSR Project Mission System Review SIRTF Spitzer Space Fa- PN Pseudo-noise code cility PNAS Proceedings of the U.S. National SLA Super light-weight ablator Academy of SMSR Safety and Mission Success Review PPR Photopolarimeter-radiometer SN Supernova PRM Periapsis Raise Maneuver SNR Signal-to-Noise Ratio Pu SO2 Sulphur dioxide PV Photovoltaic SOHO Solar and Heliospheric Observatory px Pixel SPC Signal Processing Center Q Quantity of electrical charge SPICE Spacecraft, Planet, Instruments, C- QAM Quadrature Amplitude Modulation matrix (camera angles), and Events QPSK Quadrature Phase Shift Keying SRM Solid-propellant rocket motor modulation SRPS Stirling Radioisotope Power System RJ /radii SRR System Requirements Review RADAR RAdio Detection And Ranging SRU Stellar reference unit RAT SSI Solid-state imager RCS Reaction control system SSME main engine RDR Radar STS Space transportation system (space REX Radio Science Experiment shuttle) RFA Request for action SWAP Solar Wind Analyzer around Pluto RFI Radio frequency interference Tc Combustion chamber temperature RHU TAI International Atomic Time, from the RNG Range French “Temps Atomique International” RPM Revolutions per minute TCM Trajectory-Correction Maneuver RPWS Radio & plasma wave science TCP/IP Transmission Control Protocol and RS Radio science data type (one of seven Internet Protocol in DSN) TDB Barycentric dynamical time (see Glos- RS Reed-Solomon forward error correction sary) RSS Radio science system TDM Time-division multiplex 376 Appendix F: Units of Measure, Abbreviations, Greek Alphabet

TDRSS Tracking and Data Relay Satellite UTC “Temps Universel Coordonn´e”,coor- System dinated universal time TDT Terrestrial dynamical time (see Glos- UV Ultraviolet sary) UVIS UV imaging spectrograph TEGA Thermal evolved gas analyzer UVS UV Spectrometer TES Thermal emission spectrometer VIN Inbound velocity TLM Telemetry data type (one of seven in VJH Jupiter’s heliocentric velocity DSN) VOUT Outbound velocity TNT Trinitrotoluene Ve Exhaust velocity TRK Tracking data type (one of seven in V2 German liquid-propellant rocket 1044– DSN) 1952 TRL Technology readiness level VAC Volts AC TT Terrestrial time (see Glossary) VDC Volts DC TV Television VHF Very High Frequency TVA Thruster-valve assembly VIMS Visible and IR mapping spectrome- TWNC Two-way non-coherent ter TWTA Traveling-wave tube amplifier VLBI Very long baseline UCLA Los Angeles WMAP Wilkinson Microwave Anisotropy UHF Probe, and the Planck Surveyor UMDH unsymmetrical dimethyl hydrazine WWW World-wide web USNO United States Naval Observatory X Band of microwave radio frequencies (see USO Ultra-Stable Oscillator Appendix D) UT Universal Time (see Glossary) XTWTA X-band traveling-wave tube am- UT0 (see Glossary) plifier UT1 (see Glossary) YAG Yttrium aluminum garnet UT2 (see Glossary) Zn Zinc The Greek Alphabet 377 The Greek Alphabet

Table F.2. The Greek Alphabet Uppercase Lowercase

Alpha A α Beta B β Gamma Γγ Delta Δδ E Zeta Z ζ Eta H η Theta Θθ Iota I ι Kappa K κ Λλ M μ Nu N ν Xi Ξξ Omicron O o Pi Ππ Rho P ρ Sigma Σσ Tau T τ Upsilon Υυ Phi Φφ Chi X χ Psi Ψψ Omega Ωω Glossary

AACS Attitude and Articulation Control The rate of change in veloc- Subsystem; hardware and software re- ity, magnitude or direction or both. Ex- sponsible for estimating and maintain- pressed in SI as meters per second per ing a spacecraft’s specified orientation, second (m/s2). stability, and rotation about one or Accelerometer AACS input device to mea- more axes, and for controlling the point- sure onboard acceleration. ing of scan platforms, solar arrays, or Acceptance testing Procedures that verify engine nozzles. a component works to specifications. AAS American Astronomical Society; the Ace Call sign on voice nets for the sin- major organization of professional as- gle point of contact responsible for a tronomers in North America, estab- project’s realtime operations. lished 1899. Acetylene (C2H2) AA Tauri Sun-like star about 450 light found in outer solar system atmo- years away, with disk of protoplane- spheres and protoplanetary disks. tary gas and dust, probably forming Active-sensing Category of science instru- . Spitzer Space Tele- ments that make observations by sup- scope’s infrared spectrograph revealed plying the energy needed to probe signatures of organic compounds in the a target and capture the response, disk. e.g., remote-sensing radar, and direct- A Ring In the Saturnian system, the outer- sensing alpha-proton x-ray spectrome- most of three broad main rings visible in ter (APXS). Compare passive-sensing. a small telescope. Particles in the outer Actuator In control theory, a device that part of the A Ring orbit Saturn once ev- applies an appropriate automated con- ery 14.4 hours, at 16.66 kilometers per trol to a system to change its state, second. for example reaction wheels on a space- Absolute zero Point on the Kelvin scale craft, which affect its attitude. of absolute thermodynamic tempera- Adaptive optics System on Earth-based ture at which molecular movement is telescopes that uses a deformable mir- minimum in relation to the rest of the ror to remove distortions due to atmo- body. spheric turbulence and improve resolu- Absorption Spectrum Electromagnetic ra- tion of a target. diation wavelengths absorbed by atoms Aerobraking Using an atmosphere to re- or molecules in a gas. Sunlight passing duce a spacecraft’s kinetic energy by through a planet’s or a satellite’s atmo- converting it to heat via atmospheric sphere exhibits a lack of specific wave- friction. Applies to entry and descent lengths corresponding to the amount via heat-shield, and to modification of of their absorption in the atmosphere. a non-shielded spacecraft’s orbit, for ex- Compare reflectance spectrum. ample to reduce apoapsis altitude. 380 Glossary

Aerosol A suspension of fine solid particles Alpha-particle X-ray Spectrometer or liquid droplets in a gas, such as clouds (APXS) Active direct-sensing science or smog in an atmosphere. instrument which emits alpha particles Aerosol Collector and Pyrolizer (ACP) to probe targets at close range. Active direct-sensing science instrument Alternating current (AC) Electric current that admits atmospheric samples, cap- whose direction, and polarity on its con- tures aerosols in a filter, then heats the ductors, reverses cyclicly. filter’s contents to change their state Alternator Device that converts mechani- to gas, for further analysis by another cal energy into the energy of alternating instrument (such as a gas chromato- electrical current. graph). Altimeter On spacecraft, an instrument Aerozine-50 A mixture of hydrazine and that measures distance to a body’s sur- unsymmetrical dimethyl hydrazine, for face using radar. use as liquid rocket fuel. Altimetry Science data consisting of mea- AGU American Geophysical Union; a surements from an altimeter showing worldwide scientific community that topographic relief on a body. advances understanding of Earth and Alumina Aluminum oxide (Al2O3), a com- space. widely used as an abrasive. AIAA American Institute of Aeronautics Mechanically supports catalyst mate- and Astronautics; established 1963 to rial within monopropellant hydrazine advance the state of aerospace science, thrusters. engineering, and technological leader- Aluminized Having metallic aluminum de- ship. posited on a surface, as for example the Air bags Used by Pathfinder and MER, film layers of multi-layer insula- four bags on the landers’ exterior, each tion. having six lobes of -cloth, in- Aluminum Element, symbol Al, atomic flated by gas generators prior to collid- number 13; a lightweight metal at room ing with the rough Martian surface. temperature. Albedo Measurement of the extent to Ammeter Device that registers the quan- which an object diffusely reflects tity of electrical current flowing in a cir- sunlight. Geometric albedo measures cuit. brightness with illumination from Ammonia (NH3) Compound found exten- directly behind the observer (phase sively in nature. angle zero), such as from Earth. Bond Ammonium perchlorate (NH4ClO4) Com- albedo, named for the American as- pound used widely as oxidizer in solid tronomer George Bond (1825–1865), rocket motors. takes into account all wavelengths and Amperage Non-standard term for electrical all phase angles, and can be observed current. by spacecraft. Ampere-hour (Ah) A measure of battery Algorithm Defined sequence of instructions capacity indicating the number of hours for completing a task, in computer pro- it can supply a current of 1 Ampere. gramming or mathematics, which when Amplification In electronics, replicating a given an initial state, determines an end low-power signal at higher power. state. Amplitude modulation (AM) Modifying a Allotrope One of various possible forms an radio signal to carry information by element can take, based on the struc- varying the amplitude, or height, of its tural arrangement of its atoms, e.g., waves. amorphous if random, crystal if latticed, Analyte A substance being analyzed in an coal vs. diamond. instrument, typically a gas chromato- Alpha particle Helium nucleus; two pro- graph or mass spectrometer. tons and two neutrons. Glossary 381

Angle of attack The angle between an air- Apoareion Apoapsis in Mars orbit. foil and the oncoming relative wind. Apocenter Apoapsis. Angular mass Alternate term for “moment Apocynthion Apoapsis in lunar orbit. of inertia.” Apocytherion Apoapsis in Venus orbit. Analog of linear mo- Apogalacticon Apoapsis in galactic orbit. mentum for a rotating or revolving Apogee Apoapsis in Earth orbit. mass, a conserved vector quantity: Apohadion Apoapsis in Pluto orbit. L = r × p Apohermion Apoapsis in Mercury orbit. where Apojove Apoapsis in Jupiter orbit. L is an object’s angular momentum, Apokrition Apoapsis in Venus orbit. r is its position vector with respect to Apokrone Apoapsis in Saturn orbit. the origin, Apolune Apoapsis in lunar orbit. × indicates vector cross product, and Apoposeidion Apoapsis in Neptune orbit. p is the object’s linear momentum. Aposelene Apoapsis in lunar orbit. Angular momentum de-saturation Apouranion Apoapsis in Uranus orbit. Spacecraft maneuver in which reaction Apozene Apoapsis in Jupiter orbit. wheels are driven to desired RPMs while Arcjet Electrothermal means of propulsion the vehicle is held steady by thrusters or that employs a high-current electric magnetic torquers. to produce high temperature in a Angular velocity Speed at which a body ro- rocket chamber, and introduces a fluid tates about one of its axes, expressed in propellant, e.g., argon or hydrazine, SI units radians per second. which expands out the nozzle. High ISP , Anisotropy Property of being directionally low thrust. Compare resistojet. dependent. Opposite of isotropy. Arctic Region on a planet pole-ward of Announcement of Opportunity (AO) which the Sun does not set during Message widely publicized offering de- northern-hemisphere summer if applica- tails of an opportunity to participate in ble. On Earth, the limit of the midnight a project or program. sun is 66◦ 33” north latitude. Anode Electrode through which electric Ares Vallis Valley on Mars that appears to current flow into a device. The negative have been carved by fluids. 3◦ N × terminal of a battery as it discharges. 342.5◦ E. Antarctic Opposite polar region from “arc- Expendable launch vehicles pro- tic.” duced by . Antenna A device that converts radio Arianespace World’s first commercial waves into electric current for recep- launch services provider, founded 1980. tion, and vice-versa for transmission. As of late 2008, has launched 261 Microwave antennas may also include payloads for about seventy customers. surfaces that reflect and concentrate ra- Array, DSN antennas Electronic intercon- dio waves. nection of multiple DSSs that serves to Antimony Element, symbol Sb, atomic increase effective receiving aperture, Ae. number 51, semi-metallic, solid at room Array, solar panels Two or more solar - temperature. Constituent in IR detec- els linked mechanically and/or electri- tors as indium antimonide. cally. Apastron Apoapsis in stellar orbit. Arsenic Element, symbol As, atomic num- Aperture An opening, such as for collecting ber 33. Semi-metallic substance, solid at light in an instrument; the diameter of room temperature. Important as a dop- such an opening. ing agent for semiconductors, radiation Aphelion Apoapsis in solar orbit. detectors, and photovoltaics. Apoapsis The high point in an elliptical or- Assembly Component of a spacecraft or bit; the point farthest from the center of ground system below the level of subsys- attraction. tem and above the level of subassembly. 382 Glossary

Hierarchy is: system, subsystem, assem- Audio frequency Frequencies in electronic bly, subassembly. signals or sound in the range of approx- Assigned mission Same as directed mis- imately 10 Hz to 25 kHz. sion. Audion The first electronic amplifier, a tri- Asteroid A . Remnant of so- ode vacuum tube invented by Lee De- lar system formation, many of which oc- Forrest (1873–1961) in 1906. cupy orbits in the main belt between Automatic repeat-request or Automatic Mars and Jupiter. repeat query (ARQ); error-control pro- Astromast Deployable fiberglass mast that tocol for data transmission, typically stows for launch in a small canister, and in Earth-based systems where round- can become a rigid mast up to a dozen trip light time is not a factor. Messages meters or so in length. Produced by As- (data packets) are acknowledged as re- tro Aerospace. ceived intact by the recipient, or else re- Astrometry Branch of astronomy con- broadcast after a certain period of find- cerned with precisely determining and ing no such acknowledgment. Compare explaining the positions and movements forward error correction. of stars. Autonomous navigation Spacecraft hard- Astronautics Branch of engineering, sci- ware and software subsystem that pro- ence, and technology dealing with space vides the on-board capability to esti- flight. mate the vehicle’s location and path in Astronomy Scientific study of celestial ob- space, and to execute trajectory cor- jects. rections automatically to achieve the Astrophysics Branch of astronomy dealing desired trajectory. Depends upon hav- with the physics of stars, galaxies, and ing a minimum number of natural bod- the universe. ies of known ephemeris within observ- Asymptote A line whose distance to a given ing range against the background stars, tends toward zero; a straight line such as exist within the main asteroid that approaches a curved trajectory ar- belt. bitrarily closely. Autumnal equinox Annual equinox (on ATLO Assembly, Test, and Launch Opera- Earth in the month of September) tions. Period in mission Phase D tran- the beginning of northern-hemisphere sitioning into Phase E during which autumn. At equinox, the Sun is at a a spacecraft is built up, tested, and point on the celestial sphere where the launched. celestial equator and ecliptic intersect, Atmosphere A planet’s gaseous envelope. and the Sun’s center spends nearly The depth of Earth’s atmosphere out to equal time above and below the hori- the ozone layer is about 0.5 percent the zon at every location on the planet. planet’s radius. Compare vernal (March) equinox. Atmospheric spacecraft One of eight classi- Azimuth Measurement of the angle on a fications of spacecraft. Designed to en- reference plane, such as the local hori- ter and characterize the atmosphere of zon, of a point along the arc from true a celestial body. north clockwise. Degree of freedom per- Atmospheric structure instrument pendicular to elevation, e.g., on a space- Passive direct-sensing instrument on at- craft scan platform or DSN antenna mospheric spacecraft that characterizes drive. Measured in degrees of arc. Com- the atmosphere’s temperature, pres- pare elevation. Also see Az-. sure, or other qualities, as a function of Az-el Azimuth-elevation; axes of rotation altitude. based on the local horizon and the verti- Attenuation Reduction in strength, as that cal. Rotation in azimuth varies between of a radio signal passing through a ring north, south, east and west, and rota- system or atmosphere under study. tion in elevation varies between horizon Glossary 383

and zenith. Measured in degrees of arc. Beryllium Element, symbol Be, atomic Compare RA-dec. number 4, metallic, solid at room tem- B Ring In the Saturnian system, the mid- perature, toxic. A lightweight, strong dle of three main rings visible in a small metal used in applications as diverse as telescope. Particles in the outer part of optical mirrors (e.g., Spitzer, JWST), the B Ring orbit Saturn once every 5.76 rocket engine nozzles (e.g., Saturn hours, at 17.97 kilometers per second. V), and particle detectors (e.g., Large Backscatter Light or other electromagnetic Hadron Collider). wavelengths reflected back toward the Best-lock frequency (BLF) “Rest” or “cen- observer at low phase angle, such as am- ter” frequency that a closed-loop ra- bient light from a page in a book. dio receiver, such as that on a space- Bandwidth In signal processing, the num- craft, naturally returns to after the sig- ber of Hz in a specific range of frequen- nal it was tracking ceases. The Voyager cies, such as at a radio receiver’s input. 2 spacecraft lost its ability to track a In computing, a rate of data transfer ca- varying radio signal from Earth shortly pability. after launch, so all uplink to it must be Barycenter A point about which two mas- stepped in frequency such that it arrives sive bodies orbit, e.g., the Sun and Doppler-shifted to within a few Hz of its Jupiter orbit a barycenter just outside BLF. the Sun’s photosphere. Bias A pre-existing, deliberately set condi- Barycentric Coordinate Time (TCB) De- tion, such as rotation rate of reaction fined in 1991 with TT. A time reference wheels, or the voltage or current in an based on assumptions not influenced by electronic circuit. relativistic time dilation caused by mass The expansive event considered in the solar system. TCB therefore ticks in cosmology at the beginning of space- faster than a clock on the moving Earth time, and evidenced by cosmic by about 490 milliseconds per year. background microwave radiation, and Barycentric Dynamical Time (TDB) De- the recession of galaxies. preciated. For ephemerides, TDB is Bimetallic strip A device made with two based on the solar system barycen- metals having dissimilar thermal- ter. Values are within milliseconds of expansion coefficients, to obtain TDT. mechanical motion from temperature Baseline The distance between two optical changes. Spacecraft thermal-control or radio telescopes that are undertaking louvers and residential thermostats are an interferometric observation such as a typically driven by bimetallic strips. ΔDOR or VLBI. Binary Phase Shift Keying (BPSK) radio Battery Grouping of similar objects. In signal modulation by temporarily ad- electrical systems, a number of elec- vancing or retarding the phase of the trochemical cells connected in series carrier wave by a specific angular dis- and/or parallel to provide primary or tance. Illustration p 29. secondary source of electrical power. Biprop engine Bipropellant rocket engine Bay Equipment rack or cabinet. that is fed two different liquid chemi- Beacon-mode Communications mode cals, a fuel and an oxidizer, to burn and based on semaphores represented by produce thrust. the presence or absence of specific Biprop thruster Small biprop engine. subcarriers in a spacecraft’s downlink. Bistatic radio science Observation of radio Small antennas can observe semaphores energy directed from a spacecraft to a in comparison with the large apertures natural body surface in such a way that required for capturing enough signal a reflection can be received on Earth power to decode telemetry. and analyzed to help characterize the surface. 384 Glossary

Bit Contraction of the words “binary Bus, spacecraft A spacecraft’s core me- digit.” Represents the numeric value 1 chanical housing including all the vehi- or 0. cle’s subsystems mounted within or at- Black hole Object of immense density and tached to it. Its purpose is to support mass whose exceeds the a payload of scientific instruments reli- speed of light. Observed to exist at ably with everything they need. galactic centers. Bus interface unit Electronic communica- Black powder See gunpowder. tions device that connects a spacecraft Block-V Receiver (BVR) (Roman numeral subsystem or assembly to the serial data five) A highly-evolved software-based bus, to exchange data with other sub- microwave radio receiver used by DSN systems or assemblies. to find, capture, and track a spacecraft’s C Ring In the Saturnian system, the inner- signal, separate subcarriers, and mea- most of three main rings visible in a sure Doppler shift. small telescope. Particles in the outer Blooming In a CCD, the overflow of charge part of the C Ring orbit Saturn once ev- (and image brightness) onto adjacent ery 7.92 hours, at 20.31 kilometers per pixel photo-gates due to overexpos- second. ure. Cable A wire or bundle of wires. For ra- Blowdown Mode of operating a space- dio frequency signals, the cable is often craft’s propulsion subsystem in which a pair of conductors in coaxial arrange- the pressurant gas is not pressure- ment, that is, a single central conduc- regulated, but decreases as propellant is tor surrounded in precise circular cross- used from the tank. Compare pressure- section by a cylindrical outer conductor. regulated. Cadmium Element, symbol Cd, atomic Blueberries Small spheroids of hematite re- number 48, metallic, solid at room tem- vealed on the surface of Mars in Merid- perature. Toxic. Used in rechargeable iani Planum by the Mars Exploration batteries. Rover Opportunity in 2004. Calcium Element, symbol Ca, atomic num- Bow shock The boundary between a ber 20. Hard metal at room tempera- magnetosphere and the surrounding ture, fairly reactive. medium through which it moves. Calibration Operation of an instrument Planets with magnetic fields have bow under known conditions with known in- shocks in the solar wind, and the Sun put, to record data for use in measuring has a bow shock where the heliopause errors inherent to a measuring device, interfaces with the interstellar medium. and comparing results obtained when Illustration p 337. the instrument observes a target. B plane Target plane perpendicular to Calibration Equations for convert- asymptote of the incoming hyperbolic ing telemetry values from data numbers, path that passes through target body for example 0–255, to their correspond- center. Illustration p 73. ing meaningful readings in engineering Broadcast Open-loop transmission in vir- units, for example 0-50 volts, based on tually all directions to all available re- sensor design and preflight testing. ceivers. Outermost of the four Galilean Bus, electrical Main electrical power distri- , diameter 5,262.4 kilo- bution circuit. meters. May have a subsurface water Bus, serial data Network connecting sev- ocean between ice layers. eral peripherals among subsystems and Call sign Moniker used by a person partic- assemblies on a spacecraft, over the ipating in voice-net or radiotelephone same set of wires, typically a single pair communications. A call sign identi- of conductors. fies the job function, rather than the Glossary 385

name, of each participant. For exam- that can withstand exhaust-nozzle tem- ple, “Prop” for a propulsion engineer, perature and pressure. Also called 3-D “Nav” for a navigator, “Telecom” for a carbon-carbon. telecommunications analyst. Carbon-fiber epoxy or plastic; strong, low- Camera Imaging science instrument whose mass material with many applications optical assembly focuses an image onto in aerospace and elsewhere. Compare an image detector for readout and even- fiberglass. tual transmission to Earth via teleme- Carrier Unmodulated radio signal from a try. transmitter. Used for Doppler shift mea- Canberra DSCC One of three worldwide surement, radio science experiments. Deep Space Communications Com- Can be modulated to carry telemetry, ◦ plexes in DSN. Near 35 34’ S latitude command, ranging tones, semaphores, ◦ × 148 59’ E . etc. either directly or on subcarriers. Supergiant star α Carinae, spec- Carrier suppression Reduction in the tral type F, the second brightest after power in a carrier signal along with an Sirius, visible from southern , increase of power in its modulation. 350 light years distant. Cassegrain Optical and de- Capacitor Discrete electronic component sign comprising parabolic main reflector that stores energy in the electric field and a smaller subreflector, which fold a between a pair of conductor plates sepa- long focal length into a compact struc- rated by a dielectric. Also known as con- ture. denser. Capacity typically measured in Cassini Division In the Saturnian system, micro-farads, μF, or picofarads, pF. the gap between the outer edge of the Air Force Station; Detach- B Ring and the inner edge of the A ment of U.S. 45th Space Wing at Ring. Clearly visible in a small tele- Patrick Air Force Base in Florida. East- scope. Particles in the middle of the ern rocket launch facility. All non- Cassini Division orbit Saturn once ev- shuttle launches on U.S. east coast are ery 11.76 hours, at 17.8 kilometers per conducted here. Adjacent southeast of second. NASA Kennedy Space Center, whose Cassini spacecraft NASA-ESA-ASI Or- Launch Complex 39, with Vehicle As- biter launched October 15, 1997, sembly Building, served Apollo and now entered Saturn orbit July 1, 2004, serves Space Shuttle. deployed ESA Huygens Probe toward Carbon Element, symbol C, atomic num- Titan December 25, 2004. Named for ber 6. Found naturally in many al- Italian-French astronomer Giovanni lotropes, including amorphous, dia- Domenico (Jean-Dominique) Cassini mond, graphite, and in the (1625–1712) who discovered the divi- form of buckyballs, tubes, fiber, etc. sion between Saturn’s A Ring and B Carbon dioxide (CO2) Major constituent Ring. of the of Venus and Mars. Supernova remnant, Increasing constituent, unfortunately, in strongest interstellar radio source Earth’s, as of the twentieth and twenty- in the sky, about 11,000 LY distant. first centuries. Catalyst Substance that accelerates a Carbonaceous (C-type) Asteroids, mostly chemical reaction without being con- in the outer part of the main belt. sumed. Hydrazine thrusters use iridium, About 75 percent of the minor plan- automotive catalytic converters use ets are this type. Compositions include platinum and rhodium. silicates, oxides, sulfides. Source of car- Cathode Electrode through which electric bonaceous chondrite . current flows out of a device. Carbon-carbon Graphite fiber embedded in a carbon matrix. Strong material 386 Glossary

Cathode ray Stream of electrons emitted on a particular trajectory, departing a from a heated cathode in a vacuum planet’s gravitational bond, for a trip tube. Thermionic emission. to a specific destination. Also called Cavity resonator Hollow space inside a de- escape energy. vice where electromagnetic waves (typ- Charge-coupled device (CCD) Image de- ically microwave) of specific frequencies tector, array of isolated silicon capac- are generated or selected. Compare with itors called photogates or wells, each acoustic wave generation, at desired fre- forming one pixel of an image. Charge quency, in a flute. on every photogate is read out by oper- Celestial equator Great circle on the imag- ating each line of photogates as a shift inary celestial sphere, in Earth’s equa- register. torial plane, a projection of the equator Charge transfer efficiency The efficiency ◦ out into space. Inclined about 23.5 to with which a CCD transfers photogates’ ecliptic. electronic charges during readout. Celestial mechanics See radio science celes- Chemical rocket Rocket engine fed by solid tial mechanics experiment. or liquid propellant whose chemical Celestial reference AACS input from Sun combination or decomposition provides sensors, horizon sensors, star trackers, energy for thrust. Compare electric stellar reference units, etc. Compare in- propulsion. ertial reference. Chemical thermodynamics Branch of sci- Centaur Launch vehicle high-energy upper ence that addresses the interrelation of stage powered by two Pratt and Whit- heat and work with chemical reactions, ney RL10 engines burning liquid H2 and or with a physical change of state. liquid O2, with an ISP of up to 449 s and Chemistry Branch of science that addresses 146 kN thrust. the composition, structure, and proper- Ceramic cloth Fabric made of woven fibers ties of matter, and the changes it under- of ceramic material such as Nextel®,a goes during chemical reactions. proprietary material made by 3M. Of- Chlorine Element, symbol Cl, atomic num- fers resistance to high temperature and ber 17. One of the five halogens. particle impact. Choked flow Flow of from Ceres Asteroid (minor planet) about 950 rocket combustion chamber into con- kilometers in diameter. One of five verging throat where its velocity reaches dwarf planets in solar system (count as Mach 1 at the narrowest point before di- of 2008) and largest, most massive as- verging and further expanding. teroid in main asteroid belt. One of the Circuit breaker Electrical device that pro- targets intended for the Dawn space- tects from excessive current by opening craft to orbit in 2015. Compare Vesta. the circuit. Motion of the Earth’s ro- Circularize To change an elliptical orbit tational axis. Pictured as a point on the into a circular orbit, e.g., by reducing arctic/antarctic surface, the pole’s loca- the apoapsis altitude through aerobrak- tion would be seen to move about 15 ing during repeated periapsis passages, meters with a period of about 433 days. or by propulsive means, either at apoap- Illustration p 61. sis to raise periapsis, or at periapsis to Chandra X-ray Observatory One of the lower apoapsis altitude. four NASA Great Observatories. Sensi- Class-1 Cleanroom specification in which tive to X-ray sources 100 times fainter there is fewer than one airborne par- than previous X-ray telescopes. ticle of size ≥ 0.5 μ present per cubic Characteristic Energy (C3) Intensive foot (≈0.03 m3). Compare to the mil- quantity used in planning interplan- lions of particles per ft3 in an office en- etary flights, which gives twice the vironment. energy per unit mass required to set off Glossary 387

Class-100 Cleanroom specification in which radiation from the early universe. there are fewer than one hundred air- Launched 1989, operated for four years. borne particles of size ≥ 0.5 μ present Columbium Element. See niobium. per cubic foot (≈0.03 m3). Comet Halley Periodic comet 1P/Halley, Applications of also called Halley’s Comet after English physics that do not take into ac- polymath Edmond Halley (1656–1742) count the effects of special or general who predicted its 1758 return. Can be relativity. seen from Earth every seventy-five or Clean-up TCM Statistical propulsive seventy-six years. spacecraft trajectory correction maneu- Command data One of the seven DSN ver. Reduces trajectory errors induced data types. Using modulation similar during a flyby. May be subject to to telemetry, command data sent to a cancellation depending on magnitude spacecraft can serve the purpose of di- of the errors seen. recting an activity upon receipt, a se- Cleanroom An enclosed workspace that quence of time-tagged activities over a has a controlled level of airborne con- period of weeks or months, or software taminants such as dust, microbes, and for onboard . aerosol particles. Command sequence Set of time-tagged Clementine Engineering demonstration commands, typically numbering in the spacecraft, a joint project of U.S. Bal- thousands, uplinked to a spacecraft listic Missile Defense Organization and to direct its activities for a period of NASA, Launched in 1994 to test minia- weeks or months. ture sensors and advanced spacecraft Command-loss timer (CLT) Fault- components in flight. In addition to protection routine, a watchdog timer, testing, Clementine mapped the Moon which resets to a nominal value every at various wavelengths in the visible, time the spacecraft receives and parses UV, and IR, obtained laser-ranging any command. If the timer reaches zero altimetry, , and charged and no command has been received, particle measurements. it will pass control to algorithms Closed loop in control theory, system in that begin to take actions such as to which a sensor monitors the system’s reconfigure the telecommunications output, compares it to a desired state, subsystem in the assumption that a and issues a feedback control signal to receiving component on the spacecraft adjust the system’s performance. may have failed. Closed loop radio receiver locks onto the Communications and Navigation One phase of the incoming signal via a of eight classifications of spacecraft. phase-locked-loop control system, and Designed to relay data among users tracks the incoming signal as it changes on the surface, or between surface frequency. Useful for extracting teleme- of a distant planet and Earth. Many try, command, range, and Doppler-shift examples in Earth orbit. No current data. examples of dedicated spacecraft of this Cobalt Element, symbol Co, atomic num- classification in interplanetary use. ber 27. Metallic, solid at room temper- Commutation map In a time-division mul- ature. The artificially produced isotope tiplex system, a map that determines 57Co serves as a gamma-ray source in the order of measurements to send via M¨ossbauerspectrometers. telemetry. COBE Cosmic Background Explorer; Commutator, data Electronic device for NASA spacecraft developed and flown transmitting data across a rotating gap, by Goddard Space Flight Center to such as to a de-spun section from a spun measure diffuse infrared and microwave section of the spacecraft. 388 Glossary

Commutator, power Device, such as a sys- electric motors. The gyroscopic proper- tem of brushes, which provides electri- ties of rigidity in space and precession cal conductivity for power transmission are used to apply torque to the whole across a rotating gap, such as to a de- spacecraft by rotating the spin axis of spun section from a spun section of the a CMG. Used on space stations, not spacecraft. on interplanetary spacecraft. Compare Competed Mission Mission offered to the reaction wheels. scientific community in an announce- Convection Transfer of thermal energy in ment of opportunity (AO) and selected a combination of conduction and fluid for development and flight from among movement. proposals received. Compare directed Convergent-divergent nozzle Rocket en- mission. gine or thruster nozzle, e.g., De Laval Complemented data Binary data in which nozzle, in which exhaust gas flows all the 1’s are changed into 0’s and vice- from combustion chamber through a versa. Also called inverted data. narrowing throat and into a widening Compression, data Reduction in the num- bell. ber of bits needing to be transmitted, Convolutional coding Forward error cor- by algorithms which lose no data, or by rection coding scheme used on space- ones which impose acceptable loss. craft in creating radio-link symbols, e.g., Compton Gamma Ray Observatory One of phase modulations, in response to a pat- the four NASA Great Observatories. tern of data bits. Viterbi decoding ap- Sensitive to gamma-rays in the range plied upon receipt to regenerate bits. 20 kev to 30 GeV from astronomical Cool neutron Neutral nuclear particle hav- sources. Launched April 1991, operated ing relatively low velocity, e.g., from re- in until June 2000, con- cent collision with a proton, which has ducting all-sky survey and observing in- similar mass. dividual gamma ray sources including Copper Element, symbol Cu, atomic num- gamma-ray bursts. Named in honor of ber 29. Metallic, solid at room temper- American physicist Arthur Holly Comp- ature. Used in electrical wire. Served as ton (1892–1962). comet-impacting mass for the Deep Im- Conductive Heat Transfer Transfer of pact spacecraft. thermal energy from one molecule to effect A pseudo-force; the appar- another within or between systems ent deflection of moving objects when without involving material flow. they are viewed from a rotating frame of Conductor Material through which electric reference, e.g., air masses moving south current or thermal energy can flow with on the rotating Earth are deflected west, ease. resulting in their rotation. Continuous Spectrum Range of wave- Coronal mass ejection Eruption of mate- lengths without gaps, e.g., the un- rial from the solar corona, at up to 2,700 broken series of visible wavelengths kilometers per second, consisting of up 13 produced by a piece of metal heated to to 10 kg of plasma (protons and elec- incandescence within a light bulb. trons, and other ionized matter such as Control theory Branch of engineering and helium, oxygen, and iron). mathematics that deals with the behav- Correlator Computer program used in ior of dynamical systems. VLBI observations. It analyzes random Control-moment gyro (CMG) Spinning- waves of noise from a , and of mass device, also called gyrodyne, pseudo-noise from a spacecraft, received sometimes called momentum wheel, by two DSN stations located on sep- whose rotor is on the order of 100 kilo- arate continents. It then matches up gram mass, kept at a constant speed by the wavefronts, i.e. correlates them, and based on the times of each wavefront’s Glossary 389

arrival, it establishes a precise value for mand and data handling subsystem, the right ascension and declination of etc. each of the observed objects: quasar and Curium Element, symbol Cm, atomic num- the spacecraft. ber 96. Metallic, solid at room tem- Cosmic microwave background (CMB) perature. Radioactive element, manu- Fossil radiation pervading the universe factured via nuclear reactor. Incorpo- with a thermal black body spectrum at rated in alpha-proton x-ray spectrom- 2.725 K with a peak in the microwave eters as the alpha-particle emitter. frequency 160.2 GHz. Cycle durability Number of discharge– Cosmic ray A high-velocity particle, such charge cycles a rechargeable battery as an atomic nucleus. Origin can be so- can be expected to endure. lar, or an energetic event such as a su- D Ring In the Saturnian system, the band pernova within our galaxy, or from a dis- of narrow ringlets just inside the C tant galaxy. Ring. Particles in the inner part of the D Cosmology Theoretical astrophysics Ring orbit Saturn once every 4.8 hours, at scales larger than individually at 23.81 kilometers per second. Not vis- gravitationally-bound objects in the ible in a small telescope. cosmos. Daily fireing window See . Critical Commands Sequence of com- Data A body of facts, information. Plural mands stored onboard a spacecraft of datum, which is a single piece of infor- that operate in critical mode, taking mation. Numbers input to, output from, precedence over certain levels of au- or operated on by a computer program. tonomous fault protection. An example Data management Task of ensuring best is a sequence that controls spacecraft available data set is available to users. activities during a launch, a landing, or Includes recovering data that is recover- a planetary orbit insertion. , and accounting for unrecoverable Critical Design Review (CDR) A formal data losses. review in which project personnel make Data number (DN) Telemetry value, typi- presentations to a review board of e.g., cally between 0 and 255, returned from NASA experts. The gate a flight project a transducer, e.g., pressure sensor. Com- must pass through prior to being given pare engineering unit. the go-ahead to proceed with Phase D, Dawn Ion-engine propelled NASA space- system assembly, test and launch. craft launched September 27, 2007 to Critical mode Spacecraft CTS mode un- enter into orbit around asteroid Vesta der which a critical command sequence and the Ceres, both in the runs. main asteroid belt. Dawn is scheduled Branch of physics concerned to explore Vesta between 2011 and 2012, with very low temperatures. and Ceres in 2015. Crosslink Communications link between De Laval nozzle Convergent-divergent de- two spacecraft in flight. See Relay. sign essential to rocket engines. Con- CTS Command and telemetry subsystem; sists of a tube that is roughly hourglass A spacecraft’s computer that stores shaped, causing gas to achieve super- commands received via the telecommu- sonic speed at high pressure. nications subsystem, executes them at De-spin On a spin-stabilized spacecraft, their scheduled times or sends them to rotating a platform continuously in instruments or other subsystems for ex- the opposite direction of its attitude- ecution. It collects, processes, and stores stabilizing spin, to use as a stable plat- telemetry data for downlink. Named form for pointing antennas or optical in- variously on different spacecraft, e.g., struments. command and data subsystem, com- Dead band In a closed-loop control sys- tem, a range of system states in which 390 Glossary

no control action is taken. In thruster- Deep space station (DSS) One of the 34– controlled attitude, the time between meter or 70–meter diameter radio tele- thruster firings that keep the spacecraft scope antennas of the Deep Space Net- rocking from limit to limit. work. Decalibration Transformation of teleme- ΔV (Delta-V) Change in velocity, such as try from data numbers to engineering via propulsive event or gravity-assist. units. Demodulation Process of detecting infor- Deceleration Acceleration in a negative di- mation that has been imposed onto a rection. carrier signal. Declination One of a pair of coordinates Deterministic maneuver A trajectory cor- in the celestial sphere. Angular distance rection or orbit trim maneuver that north or south of the celestial equator. must be performed as part of the origi- measured in degrees of arc. Compare nal trajectory design. Compare statisti- right ascension. Also see RA-dec. cal maneuver. Decoder Hardware or software that oper- DOR Differenced One-way Range; a DSN ates on a data stream to effect error cor- VLBI navigation technique that makes rection or parse other coding, producing radiometric observations of a spacecraft data identical to its value prior to cod- independent of the usual Doppler and ing. range (tracking data type) observables. Decom map De-commutation map; an al- Δ DOR Delta Differenced One-way Range; gorithm that matches time-division- a DSN VLBI navigation technique that multiplex downlink telemetry data with makes radiometric observations of a its users, e.g., image data to image sci- spacecraft and one or more to ence team, temperature data to thermal achieve very accurate right ascension engineers, etc. and declination measurement indepen- Deep Impact NASA spacecraft launched dent of tracking data type observables. January 12, 2005, to study the composi- Diffraction Various phenomena that occur tion of the interior of Comet 9P/Tempel when a wave hits an obstacle, such as by releasing a self-guided projectile apparently bending around a small ob- spacecraft that impacted the comet on stacle or spreading out when passing July 4, 2005, through a small opening. Deep space Realm of interplanetary space- Diffraction Grating In spectrometers, the craft, at lunar distances and beyond. wavelength-dispersing element. Slots or Deep Space 1 Engineering demonstration scores in a flat plate, arranged in a regu- spacecraft in the NASA New Mil- lar pattern spaced apart on the order of lennium Program, launched 1998 and wavelengths of light, produce reflections tested eight new technologies, then en- whose phases variously interfere so the countered asteroid Braille in 1999 and resulting wavelengths vary with view- Comet Borrelly in 2001. ing angle. Compare with reflections off Deep space maneuver (DSM) Determinis- a compact disk, CD or DVD. tic propulsive spacecraft maneuver that Digit A symbol expressing a numeric value. imparts a relatively large ΔV in order In the base-10 system, digits range from to set up for a particular gravity assist 0 through 9. In binary (base-2), they flyby during interplanetary cruise that range from 0 to 1. would not be possible to reach other- Digitize To represent a continuously vari- wise. able quantity or phenomenon in samples Deep space network (DSN) NASA’s net- consisting of discrete numeric digits. work, managed by JPL, of deep space Diode An electronic semiconductor compo- stations located at three complexes nent having two electrodes, e.g., a rec- worldwide: Goldstone, U.S.A.; Madrid, tifier with positive and negative termi- Spain; and Canberra . nals. Glossary 391

Direct current (DC) Electric current whose and characterizing properties of the in- direction, and polarity on its conduc- cident dust, e.g., mass, direction of tors, remains constant. flight, velocity, chemical composition, Direct-sensing Category of science instru- electric charge. ments that make observations while Dust detector Direct-sensing science in- admitting, or being immersed in, the strument on spacecraft capable of phenomenon that they measure, e.g., counting dust impacts. dust detector, magnetometer. Compare Dwarf planet A celestial body in solar or- remote-sensing. bit that is massive enough to be rounded Directed mission A mission assigned to an by its own gravity (in hydrostatic equi- organization by an agency based upon librium) but which has not cleared its desires of the scientific community, e.g., neighboring region of planetesimals and Galileo, Cassini. Compare competed is not a satellite. Defined 2006 by Inter- mission. national Astronomical Union; five iden- Diurnal Occurring daily. tified in solar system as of press time. Doped Having impurities introduced into E Ring The outermost ring in the Satur- an otherwise pure material to influ- nian system; a sparse collection of fine ence its properties or performance, e.g., ice particles that issue from geysers on Neodymium-doped yttrium aluminum Saturn’s moon Enceladus. Particles in garnet (Nd:YAG) near-IR laser. the middle part of the E Ring orbit Sat- Doppler residuals Navigation data com- urn once every 32.88 hours, at 12.63 prising the observed Doppler shift in a kilometers per second. Not visible in a spacecraft’s coherent downlink after ac- small telescope. counting for all known motions such as Earth Third planet from the Sun, one of Earth’s rotation and revolution, and the the four terrestrial planets. Equato- spacecraft’s nominal orbit. rial diameter 12,756.2 kilometers. Dense Doppler shift Change in received frequency N2/O2 atmosphere with variable H2O due to relative motion between source cloud cover, liquid saltwater , and receiver. water-ice polar caps. The only known Downlink Radio communications received habitat for life as of late 2008. Mean 7 from a spacecraft. distance from Sun 1 AU = 14.960 ×10 DSN Pass Space-link session. Tracking pe- km. riod during which a spacecraft passes Echo A 180-kilogram passive communica- across the sky. tions test and geodetic satellite balloon Dual-mode propulsion system Spacecraft placed in Earth orbit in 1960. Used to propulsion system designed to use test communications by bouncing radio hypergolic bi-propellants together, e.g., signals off its reflective surface, and to for TCMs, and the hypergolic fuel alone measure the shape of the Earth to a new in catalyst-based thrusters, e.g., for level of precision. attitude control. Eclipse Passage into the shadow of a solar Dust Particles of matter ranging in size system body. from a few molecules to about 0.1 mil- Ecliptic Plane in Earth’s sky in which the limeter. Can be distinguished by loca- Sun appears to remain during the year, tion; circumplanetary (e.g., in ring sys- and in which of the Moon occur. tems), circumstellar (interplanetary), EDAC Error-detection and correction; pro- interstellar (e.g., in nebulae), and inter- cess of detecting errors in a data stream galactic. and reconstructing the original data. In- Dust analyzer Direct-sensing science in- terplanetary spacecraft use forward er- strument on spacecraft capable of mea- ror correction (FEC) schemes, which suring the incidence of dust impacts, add additional bits to the data instead of depending on Automatic repeat- 392 Glossary

request, which requires a short round- or spacecraft scan platform. Also see az- trip light time. el. Edison effect Thermionic emission; cath- Ellipse Conic section, the locus of points in ode ray. a plane such that the sum of the dis- Elastic collision Exchange of momentum tances to two fixed foci is constant. The experienced by bodies passing one an- shape of any orbit. Note that a circle is other at close range, interacting via an ellipse whose eccentricity is zero. gravitation rather than physical colli- Emission spectrum Wavelengths at various sion. Total kinetic energy of the collid- intensities produced by an excited gas. ing bodies remains the same after as be- Each element’s atomic emission spec- fore the interaction. trum is unique and can be used to detect Electric propulsion Use of electric or mag- the element in an unknown compound. netic fields to accelerate mass in a Emissivity Ratio of energy a particular ma- thruster or rocket engine, rather than terial radiates to energy radiated by a chemical means. Capable of high ISP (fictitious) black body at the same tem- but low thrust. perature. A measure of a material’s abil- Electro-explosive device Pyrotechnic de- ity to radiate energy it has absorbed, vice to operate a single-use component expressed numerically between 0 and 1. e.g., propulsion-subsystem valve, Enceladus Icy moon of Saturn, 500 kilome- parachute mortar, or exploding bolt. ters in diameter, the surface of which Electrolyte Substance containing free ions exhibits a range of ages, from old and that conducts electricity, e.g., in an elec- heavily cratered to present-day geologic trical battery. activity. It orbits within the densest Electromagnetic wave Wave — e.g., light, part of Saturn’s E Ring, which is cre- radio, etc. — comprising an electric ated by geysers of water ice and other field that rises and collapses, which in compounds from its south polar region. turn creates a magnetic wave, which Encoder, data Hardware or software that rises and collapses, producing an elec- modifies a data stream for some pur- tric wave, and so propagating itself for- pose, e.g., forward error correction, on ever without any medium but space- a spacecraft. Most interplanetary space- time. craft encode data using Reed-Solomon, Electromagnetic spectrum All possible Golay, turbo, and/or convolutional en- electromagnetic radiation frequencies, coding. (or wavelengths, or energies). See Encounter Spacecraft’s close approach to Appendix D, p 342. a solar system body during which it Electron Low-mass subatomic particle makes observations to be telemetered to with negative electric charge. When Earth, and/or carries out radio science an atom is deprived of an electron experiments. (or gains an extra one) it is said to Endothermic A chemical reaction that re- be ionized. Electrons are essential for quires thermal energy to be supplied. chemical bonds, and for electricity and Compare Exothermic. . Energetic neutral atom camera Electrostatic propulsion Thrust produced Passive remote-sensing science instru- by accelerating ions with an electrically ment capable of creating images of mag- charged grid. netospheres, e.g., in Cassini’s magneto- Electrothermal propulsion Thrust pro- spheric imaging instrument, MIMI. duced by heating a gas with an electric Energetic neutral atom (ENA) arc. Fast-moving atom. In a magnetosphere, Elevation Degree of freedom perpendicular ions and electrons are trapped by mag- to azimuth, e.g., in a DSN antenna drive netic field lines, which they move about or along. When an ion collides in the Glossary 393

right way with one or more electrons is used for expressing positions of needed to neutralize the atom, it be- objects as solar system ephemerides. comes free of the magnetic field and flies Oriented with its xy-plane parallel to away. the mean Earth equator at the given Energy Scalar physical quantity that is a (J2000.0), and its z-axis pointing property of objects and systems, which toward the mean north celestial pole of is by nature conserved. Often defined that epoch. The x-axis points toward as the ability to do work. Equivalent to the mean equinox of the epoch. mass as in E=mc2. Equinox See vernal or autumnal equinox. Energy density Amount of energy stored Escape energy See characteristic energy. per unit mass, e.g., electrical energy in Eris Dwarf planet, about 2,600 km in di- a battery. ameter, orbiting the Sun in the Kuiper Engine gimbal actuator AACS output de- belt. Has a moon named Dysnomia. vice that aims a rocket engine or nozzle Ethane (C2H6), liquid in while it is operating, to align its thrust on the surface of Saturn’s moon vector along the spacecraft’s center of Titan and a component of natural gas, mass. with methane, on Earth. Melting point Engineering data Telemetry that details a –182.76 ◦C, 90.34 K, boils at –88.6◦C, spacecraft’s state and condition, such 184.5 K. as temperatures, pressures, computer Euler angle Notation that gives the rota- states, propellant quantities, voltages, tion of one spatial frame with respect currents, and switch positions. to another. Illustration p 95. Engineering demonstration spacecraft One Europa One of the four of of eight classifications of spacecraft. Jupiter, second out from the planet, di- Designed to test new technologies in ameter 3,121.6 kilometers. Most likely flight and advance their technology has a warm saltwater ocean beneath readiness level (TRL) for subsequent a relatively thin icy shell and above a use on scientific spacecraft. layer of rock. Engineering unit (EU) Unit of measure Exciter Part of the DSN Block-V receiver such as volt, ampere, newton, degree that builds a carrier signal based on a Celsius, etc., which are output from the highly stable hydrogen frequency process of decalibration from data num- reference, adds modulation for any re- bers in telemetry. quired subcarriers such as for range Enthalpy Description of a system’s ther- (tracking data) or command data, and modynamic potential, e.g., amount of then delivers it to the input of a high thermal energy released in a specific power amplifier (klystron). exothermic chemical reaction. Exoplanet Extra-solar planet. Ephemeris (plural ephemerides) Numeric Exothermic Chemical reaction that re- representation of the positions of - leases heat. Compare Endothermic. nomical objects at any given time. Exploding bolt A hollow metal bolt that Ephemeris Time (ET) Obsolete, replaced contains an explosive charge strong in 1984 by TDT and TBT. enough to break its walls, which are typ- Epoch In astronomy, a precise moment in ically thinnest where the break is de- time for which celestial coordinates or sired. are specified by inter- Extra-solar planet Body orbiting a star national agreement. other than the Sun. Equator and equinox J2000.0 Coordinate F Ring In the Saturnian system, the nar- system basis (mean equator and row ring just outside the broad A Ring. equinox) and epoch (J2000.0, which Particles in the outer part of the F Ring is 12:00 TT January 1 of the Julian orbit Saturn once every 14.88 hours, at year 2000). The coordinate system 394 Glossary

16.45 kilometers per second. Not visible Flux-gate Technology in which a magne- in a small telescope. tometer uses alternating electric cur- Fail-safe Spacecraft component or trajec- rents in coils of wire to continu- tory design which, if it were to fail, will ously magnetize, de-magnetize, and fail in a safe manner, i.e. without catas- re-magnetize a susceptible core. The trophic result. amount of current needed to change Fairing Aerodynamic capsule that protects the core’s state of magnetization varies a spacecraft atop its launch vehicle when it is in an ambient magnetic field, while in the dense parts of Earth’s at- and can serve as an indicator of the field. mosphere. Flyby Spacecraft One of eight classifica- Fault-protection monitor Spacecraft soft- tions of spacecraft. Designed for long ware routine that periodically checks a cruise period and brief, passing encoun- specific condition or conditions to deter- ters. mine whether a fault exists. Focal ratio An optical instrument’s focal Fault-protection response Prescribed ac- length divided by its effective aperture. tion to be taken autonomously by Expressed “f/#” where # is the ratio. spacecraft subsystem or main com- Also called “f-number” or “f-ratio.” puter, e.g., CTS, to mitigate a fault Focus Point in an optical instrument where that has been detected. gathered light rays converge. Feed horn Conical waveguide that inter- Force Influence which, when applied to a faces with antenna reflectors. free mass, causes it to accelerate. Ex- Fiber optics Technology of transmitting pressed as a vector quantity. and receiving signals via modulated Forward Error Correction (FEC) System light through optical fibers, which due of error control that adds redundant to total internal reflection, act as waveg- bits to a data stream prior to trans- uides. Fiber optic communication has mission, e.g., convolutional coding, largely replaced copper wire in major Reed-Solomon coding. Compare with networks. automatic repeat-query (ARQ). Field effect transistor (FET) Solid-state Forward scatter Light scattering at high amplifier discrete component. An elec- illumination phase angle, by particles tric field at the gate terminal controls whose dimensions approach the wave- the flow of electric current through a length of light, into the hemisphere of channel between the source terminal space bounded by a plane normal to the and the drain terminal. Compare with direction of the incident radiation. transistors that operate based on a Fossil radiation Radiation left over from small current to control the output the “Big Bang,” which has red-shifted current. into the microwave region of the spec- Figure of merit A quantity that character- trum. izes the performance of a device or sys- Frame In telemetry, an organized group of tem relative to other similar ones. bits that may contain packets or por- Flight readiness review (FRR) Formal ex- tions of packets, e.g., transfer frame. amination of a spacecraft’s readiness for Frame tie DSN observation using VLBI of flight, in a meeting held shortly before a planetary spacecraft and quasars, the launch period opens. to reconcile frames of reference, e.g., Flight software (FSW) Software for the planetary ephemerides, with the In- computers on a spacecraft in flight. ternational Celestial Reference Frame Flight system Spacecraft. (ICRF). Fluorine Element, symbol F, atomic num- Frangible nut Explosive nut. Illustration p ber 9, the most highly reactive of all el- 175. ements. One of the five halogens. Glossary 395

Free-fall Condition in orbit in which an ob- G Ring In the Saturnian system, the nar- server senses no gravitational accelera- row ring between the F Ring and the E tion. Ring. Particles in the outer part of the Free-molecular flow Fluid dynamics regime G Ring orbit Saturn once every 20.88 in which aerobraking of planetary or- hours, at 14.69 kilometers per second. biter spacecraft is executed, where the Not visible in a small telescope. atmospheric molecules’ mean free path Gain Increase in signal strength obtained, is larger than the spacecraft. e.g., by collecting a weak incoming sig- Free-return trajectory Trajectory in which nal over a large area, or by actively am- a spacecraft traveling away from the plifying it. primary body, e.g., Earth, is modified Galaxy Massive, gravitationally bound sys- by the gravitation of a secondary body, tem of stars, interstellar gas, dust, and e.g., the Moon, causing the spacecraft dark matter, often orbiting a supermas- to return to the primary body without sive black hole at its center. Our home requiring additional rocket thrust. galaxy is the , about 100,000 Free-space optical Telecommunications LY in diameter. Nearest galaxy is the 6 carried out over the channel of empty spiral in Andromeda, about 2.5×10 LY space between transmitter and receiver distant and on a collision course with us. 9 using, e.g., IR or visible-light laser Most distant known galaxy is 2.8 × 10 transmitters and Cassegrain telescope LY away. light “antennas.” Galileo spacecraft NASA orbiter launched Frequency Number of cycles per second, October 18, 1989, entered Jupiter or- stated in hertz (Hz). bit December 7, 1995, having deployed Frequency and timing One of the seven its atmospheric probe toward Jupiter DSN data types. Based on a frequency July 13, 1995, which entered Jupiter’s standard such as a hydrogen maser, ref- atmosphere while being tracked by the erence frequencies and clock time are orbiter during its Jupiter orbit inser- maintained and distributed to all DSN tion critical sequence. Named for Tus- subsystems. John Harrison showed the can astronomer Galileo Galilei (1564– importance to navigation of having an 1642) who discovered clear evidence accurate clock in 1761 (see longitude). that Earth is not the center of ev- The DSN frequency and timing system erything. The four Galilean moons are is an accurate chronometer that enables named in his honor for his having first interplanetary navigation. observed them on January 7, 1610. Frequency band A named range of frequen- Gallium Element, symbol Ga, atomic num- cies such as S-band (around 2 GHz) or ber 31; a metal that melts slightly above visible light. See Appendix D, p 342. room temperature. is Frequency modulation Means of imposing an important photovoltaic. information onto a carrier signal by Galvanometer Voltmeter. slightly changing its frequency. Gamma ray (γ-ray) Electromagnetic radi- 5 Frequency stability In a radio signal, con- ation in the region above about 10 ev. sistency in the amount of time between See Appendix D, p 342. Produced in peaks in its electromagnetic waves. Ex- nature by highly energetic events, e.g., pressed as Allen deviation. compression of matter at the threshold Fuel Liquid or solid chemical that decom- of a . poses explosively in a catalytic thruster Gamma-ray spectrometer Passive remote- or combines with another chemical in a sensing science instrument that mea- bipropellant engine or solid rocket mo- sures the distribution of photon energies tor to produce thermal energy for con- in the most energetic parts of the elec- verting to rocket thrust. tromagnetic spectrum (see Appendix D, p 342). On planet-orbiting spacecraft, 396 Glossary

the instrument is useful for identify- on Earth, into interstellar space. Pio- ing the abundance and distribution of neer 10 and Pioneer 11 each carried roughly twenty different elements on a gold-anodized aluminum plate etched the surface, based on the energies of with artwork reflective of the human- gamma radiation they emit as they are inhabited planet and star-system from bombarded by cosmic rays from natural which the vessel came. These records sources. and plaques will probably survive the One of the four Galilean moons interstellar dust impacts for many hun- of Jupiter, third out from the planet, di- dreds of millions of years, while they or- ameter 5,262.4 kilometers, largest moon bit the center of our galaxy, having es- in solar system. Most likely has a sub- caped the Sun’s gravitational bond. surface water ocean between ice layers. Goldstone DSCC One of three worldwide Gas chromatograph Direct-sensing science Deep Space Communications Com- instrument that separates a sample of plexes in DSN. Near 35◦15’ N latitude mixed gases into a sequentially ordered × 116◦48’ W longitude. stream of gases, e.g., for further analysis Graphite Electrically conductive allotrope by a mass spectrometer. of carbon. Geocentric Having Earth’s center as refer- Graphite fiber Carbon fiber or plastic rein- ence. Compare topocentric. forced with carbon fiber. Strong, low- Geometric albedo See albedo. mass material with many applications Circular geosyn- in aerospace and elsewhere. Compare chronous orbit in which the spacecraft fiberglass. does not wander significantly north Grating See diffraction grating. and south by virtue of its equatorial Gravitation The natural acceleration of inclination. one mass toward another, described in Geosynchronous altitude About 36,000 the general theory of relativity as stem- kilometers above Earth’s sea level. ming from the curvature of spacetime Geosynchronous orbit Spacecraft orbit governing the motion of inertial objects. about Earth having a period equal to Gravitational radiation Fluctuations, or one sidereal day, which is 23 hours 56 gravitational waves, in the curvature minutes. In a geosynchronous orbit, a of spacetime predicted by general spacecraft appears to maintain a fixed relativity, which are generated by position above a point on Earth. very massive objects accelerating, e.g., Germanium Element, symbol Ge, atomic neutron stars orbiting one another, or number 32. Semi-metallic, solid at room coalescing. Not yet directly detected, temperature. An important semicon- but it has been indirectly observed in ductor in its pure crystalline form. the in a binary system Giotto ESA spacecraft flown to Comet Hal- comprising a pulsar and a star. ley in 1986. General-relativistic GMT Greenwich Mean Time, a time scale phenomenon, see above. Compare based on Earth’s minutely variable rota- gravity wave. tion rate and the passage of a fictitious Gravity field mapping Science investi- “mean” Sun — one whose rate of pas- gation in which a planet-orbiting sage through the sky daily is an average spacecraft’s speed is tracked via of its values over Earth’s annual motions Doppler shifts in its radio link as the through perihelion and aphelion. spacecraft’s speed increases slightly Golden record Voyager 1 and Voyager 2 when approaching an area of concen- spacecraft each carry a gold-plated cop- trated mass on the planet, and slows per phonograph-style record, contain- slightly when receding from the area. ing images and sounds representing life Characterizes the planet’s distribution of mass on and below its surface. Glossary 397

Gravity assist Intentional interaction be- vibrating hemisphere, or a coil of fiber tween a spacecraft and a natural body it optic cable. passes. Called an elastic collision, some Gyroscopic effect With regard to a spin- of the natural body’s orbital momentum ning mass, the rigidity in space of its is decreased or increased, and in the ex- axis, and/or the precession that results change the spacecraft’s velocity changes from applying torque to the axis. substantially, as measured from the sys- The largest instrument tem’s center, e.g., the Sun. atop Mt. Palomar in California, a Gravity gradient The difference in gravita- 200-inch (5.1–meter) aperture reflect- tional attraction felt at one side of, e.g., ing telescope. Named in honor of the a spacecraft from that felt at its other American astronomer George Ellery side when in the presence of a substan- Hale (1868–1938). At first light in 1948 tial gravitational mass, e.g., a planet. it was the world’s largest telescope, and The difference is due to the force of is still a first-rate scientific asset today. gravity decreasing as the square of the Dwarf planet, dimensions about distance from the planet. Gravity gradi- 1960 × 1518 × 996 km, orbiting the Sun ent can produce a torque on the object. in the Kuiper belt. Rotates rapidly, with It causes the Moon to keep one side to- a period under four hours, causing its ward Earth. elongated shape. Has two moons, named Gravity wave Hydrodynamic wave, e.g., Hi’iaka and Namaka. in an atmosphere, oscillating as the Hayabusa JAXA spacecraft that ren- planet’s gravity causes the air to re- dezvoused with asteroid Itokawa spond to a disturbance. Compare grav- September 2005. Expected to return a itational wave. sample-canister to Earth in 2010. Ground system DSN and all ground-based Heliocentric orbit An orbit that has the communications and computing hard- Sun at one focus of its ellipse, e.g., ware, software, and workforce that acts Earth’s orbit, Ulysses spacecraft orbit, as the counterpart to a flight system Spitzer spacecraft orbit. (spacecraft). Heliopause Outer boundary of the helio- Ground truth Directly measured quanti- sphere, which creates a bow shock ex- ties at the surface of a planet, e.g., made ternal to it, at the turbulent interface by a lander or rover, which correspond with the interstellar medium. See Ap- with and serve to calibrate remote- pendix C, p 337. sensing measurements made from orbit. Heliosheath Region of space outside the Helps investigators interpret remote- Sun’s termination shock and inside the sensing data. heliopause. Guillotine Cable-cutting device on space- Heliosphere Bubble of plasma inflated by craft, typically driven by pyrotechnic the solar wind and confined by the so- charges. lar magnetic field and the interstellar Gunpowder Early solid-rocket propellant medium. used by the Chinese, invented in China Helium Element, symbol He, atomic num- in the ninth century. Granular mixture ber 2, gaseous at room temperature; one of , charcoal and potassium ni- of the six noble gases. Named for the trate, which releases oxygen to burn the Sun, where it was first discovered. other ingredients. Low explosive. Helium magnetometer Passive direct- Gyro Short for . sensing science instrument that uses Gyroscope A device that senses an object’s high-frequency alternating electric rotation. AACS inertial reference input current discharges and infrared optical device. Gyro technology can employ a pumping to excite ionized helium in a small spinning mass, a vibrating reed, a cell. Measuring changes in energy the 398 Glossary

helium absorbs indicates the effects of of this ideal minimum-energy transfer an external magnetic field. are adapted as needed for timing, out- Hematite Iron-bearing mineral (Fe2O3). of plane inclinations, and other plan- Typically formed or altered on Earth ning issues. Named for German engineer in aqueous conditions. Abundant on the Walter Hohmann (1880–1945). surface of Mars. Horizon sensor AACS celestial reference Hemispherical resonator gyro (HRG) input device on some spacecraft, partic- AACS inertial reference input device. ularly planet-orbiting surface-observing Senses rotation about an axis using no missions. moving parts. Relies on measuring pre- Hot neutron Neutral nuclear particle hav- cession of nodes on the rim of a small, ing relatively high velocity, e.g., from re- vibrating fused quartz hemisphere, via cent collision with a much more massive piezoelectric effects. atom. HEMT High-electron mobility transistor; a Housekeeping data Engineering telemetry special field-effect transistor. Low-noise from a science instrument that reports amplifier, typically the first stage of am- on the instrument’s state, e.g., tempera- plification for a received microwave sig- ture, configuration, electrical power lev- nal, e.g., in residential television dish els, etc. antennas. DSN HEMTS are cryogeni- HST Hubble Space Telescope; one of cally cooled to reduce contribution of the four NASA Great Observato- noise. ries. Launched April 24, 1990. A High-gain antenna (HGA) Microwave an- 11,110-kilogram spacecraft with 2.4– tenna on a spacecraft consisting of the meter aperture Ritchey-Chr´etien re- largest practical main-reflector aper- flecting telescope and multiple instru- ture. For reference, Voyager’s 3.7–meter ments. Primary mirror manufactured diameter HGA provides a 63,000-fold with spherical aberration error, accom- increase in signal strength at X-band modated by corrective optics installed frequencies, or about 48 dB. December 1993 by Space Shuttle as- High-inclination orbit Orbit whose plane tronauts. A total of four such servic- forms a large angle with the ecliptic, or ing missions have been accomplished with a planet’s equator. An orbit with as of press time. Named for Ameri- maximum inclination (90◦) is called a can astronomer Edwin P. Hubble (1889– . 1953), who, working at Mt. Wilson with HiRISE High-resolution imaging science assistant Humason (1891–1972), experiment on Mars Reconnaissance measured spectra of distant galaxies Orbiter. Can achieve 30-centimeter and discovered in 1929 that the amount pixel size images of the Martian surface of is proportional to their dis- in visible light. Its telescope aperture is tance, establishing the expansion of the 50 centimeters, focal length 12,000 mil- universe. limeters. Huygens ESA atmospheric spacecraft. Re- Hill sphere Area of greater gravitational in- leased by Cassini December 25, 2004, fluence around a body, when compared entered Titan’s atmosphere January 14, to the influence of another body’s grav- 2005 and returned telemetry to Cassini itation. that was relayed to Earth. Cassini mea- Hohmann transfer Portion of a solar orbit sured Doppler shift on the Huygens car- that a spacecraft can attain given an rier, which was also received directly on impulse of thrust (of appropriate C3) Earth where its Doppler shift, later cor- at the transfer orbit’s perihelion. Would related with Cassini data, traced the return the spacecraft toward the Sun in parachuting probe’s wind-driven move- elliptical orbit were it not to encounter ments. Huygens survived touchdown its target planet at apoapsis. Variations and reported on the methane-soggy Glossary 399

sand in which it landed. Named for visualizing images obtained by pas- Dutch astronomer Christiaan Huygens sive remote-sensing instruments, e.g., at (1629–1695) who discovered this largest visible-light wavelengths. moon of Saturn in 1655. Imaging spectrometer or spectrograph; Hydrazine (N2H4) Liquid monopropellant passive remote-sensing instrument rocket fuel that decomposes explosively having multiple pixels that make up an on contact with a heated catalyst in image, which is captured all at once rocket thrusters. (rather than via an internal scanning Hydrofluoric acid Solution of hydrogen flu- mechanism), each pixel revealing the oride (HF) in water, a corrosive acid intensity of each of a number of wave- that dissolves glass. lengths observed. Compare mapping Hydrogen Element, symbol H, atomic spectrometer. Data output is called a number 1, commonly found as the di- “cube” rather than a two-dimensional atomic H2 molecule, gaseous at room image. temperature. Most abundant element in Impact detector Passive direct-sensing in- the universe. Named in 1783 for its abil- strument that measures the incidence ity to generate water by burning in the of dust particle impacts, and may also air. do some characterization of them. Com- Hydrogen maser Frequency standard that pare dust analyzer. employs hydrogen’s physical properties Impact radius Circle drawn on a B-plane and a tuned cavity to generate and chart inside of which a spacecraft’s aim maintain a highly stable microwave fre- point will cause it to impact the target quency (near 1,420 MHz). Used in DSN body’s surface. to generate uplink carrier signals and Impulse Change in momentum (mass × provide system-wide frequency and tim- velocity) brought about by force, e.g., ing references. from a rocket’s thrust. Hydrogen peroxide (H2O2) Unstable com- Impulse turbine Device that changes the pound that decomposes in contact with velocity (rather than pressure) of a a catalyst in relatively low-power rocket jet, e.g., of steam from a divergent- engines. convergent nozzle, impacting and re- Hypergolic Either of two rocket propellants sulting in change of momentum (im- that ignite spontaneously when mixed, pulse) on a turbine’s blades, which do e.g., monomethyl hydrazine or nitrogen not require submersion. tetroxide. Incandescence Emission of visible light One of Saturn’s moons, the third from an object, e.g., rocket nozzle or largest, diameter 1,436 kilometers. Or- tungsten filament, due to its tempera- 6 bits 3.561 ×10 km from Saturn. Lead- ture. ing hemisphere has a high equatorial Index of refraction Measure of how much ridge and is covered in (probably ex- the speed of a wave, e.g., light, is re- ogenic) dark organic matter. Trailing duced when passing through a medium. hemisphere exhibits high-albedo water Liquid water’s index is 1.33, meaning ice. light slows to 1/1.33 c. Responsible for IMC Image-motion compensation; rotation bending light rays where density of a of a spacecraft or its instruments to keep medium varies. a target centered in optical fields of view Indium Element, symbol In, atomic num- during a flyby encounter. ber 49. Soft metal, solid at room tem- Imaging radar See SAR, synthetic aperture perature. Constituent in IR detectors radar. such as indium antimonide. Imaging science Discipline concerned with Indium antimonide (InSb) Semiconductor planning, capturing, compressing and used in detectors, e.g., photodiodes, sen- transmitting, analyzing, modifying, and 400 Glossary

sitive to IR wavelengths around 1 μ to Internet protocol (IP) See TCP/IP. 6 μ. Interplanetary flight Movement of a space- Indium-gallium phosphide (InGaP) Semi- craft which has departed Earth’s gravi- conductor useful in high-frequency and tational bond, having characteristic en- high-power applications, in HEMTs, ergy, C3, greater than zero. and in multi-junction solar cells. Interplanetary space Space between the Inertia Intrinsic property of mass that planets and Sun within the solar sys- demonstrates Newton’s first law of mo- tem. tion. The fundamental nature of inertia Interplanetary spacecraft Vehicle designed and of mass are subjects of investiga- to leave Earth’s gravitational bond. All tion. are robotic as of today. Inertial reference AACS input device that Interstellar space Space between the stars, registers change in spacecraft orienta- which begins outside the heliosphere. tion based on internal and Inverted data See complemented data. without external (celestial) reference. Inverter, power See power inverter. Inertial vector propagator Algorithm in Innermost of the four Galilean moons AACS that maintains knowledge of the of Jupiter, diameter 3,643.2 kilome- directions (vectors) from spacecraft to ters. Most volcanically active body specified targets of interest, based on known, constantly being resurfaced in current ephemerides. Computes (prop- the present. agates) changes to the vectors into the Ion An atom missing one or more of its future. electrons. The solar wind fills interplan- Inferior Conjunction (coinci- etary space with these. Also, an atom dence of right ascension) of an interior with an excess of electrons, e.g., in a planet or spacecraft with the Sun when chemical solution. the Earth and the planet are on the Ion engine Means of electrostatic propul- same side of the Sun. Compare superior sion that employs high-voltage grids to conjunction. accelerate ions to high velocity and gen- Infrared (IR) Electromagnetic radiation in erate thrust. High ISP , low thrust. Com- wavelengths from about 1 millimeter to pare MPD thruster. 380 nanometers. See Appendix D, p 342. Ionization The process of electrons being Produced in nature by, e.g., animals and removed from their atoms, e.g., by ab- stars. sorption of electromagnetic energy. Integrated sequence of events (ISOE) Ionosphere Highest layer in a body’s atmo- Time-ordered list of spacecraft events sphere, ionized by solar radiation. and DSN events. IR spectrometer See spectrometer. Mea- Intensive quantity Physical quantity that sures invisible “colors” in the IR. expresses units of A per units of B, e.g., Iridium Element, symbol Ir, atomic num- density (mass per unit volume), spe- ber 77. Solid at room temperature. Very cific energy (energy per unit mass), spe- hard, dense, brittle, corrosion-resistant cific impulse (impulse per unit of pro- metal. Found in meteorites at higher rel- pellant). ative abundance than typically found in Interferometry Technique of interpreting the Earth’s crust. the pattern of interference created by Iridium Earth-orbiting U.S. communica- the superposition of two or more waves, tions spacecraft with large planar solar e.g., microwave, radio, or light, to de- arrays that show bright specular flashes, termine properties of the waves’ source, called “Iridium flares,” in the local sky e.g., position in the sky through VLBI, at times published online. or rotation rate in a laser gyro. Iron Element, symbol Fe, atomic number Intergalactic space Space between the 26. Strong metal at room temperature, galaxies, i.e., outside the Milky Way. made stronger by alloying with carbon Glossary 401

to make steel. Major constituent of the Ku-band Range of microwave frequencies terrestrial planets’ cores. around 12 to 18 GHz. Isotropy Condition of being homogenous in Kuiper belt Region in the solar system be- all directions. Compare anisotropy. yond Neptune’s orbit, 30 AU, extending Isp See specific impulse. to about 55 AU from the Sun. Popu- Julian year Definition of the year as 365.25 lated with icy bodies including Pluto. days, or 31,557,600 seconds. Named af- point Any of five orbital posi- ter the Julian calendar that came into tions at which an object can in theory use in 45 BCE. remain stationary with respect to two Jupiter polar orbiter project in the massive objects, e.g., Sun and Earth. NASA that be- Labelled L1 through L5. gan preliminary design, Phase A of Lander and Penetrator Spacecraft One of its mission, in June 2005. Planned to eight classifications of spacecraft. De- launch in August 2011. Cost capped at signed to encounter the surface of a so- $700M. lar system body. Jupiter Fifth planet from the Sun, one Laser Electro-optical device that produces of the four gas giants or Jovian plan- a coherent source of light by emission of ets. Equatorial diameter 11.209 times stimulated radiation. Earth’s. H2 atmosphere with about 10 Laser gyro AACS inertial reference input percent He and traces of other gases. device. Senses rotation about an axis us- Mean distance from Sun 5.2 AU. ing no moving parts. Relies on measur- Jupiter radius 1 RJ = 71,492 km. ing Doppler-shifted light via interferom- Ka-band Range of microwave frequencies etry to measure rotation about an axis. around 26.5 to 40 GHz. Laser-Induced Remote-sensing Spec- Kapton Polyimide film proprietary to trograph. An active remote sensing DuPont, Inc., used for its high instrument. Bombards target, e.g., durability performance in extreme rock, with focused high-energy infrared temperatures, electrical properties, and light, causing part of the target to low mass. vaporize, and observes spectra of emis- Kepler’s first law of planetary motion: The sions from the resulting hot gas. Named planets’ orbits are ellipses with the Sun ChemCam on Mars Science Laboratory. at one focus. Latitude North-south coordinate measure- Kepler’s second law of planetary motion: A ments on a globe, given by parallel lines line joining the planet to the Sun sweeps measured from 0◦ at the equator to out equal areas in equal amounts of 90◦ north and south at the poles. Com- time. pare longitude. Kepler’s third law of planetary motion: Launch period Range of days during which The square of a planet’s period of revo- a launch with a nominal energy (C3) lution about the Sun is proportional to and arrival time can be attempted. the cube of the semimajor axis of the Launch window Period during a day in the planets elliptical orbit. launch period when launch is possible. Kinetic energy The energy a body pos- Also called daily firing window. sesses due to its motion, expressed as: Launch-arrival plot See porkchop plot. 1 mv2 2 Lead Element, symbol Pb, atomic number 82. Soft metal, solid at room tempera- where m is its mass and v its velocity. ture. Klystron High-power microwave amplifier Light time Time it takes radio communi- used in DSN transmitters, output of cations to propagate, e.g., from DSN to which is measured in kilowatts, e.g., 18 spacecraft and back. kW at X-band for telecommunications, Light See visible light. to 400 kW for radar astronomy. 402 Glossary

Light-emitting diode (LED) Semiconduc- LISA Laser-Interferometer Space An- tor diode that exhibits electrolumines- tenna; proposed gravitational wave cence, emitting narrow-spectrum, non- observatory. coherent IR, visible light, or UV when Lithium Element, symbol Li, atomic num- electrical current flows through its p-n ber 3, alkali metal; a low-density solid junction. LEDs are more efficient in con- at room temperature. verting electrical power to light than are Local Civil Time (LCT) Statutory time incandescent or fluorescent devices. designated by civilian authorities, a Light-induced degradation Reduction in a fixed offset from UTC, possibly ad- ’s electrical power output in its justed seasonally for daylight saving first few weeks in operation. time. Limb Visible edge of a body such as the Local mean time (LMT) Mean solar time Sun or a planet. at a planet’s local meridian (based on LINEAR Acronym for “Lincoln near-Earth the angle of the Sun). asteroid research.” MIT Lincoln Lab- Lock In telecommunications, state of a oratory program funded by U.S. Air closed-loop radio receiver in which a Force and NASA to demonstrate ap- phase-locked-loop circuit has acquired plication of technology originally devel- the incoming signal and is following it, oped for surveillance of Earth orbiting along with its every shift in phase. With satellites, to the problem of detecting telemetry data, state of a DSN teleme- and cataloging near-Earth asteroids. try subsystem in which it is success- Link Communications path between space- fully predicting and finding in a data craft engineers and their subsystems stream the codeword (pseudo-noise, PN in flight, and between science teams code) that identifies the start of a trans- and their payload of instruments on fer frame. Command lock on a space- the craft. Includes spacecraft’s commu- craft means its command data decoder nications equipment, intervening inter- is decoding binary digits from the up- planetary space, DSN equipment, earth- link carrier signal’s phase shift symbols. based communications systems, com- Log In space flight operations, a chronology puters, and routers that participate in of realtime events kept by, e.g., an Ace. the communications path. Usually in- Includes such events as beginning of a stantiated for hours at a time. DSN track, acquisition of signal, teleme- Liquid ethane (C2H6) Constituent of lakes try lock, spacecraft activities observed, on the surface of Saturn’s moon Titan. descriptions of anomalies or discrepan- Boils at 184.5 K (standard pressure). cies, and references to their documenta- Liquid helium Liquified helium gas, useful tion. as a refrigerant for low-noise amplifiers Longitude East-west coordinate measure- and infrared instruments. Boils at 4.2 K ments on a globe. Half great circles (standard pressure). called meridians intersecting both op- Liquid hydrogen Liquified hydrogen gas, posite rotational poles of a planet useful as rocket propellant. Boils at 23 or other body. British inventor John K (standard pressure). Harrison (1693–1776) first successfully Liquified oxygen gas, useful demonstrated longitude determination as rocket propellant. Boils at 90.19 K on Earth with his long-sought accurate, (standard pressure). seaworthy chronometer in 1761. Com- Liquid-propellant Liquid chemical for pare latitude. rocket engine or thruster. Called mono- Lorentz force Force on a point charge due propellant if the engine uses only one to electromagnetic fields. The basis of chemical, e.g., hydrazine, or bipropel- motor and generator design. Named for lants if two chemicals, fuel and oxidizer, named for the Dutch physicist Hendrik are required. Lorentz (1853–1928), Glossary 403

Louvers Mechanical devices on a spacecraft change orbital parameters. Operated at bus that autonomously open to permit Venus 1990 through 1994. IR to radiate, and close to contain IR, Element, symbol Mg, atomic to maintain desired temperature within. number 12, a strong, lightweight metal Driven by ambient thermal energy on at room temperature. Readily in bimetallic strips. oxygen, giving off a bright white light. Low-density parity-check (LDPC) For- Magnetic torquers AACS output devices, ward error-correction coding system electromagnets that interact with first described 1960 by American Earth’s magnetic field to manage grad student Robert Gallager (1931–). spacecraft attitude. Gallager codes, used today in digital Magnetometer Passive direct-sensing in- satellite TV, reach within a fraction of strument that measures the magnetic a dB of the Shannon limit. LDPC uses field of a planet or in interplanetary or a decoder for each bit in a message. interstellar space. Low-gain antenna (LGA) Small, nearly Magnetosphere Magnetized region gener- omnidirectional microwave antenna on ated by and surrounding an astronom- a spacecraft, with gain of perhaps 1 dB ical object, e.g., Sun, Earth, Jupiter. or so. Typically formed into tear shapes by Low-Noise Amplifier (LNA) DSN mi- pressure from external such as the crowave subsystem component down- solar wind or interstellar medium. stream of the antenna’s Cassegrain Main asteroid belt Region between the or- reflector and feed. Either a high- bits of Mars and Jupiter populated by electron-mobility transistor, HEMT, or debris remaining after solar system for- a maser. Typically cooled with liquid mation. helium to a few kelvins. Dwarf planet, about 1,500 km Luminosity Quantity of energy a body, e.g., in diameter, orbiting the Sun in the a star, radiates per unit time. Appar- Kuiper belt. ent luminosity refers to visible light ra- Mapping spectrometer or spectrograph. diated. Bolometric luminosity refers to Passive remote-sensing instrument all wavelengths. having multiple pixels that make up Project in NASA’s Dis- an image, which is captured via an covery Program that flew a polar orbit internal scanning mechanism (rather around the Moon for 1.5 years begin- than all at once), each pixel revealing ning in January 1998 to map elements the intensity of each of a number near the surface and refine the gravity of wavelengths observed. Compare field map. imaging spectrometer. Mach 1.0 The , which varies Mars Fourth planet from the Sun, one of according to the medium’s density and the four terrestrial planets. Diameter temperature. Named for the Czech- 0.532 of Earth’s. Surface temperature Austrian physicist Ernst Mach (1838– ranges from about –120 ◦Cto15◦C. 1916). Mars Climate Orbiter NASA Planetary Madrid DSCC One of three worldwide orbiter spacecraft lost during its orbit Deep Space Communications Com- insertion burn in 1998 due to buildup ◦ plexes in DSN. Near 40 26’ N latitude of navigation error stemming from ◦ × 002 00’ W longitude. metric-English unit confusion during Magellan NASA Planetary orbiter that interplanetary cruise. mapped the surface of Venus to high res- Mars Exploration Rover (MER) Twin olution using synthetic aperture radar NASA rover spacecraft, named Spirit imaging, altimetry, and radiometry, and Opportunity, which landed in 2003 and carried out atmospheric investiga- on opposite sides of Mars. tions including the first aerobraking to 404 Glossary

Mars Express ESA Planetary orbiter duces the most power out of a solar spacecraft that began orbiting Mars in panel under varying conditions of tem- 2003. perature and illumination. MPP track- Mars Global Surveyor (MGS) NASA Plan- ing circuitry computes and utilizes the etary orbiter spacecraft that operated MPP. at Mars from September 1997 until MCD Maximum-likelihood Convolutional November, 2006. Decoder. DSN electronic assembly that Mars Observer NASA Planetary orbiter runs a Viterbi algorithm in hardware to lost August, 1993, during bipropellant apply forward error correction and con- tank pressurization in preparation for vert radio symbols to data bits. orbit insertion. Mean Sun Fictitious body whose rate of Mars Pathfinder (MPF) NASA Discovery- daily passage through the sky is an av- program planetary lander that landed erage of the Sun’s motion across the July, 1997. Deployed Sojourner, the first sky throughout the entire year. Basis of operable rover on another planet. Greenwich Mean Time (GMT). (MPL) Lander space- Mechanical devices Subsystem on a space- craft in the NASA Mars Surveyor ’98 craft that incorporates deployable and program that failed during atmospheric mechanically operable assemblies, e.g., entry, descent, and landing in the high instrument booms and landing struts. southern latitudes in December 1999. Medium-gain antenna (MGA) Assembly in Mars Reconnaissance Orbiter (MRO) a spacecraft’s telecommunications sub- NASA Planetary orbiter that entered system capable of higher gain than Mars orbit in March, 2006. LGA, and wider area coverage at lower Mars Science Laboratory (MSL) NASA gain than HGA. Rover due to launch in 2011. Megapixel One million picture elements Maser Low-noise amplifier that multiplies (photogates), as in CCDs. the strength of a microwave signal by Memory effect Loss of ability of a NiCd emission of stimulated radiation, while battery to recharge completely if repeat- contributing little noise. Compare laser. edly discharged and recharged only to a Maser frequency standard Microwave fre- fraction of its capacity. quency resonant-cavity oscillator based MEMS gyros Micro-electromechanical sys- on stimulated emissions of, e.g., hydro- tem that senses rotation. Used in gen, used in DSN to generate uplink sig- handheld remote controllers and Seg- nal and other references with extremely way® personal transporters. Beginning high frequency stability. See frequency to come into use on spacecraft. and timing. Mercury First planet from the Sun, one Mass Intrinsic quality of matter that causes of the four terrestrial planets. Diam- it to have momentum, and respond to eter 0.383 of Earth’s. Mean distance gravitation. Equivalent to energy as in from Sun 0.387 AU. Surface tempera- E=mc2. tures range from –183◦C to 427◦C. Mass-expulsion control (MEC) Attitude Mercury Element, symbol Hg, atomic num- control via rocket thrusters. ber 80; a liquid metal at room tempera- Mass spectrometer Active direct-sensing ture. Vapor emits strongly at UV wave- instrument that analyzes a sample of lengths when excited. Toxic. ionized gas to determine the range of Meridian A line of longitude, from pole to atomic or molecular masses (thereby pole. the chemical species) it contains. Messenger Mercury-orbiter spacecraft Mass-expulsion device A rocket engine or planned to enter orbit about the planet thruster. on March 18, 2011. Maximum power point (MPP) Combina- Metallic (M-type) Asteroid M-type - tion of voltage and current that pro- oids comprise about 8 percent of main- Glossary 405

belt types and are found mostly in channel, e.g., phase variations on a mi- the middle of the main belt. Their re- crowave radio signal. flectance spectra generally indicate a Modulation index In phase modulation, composition of metallic iron, matching the number of degrees or radians a wave the spectra of iron meteorites. is shifted to constitute an information Meteor An object in the process of enter- symbol. ing the atmosphere from , or Momentum, linear The product of an ob- falling through it. Compare , ject’s mass and velocity. . Momentum thrust The major component Meteorite An object from outer space of force in a rocket engine, which comes found on the planet’s surface. from acceleration of mass out the noz- Meteoroid An object in interplanetary zle. Terms to the left of the + sign (see space that may be on a planet- (or description on p 127) in: spacecraft-) impacting trajectory. F =˙mve + peAe Meteorological station Direct-sensing in- Compare pressure thrust. strument or suite of instruments that Momentum wheel See reaction wheel. measure atmospheric conditions such as Monitor data One of the seven DSN data wind speed and direction, temperature, types. Indications of DSN station equip- pressure, , e.g., on the Phoenix ment performance, such as received sig- Mars lander. nal levels, transmitter power, and an- Methane (CH3) gas at room temperature tenna pointing angles. on Earth. Constituent of outer planet Monocoque Structural design in which atmospheres, and of clouds and liquid loads are supported by an external skin. lakes on Saturn’s moon Titan. From French for “single shell.” Microwave Region of electromagnetic spec- Monoprop thruster Small rocket engine trum with wavelengths measured in cen- that uses a single liquid propellant, e.g., timeters. See Appendix D, p 342. hydrazine, which comes in contact with Minor planet Asteroid. an electrically heated catalyst to initiate MIssion An operation designed to carry out explosive decomposition of the liquid. the goals of a project. Often used inter- Moon Capitalized, the Earth’s natural changeably with project. satellite. Otherwise, any object’s natu- Mission phase Period in the life of a ral satellite. project, typically denoted as pre-Phase- Moore’s Law Conjecture by Gordon A initial studies, and Phase-A through- Moore, cofounder of Intel Corporation, D development, assembly and testing, which states that the number of tran- and then Phase E operations. sistors on an integrated-circuit chip Mission plan Detailed document that will double about every two years. This serves as a central reference for car- has held true for forty years or more. rying out every aspect of mission First published in “Cramming more operations. components onto integrated circuits” in MMH Mono-methyl hydrazine (CH3N2H3) Electronics magazine, April 19, 1965. liquid rocket fuel used in bipropel- M¨ossbauerSpectrometer Active direct- lant systems, hypergolic with nitrogen sensing science instrument good at tetroxide. measuring iron-bearing minerals, e.g., MO&DA Mission operations and data in rocks. analysis; Phase E in a mission’s lifetime, MPD thruster Magnetoplasmadynamic during which it carries out its intended means of electric propulsion that data collection, and at least an initial employs the force resulting from inter- analysis is performed. action between a magnetic field and Modulation Technology of imposing in- an electric current (Lorentz force) to formation onto a telecommunications accelerate ions to high velocity and 406 Glossary

generate thrust. High ISP , low thrust. emitted from target surface. Useful in Compare ion engine. identifying water on target’s surface. Multijunction solar cell Also called Multi- New Horizons NASA flyby spacecraft bandgap, a solar cell made of multi- launched January 19, 2006, to en- ple thin-film layers of semiconductors, counter Pluto and its moon Charon each of which is responsive to a differ- on July 14, 2015, and then continue ent range of wavelengths of light. into the Kuiper belt for possible ad- Multiplex (MUX) Technology of combining ditional but as yet unidentified object multiple signals or measurements into a encounters Passed Jupiter February 28, single telecommunications channel. 2007 for gravity assist and instrument Nadir The point directly below the ob- checkout. server. Compare zenith. Newton’s first law An object at rest tends NEAR-Shoemaker (Near-Earth Asteroid to stay at rest, and an object in motion Rendezvous) NASA spacecraft that tends to stay in motion with the same orbited near-Earth asteroid Eros be- speed and in the same direction, unless ginning February 2000, then touched acted upon by an unbalanced force. down on its surface at end of mission Newton’s second law The acceleration of in February 2001. an object as produced by a net force is Neon Element, symbol Ne, atomic num- directly proportional to the magnitude ber 10, gaseous at room temperature; of the net force, in the same direction as one of the six noble gases. When ex- the net force, and inversely proportional cited, strongly emits characteristic or- to the mass of the object. ange, red, and other wavelengths. Newton’s third law For every action there Nephlometer An active remote-sensing sci- is an equal, but opposite, reaction. ence instrument that illuminates cloud Nickel Element, symbol Ni, atomic number particles in an atmosphere and observes 28; metallic, solid at room temperature. light reflected from them. Used in rechargeable batteries. Neptune Eighth planet from the Sun, one Nickel-cadmium batteries (NiCd) of the four gas giants or Jovian plan- Rechargeable battery having a high ets. Equatorial diameter 3.883 times cycle durability. Under some circum- Earth’s. Atmosphere of predominantly stances they exhibit “memory effect” H2 with about 19 percent He and 1.5 reducing their ability to cycle deeply. percent methane. Mean distance from Toxic due to their cadmium content. Sun 30.07 AU. Nickel-hydrogen (NiH2) Rechargeable bat- Neptunium Element, symbol Np, atomic tery having a high cycle durability and number 93. Metallic, solid at room tem- well-proven performance on spacecraft. perature. Not occurring naturally, this Enclosed in pressure vessels. radioactive element is manufactured in Niobium (also called columbium). Ele- a nuclear reactor. ment, symbol Nb, atomic number 41. Neutron The neutral nuclear subatomic Metallic, solid at room temperature, particle, similar in mass to the proton. high melting point (2,477◦C). Steel al- Neutron radiation Ionizing radiation con- loyed with niobium is used in rocket en- sisting of moving neutrons. Emitted by gines. nuclear fission and fusion, etc. Nitrogen Element, symbol N, atomic num- Neutron Spectrometer Passive direct- ber 7, commonly found as the diatomic sensing science instrument that uses molecule N2, gaseous at room temper- scintillators to measure energy distribu- ature. Major constituent of the atmo- tion of free neutral subatomic particles. spheres of Earth and Titan. Geometry of multiple detector ele- Non-coherent Communications mode in ments allows separation of background which spacecraft downlink radio signal neutron radiation from that being Glossary 407

is not in phase-coherence with an up- radio science and very-long baseline in- link. terferometry. NTO Nitrogen tetroxide oxidizer (N2O4); OSI Open systems interconnection; an powerful oxidizer, highly toxic and cor- early basic reference model for net- rosive. Hypergolic with various forms of work communications. Superseded by hydrazine. TCP/IP. Nutation Irregular nodding motion or wob- Opnav Image for use in optical navigation, ble in the rotation axis of a largely axi- typically of a target body, overexposed ally symmetric object, such as a planet to show the background stars. or a spinning spacecraft. Opportunity Name of the Mars Exploration Observable A parameter input to the navi- Rover that landed at Meridiani Planum gation orbit determination process, such in 2004, three weeks after its twin, as a spacecraft’s range, right ascension, Spirit, landed on the opposite side of declination, Doppler shift, or optical Mars. navigation data. Opposition effect Apparent brightening of Observatory spacecraft One of eight clas- an object, e.g., the Moon, when at op- sifications of spacecraft. Designed to position (illumination phase angle near carry out observations of typically zero). deep-space phenomena from above Optical modulator Device placed in a fiber- the Earth’s atmosphere, e.g., Spitzer, optic link that varies its opacity over SOHO, Chandra. time to vary the intensity of light in the Occultation zone Area behind a planet or link. other body as viewed from Earth or Optical navigation The process of acquir- Sun. ing opnav images on a spacecraft, and Ohm’s Law Relation between voltage, cur- after receiving them in telemetry on rent, and resistance (see description p Earth, or an onboard Autonav engine, 145): processing them to provide information V = IR on the spacecraft’s location in relation Omnidirectional Quality of an antenna de- to the target against stars recognized in noting its ability to receive from, or the image background. transmit in all directions, or at least a Optical Solar Reflector Mirror-like cell on large part of the sky surrounding the an- a spacecraft designed to reject solar tenna. heating. One-way Communications mode in which a Orbit Gravitationally bound path of one DSN station is receiving a spacecraft’s object around another, or of both about downlink, and the spacecraft has not a barycenter. (yet) received the station’s uplink. Orbit determination (OD) Computer pro- on the surface of Ti- gram suite that describes a spacecraft’s tan, Saturn’s largest moon, where the orbit given observables and laws of mo- terrain is largely made of water ice at tion. around 90 K, filled with liquid ethane Orbit insertion burn Rocket engine opera- and (perhaps) methane, as confirmed by tion upon arrival at target object, e.g., Cassini in 2008. planet, that decelerates the spacecraft Open loop in control theory, a system that from interplanetary cruise so it will be runs without self-adjustment. trapped in orbit about the object. Open loop radio Receiver that observes a Orbital Tour Mission of an orbiter space- band of frequencies, usually to record craft that includes encounters with ob- samples of them, and perform fast jects other than the primary body be- Fourier transforms to display power lev- ing orbited, e.g., Galileo observations of els at all received frequencies. Useful for Jupiter’s satellites as well as Jupiter it- self. 408 Glossary

Orbiter One of eight classifications of current, maintains voltage. Compare se- spacecraft. Spacecraft designed to en- ries connection. ter into orbit at a destination body Pass DSN space-link session. Tracking pe- and conduct observations of the body riod during which a spacecraft passes and/or of its environment and associ- across the sky. ated bodies. Passive-sensing Category of science instru- Oscillation Repetitive variation, e.g., in the ments that make observations without field strength of an electromagnetic supplying the main probing energy, e.g., wave. remote-sensing cameras and spectrome- Oscillator A device that sets up and main- ters, and direct-sensing dust detectors tains an oscillation, e.g., circuitry in a and magnetometers. Compare active- radio transmitter. sensing. OTM Orbit trim maneuver. Spacecraft Payload On a launch vehicle, the interplan- propulsive maneuver that makes a small etary spacecraft mission module and adjustment in its orbit about its target any of its own propulsion stages, e.g., body. Voyager’s mission module and injection Outer space Space exceeding 100 kilome- propulsion unit. On a spacecraft bus, ters above Earth’s surface. the science instruments. Oxygen Element, symbol O, atomic num- Periapsis raise maneuver Propulsive ma- ber 8, found in Earth’s atmosphere as neuver conducted at or near apoapsis the diatomic molecule O2, gaseous at to increase orbital energy, thus raising room temperature. O2 is not expected the altitude of subsequent periapses. to be found in any other planet’s atmo- Periapsis Low point in elliptical orbit; the sphere since it is highly reactive, unless point closest to the center of attrac- some process, e.g., photosynthesis, con- tion. tinually replenishes it. Periareion Periapsis in Mars orbit. Oxidizer A chemical that readily transfers Periastron Periapsis in stellar orbit. oxygen in a chemical reaction, or a dif- Pericenter Periapsis. ferent substance that gains electrons in Pericynthion Periapsis in lunar orbit. a redox (reduction–oxidation) chemical Pericytherion Periapsis in Venus orbit. reaction. Perigalacticon Periapsis in galactic orbit. Packet Formatted group of bits. Perigee Periapsis in Earth orbit. Packet-mode Modern means of data com- Perihelion Periapsis in solar orbit. munication wherein formatted groups of Perihadion Periapsis in Pluto orbit. bits are routed according to informa- Perihermion Periapsis in Mercury orbit. tion contained in their headers. Com- Perijove Periapsis in Jupiter orbit. pare time-division multiplex. Perikrition Periapsis in Venus orbit. Moon of Saturn that orbits just Perikrone Periapsis in Saturn orbit. outside the narrow F Ring and one of Perilune Periapsis in lunar orbit. the ring’s “shepherd” moons (the other Periposeidion Periapsis in Neptune orbit. is ). Mostly water ice, about Periselene Periapsis in lunar orbit. 114 kilometers in length. Periuranion Periapsis in Uranus orbit. Parachute mortar Pyrotechnic device that Perizene Periapsis in Jupiter orbit. fires a parachute out of its storage can- Phase angle Angle of illumination on a ister for deployment. body, 0◦ being from directly behind the Parallel connection Electrical arrangement observer, around to 180◦ in which the in which similar devices, e.g., batteries observer is behind the target looking to- or solar cells, have all their positive ter- ward the source of illumination. Spoken minals tied together and all their neg- of as “low phase” when closer to 0◦ and ative terminals tied together. Increases “high phase” when closer to 180◦. Glossary 409

Phase coherence Condition in which two or mid-air by a specially equipped aircraft more electromagnetic waves bear an un- during their parachute descent. changing relation in the timing of their Photometer Passive remote-sensing optical peaks and troughs. science instrument used to measure il- Phase modulation Imposition of informa- luminance or irradiance. tion, such as telemetry, on a carrier Type of science data con- signal (or subcarrier) by stepping the cerned with the quantity or power of phase of the carrier in predetermined electromagnetic radiation, e.g., light, ways. a target naturally radiates or reflects, Phase, project Period in the life of a captured using photometers. Field of project, typically denoted as pre-Phase- science that studies this phenomenon, A initial studies, and Phase-A through- such as in analyzing target surface com- D development, assembly and testing, position. Compare radiometry. and then Phase E operations. Photon A quantum (particle) of light or Phase, wave Fraction of a complete cycle other electromagnetic phenomenon. corresponding to an offset from a ref- Photovoltaic (PV) Describes a material erence time, measured in degrees from that is capable of converting light to 0◦ through 360◦. electric current with substantial effi- Phase-locked-loop (PLL) Closed-loop con- ciency. trol system, e.g., in a radio receiver that PICA Phenolic impregnated carbon abla- tracks an incoming signal as its fre- tor; modern thermal protection sys- quency changes. tem material for atmospheric-entry heat Phoenix lander Spacecraft in NASA’s shields that has advantages of low den- Mars Program that landed in the sity and efficient ablative capability at Martian arctic on May 25, 2008, and high heat flux. conducted surveillance and analysis of Piezoelectric Describes a material that can the icy soil. Mission ended November generate an electric potential in re- 11, 2008 near the onset of Martian sponse to applied mechanical stress, autumn. and/or change shape upon the applica- Photoelectric effect Quantum electronic tion of an electric current. Examples in- phenomenon in which electrons are clude crystal (or ceramic) microphones emitted from matter upon absorp- and earphones. tion of energy from electromagnetic Pioneer spacecraft NASA series of space- radiation, e.g., light. craft that performed first-of-their-kind Photogate An isolated photosensitive sili- explorations of the Sun, Jupiter, Sat- con capacitor that makes up one pixel urn and Venus. The different missions in a CCD image detector. had little in common except that they Photography Chemical-based method of all paved the way for later in-depth in- capturing an image on film. The vestigations, and all used spin-stabilized French artist and chemist Louis Da- spacecraft. guerre (1787–1851) developed a practi- Pitch Rotation about a spacecraft’s lateral cal means of preparing, exposing, de- axis. veloping, and fixing a plate to capture Planck constant Constant of proportion an image, called a Daguerreotype. He between a photon’s energy and its fre- −34 made a photograph of the Moon in 1838. quency: 6.626068 ×10 Js. Early in the space age before electronic Planck Surveyor Observatory spacecraft imaging, canisters of exposed film were due to launch in 2009 to image the returned from a series of Earth-orbiters anisotropies of the cosmic microwave in the Corona project, from 1959 until background radiation field over the 1972, in capsules that were recovered in whole sky with unprecedented sensitiv- ity and angular resolution. 410 Glossary

Planet A celestial body in solar orbit that Plutonium dioxide (PuO2) Form of the ra- is massive enough to be rounded by dioisotope used in RTGs on interplane- its own gravity (in hydrostatic equi- tary spacecraft. librium), and has cleared the neigh- PMD Propellant management device; borhood around its orbit. Defined in vanes or baffles within a propellant 2006 by the International Astronomical tank that use surface tension to bring Union. See also Dwarf planet. liquid to the tank exit port in the Astronomy Science con- absence of powered or gravitational cerned with observing radio-frequency acceleration. emissions from planetary systems and Polarimeter Passive remote-sensing science outer heliospheric phenomena. On Voy- instrument that measures the polariza- ager, the passive direct-sensing PRA in- tion of light reflected or emitted by a strument shares a 10-meter long dipole target. antenna with the plasma wave instru- Polarization Specific orientation of the ment. electric field component of an electro- Plasma State of matter as charged gas con- magnetic wave such as microwave or sisting of ions and electrons. light, e.g., left-circular, right circular, Plasma spectrometer Passive direct- linear. sensing science instrument that A device that selects desired po- measures qualities in ambient plasma larization of light or microwave radio by such as chemical composition, density, filtering out unwanted polarizations. flow, velocity, and temperature of ions Polar orbit An orbit whose inclination is ◦ and electrons. near 90 . Playback Readout from a spacecraft’s mass Porkchop plot Launch-arrival plot; data storage device being telemetered to computer-generated contours of Earth. characteristic energy C3 on an x-y Pluto Dwarf planet, Kuiper belt object, grid of launch and arrival dates. Often whose takes it 30 the contours take on the shape of a to 49 AU from the Sun, causing it to oc- porkchop. casionally come closer to the Sun than Potassium Element, symbol K, atomic Neptune. Discovered by American as- number 19. Alkali metal, soft solid at tronomer Clyde Tombaugh (1906–1997) room temperature, highly reactive. in 1930. Diameter 0.187 of Earth’s. Sur- Potassium hydroxide (KOH) Strongly ba- face temperature measured from Earth sic compound used in aqueous solution at –382◦C. Three satellites known at as alkaline battery electrolyte. press time. Just as the first of many as- Power flux density Quantity of energy teroids was discovered in 1801 (Ceres) transport through a unit of area, times and declared a new planet, Pluto was time. Intensive quantity. the first of many Kuiper belt objects to Power inverter Electronic device that con- be discovered. Ranked then as a planet, verts direct current (DC) to alternating it was re-classified in 2006 when more current (AC). and more similar objects were being dis- Power margin Difference between electrical covered. power generated and that actually used. Plutoid An object similar to Pluto, e.g., Power transient Sudden, temporary in- other large Kuiper belt objects. crease in electrical power consumption, Plutonium Element, symbol Pu, atomic e.g., due to inrush current when a number 93. Metallic, solid at room tem- device first turns on and warms up. perature. Radioactive element, not oc- Precession Property of a spinning mass curring naturally, manufactured via nu- wherein the direction of the axis clear reactor. changes, e.g., at right angles to an ap- plied torque. Glossary 411

Preliminary Design Review (PDR) An im- requirements, a life-cycle cost, a begin- portant step in the life of a mission ning, and an end. in which the review board determines Prometheus Innermost of the two “shep- whether a project is approved for final herd” moons straddling Saturn’s F Ring design and fabrication, Phase C. (the other is Pandora). About 145 kilo- Pressurant Gas head, e.g., helium, inside a meters in length, mostly water ice. tank of liquid propellant that provides Propane (C3H8) One of the the force to push the liquid propellant found in the outer solar system. toward an engine or thruster. Propellant The reactant in a rocket engine Pressure thrust Component of force in a or thruster, e.g., the gas that is rocket engine that comes from exhaust ionized and accelerated in an ion en- pressure against the nozzle’s interior gine, the hydrazine that decomposes in surface. Terms to the right of the + sign a monopropellant thruster, or the gran- (see description on p 127) in: ular mixture that burns in a solid rocket F =˙mve + peAe motor. Compare momentum thrust. Proton The positively charged nuclear sub- Pressure-regulated Mode of propulsion sys- atomic particle, similar in mass to the tem operation in which pressurant is neutron. admitted through a regulator into the Pseudo-noise code (PN) Pattern of bits propellant tank during a rocket burn that identifies the start of each teleme- to maintain constant pressure and con- try transfer frame. stant propellant flow rate. Compare Pulsed plasma thruster Variation of the blowdown. MPD thruster that uses solid propellant Primary battery Spacecraft battery that that ablates when the spark operates. supplies all the electrical power for Push-broom Imaging technique using a de- a spacecraft’s operation, e.g., Sput- tector consisting of a line of photogates. nik’s silver oxide-zinc battery, Huy- A two-dimensional image is built up gens’s lithium-sulphur dioxide. by spacecraft motion, e.g., Mars Re- Principal investigator Professional scien- connaissance Orbiter’s HiRISE camera. tist who leads the experiments and/or The same technique is used in office observations in one or more fields being photocopiers. carried out by a spacecraft. Typically Pyrotechnic Device on a spacecraft that at the level of an academic professor, uses an explosive charge to power a one- with a team including grad students in time operation, e.g., shutting a valve, the PI’s discipline and staff scientists, cutting a cable, releasing a bolt. engineers, and technicians. Quadrapod Four-legged support, e.g., Program Level of administration above the holding a subreflector above a main re- project level in a mission, e.g., a series flector in a DSN antenna. Comparable of spacecraft having similar cost con- to a tripod. straints or broad objectives, such as the Qualification testing Procedures that de- NASA Mars Scout program. Character- termine a component’s characteristics ized by a defined architecture and/or in operations to the extremes of en- technical approach, requirements, fund- velopes such as temperature or pressure. ing level, and a management structure Quartz Mineral abundant on Earth con- that initiates and directs one or more sisting of silicon dioxide, SIO2 in a tetra- projects. hedral lattice crystal. Program Instructions for a computer. Quasar Originally, quasi-stellar radio Compare data. source. Now known to be an extremely Project Administrative level below the pro- distant, extremely powerful active gram level e.g., the Phoenix Mars lander galactic nucleus where matter enters a flight project. Characterized by defined supermassive black hole. From Earth, 412 Glossary

quasars appear as a point source. Radio astronomy The study of celestial ob- Positions of some quasars in the sky jects at radio frequencies. form the basis of the International Radio science celestial mechanics Celestial Reference Frame (ICRF). Experiment in which a natural object’s Quaternion Mathematical construct that mass is determined by measuring the describes rotation in three dimensions. velocity changes the object induces in An algebra in which each object con- the spacecraft via gravitation. Velocity tains four scalar variables and objects measurement is via Doppler shift evi- can be operated on as single entities. dent in the frequency of the spacecraft’s Radar Active remote sensing technique, two-way coherent carrier signal. originally “radio detection and rang- Radio science data One of the seven DSN ing.” Used for science observations in data types. Uses the spacecraft radio modes such as synthetic-aperture imag- transmitter(s) and the DSN as a science ing, scatterometry, and altimetry, in instrument system to help characterize which brief pulses of relatively high a target or phenomenon in any of several power radio energy are directed toward modes. During ring or atmospheric oc- a target. In some modes these pulses are cultation experiments, the spacecraft’s modulated with identifying tags. In all signal passes through the subject of active modes, the echoes collected and study, and effects on the received signal, analyzed. such as attenuation, scintillation, polar- Radar astronomy Branch of astronomy in ization, are recorded and studied. Other which very high-power radio pulses, modes include celestial mechanics ex- e.g., S-band or X-band frequencies, are periments, gravitational wave searches, transmitted from a DSN station toward bistatic radio, relativistic effects of the a target of interest, e.g., a planet, an Sun, and solar corona characterization. asteroid, or a moon. Reflected signal is Raw image An image, e.g. from a space- captured typically by widely separated craft’s CCD, to which calibrations have receiving stations on Earth, and corre- not yet been applied to yield highest sci- lated to form images, or extract other entific quality. Not contrast enhanced, data from the echoes. or combined into a color image, etc. See RA-dec Right ascension-declination; axes page 193. of rotation based on the celestial equa- RHU Radioisotope heater unit; device con- tor. Rotation in RA varies between east taining a small amount of encapsu- and west, and rotation in declination, lated radioisotope that constantly emits normal to the celestial equator, varies heat typically at about 1 watt. Situated north and south of it. RA is measured within spacecraft bus or appendages as in hours, minutes, and seconds, tied needed for thermal control. to Earth’s rotation, and declination is Radioisotope An element that has an un- measured in degrees of arc N or S. Com- stable nucleus, which emits radiation as pare. Az-el. it breaks down. Radiation Energy in the form of electro- Radiometer Passive remote-sensing science magnetic waves (see Appendix D, p instrument used to measure the natu- 342), or moving subatomic particles. ral radio emission, e.g., microwave fre- Radio and plasma waves quency, from a target. Compare pho- Subject of scientific study concerning tometer. waves of audio frequency through radio Radiometric Type of navigation observable frequencies up to the tens of MHz gen- data acquired by DSN, e.g., Doppler erated in plasma or emitted by natural shift of a spacecraft carrier signal, processes in the magnetic environments range measurement, or VLBI observa- of the Sun and planets. tion. Compare optical navigation. Glossary 413

Radiometry Science or science data con- information, e.g., music or spacecraft cerned with the quantity or power telemetry, from it. Compare transceiver. of electromagnetic radiation, e.g., mi- Red alarm Visual and/or audio alert, e.g., crowave radio energy that a target natu- on computer screen and pager, high- rally radiates, measured using radiome- lighting a telemetry measurement that ters. Field of science that studies this exceeds limits set by engineers. Rep- phenomenon, e.g., in analyzing target resents a condition that threatens or surface composition. Compare photom- would tend to threaten spacecraft etry. health or safety. Range data Tracking data acquired by Reed-Solomon Forward error-correction DSN that measures round-trip line-of- coding scheme in which blocks of sight distance between DSN antenna data in the spacecraft’s computer and spacecraft. are rendered into polynomials whose Ranging tone Modulation applied to DSN evaluation at various points become the uplink and subsequently spacecraft data to be transmitted. downlink carrier signal used by navi- Reflectance Spectrum Wavelengths of light gators to determine round-trip line-of- reflected by an object’s surface. Be- sight distance to the spacecraft. cause the target may absorb some of Reaction control system (RCS) Spacecraft the incident light’s wavelengths, the re- propulsion system thrusters used for at- flected spectrum may be diminished in titude control and the occasional TCM those wavelengths, providing informa- or OTM. tion about the surface’s composition. A Reaction wheel AACS output device for flower that appears red to the eye has applying torque to a spacecraft. Small, absorbed blue wavelengths of light. electrically driven wheel, with mass typ- Reflection Change in a wave’s direction at ically on the order of 10 kilograms, the an interface between two different me- rotational axis of which is fixed in the dia. Includes scattering and/or specular spacecraft’s body. Typically arranged in returns. a set of three or more with orienta- Refraction Change in a wave’s direction tions that permit applying torque, in due to a change in its speed, e.g., when positive and negative directions, to the it passes from one medium to another. spacecraft in all three axes. Also called Blanket of dust, soil, or broken momentum wheels. Compare control- rock covering a rocky surface. moment gyro. Relay Electromechanical device in which Real time Operations in which there is electrical contacts, e.g., in a power dis- minimum delay (even if round-trip light tribution circuit, are operated by an time is measured in hours or days) be- electromagnet whose coil is energized by tween the ends of a system, e.g., in a smaller current, e.g., from a computer. a control system where a sensor’s in- Relay Radio communications from Earth put is processed immediately into out- to one spacecraft which transmits to puts that automatically change the sys- another or vice-versa, e.g., command tem’s state (e.g., anti-lock brakes) or and telemetry data communications be- which humans observe and optionally tween Earth, a Mars orbiter, and a Mars make control inputs. By comparison, rover. The spacecraft-to-spacecraft leg non-real time would describe operation is called crosslink. of ground-based data storage facility Remote-sensing Category of science instru- that users can access at their conve- ments that make observations of phe- nience. nomena at a distance, such as passive- Receiver Radio device that selects a desired sensing cameras, or active-sensing imag- frequency, amplifies it, and harvests ing radars. Compare direct-sensing. 414 Glossary

Resistojet Electrothermal means of propul- of lines of equal reflected distance inter- sion that employs a high-current electric secting with lines of equal Doppler shift. resistance heating unit such as a wire, SAR swath Relatively narrow strip of that causes high temperature in a rocket radar image data acquired along the chamber, and introduces a fluid pro- surface of a body. pellant, e.g., argon or hydrazine, which Saturation (light) The point at which the expands out the nozzle. High ISP ,low electronic charge on a CCD pixel is thrust. maximum and will overflow into adja- Right ascension One of a pair of coordi- cent pixels. nates in the celestial sphere. Measured Saturation (angular momentum) The point in the east-west arc. Compare declina- at which a reaction wheel’s RPM can no tion. longer be safely increased. Roll Rotation about a spacecraft’s vertical Saturn Sixth planet from the Sun, one of (Z) axis. the four gas giants or Jovian plan- Room temperature For scientific applica- ets. Equatorial diameter 9.449 times ◦ tions, an average of 21 C, or 294 K. Earth’s. H2 atmosphere with about Rover One of eight classifications of space- 3 percent He and amounts of craft. Spacecraft designed to land on a other substances, including ammonia body’s surface and travel to gather sci- and water-ice clouds. Mean distance ence data, e.g., to place direct-sensing from Sun 9.58 AU. science instruments in contact with se- Saturn radius 1 RS = 60,330 kilometers at lected targets. the equator. RTG Radioisotope thermoelectric genera- Scan platform Articulated spacecraft ap- tor; spacecraft electric power supply pendage that can point instruments in- that uses heat produced by the natu- dependently of spacecraft attitude. ral decay of a radioisotope, thermocou- Scatterometry Radar investigation in ples, and radiator fins, to generate cur- which a signal is transmitted to a rent using thermal gradient and Seebeck surface and the amount of reflected effect, with no moving parts. energy is measured. Noise is also S-band Range of microwave frequencies recorded between transmit pulses, for around 2 to 4 GHz. subtraction from the reflected signal. Safing Spacecraft condition, typically in Can be used to infer wind direction and response to an anomaly detected by speed over an ocean due to variations in a fault protection monitor, in which reflected energy from waves of various the spacecraft’s normal operations are heights and orientations. suspended, and its attitude, electrical Science data Telemetry returned from a power, and other factors are driven to spacecraft’s science instruments, e.g., states that will keep the spacecraft and cameras, spectrometers, etc., or mea- its instruments from suffering damage. surements of the spacecraft’s carrier sig- Sagittarius A* (asterisk pronounced star) nal in a radio science experiment such as Point in the sky where lies the super- atmospheric occultation. Compare engi- massive black hole at our galaxy’s cen- neering data. ter. Time-lapse observations (see Inter- Scintillation Twinkling; rapid variations in net) reveal high-velocity proper motion apparent intensity, e.g., of a spacecraft’s of stars orbiting the mass. radio signal as it passes through a ring SAR Synthetic aperture radar; imaging system or an atmosphere. Also, a flash radar technique in which radio signals of light produced in a transparent ma- reflecting back from a transmitted pulse terial by an event of ionization, used in are captured along the distance the some high-energy particle detectors. physical receiving antenna travels dur- Scintillator A transparent material used in ing reception. Image pixels are made up some high-energy particle detectors to Glossary 415

reveal passage of particles by flashes of N is the noise power S light produced in the material. ( N is the signal-to-noise ratio) Secondary battery Rechargeable battery in Shear plate Spacecraft structural member a system that is primarily powered that typically closes the inboard and by another source. Supplies electrical outboard faces of a bay, bearing load in power during relatively short periods the shear direction. when primary source is unavailable, e.g., SI International System of Units; Metric solar panels in shadow. system universally used in science, and Seebeck effect Thermoelectric effect. Con- dominant in international commerce version of temperature difference di- and trade. rectly to electrical current. Principle of Signal Radio waves generated by spacecraft RTG operation. or DSN station for communications. Selenium Element, symbol Se, atomic num- Also, an electromagnetic phenomenon ber 34, a non-metal, solid at room tem- sought out, e.g., by some science instru- perature. Photovoltaic. ments. Semaphore A rudimentary signal sent Signal level Amount of power in a signal. without telemetry, such as via a subcar- Signal-to-noise ratio (SNR) Ratio of the rier modulated onto a carrier to indi- signal power to the ambient noise power cate spacecraft health or presence of an in the frequencies of interest. anomaly, or by interruptions of the car- Silicaceous (S-type) Asteroids Asteroids rier to indicate events such as parachute made of stony material, similar to deployment. ordinary chondrite meteorites. S-type Semiconductor Substance that conducts asteroids comprise about 17 percent of electric current in one direction only, known asteroids and typically occupy e.g., crystalline silicon. Used to create main belt’s inner regions. electronic components. Silicon Element, symbol Si, atomic number Semi-monocoque Structural design in 14. An important semiconductor and which a vehicle’s skin supports part photovoltaic material. of its structural load, e.g., aircraft Silver Element, symbol Ag, atomic number fuselage. 47. Metallic, solid at room temperature. Sequence See command sequence. Single-fault tolerant State of being able to Series connection Electrical arrangement continue to operate after having experi- in which each of several units, e.g., enced the failure of one component in cells in a battery, has its positive ter- a subsystem, e.g., through redundant minal tied to the next unit’s negative hardware. terminal. Increases voltage, maintains Sky crane Liquid-propellant spacecraft current. Compare parallel connection. module designed to lower Mars Science SETI Search for extraterrestrial intelli- Laboratory to the surface. gence; Scientific investigation that ex- SLA Super light weight ablator; -like amines radio and light received from proprietary thermal protection system sources among the stars for evidence of material made by Cor- communications between intelligent life- poration used to coat the forward sur- forms. face of atmospheric heat shields. When Shannon limit Theoretical upper limit to heated by atmospheric friction, it forms rate of data communications in a noisy an IR-opaque gas layer between the hot physical channel such as radio or light. shock wave and the spacecraft. Given as C,by: Element, symbol Na, atomic num- C B S ber 11, an alkali metal. Salts im- = log2(1 + N ) where part a characteristic yellow color to B is the channel bandwidth in hertz. a flame. Vapor strongly emits yellow S is the signal power wavelengths close to 589 nm. 416 Glossary

SOHO Solar and Heliospheric Observa- craft have used solar photon pressure tory; spacecraft in Earth’s L1 Lagrange for attitude control, e.g., Mariner 10 in point making continuous, multispectral 1974, the Messenger team developed a observations of the Sun, its solar wind sequence of body and shade attitude, emissions and background stars, and the and solar-array orientations, which af- occasional nearby planet or comet. (Im- fect orbital parameters, and should re- ages and movies are easily found on- duce the number of TCMs needed in the line.) future. Sojourner Mars rover deployed on July 4, Solar wind Plasma, largely of hydrogen nu- 1997 by Pathfinder lander. First suc- clei (protons) and electrons, which the cessful rover on another planet. Length, Sun continuously emits, inflating the width, height: 65×48×30 cm. Mass: heliosphere. Ulysses spacecraft deter- 10.6 kilograms. Returned 550 images mined that its speeds are much higher and analyzed of sixteen lo- at high solar latitudes. cations near the lander during an 83- Solid rocket motor (SRM) Simple propul- lifetime. sion system comprising a mixture of Solar array drive Electric motor driven ac- granular fuel, oxidizer, and combustible tuator that orients a solar panel or array binding agent, which do not react un- in one or more degrees of freedom and til they are ignited. Molded into a low provides feedback to its controller. mass shell equipped with nozzle. Once Solar cell Piece of photovoltaic material ignited, solid propellant continues burn- with conductors attached to provide ing until exhausted, providing all its im- electric current when illuminated. pulse in one application. Solar occultation Passage of a spacecraft Solid-state data recorder Mass data stor- behind an object as viewed from the age device on interplanetary spacecraft Sun. that uses dynamic random-access mem- Solar panel Array of solar cells on a sub- ory — the commercial DRAM devices strate. that are used in personal computers — Solar photon pressure Also called solar in bulk. Protected from bit-flips caused . Constant small by radiation in interplanetary space by force due to incident sunlight. Useful error-detection and correcting “scrub- for solar-sailing. While Earth-orbiting bing” algorithms and by physical radi- spacecraft feel other small forces that ation hardening and shielding. Typical might drown out its effect, it is a capacity around 2 Gbits (despite enor- dominant small force for interplanetary mous advances in consumer products spacecraft to accommodate, such as by that have not been space-qualified as of frequent reaction wheel momentum de- press time). saturation maneuvers, if the spacecraft Solid-state power switch Electronic assem- presents an asymmetric profile, e.g., bly that provides electric power to se- Mars Climate Orbiter (p 49). lected spacecraft components on com- Solar sailing Method of harnessing solar mand. Replaces electro-mechanical re- photon pressure (not to be confused lays and thermal fuses with more reli- with solar wind) as a propulsive force able solid-state devices, which have the for navigating a spacecraft in interplan- capability to detect, control, and isolate etary, and perhaps interstellar flight. faults in flight, and provide individual- To date, no dedicated spacecraft has line reset capability. succeeded in demonstrating its use, al- Erosion of the surface of though the Messenger spacecraft used airless bodies in the solar system caused its large solar shade in 2008 to skip by cosmic ray collisions, solar irradia- a planned TCM by solar-sailing closer tion, sputtering and implantation of so- to its aim-point. While previous space- Glossary 417

lar wind particles, and bombardment by direction is reflected to a single outgoing meteors of all sizes. direction. Compare backscatter. Spacecraft Vehicle designed for flight out- Sphere-cone shape Form of atmospheric side Earth’s atmosphere. Singular and entry heat shields, with spherical com- plural. ponent at front, trailing back in a cone Space-link session DSN pass. Tracking pe- whose appropriate angle depends on riod during which a spacecraft passes medium and conditions of entry. Illus- across the sky. tration p 172. Specific energy Energy per unit mass, ex- SPICE file Acronym for “Spacecraft, pressed as Joules/kilogram. In SI base Planet, Instruments, C-matrix (camera units, m2/s2. angles), and Events” file; a file that Specific impulse Written Isp, impulse per provides context for such science ob- unit propellant, an intensive quantity servations as spacecraft and planetary describing rocket efficiency. Based on ephemerides, instrument mounting propellant mass or propellant weight, alignments, spacecraft orientations, (mass affected by Earth standard grav- sub-spacecraft coordinates, distance ity). In the latter usage, units of Isp are to target, illumination geometry, se- seconds. Simplified form (see descrip- quences of events, and data for time tion on page 124): conversions. I ve sp = g0 Spin bearing assembly Interface between a Spectral density Power per unit frequency, spinning spacecraft and its de-spun expressed as dBm/Hz or W/Hz. section, typically accommodating the Spectrograph See spectrometer. “Graph” transfer of mechanical loads, electrical refers to drawing or recording data power, radio signals, and/or data. vs measuring. Early instruments made Spin stabilization Mode in which a space- spectrographs on film (compare photo- craft’s attitude is maintained by setting graph). Instruments have evolved over the whole spacecraft spinning about one time and the “-graph” and “-meter” suf- axis. Compare three-axis stabilization. fixes overlap. Spirit Name of the Mars Exploration Rover Spectrometer Passive remote-sensing opti- that landed at Gusev crater in 2004, cal science instrument that disperses in- three weeks before its twin, Opportu- cident light (or IR, UV, X-ray, etc.) and nity, landed on the opposite side of measures the intensity of each of a num- Mars. ber of wavelengths observed. Spitzer Space Telescope One of the four Spectrophotometer See spectrometer. NASA Great Observatories. Sensitive Spectroscope See spectrometer. “Scope” to IR sources. Launched August 25, implies the instrument is fitted with an 2003, Spitzer occupies a heliocen- eyepiece for visual observation. tric orbit, trailing Earth’s position. Spectroscopy Branch of science involving Telescope is 85-centimeter aperture measurement of a quantity as function Ritchey-Chr´etienoptical design. Instru- of its wavelength or frequency or energy. ments and telescope are cooled by evap- See Appendix D, p 342. Applies to any oration of liquid helium to minimize IR part of the electromagnetic spectrum. noise. The coolant is expected to run Spectrum, electromagnetic All possible out in early 2009, but operation of one electromagnetic radiation frequencies, of its instruments in warm mode has (or wavelengths, or energies). See been funded. Originally called Space In- Appendix D, p 342. frared Telescope Facility (SIRTF), re- Specular reflection Mirror-like reflection at named Spitzer Space Telescope after microwave through optical wavelengths, launch. in which a ray from a single incoming 418 Glossary

Sputnik Series of Soviet Earth-orbiting ling engine obtains power from a ther- spacecraft, including the world’s first, mal gradient to run an alternator and launched October 4, 1957. generate electrical power. Thermal gra- Standard deviation Root-mean-square dient set up by hot radioisotope at one (RMS) deviation of values from their end and cooling fin at the other. mean, noted as sigma, σ. Stratosphere Atmospheric layer above a Standard gravity Acceleration at Earth’s troposphere and below a . surface, 9.80665 meters per second per Temperature is stratified, cooling with second (m/s2). altitude. Star scanner AACS celestial reference in- Structure subsystem Spacecraft low-mass put device that estimates attitude skeleton that provides mechanical sup- about three axes by timing the passage port and alignment for the other sub- of stars through each of two slits as the systems. spacecraft rotates. Strut Structural system member, often set Star tracker AACS celestial reference input in triangles to support instruments or device that provides information about rocket thruster clusters. Often made of excursions in attitude about a single carbon fiber tube with metallic end fit- axis, by measuring angular movement tings. of a single bright star that is constantly Subassembly Component of a spacecraft or held in its field of view. ground system below the level of assem- Star A massive, luminous ball of plasma, bly. Hierarchy is: system, subsystem, as- e.g., the Sun. Others are enormously sembly, subassembly. distant and therefore appear much dim- Subsystem Component of a spacecraft or mer. ground system below the level of system Stardust NASA Spacecraft that captured and above the level of assembly. Hier- and returned particles from comet tail archy is: system, subsystem, assembly, and interplanetary dust to Earth Jan- subassembly. uary 15, 2006. Subcarrier Tone modulated onto a carrier. Statistical maneuver A trajectory correc- May represent a semaphore or carry its tion or orbit trim maneuver that com- own modulation. pensates for the variations that are a Sublimation Change of state from solid di- normal part of the navigation process, rectly to gas. such as a small adjustment following a Submillimeter Typically describes a radio flyby. signal less than 1 millimeter in wave- Stefan-Boltzman constant Relates energy length. emission to temperature as (K is tem- Subreflector Secondary reflector on a perature in kelvins): Cassegrain HGA or DSN antenna, E =5.67x10−8W/m2/K4 smaller than the main reflector, Stellar occultation Passage of a star be- mounted on a tripod or quadrapod hind an object of interest. Often used above the main reflector. Comparable to search for or measure an atmosphere to the secondary mirror in a Cassegrain or . telescope. Stellar reference unit (SRU) AACS celes- Sufficiently-stable oscillator (SSO) tial reference input device with a tele- Assembly in a telecommunications sub- scopic field of view and star recogni- system that achieves good frequency tion system, which can provide attitude stability as a reference for generating reference information in all three axes the downlink carrier signal, typically on whether the spacecraft’s orientation is the order of less than 10−11 (Allen devi- rotating or not. ation) over a period of up to 1,000 sec- Stirling Radioisotope Power System onds. This is useful for some radio sci- (SRPS) Mechanical device whose Stir- ence experiments, such as occultations, Glossary 419

and can support a link carrying teleme- tion, a number of symbols greater than try and range modulation. Navigation one constitute a single bit of data. requires typically better stability. Synchronous rotation Rotation of a natu- Sulphur Element, symbol S, atomic num- ral or artificial satellite as it keeps one ber 16. A yellow non-metallic solid at side toward the primary body due to room temperature. gravity gradient, as the Moon is in syn- Sun Center of mass of the solar system. G2 chronous rotation with the Earth. in stellar spectral class. Inflates bubble System noise temperature Contribution of of plasma called the heliosphere, which radio noise from the receiving antenna, collides along a bow-shock in the inter- its reflectors, and waveguides, low-noise stellar medium. Solar-generated radia- amplifier, etc., measured in kelvins. tion and magnetic field dominates the System A flight system (spacecraft) or a heliosphere. ground system (DSN etc.). Hierarchy is: Sun sensor AACS celestial reference input system, subsystem, assembly, subassem- device that provides information on at- bly. titude excursions, e.g., in pitch and yaw. TAI Temps Atomique International; the Sun-Earth-probe angle (SEP) Angle be- weighted average of the time kept by tween the Sun, the Earth, and the hundreds of atomic clocks in over fifty spacecraft (probe). Approaches zero national laboratories worldwide. TAI at superior conjunction each year for minus UT1 was approximately 0 on Jan- spacecraft operating near the ecliptic. uary 1, 1958. Sun-synchronous orbit Spacecraft orbit Tantalum Element, symbol Ta, atomic about a planet in which the orbit plane number 73. Dense metal, solid at room is maintained in an orientation that temperature. Used in high-performance provides a desired solar illumination of capacitors, and as radiation shielding the surface around spacecraft periapsis, for sensitive electronics in interplane- e.g., 2 p.m. local solar time, to take ad- tary space. vantage of a desired length of shadows Target plane See B-plane. on the surface. Target-motion compensation Superior conjunction Conjunction (coinci- See image motion compensation. dence of right ascension) of a planet or TCG Geocentric Coordinate Time; defined spacecraft with the Sun when the Earth in 1991 with TT. and the planet are on opposite sides of TCM Trajectory correction maneuver; the Sun. This period may pose difficul- spacecraft propulsive maneuver that ties communicating with a spacecraft makes a small adjustment in targeting due to the Sun’s radio noise. Compare and/or arrival time. Compare OTM. opposition. TCP/IP Transmission control protocol, In- Supernova Explosion of a dying star that ternet protocol; suite of communica- releases a burst of radiation that can tions protocols in use on the Internet briefly outshine an entire galaxy, while and other networks, named for two of creating heavy elements and ejecting its significant protocols. Designed as a matter into interstellar space. system of layers, each with well-defined Swing-by Flyby of a planet by a spacecraft activities and interfaces with adjacent for the purpose of obtaining a gravity layers. assist. TDT Terrestrial dynamic time; obsolete, Symbol Unit of modulation, e.g., in mi- replaced by TT in 2001. crowave binary phase key shift, in which Telecommunications channel A band of the phase of the carrier signal is stepped frequencies used for communications. back and forth between two predeter- Telemetry channel A series of repeating mined values. In interplanetary applica- measurements in telemetry such as the 420 Glossary

temperature at a specific point. Illustra- DSN station B is in lock with the tion p 40. spacecraft’s downlink. The downlink is Telemetry data One of the seven DSN phase-coherent with the uplink, creat- data types. Symbols modulated on a ing the substantial frequency stability spacecraft’s downlink carrier are re- of a massive ground-based maser. constituted into digital bits representing Thrust Force of reaction, e.g. upon operat- science instrument observations such as ing a rocket. images, spacecraft engineering condi- Thruster Small liquid-propellant rocket en- tions such as pressures and tempera- gine. tures, and optical navigation observa- Thruster-valve assembly Small liquid- tions. propellant rocket engine with Telepresence Technologies that allows a electrically controlled valve to admit person to feel present, or to have an ef- propellant(s) on demand. fect, at a location other than their true Thrust-vector control Mechanical means of location. changing direction of a rocket nozzle Termination shock Region in the outer he- and/or its exhaust stream direction. liosphere where the solar wind slows to Time-division multiplex (TDM) Scheme subsonic speed and bunches up. Voyager for transmitting more than one 1 and Voyager 2 have penetrated this measurement over a single telecommu- region while measuring and telemeter- nications channel, by arranging for each ing ambient conditions to Earth. measurement to take turns over time. Thermal emission spectrometer Passive re- Titan Largest satellite of Saturn and sec- mote sensing far-IR optical science in- ond largest moon in solar system after strument that captures spectra natu- Jupiter’s Ganymede. Discovered 1655 rally emitted or reflected from targets. by Christiaan Huygens. Diameter 5,150 Can be used to identify mineral compo- kilometers, larger than the planet Mer- sition. cury. Nitrogen atmosphere has methane Thermal energy Difference between the in- and ethane clouds and probably , ternal energy of an object (due to mo- surface pressure 146.7 kPa (≈1.5 bar). tion of its molecules, chemical bonds, Lakes on surface are filled with liquid etc.) and that which it would have at ab- ethane and probably methane. Bulk of solute zero, 0 K. Increased or decreased Titan is about half water ice and half by heating or cooling. rocky material, density 1.88 g/cm3. Ex- Thermionic emission Electrons expelled plored by Cassini and Huygens space- from a hot material in vacuum. Cathode craft 2004 through present. rays. Edison effect. Element, symbol Ti, atomic Thermocouple Union of two dissimilar number 22. A strong, lightweight metal metals that generates electric current at room temperature. proportional to temperature gradient. Topocentric Relative to a point on a body’s Thermopile Collection of multiple thermo- surface rather than its center. Compare couples into a single unit. geocentric. Instrument which measures Total impulse Integral of a rocket’s thrust temperature, e.g. as part of a suite of over time. atmospheric structure instruments. Tracking data One of the seven DSN data Three-axis stabilization Mode in which a types. Provides radiometric measure- spacecraft has individual control over its ment of a spacecraft signal’s Doppler attitude in pitch, yaw, and roll. Com- shift, the line-of-sight range or distance, pare spin-stabilization. and its right ascension and declination. Three-way coherent Telecommunications Trajectory A path through space. An orbit mode in which a spacecraft receives or a portion of an orbit. an uplink from DSN station A, while Glossary 421

Transceiver Radio device that combines re- Tungsten Element, symbol W, atomic ceiver and transmitter. number 74. Metal, solid at room tem- Transfer frame Formatted group of bits, perature, has the highest melting point defined by CCSDS within the data link of all metals (3,421.85◦C), and high- layer, which groups telemetry data into est tensile strength at elevated temper- units for transmission to Earth. May ature. contain many packets, or one packet Turbo code Forward error correction sys- may span transfer frames. tem in which encoding occurs in paral- Transformer Electrical device that uses in- lel. At the receiving end, each of two de- duction to transfer electrical energy coders is given a different encoded ver- from one circuit to another. Can step sion of the original data. The algorithms voltage up or down across circuits. collaborate to decode the message, iter- Transistor Semiconductor device used to ating several times and comparing notes amplify a signal or switch electrical cur- to reach a consensus on a correctly de- rent. coded result. Transmitter Electronic component that Turing test Proposal, by English mathe- amplifies a radio frequency signal to matician Alan Turing (1912–1954), for high power, e.g., for concentration by a test of a machine’s ability to demon- an antenna in a beam aimed toward a strate intelligence in which a human spacecraft or the Earth. judge engages in a natural language con- Trans-Neptunian object An object that or- versation with one human and one ma- bits the Sun at greater distance than chine. If the judge cannot reliably tell Neptune, e.g. in the Kuiper belt. which is which, the machine is said to Traveling-wave tube amplifier Electronic pass the test. vacuum-tube on a spacecraft that 2001 Mars Odyssey NASA Planetary or- inputs a low-power microwave signal biter spacecraft, investigating Mars and outputs a high-fidelity replica of since 2001. the signal at a suitable power level for Two-way Communications mode in which sending across interplanetary space. a spacecraft receives an uplink from Triode Electronic vacuum tube amplifier DSN, and the same DSN station re- with three elements: heated cathode, ceives a downlink from the spacecraft. grid, and anode plate. Can be either coherent or non-coherent. Triple-point Temperature and pressure Two-way coherent Telecommunications conditions at which a substance can mode in which a spacecraft receives an exist at solid, liquid, or gas. This exists uplink from DSN, while the same DSN for water on Earth’s surface, and for station is in lock with the spacecraft’s methane on or near the surface of downlink and the downlink is phase- Saturn’s moon Titan. coherent with the uplink, enjoying Triton Largest of Neptune. the substantial frequency stability In a retrograde orbit. Diameter 2,706.8 of a massive ground-based frequency kilometers. Nitrogen covered large reference. areas at the time of Voyager 2 ’s en- Two-way non-coherent (TWNC) Telecom- counter in 1989, when active nitrogen munications mode in which a spacecraft geysers were also observed. receives an uplink from DSN, and the Troposphere Atmospheric layer above a same DSN station is in lock with the body’s surface. Often turbulent. spacecraft’s downlink, but the downlink Truss Structural element made up of trian- is not phase-coherent with the uplink. gular supports. Instead, an on-board oscillator gener- TT Terrestrial time; defined in 1991 to be ates the downlink frequency. consistent with the SI second and gen- Ultra-stable oscillator (USO) Assembly in eral relativity. a telecommunications subsystem that 422 Glossary

achieves good frequency stability as a UT0 Uncorrected UT as obtained from reference for generating the downlink meridian circle observations or via GPS. carrier signal. This is useful for some ra- UT1 UT corrected for polar motion. dio science experiments, such as occul- UT2 Largely obsolete. UT1 corrected for tations, and can support a link carrying seasonal variations in the Earth’s rota- telemetry modulation, although naviga- tional speed. tion requires better stability. UTC Temps Universel Coordonne. Coor- Ultraviolet (UV) Electromagnetic radia- dinated universal time; introduced in tion in wavelengths of about 400 1972, UTC differs from TAI by an in- nanometers to 10 nanometers, or ener- tegral number of seconds. Leap seconds gies of about 3.1 eV to 124 eV. See Ap- are introduced in UTC as needed, typ- pendix D, p 342. Produced in nature by ically on January 1, to keep the differ- stars. ence between UTC and GMT less than Ultraviolet Spectrometer See spectrome- 0.9 s. ter. Measures invisible “colors” in the Vacuum tube Sealed envelope, typically UV. glass, evacuated to about 1 μP, inside of Ulysses ESA spacecraft launched 1990, which thermionic emission moves from a which increased its solar orbit inclina- heated cathode toward a target having tion to 80.2◦ via Jupiter gravity assist, opposite polarity. and observed the inner heliosphere at Vaporization Change of state from liquid to high latitudes. Mission ending at press gas via evaporation or boiling. time. Vector System of notation for any quantity UMDH Unsymmetrical dimethyl hy- that has both magnitude and direction, drazine (C2H8N2), liquid rocket fuel. such as spacecraft velocity, angular or Universal time (UT) Defined by the linear momentum, magnetic fields, etc. Earth’s rotation, formerly determined Notation includes arrows. using astronomical observations. GPS Vectran Manufactured fiber that forms the serves today. Refer to TAI and UTC. cloth used in space suits and Mars lan- Universe Everything that exists, including der airbags. Stronger than . space-time, energy, and matter. Vega Soviet program that included two Uplink Signal sent from DSN to spacecraft. flyby spacecraft, each of which encoun- May be pure carrier, or carrier modu- tered Venus, dropped off landers and at- lated with ranging tones and/or com- mospheric spacecraft, and then encoun- mand data, on the carrier or on subcar- tered Comet Halley. rier(s). Velocity Vector quantity of speed and di- Element, symbol U, atomic num- rection. ber 92. Metallic, radioactive, solid at Venera Soviet program that included six- room temperature. teen orbiter, lander, and atmospheric Uranus Seventh planet from the Sun, one missions to Venus. Thirteen were suc- of the four gas giants or Jovian plan- cessful. ets. Equatorial diameter 4.007 times Venturi effect Reduction of fluid pressure Earth’s. Atmosphere of H2 with about at increased speed, e.g., over an airfoil. 15 percent He and 2 percent methane. Venus Second planet from the Sun, one of Discovered by William Herschel (1738– the four terrestrial planets. Diameter 1822) in 1781. Mean distance from Sun 0.949 of Earth’s. Dense, high-pressure 19.2 AU. CO2 atmosphere overcast with SO2 UT Universal Time, the new name prof- clouds. Mean distance from Sun 0.723 ◦ fered in 1928 for GMT by the Interna- AU. Mean surface temperature 460 C. tional Astronomical Union. See also its Venus Express ESA’s follow-on from its variations UT0, UT1, and UT2, below. Mars Express. Many instruments are simply upgraded versions of those on Glossary 423

the Mars platform. After a 153-day versations using telephone technology. cruise to Venus, the spacecraft entered Each of a dozen or so nets can be en- Venusian orbit on April 11, 2006. abled for listening, muted, or selected Vernal equinox Annual equinox (on Earth, for transmitting. Voice protocol adheres in the month of March), the beginning to international standard phraseology of northern-hemisphere spring. On an similar to air traffic control radio com- equinox, the Sun’s center spends nearly munications. equal time above and below the horizon Voice-over-Internet-protocol (VOIP) Pro- at every location on Earth. At equinox, cess wherein audio-frequency waves the Sun is at a point on the celes- are sampled many times per wave, tial sphere where the celestial equator represented numerically, and sent via and ecliptic intersect. Compare autum- Internet-protocol packet-mode commu- nal (September) equinox. nications. Upon receipt, packets are Vesta Asteroid (minor planet) in main as- sorted into correct order, missing pack- teroid belt, about 530 kilometers in di- ets retrieved if possible, and audio wave- ameter. Brightest asteroid, second most forms reproduced, all at high-enough massive in belt. One of the targets in- speed to be virtually undetectable in tended for the Dawn spacecraft to orbit real time. in 2011. Compare Ceres. Volatiles Substances that evaporate, e.g., Vidicon Image sensor based on vacuum when exposed to vacuum or increased tube incorporating phosphor-scanning temperature. electron beam. Older technology, re- Voltage converter A device that outputs a placed by CCD image detectors. specific AC or DC voltage from an AC Viking NASA mission to Mars with two or- or DC input at higher or lower voltage biters and two landers, which touched than the device produces. Any deficit of down June and July 1976 and returned source voltage is accommodated, at the imaging and other science data for years expense of increased current draw, by via telemetry. elaborate circuitry. Excess energy con- Visible light Electromagnetic waves in the verted to heat. wavelength range of about 380 nanome- Voltage regulator Device that produces a ters to 750 nanometers, to which the hu- steady DC voltage, regardless of cur- man eye is sensitive — about one oc- rent draw, from an input of unsteady tave. but higher voltage. Excess energy con- Viterbi algorithm in information theory verted to heat, which can be used for serves to discover the most likely se- specific purposes on a spacecraft. quence of hidden states. Applied to Voltage Electromotive force; electrical ten- decode modulated radio symbols into sion; difference of electrical potential. telemetry bits in the DSN’s maximum- Analogous to the pressure of water in likelihood convolutional decoder. a pipe. VLBI data Very long baseline interferom- Voltaic pile Crude electrochemical battery etry data, one of the seven DSN data made, e.g., of copper and zinc discs sep- types, comprises sampled, time-tagged, arated by -soaked paper. packetized representations of incoming Voyager 1 spacecraft Launched September microwave signals from a single source, 5, 1977 after Voyager 2, returned obser- collected by two widely separated an- vations of the heliosphere, and the Jo- tennas. Transmitted to a correlator for vian and Saturnian systems. Penetrated processing. Useful for spacecraft naviga- Sun’s termination shock July 2008 at 94 tion, study of Earth’s crustal dynamics, AU on northerly trajectory. Operations and radio and radar astronomy. continue at press time. Voice net Used in realtime flight opera- Voyager 2 spacecraft Launched August 20, tions, one of a set of several live con- 1977, before Voyager 1, returned ob- 424 Glossary

servations of the heliosphere, and the rangement. Illustration p 197. See also Jovian, Saturnian, Uranian, and Nep- Chandra, p 300. tunian systems. Penetrated Sun’s ter- X-band Range of microwave frequencies mination shock July 2008 at 86 AU around 8 to 12 GHz. on southerly trajectory. Operations con- Xenon Element, symbol Xe, atomic num- tinue at press time. ber 54, gaseous at room temperature, Watchdog timer Software algorithm that one of the six noble gases. Used in strobe regularly checks a situation, and decre- lamps due to its bright emission of light ments a counter when a check returns a when excited. Serves as propellant in ion negative result, then passes information engines on spacecraft. or control to a different algorithm if or X-ray Electromagnetic radiation in the re- when the count reaches zero (or a pre- gion from about 102 to about 105 ev. set value). Positive results of check will See Appendix D, p 342. Produced in normally reset the counter to a default nature by highly energetic events, e.g., value. compression of matter at the threshold Wave-front Leading edge of an expanding of a supermassive black hole. sphere of electromagnetic energy, a sur- X-ray fluorescence spectrometer Direct- face of points having the same phase, as sensing science instrument. In active- its electric field and magnetic field prop- mode, illuminates target at close range agate one another at the speed of light. with built-in x-ray or γ-ray source Waveguide Pipe-like structure usually rect- and observes secondary, fluorescent, angular in cross section with smoothed lower-energy x-rays from the target, interior walls, which guides the propa- to identify chemical elements. Passive gation of microwave radio signals with mode would observe fluorescence from low loss of signal strength. Compare targets illuminated by natural source with fiber-optic filament that guides such as Sun. light. Yaw Vehicle rotation about (typically) its Wavelength The physical distance between longitudinal Y axis. subsequent peaks (or troughs) in the Yttrium Element, symbol Y, atomic num- electric or magnetic field strength of a ber 39. Metallic, solid at room temper- propagating electromagnetic wave, sym- ature. Used as the phosphor that pro- bol λ. duces red color in a television cathode WMAP Wilkinson Microwave Anisotropy ray tube. Constituent in the yttrium- Probe. Project in NASA Explorer Pro- aluminum garnet (YAG) laser. gram. Launched 2001, produced first Yo-yo Spacecraft despin mechanism that microwave full-sky map at resolution unreels and releases two tethered masses < 1◦. Named for American cosmologist to dissipate its angular momentum, and David Wilkinson (1935–2002). Opera- reduce the spin rate of a spacecraft. tions continue as of late 2008 Zenith The point directly above an ob- Wolter telescope Configuration that gath- server. Compare nadir. ers high-energy photons using grazing- Zinc Element, symbol Zn, atomic number incidence mirrors, e.g., in concentric ar- 30. Metallic, solid at room temperature. Index

Absolute zero, 19, 334 Atmospheric entry, 172 Acceleration, 54 Atmospheric instruments, 213 Accelerometer, 106 Atmospheric opacity, 342 Acceptance testing, 262 Atmospheric spacecraft classification, 245 Ace, 4, 35, 77, 164 Atmospheric torque, 115 Active-sensing instruments, 183 Attitude control, 87, 89 Adaptive optics, 181 – scientific experiments with, 114 Administration, project, 248 Audion, 22 Air-mass coefficients, 177 Autonomous navigation, 57 Albedo, 167 Allen, Harry Julian (1910–1977), 172 B-plane, 73 Altimeter, 200 Backscatter, 196 AM0, AM1, 177 Bandwidth, 21, 26–28 American Astronomical Society, 230 Battery, electrical American Geophysical Union, 230 – primary, 148 – rechargeable, 150 Amplification, 21 – reconditioning, 150 Andr´e-MarieAmp`ere (1775–1836), 145 – secondary, 149 Angular momentum desaturation, 50, 111 Bay, 157 Announcement of opportunity (AO), 241 Beacon mode communication, 43 Ansari, Anousheh (1966–), 289 – Deep Space 1 spacecraft, 44 Antenna gain, 13 Becquerel, Alexandre-Edmond Arcjet, 139 (1820–1891), 177 Ariane launch vehicle, 122 Berrou, Claude (1951– ), 36 – compared, 125 , Chuck (1926– ), XVII Armstrong Neil (1930– ), 290 Binary digit, 45 Array Binary phase shift keying (BPSK), 29 – antenna, 17, 18 Bistatic radio science, 225 – solar, 146 Bit, 45 Arrival segment, 267 Bit error rate, 34 Articulation, 92 Black hole, 59 Asia Oceania Geosciences Society, 230 Black powder, 121 Assembly (component category), 143 Block-V receiver (BVR), 26 Assembly, test, and launch operations, 263 Blowdown mode, 131 Assigned missions, 248 Bohr, Niels (1885–1962), 205 Astrometry, 95, 314 Boltzmann constant, 21 Astronautics, 122 Boltzmann, Ludwig (1844–1906), 20 Astronomy, 95 Boole, George (1779–1848), 32 Asymptote, 72 Boom, extensible, 175 ATLO, 263 Brahe, Tycho (1546–1601), 53 426 Index

Bryan, George Hartley (1864–1928), 105 – propulsion system, 133 Bunsen, Robert (1811–1899), 203 – rockets compared, 125 Bus – scan platforms deleted, 188 – electrical distribution, 153 – stellar reference unit, 330 – serial data, 160 – structure, 157, 158 – spacecraft, 143 – sunshade, 92, 166 Bus interface unit, 160 – TCM-1, 75, 77 – telecom link compared, 18 C3 (characteristic energy), 256 – thermal control, 168, 171 Calculus, 55 – thermal-vacuum testing, 173 Calibration, 226 – velocity measurement, 64 Camera, 186 – view of Enceladus, 196 Carrier gas, 214 – view of Prometheus, 194 Carrier signal, 15 Cavendish, Henry (1731–1810), 54 Cassegrain design, 13 Celestial attitude reference, 95 Cassegrain, Nicolas (1625-1712), 13 Celestial mechanics experiment, 221 Cassini, Giovanni Domenico (Jean- Celestial reference, 101 Dominique) (1625–1712), 2 Celestial reference frame, 95 Cassini-Huygens Program manager, 9 Centaur upper stage, 78, 119, 120, 122 on Iapetus, 2 – rockets compared, 125 Cassini spacecraft, 232, 248, 304 Ceres, 386 – anomalous signal loss, 6, 7, 9 Challenger loss, 248 – atmospheric torque, 115 Chandler, Seth Carlo (1846–1913), 60 – classification, 245 Chandra X-Ray Observatory, 300 – computers, 159 – cost, 246 – classification, 244 – data bus, 160 – view of supernova SN 1604, 342 – data storage, 160 Channel – electrical power source, 152 – communications, 28–33, 35 – electrical power switching, 153 – telemetry, 38, 40, 87 – end of mission, 277 Characteristic energy (C3), 256 – engineering data, 39, 40, 135 Charge-coupled device (CCD), 189 – fault protection, 116, 163 Charge transfer efficiency, 191 – gravity assist, 81 Charged particle instruments, 218 – gyros, 104 Chemical thermodynamics, 127 – Huygens probe Doppler problem, 163 Chemistry, 127 – Huygens probe release, 98 Choked flow, 126 – Iapetus encounter, 1, 1, 2–5, 163 Chronology of interplanetary flight, 347 – instrument boom, 176 Clarke, Sir Arthur C. (1917–2008), 10, 123 – instruments, 213, 217–219, 248 Cleanroom, 264 – – compared, 188 Clementine spacecraft, 105, 225 – – confirm Titan surface liquid, 208 Closed-loop control system, 93 – – magnetospheric imager, 199 Closed-loop receiver, 26 – – objectives, 185 Coding scheme, 33 – – optical, 187, 191, 209, 210 Coherence, 63, 221 – – radar altimeter, 200 Color image acquisition, 193 – – radar imaging, 198, 199, 200, 322 Command and telemetry subsystem, 159 – launch mass, 257 Command data, 10, 41 – measurement of Enceladus’s plume, 213 Command error, 42 – occultations, 220 Command-loss timer, 164 – operations compared, 275 Command sequence, 2, 42 Index 427

– and DSN, 3 – , 146 – implementing, 5, 268 – spin-stabilized launch, 99 – restarting S33, 9 – structure, 157 Communications and navigation spacecraft dB (decibel), 13 classification, 246 de Laval, Gustaf (1845–1913), 126 Competed missions, 247 de Laval nozzle, 126 Compton Gamma Ray Observatory, 244 Decadal surveys, 247 Conduction, thermal, 168 Deci-hertz Interferometer Gravitational Consultative Committee for Space Data Wave Observatory, 285 Systems (CCSDS), 40 Decibel (dB), 13 Control-moment gyro, 108, 112 Declination, 56, 64 Control theory, 93 Deep Impact spacecraft, 58, 207, 314 Convergent-divergent nozzle, 126 Deep space maneuver, 71 Convolutional coding, 33 Deep Space Network, 10, 143 Coordinate systems, 58 Deep Space Station 14 (Goldstone), 5 Coordinated universal time (UTC), 60 Deep Space Station 43 (Canberra), 56 Coriolis effect, 106 Deep Space Station 54 (Madrid), 75, 77 Coriolis, Gaspard-Gustave (1792–1843), Deep Space Station 55 (Madrid), 6, 331 118 Deep Space Station 63 (Madrid), 4 Correlator, 69 Deep Space 1 spacecraft, 248, 316 Cosmic Background Explorer, 19 – autonav, 57 – classification, 244 – beacon mode, 44 Cosmic microwave background, 19 – classification, 243 Cosmic ray, 9, 341 – ion engine, 137, 243, 284 spacecraft, 291 spacecraft, 248 Critical commands, 164, 165 Deep-space communications complex, 11 Critical mode, 91 DeForest, Lee (1873–1961), 22 Cross-strapping, 162 Deterministic maneuver, 71 Cruise segment, 267 Diode, 23 Cryogenic propellants, 132 Direct-sensing instruments, 183 Cupido, Luis, 44 Directed missions, 248 Current, electric, 145 , 247 – alternating, 145 Division for Planetary Sciences, AAS, 230 – direct, 145 Division on Dynamical Astronomy, AAS, Cycle durability, 150 230 Doppler, Christian (1803–1853), 62 Daily firing window, 256 Doppler residuals, 63 Daily tactical timeline, 270 Doppler shift, 62 Dalton, John (1766–1844), 234 Dust detectors, 217 , 35 Dwarf planets Data management, 227 – Ceres, 386 Data number, 40, 135 – Eris, 393 Data storage, 159 – Haumea, 397 Data structure, 37 – Makemake, 403 Davy, Humphry (1778–1829), 149 – Pluto, 410 Dawn spacecraft, 137, 148 – competed mission, 247 Earth, 391 – ion engine, 136, 137, 138, 284 – noise temperature, 19 – new technology, 243 – spacecraft link with, 10 – rockets compared, 125 Earth-mass exoplanet, 286 – solar array compared, 146 Earth-protective measures, 288 428 Index

Earth-receive time, 82 Fleming valve, 22 Echo balloon, 10 Flyby spacecraft classification, 244 Edison effect, 23 Forward error correction, 32 Edison, Thomas Alva (1847–1931), 22 Forward scatter, 196 Egg, 165 Foucault, L´eon(1819–1868), 117, 202 Eggers, Jr., Alfred J. (1922–2006), 172 Fourier, Jean Baptiste Joseph (1768–1830), Ehricke, Krafft (1917–1984), 79 20 Einstein, Albert (1879–1955), 25 Frame Elastic collision, 80 – celestial reference, 95 Electric propulsion, 136 – – frame tie, 60 – electromagnetic, 139 – spacecraft structure, 156 – electrostatic, 136 – synchronizer, 35 – – ion engine, 136 – telemetry, 34 – electrothermal, 138, 139 Free-space optical telecommunications, – Hall-effect, 138 282 – magnetoplasmadynamic, 139 Free-space path loss, 15 Electrical power subsystem, 144 Frequency band, 26 Electrochemistry, 149 Electromagnetic spectrum, 341 Gain Electromagnetic thruster, 139 – amplifier, 22 Energy quanta, 145 – antenna, 13 Engineering demonstration spacecraft Galilei, Galileo (1564–1642), 54, 181 classification, 243 Galileo spacecraft, 232, 302 Engineering unit, 40, 135 – assigned mission, 248 Enthalpy, 130 – atmospheric probe, 149, 172, 173 Ephemeris, 70 – – heat shield compared, 173 Epoch, 59 – classification, 245 Equipotential ground plane, 156 – cost, 246 Eris, 393 – data storage, 159 Error detection and correction, 31, 38 – destruction, 277 Escape energy, 256 – dual-spin design, 100 Euler angles, 95 – Europa encounter, 274 Euler, Leonhard (1707–1783), 78 – gravity assist, 81 Europa saltwater ocean, 286 – high-gain antenna, 17, 265, 275 European Geophysical Union, 230 – instrument boom, 176, 176 Exoplanet, 285 – instruments, 218 Explosive bolt, 174 – – imaging, 187, 188, 191, 320 Extensible boom, 175 – mission redesigns, 248 – – post launch, 275 Fail-safe, 152 – optical communications experiment, Fairing, payload, 120 282, 283 Fast Fourier transform (FFT), 20, 44 – orbital tour, 273, 273 Fault protection, 9, 116, 161 – probe release, 99 Feedback, 93 – propulsion system, 133 Feynman, Richard P. (1918–1988), XV, – scan platform, 113 206 – structure, 157 Financial perspective, 242 – Sun sensor, 102 Flagship, 248 – sunshade, 92, 166 Flandro, Gary (1934–), 79 – telecom link compared, 18 Fleming, Sir John Ambrose (1849–1945), – thermal control, 168 22 Gallager, Robert (1931– ), 36 Index 429

Gamma ray, 341 Heat pipes, 171 Garvin, James, 241 Heat shield, 173 Gas chromatograph, 214 Heliosheath, 88 Genesis spacecraft Heliosphere, 333 – heat shield compared, 173 Hemispherical resonator gyro, 105 Geological Society of America, 230 Herschel, William (1738–1822), 202 Geophysical Society of America, 230 High Energy Solar Spectroscopic Imager Geysers spacecraft, damage, 158 – Enceladus, 196, 213, 286 High-electron mobility transistor, 24 – – and Saturn’s E Ring, 197 High-fidelity telepresence, 288 – – confirmed by imaging science, 186 High-gain antenna (HGA), 7, 14 – – discovered by magnetometer, 217 Hill sphere, 83 – – mass spectrometer measurement, 213 Hill, George William (1838–1914), 83 – – stellar occultation, 220 Hohmann transfer, 51, 81 – – thermal signature, 209 Hohmann, Walter (1880–1945), 51, 91 – – visible at high phase, 197 Horizon sensor, 104 – Triton, XVII Housekeeping, 91 Giotto spacecraft, 213, 218 Hubble, Edwin P. (1889–1953), 398 Glavieux, Alain (1949–2004), 36 Hubble Space Telescope, 104, 111 Gnomodex convention, 270 – batteries, 150 Goddard, Robert H. (1882–1945), 125, – classification, 244 126, 133, 136 – pointing requirements, 92 Goldstein, Barry, 253, 262, 277 – structure, 157 Grand tour, 79, 120 – Titan observations, 185 Gravitational wave astronomy, 285 – view of supernova SN 1604, 342 Gravitational waves, 224 Hulse, Russell A. (1950–), 224 Gravity assist, 79, 80, 140 Human journeys, XV, 287 Gravity field survey, 97, 225 Humanistic perspective, 289 Gravity propulsion, 78 Humason, Milton (1891–1972), 398 Gravity waves, 224 Huygens probe, 184, 308 Greek Alphabet, 377 – assembly, 98 Grotrian, Walter (1890–1954), 234 – atmospheric measurements, 221 Ground truth, 226 – batteries compared, 151 Guidance, 53 – battery, 149 Guillotine, 175 – Doppler problem, 163, 275 Gunpowder, 121 – heat shield compared, 173 Gyrodyne, 112 – instruments, 212, 214, 215 Gyroscope, 104 – – atmospheric structure, 327 – hemispherical-resonator, 105 – objectives, 185 – laser, 105 Hydrazine, 130 – micro-electromechanical, 105, 284 – mono-methyl, 133 – spinning-mass, 104 Hydrogen peroxide, 131 Hypergolic reactant, 133 Hale Telescope, 181 Hale, George Ellery (1868–1938), 397 Iapetus, 2 Hall, Charles F. (1920–1999), 181 – Cassini view, 8 Hall-effect thruster thruster, 138 – Voyager view, 2 Haumea, 397 Icarus journal, 230 Hayabusa spacecraft, 208, 209, 216 Image detector, 189 al-Haytham, Ibn (965–1039), 54 Image motion compensation, XVII, 42, 90 Heartbeat, 160 Images, finding full color, XVI 430 Index

Imaging radar, 197 – laws of planetary motion, 53 Imaging science, 186 Key decision point, 252 Impact detectors, 217 Kirchhoff, Gustav (1824–1887), 203 Impulse, 124 Klystron, 28 – specific, 124 Kohlhase, Charles, 258, 259 – total, 125, 129 Ku band, 12 Inertia, 54, 82 Kuiper belt, 333 Inertial attitude reference, 104 Inertial vector propagator, 92 Lander and penetrator spacecraft Infrared, 202, 341 classification, 245 Infrared Astronomical Satellite, 244 Laser, 24 Infrared image detector, 192 Laser gyro, 105 Injection propulsion unit, 120, 123 Laser-induced remote-sensing spectro- Interferometer, Keck, 19 graph, 216 Interferometry, 68 Laser Interferometer Gravitational Wave Intergalactic space, 92, 334 Observatory, 224, 285 International celestial reference frame, 59 Laser-Interferometer Space Antenna, 285 International cooperation, 289 Launch-arrival plots, 254 International Space Station, 112 Launch period, 256 International System of Units (SI), 369 Launch window, 256 Internet Archive, 229 Lee, Gentry (1942–), 268 Interplanetary space, 333, 337 Leibniz, Gottfried Wilhelm (1646–1716), Interstellar space, 333 82 Inverter, 145 Lick Observatory, 232 Isotropic transmitter, 13 Light-induced degradation, 147 Lincoln Near-Earth Asteroid Research J2000.0 epoch, 59 (LINEAR), 289 James Space Telescope, 12 Linda Morabito (a.k.a. Hyder, Kelly, 83 – Ka-band telemetry, 282 Link budget, 15 Jason 2 spacecraft, 201 Liquid bipropellant, 132, 133 Jefferson, Thomas (1743–1826), 84 Liquid monopropellant, 129 Jet engine, 139 Lorentz, Hendrik (1853–1928), 141 Jucunda, Sister Mary, 289 Louvers, 171 Juno spacecraft Low-density parity-check (LDPC), 36 – competed mission, 248 Low-gain antenna (LGA), 7, 14 – hybrid propulsion, 136 Low-noise amplifier (LNA), 22 – Jupiter gravity field, 226 Lunar Prospector spacecraft, 96 – Ka-band telemetry, 282 – evidence of lunar surface water, 211 – public outreach camera, 186 – instrument boom, 176 – solar panels, 146 – solar panel, 148 Jupiter, 189, 401 – spin stabilization, 97 – atmospheric features, 338 Lunar Reconnaissance Orbiter, 12 – gravity assist, 80 Lunine, Jonathan (1959–), 208 – ring discovery, 196 – temperature, 336 Maas, Dan (1981–), 117 Mach, Ernst (1838–1916)., 403 Ka band, 12 Magellan spacecraft, 108, 248 Kapton, 169 – atmospheric experiments, 116 Keck Interferometer, 19 – batteries compared, 151 Kennedy, John F. (1917–1963), 248 – data storage, 159 Kepler, Johannes (1571–1630), 53 – radar altimeter, 200 Index 431

– solar array compared, 146 – imaging instruments, 187, 191, 192, 321 – structure, 157 – – compared, 188 – Sun sensor, 102 – Ka-band telemetry, 282 – synthetic aperture radar, 198, 199 – porkchop plot, 257 – thermal control, 168, 169 – signal, 44 Magnetometer, 216 – telemetry rate, 36 Magnetoplasmadynamic thruster, 139 – turbo code, 36 Magnetosphere, 333 Mars Science Laboratory, 312 Magnetospheric imager, 198 – assembling, 263 Makemake, 403 – heat shield compared, 173 Mariner-class spacecraft, 107, 232 – instruments, 216 – assigned mission, 248 – – ChemCam, 325 – imaging instruments, 181 Mars Scout program, 242, 247 – structure design, 157 Mars Surveyor 2001 spacecraft, 243 Mariner Mark II, 248 Maser, 24 Mariner 10 spacecraft, 83 Mass, 82, 124 – first-ever gravity assist, 80 Mass Spectrometer, 212 – imaging instruments, 188 Matrix organization, 250 – – compared, 188 Maximum power point, 147 Mars, 269, 272, 403 Maximum-likelihood convolutional – ancient flooding, 186 decoder, 33 – launch opportunity, 52, 254 Maxwell, James Clerk (1831–1879), 93, – orbit insertion, 49, 72, 74 349 – subsurface water ice, 242 Maxwell, Scott (1971–), 270 Mars Climate Orbiter, 49, 110 Mechanical devices subsystem, 174 – metric vs. English units, 51 MEMS gyro, 105, 284 – search abandoned, 50 Mercury (planet), 404 Mars Exploration Rover, XXI, 82 Messenger spacecraft, 146, 232, 247, 306 – communications relay, 246 – classification, 245 – heat shield compared, 173 – gravity assist, 80 – imaged on martian surface, 192 – gyros, 104 – instruments, 210 – instruments, 188, 212 –– M¨ossbauer spectrometer, 329 – laser altimeter, 201 – operations compared, 275 – Mercury orbit insertion, 71 Mars Express spacecraft, 102, 105 – propulsion system, 133 – communications relay, 246 – solar array compared, 146 – structure, 157 – sunshade, 92, 166 Mars Global Surveyor, 42, 51 – thermal control, 165, 168–170, 170, 171 – batteries compared, 151 – turbo code, 36 – communications relay, 246 Micro-electronic mechanical system – gravity survey, 226 (MEMS) gyro, 105, 284 – instruments, 210 Microwave, 11, 341 – – laser altimeter, 201, 323 MIL-STD-1553B, 160 – solar array compared, 146 Minovitch, Michael (1935–), 78 – structure, 157 Mir space station, 113 Mars Observer spacecraft, 134 Mission architecture, 257, 258 Mars Polar Lander, 243, 253 Mission design, 257, 258 Mars Reconnaissance Orbiter Mission formulation, 241 – batteries compared, 151 Mission implementation, 241 – communications relay, 246 Mission integration, 257, 258 432 Index

Mission module, 120, 124 Newton, Sir Isaac (1643–1727), 53, 202 Mission phase, 251 – laws of motion, 54 – Pre-Phase A: Concept studies, 253 – universal gravitation, 54 – A: Concept, technology development, Nitrogen tetroxide, 133 259 Noise temperature, 19 – B: Preliminary design, 259 Nozzle, 125 – C: Final design and fabrication, 262 – de Laval, 125 – D: Assembly, test, launch, 262 – solid rocket motor, 129 – E: Flight operations, data analysis, 266 Nunn-McCurdy act, 261, 278 – F: Closeout, 276 Mission planning, 257, 259 Oberth, Hermann (1894–1989), 132, 136 Mission redesign in flight, 275 Observatory spacecraft classification, 244 Mitchell, Bob (1940–), 9 Occultation, 219, 220 Modulation, 29 Ohm, Georg Simon (1789–1854), 145 Modulation index, 29 One-way mode, 64 Monitor data, 28 Opacity, atmospheric, 342 Monitor, fault protection, 161 Open systems interconnection model, 37 Mono-methyl hydrazine, 133 Open-loop control system, 93 Monocoque, 156 Open-loop receiver, 28 Moore’s law, 284 Opportunity rover, 82, 216, 227 Moore, Gordon E. (1929–), 284 Opposition effect, 195 Mozi (ca. 470–390 BCE), 54 Optical modulator, 26 Multi-layer insulation, 168 Optical navigation, 56 Multiplexing Optical solar reflector, 169 – packet mode, 37 Orbit, 53 – time-division, 37 Orbit determination, 53 Orbit insertion, 49, 71, 72 NASA 2007 budget, 242 Orbit trim maneuver, 71 NASA Office of Space Communications, Orbital mechanics, 53, 94 282 Orbital tour, 272 NASA Science Mission Directorate, 247 Orbiter spacecraft classification, 244 National Academy of Sciences, 230 Orbiting Carbon Observatory, 288 National Research Council, 247 Orientation, 87, 95 Nature magazine, 45, 229 Outer space, 334 Navigation, 49 NEAR-Shoemaker spacecraft, 104, 222 Packet-mode communication, 37 – data storage, 160 Parallel electrical connection, 145 Nephlometer, 184 Parts qualification, 263 Neptune, 406 Passive-sensing instruments, 184 New Frontiers program, 248 Pathfinder lander, 82, 251 New Horizons spacecraft, 232, 296 – communications relay, 246 – beacon mode, 43, 44 – competed mission, 247 – classification, 244 – cost, 246 – competed mission, 248 – imaged on martian surface, 192 – fault protection, 163 Payload, 183 – hyperbolic trajectory, 82, 334 , 120 – imaging instruments, 191 Peer-reviewed journals, 229, 287 – Jupiter gravity assist, 79 Phase angle, 195 – Pluto encounter, 221 Phase-locked-loop, (PLL), 27 – spin-stabilized launch, 101 Phased-array antenna, 46 , 248 Phillips Laboratory, 282 Index 433

Phobos spacecraft, 42, 140 Propellant management device, 136 Phoenix lander, 268, 310 Propulsion system, 119, 127 – approval, 262 Pyrotechnic fasteners, 174, 264 – competed mission, 247 – cost, 242 Qualification testing, 262 – descent radar, 252 Quanta, 205 – end of mission, 277 Quantum efficiency, 191 – fault protection, 165 Quasar, 59 – heat shield compared, 173 Questions, scientific, 182 – imaged while parachuting, 192 Quickscat spacecraft, 201 – instruments, 184, 213 – landing event, 268 Rackus, Richard, 258 – objectives, 243 Radiation, 166, 341 Radio and plasma wave instruments, 217 – project start, 241, 247 Radio frequency, 11 – termination review, 261 – spacecraft’s, 63 Photoelectric effect, 145 , 11, 341 Photon propulsion, 284 Radioisotope heater unit, 171 Photovoltaics, 146 Radioisotope thermoelectric generator, 150 Pioneer spacecraft, 10, 96, 117, 248 Radiometer, 201 – commanding, 159 Radiometric observables, 55 – gravity assist, 80 Range, 66 – hyperbolic trajectory, 82 Range-safety radio, 120 – instruments, 217 Ranger 7 spacecraft, 157 – interstellar objects, 334 Ranger spacecraft, 263 – spin-stabilized, 96 Raw data sets, 231 – structure, 157 Reaction wheels, 108 – Venus, 97, 149, 184 Reaction-wheel desaturation, 107 Pitch, 89 Realtime, 5, 92 Planck Surveyor spacecraft, 19, 244 Realtime support area Planetary Society, The, 291 – Cassini, 4 Plasma and radio wave instruments, 217 – Mars Exploration Rover, 37 Plasma instrument, 219 – Voyager, 87 Pluto, 410 Reed, Irving (1923– ), 33 Plutonium-238, 150 Reed-Solomon coding, 32 Poincar´e,Henri (1854–1912), 78 Reflecting optics, 187 Polar motion, Earth’s, 61 Refracting optics, 187 Porkchop plots, 254 Release devices, 174 Poverty vs. , 289 Remote-sensing instruments, 183 Power, electric, 145 Residuals, navigation, 56 Power margin, 155 Resistance, electrical, 145 Pressure-regulated mode, 131 Resistojet, 138 Pressurization, propulsion system, 134 Response, fault protection, 161 Primary mission, 266 Restricted three-body problem, 78 Principia, 53 Reviews, 252 Print media, 287 Right ascension, 55, 64 Probabilistic risk assessment, 250 Ritter, Johann (1776–1810), 202 Program vs. project, 248 Roche sphere, 83 Project administration, 248 Roche, Edouard´ (1820–1883), 83 Project lifecycle, 259 Rocket engine, 121 Project vs. program, 248 – electric, 136 434 Index

– liquid propellant, 129, 132, 133 Signal processing center, 11 – solid propellant, 127 Signal-to-noise ratio (SNR), 19 – solid-liquid hybrid, 136 Single-fault tolerance, 162 Rocket equation, Tsiolkovsky, 123 Smith, Peter, 265 Rocket science, 122 Sojourner rover, 82, 247 Rocket thrusters – alpha proton x-ray spectrometer, 328 – and attitude control, 94 – communications relay, 246 – Cassini, 133 Solar and Heliospheric Observatory, 189 – chemical, 121 Solar array, 146 – electric (ion), 136 Solar cell, 146 – Magellan, 107 Solar panel, 146 – Spitzer, 130 Solar sailing, 284, 416 – Viking, 133 Solar system, 333 – Voyager, 107 – distances in, 334 Roll, 89 – distribution of mass in, 333 Rosetta spacecraft, 218 Solar wind, 110, 333 Rover spacecraft classification, 245 Solid rocket motor, 123, 127, 129 Rowland, Henry (1848–1901), 203 – Dawn, 99 Royal Astronomical Society, 230 – Magellan, 108 Royal Society, 230 – Thiokol Star series, 125, 128 – Voyager, 107, 120 S band, 12 Solomon, Gustave (1930–1996), 33 Safing, 162 Space, 333 Sagan, Carl (1934–1996), XVII Space age, 351 Sagnac, Georges (1869–1926), 105 Saltwater ocean on Europa, 232 Space Flight Operations Facility, 11 Saturn, 414 Space Infrared Telescope Facility, 298 – energy to reach, 256 Space-link session, 4 – orbit insertion, 72 Space loss, 15 – rings identified, 339 Space Science Reviews, 229 – temperature, 336 Space Shuttle, 82, 248 Scan Platform, 188 – rocket engine, 122 , 201 – rockets compared, 125 Schr¨odinger,Erwin (1887–1961), 234 Space weathering, 208 Science data pipeline, 227 Spacecraft, 417 Science experiments, 219 Spacecraft classification, 243 Science instruments, 177, 181, 183 – atmospheric, 245 – the four categories, 183 – communications and navigation, 246 Science magazine, 45, 229 – engineering demonstration, 243 Science News magazine, 230, 287 – flyby, 244 Scout, Mars, 242 – lander and penetrator, 245 Search for extraterrestrial intelligence – observatory, 244 (SETI), 286 – orbiter, 244 Seebeck effect, 152 – rover, 245 Seebeck, Thomas (1770–1831), 152 – size and complexity, 246 Semi-monocoque, 156 Specific energy, 149 Series electrical connection, 145 Specific impulse, 124 Shannon limit, 32, 36 Spectral density, 20 Shannon, Claude (1916–2001), 32 Spectrograph, 202 Shear plate, 157 Spectrometer, 202 SI (International System of Units), 369 – active, 215 Index 435

– alpha-particle x-ray, 184, 215 Sun shades, 170 – gamma-ray, 211 Superior conjunction experiments, 223 – imaging, 209 Surface operations, 270 – infrared, 209 Symbols and bits, 29 –M¨ossbauer, 216 Synthetic aperture radar (SAR), 197 – mapping, 209 System of Units, International (SI), 369 – neutron, 211 Systems, 139, 143 – plasma, 219 – thermal emission, 210 TacSat 2 spacecraft, 106, 284 – x-ray fluorescence, 216 Tactical timeline, 270 Spectroscope, 202 Target motion compensation, XVII, 42, 90 Spectrum, 202 Target plane, 72 Taylor, Jr., Joseph H. (1941–), 224 – absorption, 203 Technology readiness level, 243 – continuous, 203 Telecommand, 41 – electromagnetic, 341 Telecommunications, 1 – emission, 203 Telemetry data, 10, 28 – reference, 208 – channel, 38, 40 – reflectance, 206 – Ka-band, 281 Spin stabilization, 96 Telepresence, 1, 420 Spirit rover, 82 Television camera, 181 Spitzer Space Telescope, 111, 209, 298 Television coverage, 228 – classification, 244 Temperature in space, 334 – instruments, 192 Temps Atomique International, 60 – – infrared spectrograph, 324 Temps Universel Coordonn´e,60 – structure, 157 Termination review, 261 – view of protoplanetary disk, 210 Termination shock, 216, 333 – view of supernova SN 1604, 342 Testing, 265 Spring-loaded hinge, 175 , 291 SpringerLink, 229 Thermal control subsystem, 165 Sputnik, XXI, 148, 351 Thermal infrared instrument, 209 – batteries compared, 151 Thermal-vacuum testing, 173 Squyres, Steve (1957– ), XXI Thermionic emission, 23 Stability, 95 Thermocouple, 152 Star-watching device, 102 Thitimajshima, Punya (1955–2006), 36 Stardust spacecraft, 218 Thomson, J. J. (1856–1940), 23 – heat shield compared, 173 Three-axis control, 99 – structure, 157 Three-body problem, restricted, 78 Starfire optical range, 282 Three-way mode, 65 Statistical maneuver, 71 Thrust, 121 Stirling radioisotope power system – momentum, 127 (SRPS), 283 – pressure, 127 Stone, Ed (1936– ), 88 Thruster-valve assembly, 131 Strategic timeline, 270 Time-division multiplexing, 37 Structural testing, 157 Titan III launch vehicle, 78, 119 Structure subsystem, 155 – rockets compared, 125 Strut, 156 Titan’s lakes, 200, 202, 208 Stuhlinger, Ernst, 289 Total impulse, 125, 129 Subassembly, 143 Townes, Charles Hard (1915– ), 25 Subsystems, 143 Tracking data, 10 Sun sensor, 101 Trajectory, 53 436 Index

Trajectory correction maneuver (TCM), Voltage, 144 49, 71 von Braun, Wernher (1912–1977), 132 Transfer frame, 34 von Fraunhofer, Joseph (1787–1826), 202 Triton, XVII Voyager spacecraft, 87, 294 TRL, technology readiness level, 243 – almost lost, 42 Truss, 156 – assigned mission, 248 Tsiolkovsky, Konstantin (1857–1935), 122 – attitude changes, 87, 88 Tullius, John, 4 – classification, 244 Tunguska, 288 – computers, 159 Turbo code, 36 – data storage, 159 Turing, Alan (1912–1954), 117 – electrical power source, 150 2001 Mars Odyssey spacecraft, 73, 114 – extended mission, 276 – instrument boom, 176 – fault protection, 116 – instruments, 211, 212 – grand tour, 79 – Mars arrival, 75 – high-gain antenna, 14, 14 – solar array compared, 146 – hyperbolic trajectory, 82, 334 – targeting, 74 – imaging instruments, 188, 189 – water ice discovery, 242 – in Von K´arm´anAuditorium, 89 Two-way mode, 65 – instrument boom, 176 Tycho Brahe (1546–1601), 53 – instruments, 187, 188, 216–218 – – magnetometer, 326 Ultra-stable oscillator (USO), 63, 221 – – optics compared, 188 Ultraviolet, 202, 341 – jovian ring discovery, 196 Ulysses spacecraft, 97, 218, 219, 277 – last encounter, XVII Units of measure, 369 – launch, 119 Universal time, coordinated (UTC), 60 – light time, 65 Uranus, 422 – moments of inertia, axial, 89 UTC (Coordinated universal time), 60 – occultations, 220, 221 Vega spacecraft, 218 – Pluto opportunity, 79, 220 Venera spacecraft, 226, 227 – redesign post launch, 275 Venus, 227, 422 – rockets compared, 125 – albedo, 167 – scan platform, 113 – energy to reach, 256 – solid rocket motor, 120, 123, 128 – surface temperature, 336 – structure, 157 Venus Express spacecraft – Sun sensor, 102 – batteries compared, 151 – telecom link compared, 18 – solar array compared, 146 – termination shock penetrated, 216 – structure, 157 – thermal control, 168 Very long baseline interferometry, 67 – transmitter, 17 Viking spacecraft, 113 – view in real time, 87 – cost, 246 – heat shield compared, 173 Watchdog timer, 161 – imaged on martian surface, 192 Wavelength, 11 – instruments, 213 Webster, Julie (1953–), 7 – propulsion system, 133 Weight, 124 Visible light, 341 Wilkinson Microwave Anisotropy Probe, Viterbi decoding, 34 19 Viterbi, Andrew J. (1935– ), 33 Wolter, Hans (1911–1978), 197 VLA, Very Large Array, 18, 19 Wolter Telescope, 197 Volta, Alessandro (1745–1827), 145 WWW media, 228 Index 437

X axis, 89 Yttrium aluminum garnet (YAG) laser, X band, 12 323 Xray,341 Yaw, 89 Z axis, 89 Y axis, 89 Zero, absolute, 19, 334