Eos, Vol. 71, No. 39, September 25, 1990

corded data rate to the tape recorders is about one-fifth the playback rate for a 10- Mars Observer's hour link to a 34 m NASA Deep Space Net­ work tracking station. The normal sequence of collecting scientific data will be to record Global Mapping Mission continuously for 24 hours and then to play the data back in one 10-hour link. The map­ ping orbit is a 117-minute orbit with a 7-day A. L. Albee and D. F. Palluconi repeat cycle. As a result, the planet is repeat­ edly mapped in 26-day cycles with a 58.6 km California Institute of Technology, Pasadena, California nominal path separation. Orbit trim adjust­ PAGES 1099, 1107 ments make it possible to obtain uniform cov­ erage during the course of the mission with The Mars Observer mission, scheduled for face, and provide a basis for comparison with an ultimate spacing of ground tracks at the launch in September 1992, will provide an Venus and Earth. equator or 3.1 km. orbital platform at Mars from which the en­ The Mars Observer spacecraft provides a tire Martian surface and atmosphere will be Mission Description three-axis stabilized, nadir-oriented platform observed beginning in late 1993. Mars Ob­ for continuous observations of Mars by the server will extend the exploration and charac­ Mars Observer will be launched by a Titan science instruments (Figure 2). The space­ terization of Mars by providing new and sys­ III, built by Martin Marietta, with an upper craft is being built by the General Electric As­ tematic measurements of the surface and at­ Transfer Orbit Stage from Orbital Sciences tro-Space Division. The Gamma Ray Spec­ mosphere of the planet. These measurements Corporation. After the 11-month transit the trometer and Magnetometer sensor assem­ will be made from a low-altitude polar orbiter spacecraft will be injected into an elliptical or­ blies are mounted on individual booms on over a period of one Martian year (687 Earth bit around Mars with periapsis near the north the spacecraft. All other instruments are rig­ days), permitting repetitive observations of pole. The orbit is then adjusted through a se­ idly mounted to the spacecraft structure. No the surface and of the seasonal variations of ries of maneuvers to a near-circular, sun-syn­ movable scan platform is provided; the space­ the atmosphere. The mission is being de­ chronous (2:00 A.M./P.M.), low altitude, craft is continuously nadir pointed, rotating signed in a manner that will provide new and near-polar orbit. Due to the non-uniformity at the orbital rate. Those instruments that re­ valuable scientific data at a significant reduc­ of the gravity field, the altitude varies from quire scanning or multiple fields of view have tion in cost and operational complexity. 376 km near the south pole to 430 km near internal scanning mechanisms. The footprints The scientific objectives for the mission em­ the north pole. During the Martian year in for the instruments are shown in Figure 3. phasize qualitative and quantitative determi­ this mapping orbit the instruments acquire nation of the elemental and mineralogical data in a systematic program of global map­ composition of the surface; measurement of ping. At the end of the mission the spacecraft Experiments and Instruments the global surface topography, gravity field, can be boosted to a permanent quarantine or­ and magnetic field; and the development of a bit. The instruments for Mars Observer closely synoptic data base of climatological condi­ The mapping timeline, relative to the Mar­ match the scientific objectives. Collectively the tions. This mission will provide a basic global tian seasons and the likely dust storm period, instruments cover much of the electromag­ understanding of Mars as it exists today and is summarized in Figure 1. The Mars orbit netic spectrum and form a highly comple­ will provide a framework for understanding insertion (MOI) period ends just before solar mentary set. Each instrument produces well- its past. conjunction and the beginning of the dust defined sets of measurements which address The formal scientific objectives of this geo- storm period. Since it is scientifically impor­ specific major objectives, but nearly every science and climatological mission are to de­ tant to make observations for an entire global data set also contributes to a much wider va­ termine the global elemental and mineralogi­ mapping cycle (26 days) before the onset of a riety of scientific investigations. Five interdis­ cal character of the surface material; define major dust storm, it is hoped that the fuel ciplinary scientists have been selected in addi­ globally the topography and gravitational margin will permit a shorter MOI phase than tion to the instrument teams in order to ex­ field; establish the nature of the magnetic shown. ploit the strong synergism in the data sets. field; determine the time and space distribu­ The playback data rate for a 10-hour link Moreover, participating scientists, including tion, abundance, sources, and sinks of volatile varies by a factor of 4 with Earth-Mars dis­ 10 from the Soviet Union, will be added after material and dust over a seasonal cycle; and tance during the mission. The continuous re­ launch to further exploit the data returned explore the structure and aspects of the cir­ culation of the atmosphere. These first-order scientific objectives can be MOI BEGIN LGC addressed within the framework of a low-cost orbital mission. All five objectives involve MISSION MOI z MAPPING PHASE (DURATION = 687 days) global mapping. For the geoscience objec­ PHASE: PHASE tives, this mapping is mainly time-indepen­ dent and therefore two-dimensional: latitude DUST STORM PERIOD MARS 94 ACTIVITY and longitude. For many climatology objec­ I tives, the mapping is four-dimensional: lati­ SOLAR (HIGHLY VARIABLE) CONJ tude, longitude, altitude and season. As a re­ sult of this mission we should have a system­ MARS NORTHERN SOUTHERN SOUTHERN NORTHERN NORTHERN SOUTHERN SEASON: SUMMER SPRING SUMMER SPRING SUMMER SPRING atic global characterization of Mars today. This characterization will help us to under­ V V stand the geologic and climatologic history of MAXIMUM MARS MINIMUM MARS EARTH RANGE PERIHELION EARTH RANGE APHELION Mars, the evolution of its interior and sur- (2.45 AU) (1.38 AU) (0.68 AU) (1.67 AU)

16 ksps

DATA RATES 3 ksps f" 8 ksps RECORD: 4ksps Cover. By the end of 1993, the Mars DATA RATES ASSUME 34-meter DSS (HEF) Observer spacecraft will begin mapping PLAYBACK: 21 ksps 43 ksps 85 ksps 43 ksps 21 ksps the surface and atmosphere of Mars, ex­ tending the exploration and characteriza­ I h H H—r H h H h- tion of the planet by providing new and JUL OCT JAN APR JUL OCT JAN APR JUL OCT JAN systematic measurements over a period of 1 1 1 1 1 1 1 1 1 1 1 one Martian year. See "Mars Observers' 1993 + Global Mapping Mission" by A. L. Albee and D. F. Palluconi, this issue. Fig. 1. Timelines for the mapping phase of the Mars Observer mission.

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examine local areas at extremely high spatial resolution in order to quantify surface/atmos­ phere interactions and geological processes.

Thermal Emission Spectrometer (TES). The principal investigator for TES is P. Christen- X \ ^\6-PANEL SOLAR ARRAY sen of Arizona State University. The instru­ ment is a Michelson interferometer that cov­ ers the spectral range 6.25 to 50 micrometers with 5-10 wavenumber spectral resolution. Separate solar reflectance (0.3 to 3.9 micro­ meters) and broad band radiance (0.3 to 100 micrometers) channels are included for radia­ tion balance measurements. It has six 8.3 mrad fields of view, each with 3 km spatial resolution at nadir. Objectives of this investigation are to deter­ mine and map the composition of surface +Z (NADIR) minerals, rocks and ices; study the composi­ tion, particle size, and spatial and temporal distribution of atmospheric dust and of con­ densate clouds; study the growth, retreat and total energy balance of the polar cap depos­ Ps ORBITAL its; measure the thermophysical properties of ROTATION the Martian surface (thermal inertia, albedo) that can be used to derive surface particle HIGH-GAIN +X (VELOCITY) ANTENNA size and rock abundance; and determine at­ mospheric temperature, pressure, water va­ Fig. 2. The Mars Observer spacecraft and its payload in the fully deployed config­ por, and ozone profiles, and seasonal pres­ uration of its mapping orbit at Mars. sure variations.

Pressure Modulator Infrared Radiometer (PMIRR). The principal investigator for MOC W/A (140° Cross Track) PMIRR is D. McCleese of the Jet Propulsion Laboratory. The instrument is a limb, off-na­ dir and nadir scanning radiometer. Measure­ ments are made in 9 spectral bands with 5 fil­ Fig. 3. Footprints ter channels and 2 pressure modulator cells for the nadir-panel in­ (one containing carbon dioxide, the other wa­ struments: Mars Ob­ ter vapor). The detectors are cooled to 80 K server Camera (MOC, by a passive radiator. wide angle and narrow The objectives of this investigation are to angle), Thermal Emis­ map the three-dimensional and time-varying sion Spectrometer thermal structure of the atmosphere from the (TES), Mars Observer surface to 80 km altitude; map the global, Laser Altimeter vertical and temporal variation of atmospher­ (MOLA), and Pressure ic dust and condensates; map the seasonal Modulator Infrared and spatial variation of atmospheric pressure Radiometer (PMIRR). and the vertical distribution of atmospheric water vapor; and monitor the polar radiation balance.

Mars Observer Laser Altimeter (MOLA). The 58.6 km Orbit Walk Eastward at Equator Every Seven Martian Days principal investigator for MOLA is D. Smith of Goddard Space Flight Center. The instru­ ment is a diode-pumped 1.06 micrometer Nd:YAG laser transmitter and a 50 cm diam­ from the mission. Each of the instruments Martian surface and albedo neutrons (H, O, eter parabolic receiver, which provide 100 m and their experimental objectives are de­ Mg, Al, Si, S, C, K, Ca, Fe, Th, U) and to de­ diameter footprints with 2 m vertical preci­ scribed below. termine the arrival times and spectra of gam­ sion at 10 pulses per second (about 300 m ma-ray bursts. spacing). Gamma Ray Spectrometer and Neutron Detector The key objectives are to determine a glob­ (GRS). The team leader for the GRS experi­ Mars Observer Camera (MOC). The principal al, geodetically referenced 0.2° x 0.2° topo­ ment is W. Boynton of the University of Ari­ investigator for MOC is M. Malin of Arizona graphic grid to a vertical precision of 30 m to zona. This boom-mounted instrument has a State University. The instrument is a line address global problems in geology, geophys­ high spectral-resolution germanium detector scan camera, which incorporates both wide- ics, and atmospheric circulation; and measure cooled to 100 K by a passive radiator. It will angle and narrow-angle optics for producing globally distributed topographic profiles with measure the intensities of characteristic gam­ global coverage (7.5 km/pixel), selective mod­ a vertical precision of 2 m to address local ma-ray lines that emerge from the Martian erate-resolution images (480 m/pixel), and and regional geologic and geophysical prob­ surface within the energy range 0.2 to 10 very selective high-resolution (1.4 m/pixel) lems. MeV. A boron-doped plastic scintillator will images. serve as a charge-particle shield and as a neu­ Objectives of this investigation are to obtain Radio Science. The team leader for the Ra­ tron detector to determine the abundance of global synoptic views of the martian atmo­ dio Science investigation is G. L. Tyler of hydrogen. sphere (clouds) and surface to study meteoro­ Stanford University. The instrument is the Key objectives of this investigation are to logical, climatological, and related surface spacecraft radio subsystem, x-band up and determine the elemental composition of the changes on a daily basis; monitor surface and down, supplemented with an ultrastable oscil­ surface of Mars with a spatial resolution as atmosphere features at moderate resolution lator to maximize the science during occulta- high as a few hundred kilometers through for changes on time scales of hours, days, tion exits. Radio occultation observations pro­ measurements of gamma-rays excited at the weeks, months and years; and systematically vide data on the atmosphere and radio Dopp-

This page may be freely copied. Eos, Vol. 71, No. 39, September 25, 1990

ler tracking of the spacecraft motion provides ly enhance the telemetry from balloon-sus­ sion sequence plan, schedules and command­ data on the gravitational field. pended experiments, which are expected to ing opportunities, and orbit/viewing forecasts. Key atmospheric and gravitational objec­ include imaging, atmospheric, and other in­ Investigators and analysts will access the data tives are to determine profiles of refractive struments. This relay function would occur in base to participate in the planning process index, number density, temperature, and late 1995 near the end of the nominal Mars and to provide analysis products, including pressure at up to 200 m vertical resolution Observer mission. spacecraft and instrument performance and for the lowest few scale heights at high lati­ The interdisciplinary scientists with geosci- status, and higher-order data products, such tudes in both hemispheres on a daily basis for ence objectives are R. Arvidson of Washing­ as intermediate and final science products. a Martian year; characterize the small scale ton University, M. Carr of the U. S. Geologi­ AH of the instruments are "mapping" in­ structure of the atmosphere and ionosphere; cal Survey, Menlo Park, and L. Soderblum of struments in some sense. Efficient compari­ develop a global, high-resolution model of the U. S. Geological Survey, Flagstaff. The in­ son of such data requires global digital data­ the gravitational field; and determine both lo­ terdisciplinary scientists with atmospheric and bases that are each accessible to end users cal and broad scale density-structure and climatologic objectives are A. Ingersoll of the and that can be manipulated without the as­ stress state of the Martian crust and upper California Institute of Technology, B. Ja- sistance of technological experts. A sinusoidal mantle. kosky of the University of Colorado, and J. equal-area projection will be used as a base. Pollack of Ames Research Center. In this projection each parallel of latitude is Magnetometer and Electron Reflectometer. The an image line with its length scaled by the co­ principal investigator of the Magnetometer is sine of its latitude. A global digital image mo­ M. Acuna of the Goddard Space Flight Cen­ Operations and Data Analysis saic is being constructed from selected Viking ter. The instrument has two triaxial fluxgate The Mars Observer mission operations at images. Each pixel represents 1/256° (about magnetometers and an electron reflectometer the Jet Propulsion Laboratory (JPL) will be 230 m); lower resolution versions can be mounted on a 6-meter spacecraft boom. The supported by the NASA Deep Space Network readily produced by factors of negative pow­ magnetometer measures the components of and the J PL Space Flight Operations Center. ers of 2. Such a base and system is designed the magnetic field, providing the orientation The science investigation teams will be re­ to allow efficient computer storage and man­ and magnitude of the ambient field. The motely located at the home institutions of the agement, user access, coregistration of data electron reflectometer measures the energy principal investigators, team leaders, and oth­ bases, rapid manipulation of data bases for spectrum and angular distribution of incident er key science personnel. Workstations and effective analysis and interpretation, and in­ and reflected electrons. electronic communication links will connect expensive preparation of image maps on any Key objectives of this investigation are to the mission planning and data analysis activi­ desired projections. The data bases will be establish the nature of the magnetic field of ties of these scientists, engineers, and mission widely distributed, probably on digital (CD- Mars, map the Martian crustal remanent field managers. ROM) disks. using the fluxgate sensors and extend these The Mars Observer project will utilize data in-situ measurements with the remote capa­ standards for packet telemetry and telemetry bility of the electron reflectometer sensor, Acknowledgments channel coding and will use a standard for­ and characterize the solar wind/Mars plasma matted data unit for data transfer among The research described here was carried interaction. ground systems. Mission data will be stored in out by the Mars Observer Project at the Jet Mars Balloon Relay (MBR). The MBR radio a project data base. Analysis data will consist Propulsion Laboratory, California Institute of system is being provided by the French space of a record of each instrument's packet te­ Technology, under contract with the National agency (CNES) to relay scientific telemetry lemetry data provided as an experiment data Aeronautics and Space Administration. The from balloons or landers that will be de­ record; spacecraft position and pointing in­ authors are the project scientists for the Mars ployed at Mars by the Soviet Mars 1994 mis­ formation data available as a supplementary Observer mission and acknowledge the con­ sion. Work is proceeding on the Mars 94 mis­ experiment data record; and related data tribution of the entire project staff. The sci­ sion despite current political problems. The such as spacecraft status, commands, data ence objectives for the individual investiga­ MBR system will utilize the buffer memory of availability, and ancillary data. Planning tions are summarized from the science plans the Mars Observer Camera in order to great- products available will be the up-to-date mis- prepared by the individual investigators. News

The Senate bill reduces NASA's budget to vanced X-Ray Astrophysics Facility, and the Senate Recommends NSF $13.45 billion, which is more than $1.5 billion possible suspension of space shuttle flights Funding Increase, NASA less than Bush requested. Recommended cuts until 1993. include $863 million from Space Station Free­ Cuts dom and $30 million from the Moon/Mars ini­ Saturn's 18th Moon tiative. A $50 million reduction in funding PAGE 1099 for the Comet Rendezvous Asteroid Flyby Located (CRAF)/Cassini mission could mean the can­ The Senate VA, HUD, and Independent PAGE 1099 Agencies Appropriations Subcommittee, cellation of the CRAF portion of the com­ chaired by Barbara Mikulski (D-Md.), recom­ bined program. On the brighter side, fund­ The discovery of a new moon orbiting Sat­ mended on September 12 to increase fiscal ing for the Earth Probes satellite program urn brings to 18 the number of the planet's year 1991 funding of the National Science was increased by $31 million and basic Earth moons. Temporarily designated 1981 SI3, Foundation (NSF) by $27 million above the science research and modelling received an the moon has a diameter of only 20 km and level approved by the House. At the same additional $17 million. apparently creates the 320-km-wide "Encke's time the subcommittee approved a spending The subcommittee's recommendations now gap" in the planet's "A" ring, its outermost level for the National Aeronautics and Space await approval by the Senate, after which the major ring. Administration (NASA) that is $855 million bill goes to a House-Senate conference to re­ The small, bright object was found by below that recommended by the House. solve the differences between the two bills. If, Mark Showalter of the National Aeronautics NSF funding under the Senate bill (H.R. however, a final bill is not signed by the Pres­ and Space Administration, Ames Research 5158) would be $2.36 billion, an increase of ident before the beginning of the 1991 fiscal Center, Moffett Field, Calif., while analyzing 14% over last year. Like the House bill, the year on October 1, automatic reductions im­ images taken by the Voyager 2 spacecraft Senate's bill eliminates funding for a gravita­ posed by the Gramm-Rudman-Hollings Act during its 1981 flyby of Saturn. Showalter tional wave observatory. Science education will take effect. For NSF, this would mean a used a computer program he wrote to sort programs were increased to $322 million, possible 50% cut in funding to grantees. through 30,000 images. higher than both the House bill and Presi­ NASA could face cancellation of two or three A "moonlet wake" pattern, resembling a dent Bush's request. scientific projects, such as CRAF and the Ad- motorboat wake, was first noticed in the ring

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