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I The First Mission of the Tethered Satellite System

Table of Contents

A Line To The Universe 1

The First Tethered Satellite System Mission 2

Major Tethered Satellite System Elements 6

Tether Dynamics 10

TSS-1 Science Background 14

TSS-1 Science Investigations 23

Mission Scenario 28

TSS-1 Crew 30

A Line To The Future 32

Quick Reference To Experiments And Investigators 35

For Further Reading 36

Glossary Of Abbreviations And Acronyms 37

N/ A ORIGINAL PAGE National Aeronautics and PHQTOGRAPH, Space Administration il A Line To The Universe

The first Tethered Satellite System (TSS-1) will soon be launched aboard the Space Shuttle. Circling Earth at an altitude of 296 kilometers (kin), the reusable tether system will be well within the tenuous, electrically charged layer of the atmosphere known as the iono- sphere. There, a satellite attached to the orbiter by a thin conducting cord, or tether, will be reeled from the Shuttle payload bay. This will grant scientists experi- mental capabilities never before possible. On this mission, the satellite will be deployed 20 km above the Shuttle. The conducting tether will generate high voltage and electrical currents as it moves through the ionosphere and allow scientists to examine the electrodynamics of a conducting tether system. These studies will not only increase our understanding of physical processes in the near-Earth space environment but will also help provide an explanation for events witnessed elsewhere in the solar system. In addition, the Deployment of the Tethered Satellite System upward mission will explore the mechanical dynamics of teth- from the Shuttle On TSS-I allows scientists to gather ered systems, providing information that will improve data on performance, while providing an excellent future missions and possibly lead to a variety of future platform for a variety of plasma physics and electro@- =..... tether applications. namics investigations. Tethered spacecraft can be deployed toward or away from Earth. Downward deployment (toward Earth) on future missions could place the satellite in regions of MIllilllAL ".... "" the atmosphere that have been difficult to study because they lie above the range of high-altitude balloons and below the minimum altitude of free-flying satellites. A series of Tethered Satellite System flights, exploring in both directions from the Shuttle, could gather data previously impossible to obtain. Each flight would The Tethered Satellite allow scientists and engineers to conduct new experi- System has the potential to be deployed toward the ments, explore phenomena discovered through previous Earth. On such a future missions, and develop new uses for tethers in space mission, large-scale exploration. investigations of previ- ously inaccessible regions of the atmosphere could be performed. The First Tethered Satellite System Mission

_%____ Mission Objectives _, _;_._r n The era of space-age tethered operations moves ._, _ $_ _ - _/7..-_._ _---_y toward reality with the launch of TSS-I. The C "_P_"_'_ _ / primary objective of this m_ss,on ts to demon- _ A_:._,_,_ _ i [ strate the technology of long tethered systems e_ efrtevat ._ in space and to demonstrate, through scien- ---_ ._i.i._ _ _,:"! " : tific investigations, that such systems are Science Goals _%_ _ useful for research. Speeding through _ _

the magnetized iono- Engineering Goals spheric plasma at almost 8 km Manipulating a satellite on a tether from the per second, a 20-kin long Launc orbiter is a unique engineering challenge, conducting • " and tether :i_%ii_y:_'_t///, t Because gravity, cenmfugal force, atmo- !_'_'a_/i_l _/ spheric drag vary with altitude, each of the should _ .. _i_: _ , two bodies in a tethered system, one orbiting create __--'____yar_ah/-_ : above the:other:is subject to different influ __: :avari= r -'='_r. __ encesi_Consequently, the primary engineering .....ety ofvery :" " " ' _ ...... goalofrss-i is to demonstrate that a satellite interesting ptasma- ii'.i,_-_i: _ -..: can be deployed, stabilized, and retrieved on a electrodynamic phenomena. These are - long tether in space and that an electrically expected to provide a variety of unique exper- i " conducting system can be operated success- imental capabilities, including the ability to fully. Tether dynamics and control are not collect an electrical charge and drive a large intuitive; while reeling out a satellite on a current system within the ionosphere, to tether is somewhat analogous to flying a kite, generate high voltages [on the order of the analogy breaks down when the environ- 5 kilovolts (kV)] across the tether at full ments in which the systems operate are com- deployment, to control the satellite potential pared. Unlike a kite in the atmosphere, the and the satellite's plasma sheath, and to gener- tethered satellite is in an_electrically charged ate low-frequency electrostatic and electro- environment and is controlled by gravity magnetic waves. It is believed that these gradient rather than aerodynamic forces. TSS-1 capabilities can be used to conduct controlled will improve our understanding of tether experimental studies of phenomena and dynamics and allow scientists and engineers processes that occur naturally in plasmas to develop more sophisticated tether control throughout the solar system, including Earth's models for future tethered missions, magnetosphere.

2 Anecessary first step toward these studies --and the primary science goal of TSS-1 -- is to characterize the electrodynamic behav- ior of the satellite-tether-orbiter system. Of particular interest is the interaction of the system with the charged particles and electric and magnetic fields in the ionosphere, includ- ing the nature of the external current loop within the ionosphere and the processes by which current closure occurs at the satellite .Liiiiiiiiiz and the orbiter. This will be investigated by a series of experiments conducted with electron accelerators and tether current-control hardware, along with a set of interdependent diagnostic instruments provided by the of the Tethered Satel!i!e System mission. thrusters will spin the satellite so that it rotates TSS- 1 investigators. Flight and science operations are controlled a quarter turn each minute, allowing data to from Johnson Space Center, while Kennedy be collected as the satellite sensors rotate Organization Space Center is responsible for integrating through different electric and magnetic fields. The Tethered Satellite System is a joint payloads into the orbiter and launching Approximately 6 hours later, the satellite venture of the United States' National the Shuttle. is fully deployed 20 km from the Shuttle. Ten Aeronautics and Space Administration An Investigator Working Group, com- hours of on-station operations begin with the (NASA) and Italy's Agenzia Spaziale Italiana posed of TSS-I Principal Investigators and satellite's spin being stopped for an orbit as (ASI, the Italian Space Agency). Based on Associate Investigators, advises NASA and data on tether system dynamics are collected. a 1984 Memorandum of Understanding ASI in the design, development, and opera- After this orbit, thrusters will spin the satellite between NASA and ASI, the Italian agency tion of TSS-1. This group develops and so that it rotates at slightly less than one full has responsibility for developing the reusable reviews all science requirements for the turn each minute. As the Tethered Satellite satellite, while NASA has responsibility mission, recommends mission profiles and System stimulates and interacts with the for developing the deployer system and the experiment sequence_; and specifies how data ionosphere, instruments in the satellite and the tether, integrating the payload, and providing should be acquired, processed, handled, and Shuttle's payload bay measure the response, transportation into space. In addition, the distributed. The Investigator Working Group determine how the Tethered Satellite System U.S. Air Force Phillips Laboratory, by agree- also oversees science activities during collects an electrical current from the iono- ment with NASA, is participating in the the flight. sphere, study the power generation properties program by providing an experiment that of the entire tether system, and characterize supports the TSS-I mission as well as Air Mission Profile the surrounding environment. Force research interests. The deployer system The Shuttle will carry TSS-1 in its payload Retrieval operations begin with the reel and the tether were developed by the Martin bay to a circular orbit where the satellite will assembly winding in the tether. The satellite Marietta Astronautics Group in Denver, be deployed spaceward on a conducting approaches to within 2.4 km of the orbiter, Colorado, and the satellite by the Alenia tether. Thus begins an adventure that could where it stops for 5 hours to gather additional Space Systems Group in Turin, Italy. revolutionize the architecture of space struc- data and stabilize the system for final Both NASA and ASI are sponsoring tures and expand the PoSsibilities for space retrieval. Retrieval resumes and crewmembers experiments to address the goals of the TSS-I investigations. take manual control for final approach mission. Research guidelines specify that The deployed mission begins when a and docking. experiments study Tethered Satellite System crew member unlatche_s the satellite and the electrodynamics and plasma interactions. deployer boom extends. Then the satellite's The experiments selected are compatible with tether-aligned thrusters fire, gently lifting it the engineering objectives and yield comple- away from the boom and the Shuttle. At mentary data. a distance of 6 km fro_mthe Shuttle, other NASA's Marshall Space Flight Center, Huntsville, Alabama, is providing the overall management of the Tethered Satellite System project for NASA Headquarters. Johnson .... .÷_ Space Center, Houston, Texas, and Kennedy Space Center, Florida, are also integral parts

3 Regions of the Atmosphere

Earth'selectricallyneutralatmosphereis composedof fourprimary layers.The|owestlayer,lhe onewelivein onEarth'ssurface,Js knownasthetroposphereandextendsashighas16kmabove sealevel. Extendingfromabout16to 48 kmis thestratosphere. Ninety-ninepercentof theair intheatmosphereis locatedin these tworegions.Abovethe stratosphere,from48to 85 kmis the meso- sphere.Theuppermostlayeristhethermosphere,whichextendsto approximately1,000 km. Theupperthermosphereis alsocharacterizedbythe presenceof electricallychargedgases,orplasma.Thisregion,whichextends L

k k __ from85to approximatelyt,000 km, is alsoknownasthe ionosphere. Theboundariesof the ionospherevaryaccording1osolaractivity. Overlappingtheionosphereisthe magnetosphere,whichextends fromapproximatelyS_Oto 60,000kmonthes_e towardstheSun,and trailsoutmorethan300,000kmawayfromthe Sun.Themagneto- _:'_ "_ _ _ " -: "--_ 7 ..... sphereis theregionof spacesurroundingEarthinwhichthe geomag- neticfield playsa dominantroleinthe behaviorof chargedparticles. Layers of the Atmosphere TSS-1will allowscientiststostudya varietyofionosphericprocesses. Forexample,it will generatelarge-scaleelectricalcurrentloopsin theionosphere.Thesecurrentloopsmaybesimilarto currentsthat occurinthe polarregionsof theatmosphereassociatedwithauroras. Conductingtethersmayalsoprovidean alternatesourceof powerfor futurespacecraft.Thismissionwill helpquantifytheamountof elec- tricalpowerthatcanbeproducedbyconductingtethers. Thelowerregionofthe thermosphere,fromapproximately130to 180km, hasbeenverydifficulttoexplore.Satellitescannotorbilin thisregionbecausetheywouldrapidlyfallfromorbitandburnup fromatmosphericfriction.Balloonscannolreachthisaltitude,and soundingrocketspassthroughtheregiontooquicklytoobtainmore thana quickverticalprofileof a particularspot.WhileTSS-1will be deployedawayfromEarth,futuremissionscanbe deployeddown- ward.ThesefutureTetheredSatelliteSystemmissionscanspenddays atthesealtitudes,gatheringvaluabledatain a previouslyinacces- s_le regionofouratmosphere. Justasthebarmagnetproduces field!ines,so t#o does Earth. You can Visualiz_ thcse field lines by thinkin_'_f _e Earth as having a bar ma_n_runningfrom the North to S_h-poles.

, , . , ,_

Earth'sMagnetic Field and HowTSS-1Will ProducePower ...... I TSS-1makesuseof Earth'smagneticfieldandelectricallycharged-- ofa batterybeforea currentcan ionosphereto producea currentthroughthetetherforavariety flow.Inthe caseof TSS-1,the ofexperiments.Tounderstandsomeof thediscussionsaboutthe _ circuitmustbeclosedbythe mission,a basick_edge ofEarth'smagneticfield is helpful, - _-_ conductingionosphere.Theelec- tronscollectedbythesatellite All magneticobjectsproduceinvisiblelinesof force,extending = will flowthroughthe tethertothe betweenthe polesofthe object.Aneasywaytovisualizethisisto _-- orbiter,whereelectronaccelera- ...... spreadironfilingsona sheetof paperandplacea barmagnetunder torswill returnthemtothe iono- :...... the paper.Theironfilings-w_Farrangethemselvesaroundthe sphere.AtthealtitudeofTSS-1, _-_...... andalongthe magnetficfieldllnes. -_ currentsnormallycanonlyflow Inthesimplestterms,Earthcanbethoughtof asa dipole alongEarth'smagneticfield fii_ggfiet.Magneticfield linesradiatebetweenEarth'snorthandsouth lines.Asa result,regionsof _ magneticpoles,justastheydobetweenthepolesofa barma positiveandnegativecharge createdat theendsof thetether Chargedparticlesanda]-mosphericmoleculesbecometrappedon TSSPower Production ...... thesefi_eldI!nes(justastheTronfilingsare trapped),formingthe streamoutalongthe geomagnetic magnetosphere.Earth'sfield linesare notas symmetricalasthoseof _jeld lines.Thesearecalledfield-alignedcurrents.However,when thebarmagnet._l'heimpacto_e solarwindcausesthe compression the currentsreachthe loweranddenserpartof theionosphere, ofthelinesfacingsunward,whilethe fieldlinesfacingawayfrom .... _knownastheE-region,collisionsbetweenthe chargedandneutral theSunstreambackto formEarth'smagnetotail, particleswilleffectivelyscatterelectricchargesacrossthefield lines,formingwhatare knownascrossfieldcurrentbranches.These TheTetheredSatelliteSystemcanproducepowerbecausea high __,;.._ branchesplayan importantroleinTSS-1powerproductionbyallow- potentialisgeneratedacrossthe tetherasa resultof itsrapid,,o,u, acrossEarth'smagneticfield lines.Thiseffectis analogousto the --...... ingthe circuittobe closed. waypoweris genera[edbyan automobilealternator.Theelectric potentialattraclsfreee_ctrons to the satelliteasit passesthrough theIonosphericplasma.Fora current(aflowofchargedparticles)to ORIGfNAL ,_ A_.._ be produced,thecircuitmustbecompleted-- justasa wiremust closethe circuitbetweentwopoTes COLOR PHOTOGRAPH

5 Major Tethered Satellite System Elements

The TSS-1 hardware is short broadcasting tower. Like a

- Satellite mounted on two carriers in the bolt forced upward by a rotating payload bay. The deployer rides nut, the boom unfolds and

Dep4oyer on a Spacelab Enhanced extends slowly out of the turning Multiplexer Demultiplexer Pallet canister on rollers that follow SPREE t' : __ : Hardware Reel Mechanism (called an EMP), a general-pur- four tracks. As the canister pose unpressurized platform. The rotates, fiberglass battens, similar pallet provides both functional to ones that give strength to sails, and structural support to the are released from their stowed, deployer, and its enhanced fea- bent-in-half positions, to act as tures include temperature control, horizontal crossmembers to hold SETS Hardware power distribution, and command the longerons, or vertical mem- Satellite and data transmission capabilities. bers, erect. Diagonal tension Support The second carrier is the Multi- cables further strengthen the Core Equipment Purpose Equipment Support boom, and flat ribbon-like cables Structure, an inverted A-frame provide the connection for elec- Eq_pme_ Support Structure truss located immediately aft of trical functions at the boom tip. the enhanced pallet. This struc- During retrieval, the canister

The Tethered Satellite System The Tethered Satellite System ture holds deployer core equip- rotation is reversed. Tracks guide has five major components: ment and two of the mission's the rollers back, forcing the the deployer system, the tether, experiments. battens into their original bent the satellite, the carriers on which position, and the longerons fold the system is mounted, and the The Deployer System smoothly into the boom canister. science instruments. These spe- The deployer system includes the The tether reel mechanism, which cific elements are supported by satellite support structure, the controls the length, rate, and the standard capabilities of the deployment boom, the tether reel tension of the tether, is critical to Space Shuttle orbiter, payload bay mechanism, a system that dis- tether control. This assembly mounting equipment, and control tributes power to the satellite consists of the tether reel and the and command facilities on before deployment, and a data reel motor. It is controlled by the ground. acquisition and control assembly. Umbilical cables woven The TSS-I deployer system has through the deployment structure undergone many tests to ensure provide power and data lines to proper operations during the mission. the satellite before deployment. When the umbilicals are discon- nected after checkout, the satel- The Tethered Satellite System is lite operates on its internal seen here undergoing integration at the Kennedy Space Center. battery power. If the safety of the orbiter becomes a concern, the tether can be cut and the boom and satellite jettisoned. When fully extended, the boom is a 12-meter (m) four- sided framework resembling a

ORIGINAL PAGE COLOR PHOTOGRAPH 6 the motor control assembly and Manufactured for Martin-Marietta TSS-1 Tether Characteristics a data acquisition and control by the Cortland Cable Company Diameter (outer): 2.54 mm assembly. The reel mechanism of New York, the tether has a Deployed length: 20 km is capable of letting out the tether center of Nomex TM that is wrapped Breakstrength: 1,780 N at 16 km per hour; during the with copper wire which acts as Maximum allowable tension: 700 N TSS-1 mission, however, the the electrical conductor. The layer tether will be reeled out at a much of wire is insulated with Teflon", Maximum expected load: 53 N slower rate. which is then covered with braided Maximum allowable mass: 8.2 g/m Temperature range: -I00 to +125 °C Kevlar" 29 to give strength to the Electrical characteristics: The Tether tether. The outer jacket of the current (maximum) - 1 A at 10 kV The tether's length and electrical tether is braided Nomex" which dc resistance - 0.12 ohms/m properties affect all aspects of protects the tether against the nominal operating voltage - 5,000 Vdc tethered operations. With its corrosive effects of atomic oxygen Maximum expected operational current: 500 to 750 mA satellite fully deployed, the and mechanism-induced abrasion. TSS-1/orbiter combination is 100 times longer than any previ- Mission life." 1 mission ous spacecraft, and when the tether's current is pulsed by electron accelerators, it becomes 7 the longest and lowest frequency antenna ever placed in orbit. Also, for the first time, scientists can measure the charges collected by spacecraft with high electrical potentials. All these capabilities are directly related to the struc- ture of the shoe lace-thick tether, a conducting cord designed to anchor a satellite miles above the orbiter. The TSS-1 tether is 22-kin long and is expected to develop a 5,000 volt (V) potential and carry The different layers of the tether a current of up to 1ampere (A). can be seen in this photograph.

Deployer System Characteristics

• Deployer System Total mass: 2,027 kg Thermal control: 4 coldplates, Multi-Layer Insulation (MLI), thermal tent covering pallet Power."500 to 1,000 W (average); 1,500 W (peak) Data: 16 kbps (telemetry); 2 kbps (command) • Tether Reel Assembly Capacity: 22-km conducting tether; llO-km nonconducting tether • Boom Extended length: 12 m

ORIGINAL PAG-E The Deployer System COLOR PHOTOGRAPH The Satellite form the outer skin of the satel- housed in the Service Module, or The components of the Before it is deployed, the satellite lite. These panels contain the lower half. A pressurized tank Payload Module will change from mission to mission. For is located on a satellite support connectors for the umbilical containing gaseous nitrogen for structure where six latches hold it cables from the deployer; win- the cold gas thrusters is located in TSS-1, the module houses three in place. Once removed from this dows for Sun, Earth, and charged the center of the satellite. This experiments (Research on structure, the satellite rests on a particle sensors; and access doors tank, along with the various Electrodynamic Tether Effects, Research on Orbital Plasma Teflon'-coated docking ring at for installation or replacement of thrusters and associated plumb- the tip of the deployment boom. each satellite battery. At the base ing, form the Auxiliary Electrodynamics, and Magnetic A l-m fixed instrument boom of the satellite, a bayonet pin Propulsion Module. Separating Field Experiment for Tethered extends out of the satellite's skin attaches the tether to the satellite the science instruments and sup- Satellite System Missions), the at the equator; a short mast oppo- structure, and a connector routes port equipment into three mod- satellite core science equipment site the boom carries the S-band the tether conductor to an amme- ules that can be integrated into (a triaxial accelerometer and a antenna. For TSS-1, the satellite ter and then to the satellite's skin. the satellite independently allows current meter), and the deploy- will have two deployable/ The satellite is divided into the satellite to be refurbished, able/retrievable instrument retrievable instrument booms. two hemispheres: science instru- reconfigured, and readied for booms, which have a maximum Aluminum-alloy panels covered ments are located in the Payload subsequent flights. extension of 2.4 m. The experi- with electrically conductive paint Module, or upper half (opposite from the tether), and the support subsystems (power distribution, data handling, telemetry, and navigational equipment) are Satellite Characteristics for TSS-1

Diameter: 1.6 m Actual mass: 518 kg Payload mass: 68 kg Deployable booms: 2 Fixed boom length: I m Thermal control: white conductive paint on outer skin; black paint on internal skin; multilayer insulation blankets covering portions of the internal skin; heaters in payload and service modules and on batteries and sensors

The TSS-I satellite is seen here Propellant: cold gas nitrogen undergoing final checkout in Italy, Lifetime: at least 3 missions before being shipped to the U.S.

ORIGINAL PAGE COLOR PHOTOGRAPH

8 ment electronics are located on tank, pipes, valves, and mounting handling, attitude measurement the floor and internal side panels hardware, occupy the equatorial and control, telemetry and com- of the module. Experiment sen- floor of the satellite. A set of mand, thermal control, support sors are mounted on the deploy- thrusters near the tether attach- structures, and the tether attach- able/retrievable booms, the fixed ment can provide extra tension on ment are located at various points boom, and the surface of the the tether, while a set of thrusters on satellite shell sections and the Payload Module. around the equator can be used to internal panels, permitting easy The Auxiliary Propulsion reduce or eliminate pendulum- access to the components. Module, in conjunction with the type motions in the satellite. A Within the Service Module are tether reel and motor, controls the final set of thrusters, also on the the gyros, Sun sensors, and Earth motion of the tethered satellite. equator but directed off to one sensors that measure and control This module also initiates, main- side, will be used to spin and satellite attitude. Thermal control tains, and controls the satellite despin the satellite. is primarily passive, but there are spin at up to 0.7 rotations per The Service Module contains some active heaters. An S-band minute upon command from the all the satellite support subsys- antenna provides a communica- Shuttle. Most components, such tems, except the propulsion sys- tions link between the satellite as the spherical high-pressure gas tem. Power distribution, data and the orbiter.

O

In this photograph of the payload module, it is possible to see the internal structure, wiring, and the electronics packages for various experiments.

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This photograph of the service module shows some of the sensors and instruments located in this half of the satellite. It also shows the tank and piping for the auxil- iary propulsion system, the tether attachment point, and in-line An exploded view of the TSS satellite thrusters (upper left). Or_'_lt_',,"_LDlr, ' ! ,_ PACE COLOR PHOTO_RAI.:'_ 9 Tether Dynamics

While space-based tethers have been studied theoretically since early in the century and later modeled extensively on comput- ers, the TSS-I investigations of electrical generation and plasma physics in the upper atmosphere will be the first time such a large, \ \ electrodynamic tethered system \ has ever been flown. In many respects, this mission is like the \ first test flight of a new airplane: the lessons learned will improve both scientific theory and future operations on tether missions. The use of tethers in space is not new, but the applications have been extremely limited. The application most people remem- ber are the tethers that connected spacewalking astronauts to their spacecraft; these were used until the advent of the Manned Maneuvering Units used on the Shuttle. These applications, however, used very short tethers that were not stabilized by gravi- tational forces and, therefore, have little relation to the Tethered

10 SatelliteSystem.TheTSS-1 significantly increases the dis- ...... experience libration, or back missionwillbeusinga20-km tance around it. As a result, a ...... and forth movement of the tether. longtetherthatwillbestabilized higher satellite will move at a If the satellite were stopped bygravitationalforces.Since slightly higher speed but will take suddenly, the gravity gradient thedynamicsoftheTethered longer to travel around its orbit ..... Would bring the tether back to SatelliteSystemarecomplexand than a satellite below it. If the the vertical orientation. canonlybetestedfullyinorbit,it two satellites are tied together - However, the tether would over- isimpossibletopredictbeforethe with a tether, they will be forced shoot and go out in the forward missionexactlyhowthesystem to travel at a higher speed than ...... direction, and then come back willact.Whilethedynamicshave required for its orbit and, there- ...... again. The satellite would be beenextensivelytestedandsimu- fore, its centrifugal force will be ...... moving in much the same back- lated,it ispossiblethattheactual greater than the pull of gravity. If ...... and-forth movement as a pendu- dynamicswillbesomewhat the tether were cut, it would lure in a clock but without the differentfrompredictions.In move to a higher orbit where the friction needed to stop the additiontothenormalmechani- two forces would, again, be in -motion. Indeed, to dampen this caldynamicstherearealsothe balance. With the tether in place_..... pendulous motion, or libration, complexitiesofawidelysepa- however, the net effect of the ...... would require much more time rated,multi-componentsystem unbalanced forces is to create than a typical Shuttle mission. andtheforcescreatedbytheflow tension in the tether. This is the Libration will be controlled of current through the system. force that causes the Tethered ...... -i_y varying the speed at which Satellite System satellite to rise the tether is reeled. By avoiding Deployment above the orbiter as the tether is ...... :'sudden stops and decreasing the A satellite is maintained in its reeled out. Very close to the .... reel-rate slowly, the rate at which orbit around Earth by a balance orbiter, there is little difference ifi...... the gravity gradient brings the between the force of gravity, the two orbits and the tension ..... tether closer to the vertical is also which pulls it toward Earth, and a force is insufficient to overcome ..... Slowed. If the motion is slowed centrifugal force, which pushes it friction in the deployer mecha- just right, the tether will come to away from Earth. The centrifugal nism. Therefore, until the satellite a halt in a stable, vertical posi- force results from the motion of reaches a separation of approxi- tion, with no residual libration. the satellite around its circular mately 1,000 m, the tension is -- orbit. This is the same force that augmented by small tether-aligned ...... one can experience by swinging a thrusters on the satellite. Beyond ball around on the end of a string. this point, the tension in the At the orbital altitude for tether is the only force required. TSS-1, a speed of approximately But deployment of the satel- 7.6 km per second is required to lite is not quite as smooth as it create sufficient centrifugal force might seem. While the process is ...... to balance gravitational attraction. inherently stable, the system can ...... If the altitude is changed, how- ever, the two opposing forces will no longer be in balance unless the Shuttle's speed is also changed. Going higher requires a slightly greater speed, although it will take longer to complete an orbit because increasing the altitude makes the orbit a larger circle and \ ,

Libration

11 Tether Oscillations Many different factors may Retrieval By experimenting with a ball cause oscillations; the movements While deployment is an inher- hung on a piece of elastic cord of the satellite or Shuttle are but ently stable process, retrieval of (a paddle ball, for example) two of these. On TSS-1, one the tethered satellite is inherently it is possible to simulate all the potential cause of oscillation will unstable. As it comes toward the different types of oscillation that be of particular interest. As the Shuttle, the satellite is also mov- are possible on a space-based system produces an electrical ing towards Earth's axis of rota- tether system. The elastic cord, current, it also produces a mag- tion and so moves "east" or \ representing the tether, may netic field around the tether. This ahead of the orbiter. Any libration compress and stretch causing magnetic field will interact with produced by this movement will Oscillation the ball to bounce up and down Earth's magnetic field resulting tend to grow as the satellite and Longitudinal (referred to as longitudinal oscil- in a force expected to produce orbiter get closer to each other, lation). It may also develop skiprope oscillations. because of the conservation of wave-like motions (transverse Because it is necessary to angular momentum. oscillation), or even move in a maintain control of the satellite, Retrieval will, therefore, be circular, or "skiprope" motion. much study has gone into identi- very carefully controlled. The Even if the string itself is not fying the different types of possi- retrieval rate is programmed into moving much, it is possible to ble motions and methods to the deployer system computer to get the ball rocking back and control them. Dynamicists hope keep the libration angle under forth about its attachment point to observe all these types of control. The gravity gradient will (pendulous motion). oscillations during TSS-1 to see be used to keep the tether taut Each type of motion occurs how real-world tether behavior until the satellite is approximately with a particular frequency, which compares to the mathematical 200 m from the orbiter, when the depends on the length and tension simulations done over many satellite's thrusters will be turned of the tether. When the frequen- years. This will increase the on. At this point, the crew will "Sklprope" '_ _ / cies are different, the motions do knowledge and understanding take manual control of the last

1 / not interact. However, at some of tethered systems. stages of retrieval. Then, using tether lengths, the frequencies of the tether reel rate, satellite two or more types of oscillation thrusters, and movement of the can become very close. At this orbiter itself, the crew will point, energy can be transferred keep the satellite lined up as it from one type of motion to is returned to its docking ring on another, a phenomenon known the deployer. as resonance. For instance, the transverse oscillations in the tether may cause the satellite to rock back and forth in pendulous motion. Trans

Oscillation

Pendulous Motion ORfGINAL PAGE COL_#, PHOTOGP-.APH t2 -z ii ii!!i _i!!i_I

_ . The-Conservationof AngularMomentum

:- - Many ollhe dynamics theories affecting, or-Se[ngi-e-st-e-don, TSS--1 arequite complex. While theconservation of angular momentqgLmay seem_.'om_plex,_ilTs quffe easy to visualize_

Take__a-b_l|attached to the endofa_s|r[n0...... and move it in a steady m_and lorth, like a pendulum. Once a steady swing has :...... been:es_blis_, take the thumb and forefinger of your other hand !. _ and make a circle aroundthe top of the string. This will not interfere :_ ...... _.... wilh_wing, so no changewill be noticed. i ...... - - - " Whil_ keepingyour swing steady, slowly begin to raise the hand_ _;_-;...... _-_ ...... ;_ :..:i__. _._ .....hoid[ng_Se string. As your handgoes higher, the string begins_L]lit :_i_...... _--_- .- _: ._-__-__.. tS_he circle made byyou fingers. As this happensthe frequen_of the balls movementincreases. The shorter the string, ...... thefasTer_e ball travels and the further from the vertical it tries_to ..... go. Asyou IoweY_hestring backdown, the ball will eventually _re_turn - to its original motion.

...... _ _ _ The_ forJhls is that th_ene,,gyin the system remains the _ same. As-the length of the stringgrows shorter, the same amonnt of ene_is preenS. This producesa longer and faster arc.

O__!_JNAL PA_

13

i _tlllliil_'_!_' TSS-1 Science Background

The TSS-1 mission will study the required to characterize this electrodynamic properties of a environment and Tethered tethered satellite system and its Satellite System perturbations interaction with Earth's iono- accurately and completely. The spheric environment of charged TSS-1 science investigations are gas and magnetic and electric interdependent; they must share fields. These studies will help information to achieve their demonstrate the Tethered Satellite objectives. In fact, these investi- System's capabilities as a gations may be considered to be research facility for investiga- different parts of a single com- tions in electrodynamics and plex experiment. space plasma physics. Most of The motion of the Tethered the TSS- 1 experiments require Satellite System through Earth's essentially the same set of mea- magnetic field generates a volt- surements, with instrumentation age across the conductive tether. from each investigation providing As a result, it is able to extract an different parts of the total set. electrical current from the iono- While some instruments measure spheric plasma at the satellite and magnetic fields, others record emit that current by means of particle energies and spectra, electron accelerators in the pay- and others map electric fields. load bay. Investigators will use A complete set of data on the the ability to vary this current and plasma and field conditions is control the electrical potential of the satellite to create and study a variety of phenomena and pro- To prepare for the mission, numer- cesses. These include electric ous tests using scale models of power generation, wave genera- the TSS satellite, such as this one tion and propagation, neutral gas in the Frascati (Italy) Plasma Chamber, were conducted to test ionization, and basic physical instruments, paints, and materials. processes that occur naturally in plasmas surrounding Earth and other planets, moons, and comets. Although some of these phenom- ena have been studied in labora- tories, very small scale-size, chamber wall effects, unnatural plasma distributions, and other problems hamper the ground- based experimenter. For the Tethered Satellite System, Earth's ionosphere is a vast, unbounded laboratory for space plasma experiments that can be con- ducted in no other way.

The spiral path of an electron beam around magnetic field lines can be seen clearly in this photo- graph taken in a plasma research chamber. ORIGrNAL PAGE CI:]I_R PHOTOGRAPH 14 / /

_-_ Lightning is a commonly 1 seen form ofplasma.

TheFourthStateof Matter-

_re-a-re threeclassi_statesof matter:solid,liquidandgas.Then, Piasm_is foundbothin ordinaryandexoticplaces.Whenan electric splasma,which_me scientistsconsiderto hethefourth curren|is passedlhroughneongas,it producesbothplasmaand tt-er_1'beplasmastateof matteris notrelatedto blood __. Li-ght_ng_rlcal discil-a-rgeintheatmosphere _'- _asma, themostcommonusageoftheword.Rather,theterm thatcreatesa jaggedcolumnof ionizedair, orplasma.Partofa plasmahasbeenusedinphysicssincethe1920sto representan _met's streamingtail is plasmafromgasionizedbysunlightand ionizedoas,andspaceplasmaphysicsbecamean importantscien- otherunknownprecesse-s.TheSunis a 1.5-million-kilometerball of nl-'T'_[_r_pline in theearly1950swiththe discoveryoftheVanAllen plasma,heatedby nuclearfusion. --: radiationbelts. _-...... _ Scientistsstudyplasmaforpracticalpurposes.Inan effortto har- "---:_-Matter changesstateas it is exposedto differentphysicalcondi- n_s fusionenergyhereonEarth,physicistsare studyingdevices -- tions.Ice is a solidwjthhydrogen(H) andoxygen(0) molecules that cre-aieandconfineveryhotplasmasin magneticfields.In _arra_ge--d-in regula_patterns,butif theice melts,the H2Oentersa space, plasmaprocessesare largelyresponsibleforshieldingEarth news_E_e!liquidwater.Asthewatermoleculesarewarmedmore, fromcosmicradiation,andmuchoftheSun'sinfluenceonEarth eccursbyenergy_oug_l the ionizedlayersof theupper a_osphere. _____ o!all|lle-electronsorbitingaroundit sothatthe netchargeis zero. _tom ISelec|ficallyneutral. The Sun, seen here in a Solar Max _enough energyto escapeits atom. "_is atomis e one image of the corona, is a plasma heated by nuclear fusion. an ion. In-asufficJent!y_eaeI gas, onza;ion appensmany __------ereaUngErowdsoffreee ecrons ogeL:erwl ons. owever,not ---_ all theatomsare necessarilyionized;somemayremaincompletely __ Intactwithnonet_ _s_onzzedgasmnxture', ions,electrons, plasnlainciuJd-eselec[ronsandiOhS_,_selectri_ _, it Is macio-scopicallyneutral:in measurablequantitiesthe ---- nt ionsare ever

particlesareaffectedbyelectricandmagnelicTie_dsappliedto m th-eplasma, andthemotionsoftheparticlesinthe plasmagenerate fieldsandelectriccurrentsfromw_tthin.Thiscomplexsetof m interactionsmakesplasmaaunlque, of matter.

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# particles per cc, while neutral gas density at Earth's surface is approximately 100 billion billion particles per cc. Never the less, the ionosphere effectively reflects most radio waves back to Earth, and it is this process that led to its discovery. With the advent of man-made satellites, it became possible to measure the characteristics of the space environment near Earth directly -- and it was discovered that Earth's ionized atmosphere extends much higher than originally thought. The region between the ionospheric E-layer _ (approximately 140 km) and the boundary between Earth's mag- netic field and interplanetary magnetic fields (approximately 64,000 km on the sunward side), known as the magnetopause, contains minute quantities of Earth's Magnetosphere. The Plasma Universe through ground-based radio wave Earth's ionized atmosphere. The More than 99 percent of matter observations: a region of plasma behavior of the gas in this region in the Universe exists in the that exists above Earth's electri- is controlled by the geomagnetic plasma state -- that is, as a mix- cally neutral atmosphere. Plasma field, and the region is, therefore, ture of ionized and neutral gases. begins to dominate Earth's envi- referred to as the magnetosphere. Although nature rarely produces ronment in the ionosphere, which On the night side of Earth, the plasma on Earth's surface, it is extends upwards from about 85 km magnetopause trails away from common elsewhere. The electri- above the ground. The ionosphere the Sun forming the magnetotail, cally neutral environment to has distinctive layers that differ which has been found to extend which we are accustomed is a in composition and density: the more than 384,000 km, the dis- rare exception. Plasma processes F1 layer (around 200 km) and tance from Earth to the moon, are important factors in the F2 layer (around 300 to 400 kin). forming a shape similar to a behavior of stars, interstellar The plasma in these layers, comet's tail. clouds, comets, the aurora, and consisting mainly of electrons even in our upper atmosphere. and atomic oxygen ions, is sus- Our understanding of astrophysi- tained by the ionizing action of cal and many geophysical phe- solar ultraviolet radiation on the nomena depends on our neutral atmospheric gas. All knowledge of how matter ionospheric layers tend to merge behaves in the plasma state. at night. Even before the space era, an Ionospheric plasma is very unexpected discovery was made tenuous. In the F2 layer, where the plasma is the most dense, there are rarely more than 1 million electron-ion pairs in a cubic centimeter (cc), or thimble- ful, of space. In comparison, the neutral gas density for the same region is typically l billion ORIGINAL PAGE COLOR PHOTOGRAPH 18 Plasma is strongly influenced system, and accelerate some By characterizing the mag- In addition to natural varia- by magnetic and electric forces, electrons and ions to higher netic and plasma environments tions, the Shuttle alters the space and in turn, plasma particles energies. in our own neighborhood, we are plasma when it dumps water, affect the distribution of magnetic The visible manifestation of able to recognize and understand fires thrusters, or changes atti- and electric fields. Beyond the the high-energy electrons are plasma processes in the rest of tudes. In fact, some scientists magnetopause, energetic plasma seen in the aurora, the colorful the Universe. Already, auroras have compared the Shuttle to a from the Sun, called the solar Northern and Southern Lights have been spotted on Jupiter, comet enclosed by a halo of wind, rushes past Earth at speeds that appear at 90 to 160 km above and the same types of phenomena water vapor and other ions that ranging from 300- to 1,000-km Earth. The auroral colors are appear to occur in the magneto- interact with the natural plasma. per second. While most of this determined by the nature of the spheres of Saturn and Uranus. The environment near the Shuttle solar wind goes around Earth, atoms that are struck by magneto- Many high-energy X-rays will be thoroughly characterized some of it penetrates the magne- spheric electrons and the energies and gamma rays detected by before, during, and after the tosphere. The interaction between of the collisions: the night sky is astronomical observations come satellite is deployed. In this way, the solar wind and the magneto- painted with the reds and greens from magnetized plasmas near investigators can separate natural spheric plasma acts like an elec- of oxygen and hydrogen and the stars, galaxies, and other objects. variations and disturbances tric generator [called the magneto- purples and pinks of nitrogen. A visual image of our Universe caused by the Shuttle from inter- spheric MagnetoHydroDynamic A typical 3-hour aurora, covering reveals only the superficial actions between the Tethered (MHD) generator], creating a million square kilometers, appearances, but plasma studies Satellite System and the plasma. electric fields deep inside the discharges approximately 100 will show us the invisible struc- While the Shuttle and tether magnetopause. These fields in million kilowatt hours of electric ture of space and the processes are monitored by instruments in turn give rise to a general circula- energy into Earth's immediate that may have formed the solar the payload bay, instruments on tion of the plasma, or a current environment, system from dust and plasma. the satellite simultaneously mea- sure the space plasma and fields Mission Science around the satellite. The physical Objectives processes in the region around One of the most important TSS- 1 the satellite determine how many science objectives is to measure particles it collects and, hence, the plasma and field environment the magnitude of the current in of the electrodynamic tether the tether. system. These measurements will be obtained over a wide range of conditions, since the ionospheric density varies naturally along an orbit from day to night and with the inclination of the geomag- netic field, causing the voltage across the tether to change by a factor of two or more during a complete orbit. This results in increases and decreases in the maximum current the Tethered Satellite System can collect.

Colorful auroral displays, such as this view of the Aurora Austrialis photographed from the Shuttle, are the result of collisions between electrons and magnetospheric plasma. A typical 3-hour display can discharge I00 million kilowatt hours of electric energy into Earth's ORiG!NAL PAGE immediate environment. COLOR PHOTOGRAPH 'lid The ideal goal for each experi- of this type is largely unknown, near the satellite. For example, ages will expel ions, ionize neu- ment would be to cover all ranges and its effects on the current the character of the satellite's tral particles, and possibly gener- of electromotive force and flowing to the satellite and on the plasma sheath and wake will be ate instabilities in the plasma near plasma conditions experienced ambient neutral and charged affected, and the type and ampli- the satellite. In the majority of by the Tethered Satellite System particJes are uncertain. tude of waves excited may TSS-] operations, the satellite during both the day and night As the electrons accelerated change. These changes can in will vary from electrically neutral portions of an orbit at all tether by the electrically biased satellite turn affect the current and voltage to positively charged. Wake- lengths. Since TSS-1 is the test collide with the neutral particles of the tether. filling processes are of interest flight of a new, reusable system, in the vicinity of the satellite, In addition to mapping the because they can affect the tether most measurements during the some of these particles may be sheath and wake, investigators current and voltage and because mission will be made at a single ionized, releasing more electrons will attempt to change the the same processes affect the tether deployment distance. that will then be attracted to the sheath's structure and study the environments, and, therefore, positive surface of the satellite resulting processes. Laboratory the measurements made from all Wakes and Sheaths and may add significantly to the investigations have shown that spacecraft. These processes may Some special features are likely current collected by the tether the satellite potential can be set also occur in the environments of to develop in the vicinity of the system. This process should be to determine the dominant mech- some natural celestial bodies -- satellite as it actively perturbs the enhanced when the satellite anism involved in the plasma such as the Moon or asteroids. space plasma. Traveling at high thrusters release more neutral sheath and the near- and mid- speed (around 27,200 km per gas, which can become ionized in wake regions. For example, if the Antennas and Waves hour), the satellite affects the the sheath. satellite is maintained at a few Waves are large-scale coordi- density, temperature, and electri- The plasma sheath around the tens of volts negative, a plasma nated disturbances. While the cal properties of the surrounding satellite is predicted to be unsta- sheath will exist, and the electric medium in which a wave travels plasma. A plasma sheath contain- ble and to change in size and field within the sheath will focus does not necessarily move as a ing an electric field develops shape with variations in iono- ions into the wake. If the satellite whole in the direction of the around the satellite, while a spheric density, magnetic field is maintained at the ambient wave, the wave creates small- wake, in some respects resem- alignment, and the voltage devel- plasma potential, however, no scale motion in the medium. bling the wake left by a boat in oped across the tether. As the plasma sheath develops and the This motion varies with the type water, trails behind. sheath changes, it may produce plasma rapidly expands from of wave: a wave on the surface of Sizable voltage drops are instabilities in the plasma that denser regions to fill the void. a lake moves molecules in small predicted to occur across the result in an unsteady tether cur- If the satellite is maintained a few circles, and sound waves move plasma sheath surrounding the rent and voltage. Electron heating tens of volts positive, it will repel air molecules back and forth. positively biased satellite. The in the sheath would also affect the ambient ions while attracting' Just as a water wave lifts swim- physics of a high-voltage sheath the plasma processes taking place electrons. Higher positive volt- mers up and sets them down as it passes, plasma waves can shift a net electrical charge in a plasma from one ionospheric region to another. _ff: • : - ,(\!.,,,./. ;...... :=::...... \/ -\ Waves of every kind carry energy and momentum obtained from their source, which may be transferred to objects they impact: ocean waves transform the shore, sound waves crack Wo/er glass, and electromagnetic (infrared and ultraviolet) waves heat Earth. Similarly, plasma and electromagnetic waves transfer _d,o energy between electrons, ions, and neutral particles. Scientists

= _!_,_,:_ii_ ¸ are very interested in how energy : ;i' i,'*_:;V!iil is exchanged between iono- spheric and atmospheric layers, and waves (and wave- particle

20 interactions) are partially respon- The TSS-1 tether will be the system that may be generated in layers by measuring electrons sible for this transfer. longest antenna ever placed in the ionosphere by the Tethered beamed from below the satellite One TSS-1 goal is to study orbit. It can either be used pas- Satellite System. and energetic ions created by the how waves are generated natu- sively, for receiving radio waves When the field-aligned collapse of double layers near rally in the ionosphere. The iono- from other sources, or actively, branches of the auroral currents the satellite. sphere supports a variety of as a transmitting antenna. To exceed the capacity of the plasma plasma waves from many sources, transmit, the current passing to carry a charge, a drop in elec- Simulating Phenomena including whistle-like noises through the tether may be modu- trical potential occurs. This may of the Plasma Universe triggered by magnetic storms and lated by pulsing it on and off at take the form of electric double Immersed in the ionospheric lightning, which can be heard on the required frequency. The layers -- plasma structures in plasma, the Tethered Satellite a radio. In a plasma, the particles longer the tether, the lower the which two layers of excess elec- System will allow scientists to vibrate and oscillate in unison, frequency at which it can radiate tric charge, one positive and the study many space plasma phe- and the plasma waves, when waves efficiently. This unique other negative -- exist in close nomena first hand. The electrody- converted to sound by a radio ability to produce low-frequency proximity. Between the two, there namics of the satellite system receiver, form a symphony of waves makes a number of active is an electric field that can accel- involve a number of phenomena, sound. TSS-1 instruments on the experiments possible. erate charged particles. Plasma such as wakes, sheaths, and satellite and in the payload bay theory and laboratory experi- currents, that will be carefully can measure the generation and Currents in Space ments have shown that double studied throughout the mission. propagation of naturally occur- Currents are created in the polar layers can form when currents are Once the basic phenomena of the ring plasma waves. regions of the magnetosphere driven along magnetic fields in a Tethered Satellite System are A plasma may also emit and by the magnetospheric plasma. There is some evidence characterized, some experimental absorb light, radio, and other MagnetoHydroDynamic genera- that weak double layers exist parameters, such as satellite electromagnetic waves created tor. The generator is driven by naturally in the ionosphere, but potential and tether current, can by shifting electric and magnetic the motion of the plasma at the because they are so thin, they be varied to model important fields. Radio signals of the right boundary of the magnetosphere. are difficult, if not impossible, to basic processes that occur natu- frequency are able to pass through These auroral current systems observe directly. Their effects on rally in our magnetosphere, solar the ionosphere and travel up into are aligned with Earth's magnetic charged particle distributions can system, and beyond. the magnetosphere, where they field in the magnetosphere but be measured, however, and Because of the difficulty, grow and trigger a noisy chorus have cross-field branches in the Tethered Satellite System instru- expense, and time required to of signals at different frequencies. lower ionosphere. This is very ments should be able to detect the send probes to other parts of the By injecting known amounts of similar to the type of current presence and motion of double solar system, scientists want to radio waves into the space plasma, scientists can study the composi- A tethered satellite research facil- tion, distribution, and motion of ity can be used to duplicate elec- trodynamic phenomena observed the plasma. Since the speed and elsewhere, such as the interaction pattern of waves are influenced of Jupiter and Io, the small orange by the medium in which they moon in the upper left. travel, the way in which the iono- sphere affects radio wave propa- gation can tell us much about the ionospheric plasma.

ORIGINAL PAGE COLOR PHOTOGRAPH field lines between Io and Jupiter core, they became ionized and into the lower Jovian ionosphere. subject to the effects of the core's The current that will be magnetic field. Alfv6n hypothe- created by the tether's motion sized that when the falling neutral through Earth's ionosphere is gas reached a certain "critical" predicted by some scientists to velocity, massive ionization be similar to the current system occurred, and the gas was generated by the motion of Io. trapped, suspended in space some In this scaled-down model of the distance from the core by its Jovian system, the Tethered magnetic field. This velocity Satellite System serves as the was assumed to be related to the conducting moon, and Earth with energy required to ionize the gas. its ionosphere and magnetic fields Since the energy required to mimics Jupiter. Parameters to be ionize different elements varies, measured include field-aligned clouds of gases would become currents, turbulence, radio fre- trapped at various distances from TSS-I may help scientists better understand both the processes occurring quency emissions, and wave- the evolving Sun based on the in comets as they travel and how they were formed. particle interactions. composition of the cloud. The ionized particles were concen- Comets model plasma environments Jupiter and Io trated in the plane of the solar around other celestial objects Scientists have detected intense, Comets are essentially balls of ice equator, eventually coalescing accurately. Observations to date naturally occurring, radio- and dust that streak through the into planetary bodies. reveal that plasma may interact frequency emissions from Jupiter. solar system. When they approach Scientists, therefore, want to with the surface of a body These emissions may last more the Sun, the intense radiation study how a high-speed cloud of (the Moon or artificial satellites), than an hour at a time and consist converts some of the ice to gas neutral gas interacts with a mag- with the gaseous atmosphere of of bursts of extremely intense l- which ionizes very rapidly -- netized plasma. The motion of the object (comets or Venus), or to 2-second pulses. The radiated apparently as a result of several the Tethered Satellite System with the intrinsic magnetic field energy from a single pulse may processes. The solar wind and the through the geomagnetic field of the body (Earth or Jupiter). be as great as 100 thousand mil- interplanetary magnetic field offers this opportunity. It provides These interactions affect both the lion joules, the equivalent of the force the ionized gas to stream the essential ability to control space plasma and the electrody- energy released from 25 tons of behind the comet, forming the spacecraft potential, combined namic characteristics of the body. dynamite. familiar cometary tail. It is with the ability to release con- Shock waves occur in front of These emissions have been thought that one of the ionization trolled amounts of neutral gas from the satellite thrusters. planets, waves are generated and correlated with the motion of processes results from the rapid interact with charged particles, Jupiter's moon, Io. Unlike Earth's motion of the neutral cometary In particular, the system can be used to establish the conditions and wakes and sheaths may form. moon, Io orbits deep inside the gas through the interplanetary Not enough on-site data has been Jovian magnetosphere, where it medium. This ionization mecha- necessary for the ignition of collected to understand these moves at hypersonic speeds nism is known as "critical veloc- critical velocity ionization. Local measurements can be made to processes fully, and laboratories through the magnetic field and ity ionization." are not large enough to model the magnetospheric plasma. Volcanic This effect, hypothesized by study the creation and growth of vast size of the processes created activity on Io ejects gases, form- Nobel Prize winning Swedish plasma instabilities, the heating by the movement of planets ing an atmosphere, which is plasma physicist Hannes Alfv6n of electrons, the conditions at through space. The Tethered ionized to form a region similar to and subsequently observed in which critical velocity ionization Satellite System, however, may Earth's ionosphere. As Io sweeps laboratories, may explain the becomes self-sustaining in space, and its effect on the ambient bridge the gap between these two through the Jovian magnetic field, rapid ionization in comets and extremes, allowing scientists to a potential of approximately may also help explain how ionospheric medium. investigate actively such large- 400,000 volts is created across its comets and planets formed in scale plasma phenomena. conducting atmosphere, and the solar system. According to massive currents on the order of Alfv6n's theory, the gravitational 5 million amperes flow along the field of the ionized core of a primordial dust cloud attracted the surrounding dust and gas, and as the atoms fell toward the ORIQ_NA!. PAGE 22 COLOR Pi-.I,OTOGRAPH TSS-1 Science Investigations

TSS-1 is comprised of 12 investigations. Seven investigations address Research on Orbital Plasma Electrodynamics the science goals of the TSS- 1 mission, using equipment that either (ROPE) stimulates or monitors the tether system and its environment. Two Noble Stone, Principal Investigator investigators will use ground-based instruments to measure electro- NASA Marshall Space Flight Center

magnetic emissions from the Tethered Satellite System as it passes I This investigation is designed to study the behavior of the ambient overhead, and three investigators were selected to provide theoretical B ionospheric charged particle populations and of ionized neutral support in the areas of dynamics and electrodynamics. particles around the TSS-1 satellite under a variety of conditions. Since [] Indicates instrument(s) located in orbiter the collection of free electrons from the surrounding plasma produces [] Indicates instrument(s) located on ground current in the tether, knowledge of the behavior of charged particles is I Indicates instrument(s) located on deployer essential to understanding the physics of tether current production. Indicates instrument(s) located on satellite From its location on the l-m fixed boom, the Differential Ion Flux Probe measures the energy, temperature, density, and direction of ambient ions TSS Deployer Core Equipment and Satellite Core that flow around the satellite and neutral panicles that have been ionized Equipment (DCORE/SCORE} in the satellite's plasma sheath and accelerated radially outward. In this Carlo Bonifazi, Principal Investigator instrument, an electrostatic deflection system, which determines the Agenzia Spaziale Italiana charged panicle direction of motion over a range of 100 degrees, routes The Tethered Satellite System Core Equipment will demonstrate the particles to a retarding potential analyzer, which determines the energy of capability of a tether system to produce electrical energy and allow stud- the ion stream, measuring particle energies from 0- to 100-electronvolts ies to be made of the electrodynamic interaction with the ionosphere. It (eV). The directional discrimination of the Differential Ion Flux Probe does this by controlling the current flowing through the tether between will allow scientists to differentiate between the ionospheric ions flowing the satellite and the orbiter, and by making a number of basic electrical around the satellite from ions that are created in the satellite's plasma and physical measurements of the Tethered Satellite System. sheath and accelerated outward by the sheath's electric field.

B Deployer Core Equipment consists of several instruments and The Soft Particle Energy Spectrometer instrument is a collection of five sensors on a pallet aft of the deployer in the cargo bay. A master electrostatic analyzers that measure electron and ion energies from 1- to switch connects the tether conductor to science equipment in the orbiter; 10,000-eV. Three analyzer modules provide measurements at different a power distribution and electronic control unit provides basic power, locations on the surface of the satellite's hemispherical payload module. command, and data interfaces for all deployer core equipment except the These sensors determine the potential of the satellite and the distribution master switch; and of charged panicles flowing to its surface. Two other Soft Panicle Energy a volt meter measures the tether potential with respect to the orbiter Spectrometer sensors, mounted with the Differential Ion Flux Probe on structure. The Core Electron accelerator has two electron beam emitters the end of the boom, measure ions and electrons flowing both inward and that can eject up to 500 milliamperes of current from the system. Two outward from the satellite. These measurements can be used to calculate other instruments complement the electron accelerator's operations: a the local potential of the plasma sheath. vacuum gauge to measure ambient gas pressure and prevent operation if The sensor package on the boom is electrically isolated from the satellite pressure conditions might cause arcing and a device to electrically con- and its potential is controlled by the floating power supply. For satellite nect either generator head to the tether. potentials up to 500 volts, the sensor package will be maintained near the Satellite Core Equipment consists of a linear three-axis accelerom- local plasma potential to allow unambiguous measurements to be eter and an ammeter. The accelerometer (along with the satellite's obtained. The potential of the sensor package can also be swept, allowing gyroscope) will measure satellite dynamics, while the ammeter will the package itself to serve as a diagnostic probe. provide a slow sampling monitor of the current collected on the skin of the TSS-I satellite.

The DCORE The ROPE equipment can experiment be seen in the two will gather boxes below and data around to the right of the the TSS-I satellite in this satellite simi- photograph taken lar to these during payload spectrograms integration at the obtained Kennedy Space during a Center. previous space plasma experiment.

0,,, _,,.-d. P/_.GE 23 COLOR PHOTOGR/_H TSS-I Science Investigations

Research on Electrodynamic Tether Effects Magnetic Field Experiment for TSS Missions (RETE) (TEMAG) Marino Dobrowolny, Principal Investigator Franco Mariani, Principal Investigator Consiglio Nazionale delle Ricerche/Instituto Fisica Spazio Second University of Rome Interplanetario The primary goal of this investigation is to map the magnetic I The behavior of electrostatic waves and plasma in the region fields around the satellite. If the magnetic disturbances produced B around a tethered satellite affects the ability of that satellite to by satellite interference, attitude changes, and the tether current can be collect ions or electrons and, consequently, the ability of the tether to removed from measurements of the ambient magnetic fields, then the conduct an electric current. This investigation provides a profile of the Tethered Satellite System will prove an appropriate tool for magnetic electrical potential in the plasma sheath and identifies waves excited by field studies. this potential in the region around the satellite. Probes, placed directly Two triaxial fluxgate magnetometers, very accurate devices designed to into the plasma in the vicinity of the satellite, map alternating (ac) and measure magnetic field fluctuations, are located on the fixed boom. One direct current (dc) electric and ac magnetic fields produced as the current sensor at the tip of the boom and another at midboom characterize iono- in the tether is changed by instabilities in the plasma sheath or as the spheric conditions at two distances from the satellite, determining the Fast-Pulse Electron accelerator or Core Electron accelerator are fired in magnetic signature produced as the satellite moves rapidly through the the payload bay. ionosphere. Combining measurements from the two magnetometers The instruments are mounted in two canisters at the end of a pair of allows realtime estimates to be made of the magnetic fields produced by 2.4-m extendible booms. As the satellite spins, the booms are extended the presence of satellite batteries, power systems, gyros, motors, relays, and sensors measure electric and magnetic fields, particle density, and and permanent magnets. The environment at the tip of the boom should temperature at various angles and distances in the equatorial plane of the be less affected by the spacecraft subsystems. After the mission, the satellite. To produce a profile of the plasma sheath, measurements of variable effects of switching satellite subsystems on and off, of thruster dc potential and electron characteristics are made both while the boom is firings, and of other operations that introduce magnetic disturbances will fully extended and as it is being extended or retracted. The same mea- be modeled on the ground in an attempt to remove these spurious signals surements, taken at only one distance from the spinning satellite, produce from the data. a map of the angular structure of the sheath. The two magnetometers will make magnetic field vector readings One boom carries a wave sensor canister, which contains a three-axis 16 times per second to obtain the geographic and temporal resolution alternating current electric field meter and a two-axis search coil ac needed to locate short-lived or thin magnetic structures, and twice per magnetometer to identify electric fields and electrostatic waves and second to allow discrimination between satellite-induced magnetic noise, characterize the intensity of surrounding magnetic fields. Highly sensi- the magnetic signals produced by the tether current, and the ambient tive radio receivers and electric field preamplifiers within the canister environment. The magnetometers will alternate these rates: while the one complement the operations of the probes. on the tip of the boom operates 16 times per second, the midpoint magne- tometer will operate twice per second, and vice versa. Data gathering On the opposite boom, a plasma package determines electron density, begins as soon as possible after the satellite is switched on in the payload plasma potential and low-frequency fluctuations in electric fields around bay and continues as long as possible during satellite retrieval. the satellite. A Langmuir probe with two metallic sensors samples the plasma current; from this measurement, plasma density, electron temper- ature, and plasma potential may be determined. This potential is then compared to that of the satellite. Two other probes measure low-fre- quency electric fields.

24 /

TSS-1 Science Investigations

Shuttle Electrodynamlc Tether System (SETS) Shuttle Potential and Return Electron Experiment Peter Banks, Principal Investigator (SPREE) University of Michigan Marylin Oberhardt, Associate Investigator Department of the Air Force, Phillips Laboratory i,_ This investigation is designed to study the ability of the tethered satellite to collect electrons by determining the current and voltage The SPREE will measure the charged particle populations around of the tethered system and measuring the resistance to current flow in the the orbiter for ambient space conditions and during active TSS-1 tether itself. The experiment also explores how tether current can be operations. SPREE supports the TSS-1 electrodynamic mission by deter- controlled by the emission of electrons at the orbiter end of the system mining the level of orbiter charging with respect to the ambient space and characterizes the charge that the orbiter acquires as the tether system plasma, by characterizing the particles returning to the orbiter as a result produces power, broadcasts low-frequency radio waves, and creates of TSS- I electron beam operation and by investigating local wave parti- instabilities in the surrounding plasma. cle interactions produced by TSS-1 operations. The hardware is located on the Multi-Purpose Equipment Support SPREE is mounted on the portside of the Mission Peculiar Experiment Structure near the center of the payload bay and adjacent to the deployer Support Structure (MPESS). The sensors for SPREE are two pairs of pallet. A Spherical Retarding Potential Analyzer, mounted on a stem at Electrostatic Analyzers, each pair mounted on a Rotary Table Motor one corner of the support structure, records ion current density, tempera- Drive. The sensors measure the flux of all electrons and ions in the orbiter ture, and energy and determines the potential of the orbiter. The potential at the SPREE location. The energy range is sampled either once or eight of the surrounding plasma and charged particle density and temperature times per second. The sensors measure the electrons and ions simultane- are measured by a Spherical Langmuir Probe, also mounted on the tower. ously over an angular field-of-view of 100 degrees x 10 degrees. At the center of the support structure, the Charge and Current Probe This field-of-view combined with the motion of the rotary tables allows measures the return current to the orbiter, recording large and rapid SPREE measurements over all angles out of the payload bay. changes in orbiter potential, such as those produced when electrons are The Data Processing Unit (DPU) performs all SPREE command and conducted from the tether to the orbiter frame or when an electron beam control functions and handles all data and power interfaces to the orbiter. is emitted. In addition, the DPU processes SPREE data for use by the crew and the A Fast-Pulse Electron accelerator emits electron beams of 50 and 100 ground support team. A portion of the SPREE data is downlinked real- milliamperes (mA) at 1 kiloelectronvolt (keV), stimulating wave activity time and the full data set is stored on two SPREE Flight Data Recorders over a wide range of frequencies. These beams discharge the orbiter (FDR). Each FDR holds up to 2 Gigabytes of data for post flight analysis. and produce electrical changes in the system and can be pulsed with on/off times ranging from 105 to 106 nanoseconds. The Fast-Pulse The SPREE hardware is Electron accelerator is located as close to the Core Electron accelerator located on the left side of the Mission Peculiar Equipment as possible and aligned so that the beams of both instruments are adjacent Support Structure in this and parallel. view of the tether payload. For the Fast-Pulse Electron accelerator beam to be aimed with precision for several experiments, a three-axis fluxgate magnetometer will measure the magnetic fields in the payload bay. These measurements will map the magnetic field lines in the payload bay, which is crucial since electron beams spiral in response to these fields. Using this information, the elec- tron beam can be aimed at various targets, including orbiter surfaces to study the fluorescing that occurs.

50000

30000

2000,0

This graph is a premission prediction

1000'0 1 J of the voltage generated across the tether over time. The SETS and The SETS hardware can be seen in the center of this DCORE experiments will make photograph of the Tether System. 0.0 ._ .... _., = .... t .... i 0.0 50 10.0 15.0 200 25.0 30.0 35.0 40.0 detailed measurements of tether elapsed time from satellite release (hours} generated potential OR!GIN,_d_ Pb._E COLOR Pi-tOTOGRAPH 25 TSS-1ScienceInvestigations

Tether Optical Phenomena Experiment (TOP) Investigation of Electromagnetic Emissions Stephen Mende, Associate Investigator for Electrodynamic Tether (EMET) Lockheed Robert Estes, Principal Investigator Smithsonian Astrophysical Observatory _ Using a hand-held camera system aboard the orbiter with image intensifiers and special filters, this investigation will provide Observations at the Earth's Surface of visual data that may allow scientists to answer a variety of questions Electromagnetic Emissions by TSS (OESEE) concerning tether dynamics and optical effects generated by TSS-1. In Giorgio Tacconi, Principal Investigator particular, this experiment will examine the high voltage plasma sheath University of Genoa surrounding the satellite, by which the electron accelerators return current One goal of these investigations is to determine the extent that to the plasma. waves generated by the tether interact with trapped particles and In place of the image-intensified conventional photographic experiment precipitate them. Wave-particle interactions are thought to occur in the package, that has flown on nine previous Shuttle missions, a charge- Van Allen radiation belts where waves transmitted from Earth jar regions coupled device electronic system will replace the film back. This new of energetic plasma and cause particles to rain into the lower atmosphere. system combines the image intensifier and the charge-coupled device in Although poorly understood, wave-induced precipitation is important the same package. The advantage of charge-coupled devices over film is because it may affect activity in the atmosphere closer to Earth. Various that they allow realtime observation of the image, unlike film, which has wave phenomena that need to be evaluated are: discrete emissions, light- to be processed after the mission. It also provides higher resolution in ning-generated whistlers, and sustained waves such as plasma hiss. Wave low-light situations than conventional video cameras. receivers on the satellite detect and measure the characteristics of the The imaging system will operate in four configurations: filtered, interfer- waves, and particle detectors sense wave-particle interactions, including those that resemble natural interactions in radiation belts. Ground stations ometer, spectrographic, and filtered with telephoto lens. The basic system consists of a 55 mm F/1.2 or 135 mm F/2.0 lens attached to the charge- may also be able to detect faint optical emissions produced as waves disturb particles and enhance ionization. coupled device equipment. Various slide mounted filters, an airspaced Fabry Perot interferometer, and spectrographic equipment will be attached Another goal is to determine how well the Tethered Satellite System can to the equipment so that the crew can perform various observations. broadcast from space. Ground-based transmissions, especially below For a current to be developed by the Tethered Satellite System, electron 15 kHz, suffer from inefficiency. Most of the power supplied to the antenna, large portions of which are buried, is absorbed by the ground. Because of accelerators have to return electrons to the plasma surrounding the orbiter. The interaction between these electron beams and the plasma is the large antenna size and consequent high cost, very few ground-based not well understood. By using the charge-coupled device to make visual, transmitters operate at frequencies below 10kHz. Since the Tethered spectrographic, and interferometer measurements, this process, and how Satellite System operates in the ionosphere, it should radiate waves more it affects both the spacecraft and the plasma, can be better understood. efficiently. For frequencies less than 15 kHz, the radiated signals from a 1-kW space transmitter may equal that from a 100-kW ground transmitter. Thruster gases may also play a critical role in Tethered Satellite System operations. By observing optical emissions during the build-up of the Waves generated by the tether will move in a complex pattern within the ionosphere and into the magnetosphere. Magnetometers at several loca- system-induced electromotive force and during gas discharges, scientists can gain a better understanding of the interaction between a charged tions in the chain of worldwide geomagnetic observatories and extremely spacecraft and the plasma environment and how the current system closes low-frequency receivers at the Arecibo Radio Telescope facility, Puerto at the poles of the voltage source. Rico, will try to measure the emissions produced and track the direction of the waves when electron accelerators in the orbiter payload bay pulse the tether current over specific land reference points. An Italian ocean surface and ocean bottom observational facility also provides remote measurements of TSS-1 emissions. These instruments measure emissions in the frequency range from dc to about 3 kHz.

(Far Left) Ground stations around the world will attempt to detect and measure the different types of electromag- netic waves generated by the TSS.

The Arecibo Radio Observatory will be the focus of Caribbean operations . l.i 6 I ,. during TSS-I.

26 O_G_NAL PAOE COLOR P_qOTOGRAPH TSS-1 Science Investigations

The Investigation and Measurement of Dynamic Theory and Modeling in Support of Tethered Noise in the TSS (IMDN) Satellite Applications _I'MST) Gordon Gullahorn, Principal Investigator Adam Drobot, Principal Investigator Smithsonian Astrophysical Observatory Science Applications International Corporation Theoretical and Experimental Investigation of TSS Dynamics (TEID) system'sThis investigationoverall currentwill developand voltagenumericalcharacteristics,models of ofthethetetherplasma Silvio Bergamaschi, Principal Investigator sheaths that surround the satellite and the orbiter, and of the system's Institute of Applied Mechanics response to the operation of the electron accelerators. Also of interest are I TSS-1 will be the longest structure ever flown in space, and its the plasma waves generated as the tether current is modulated. All data B dynamic behavior will involve oscillations over a wide range of collected on the mission will be combined to refine these models. frequencies. Although the major dynamic characteristics are readily Two- and three-dimensional mathematical models of the electrodynamics predicted, future applications of long tethers demand verification of the of the tether system will be developed to provide an understanding of the theoretical models. Moreover, higher frequency -- essentially random -- behavior of the electric and magnetic fields, and the charged particles, oscillations are more difficult to predict. This seemingly random behavior surrounding the satellite. These studies are expected to model the plasma is called "dynamic noise" by analogy to radio static, and an understanding sheath surrounding the satellite under a variety of conditions. This of its nature is needed for possible future uses of tethered platforms for includes those in which the motion of the tether and neutral gas emis- microgravity facilities and for studying variation in the small scale struc- sions from thrusters are not considered, those that incorporate the effects ture of Earth's gravitational and magnetic fields, caused by variations in of tether motion, and those that factor in the gas emissions. the composition and structure of Earth's crust. These gravitational varia- The sheath surrounding the orbiter has several unique features that are tions may be related to mineral sources. related to the ability of the electron accelerators to control the orbiter's These two investigations will analyze data from a variety of instruments potential. Models of the orbiter's sheath when small currents are flowing to investigate Tethered Satellite System dynamics. Primary instruments in the tether will consider the potential of the orbiter to be negative; for will be accelerometers and gyros on board the satellite; tether tension and large currents, models will be developed assuming a positive orbiter length measurements and magnetic field measurements will also be used. potential. In this way, the sheath structures and impedance characteristics The dynamics will be observed realtime at the Science Operations Center of the orbiter/plasma interface can be studied. and subjected to detailed postflight analysis. Basic models and simula- The response of plasma to the electromotive force produced by the tions will be verified (and extended or corrected as needed); these can motion of the tether system through the geomagnetic field is another then be used confidently in the design of future tethered missions, both of focus of this investigation. Using data from other studies, kinetic plasma Tethered Satellite System and of other designs. The dynamic noise inher- processes will be analyzed or numerically simulated by computer to ent to the system will be analyzed to determine the suitability of tethered model the reaction of the ionosphere to the passage of TSS- 1. systems to serve as platforms for sensitive observations of the geomag- netic and gravitational fields, and if required, to develop possible damp- This investigation also models the relationship between the efficiency of ing methods. wave generation and the amount of current flowing through the tether to examine how the tether antenna couples to the ionosphere, and how ultra- and very-low-frequency waves propagate through the ionosphere. These models will complement the information gathered by TSS-1 instruments with emissions recorded at ground stations.

The TMST experiment has developed numerical models of the TSS current and voltage characteristics. Graphic displays of data during the mission will be similar to this premission prediction that examined a case where the satellite was biased to 200 volts.

27 Mission Scenario

Twenty-four hours before deploy- When these _i the deployer corn- electrodynamic configurations. ment, a crew member at a console operations are Satellite puter that controls Direct current operations will in the aft flight deck activates complete, satellite _ Release the reel assembly. permit the study of the most the Tethered Satellite System, to internal power is '_ ..... _._ Once it passes 6 fundamental state of the electro- check the different systems. switched on, and a _:_:i!_'. kin, the satellite is dynamic Tethered Satellite The satellite systems are checked crew member .- ___ ...__spun at 0.25 rpm System, allowing the tether cur- electronically through two cables, releases the latches so that sensing rent to determine its own behav- called " and the first umbilical cable. instruments in the satellite and the ior. During current-voltage The 12-m satellite deploy- orbiter can measure the response operations the tether current will whichpro- _ _ • _: _ ment boom slowly extends of the system as it travels through vide electri- ="=i_ ...... _.; from its housing, lifting the the electrical and magnetic fields caI power satellite out of the payload in the ionosphere. umbilicals, _ and link the bay. Once the boom is Six hours pass as the satellite _II_Y satellite and extended, a second umbilical steadily and gradually approaches orbiter instruments. Portions of is used for a last-minute checkout Station 1, its fully deployed posi- the pallet-mounted science pay- of the satellite's support systems at tion 20 km from the Shuttle. Ten _ On-Station load gather data during different the boom tip and disconnected. hours of operations begin with the " Operations orbital phases and attitudes to The satellite is then sent on its way satellite's rotation being stopped \ establish basic operating charac- as its thrusters fire, gently lifting so that investigations can be per- be stepped rapidly through sev- teristics and obtain general it away from the docking ring. formed on tether dynamics over eral different levels m let the measurements of the Shuttle's Using a tether reel assembly, the course of an orbit. After these relationship between the tether electrical and optical environment. the crew reels the satellite out investigations, gas-jet thrusters current and the magnitude of the Engineers and scientists compare slowly and carefully, as they and spin the satellite, so it rotates tether's motional electromotive these baseline data with measure- ground controllers monitor status 0.7 revolutions each minute. The force to be studied. Alternating ments made later in the mission to and develop a sense for tether Deployable/Retrievable Booms current operations will permit the determine the effects of the sys- control. A sensor at the tip of the extend to their first stopping point investigation of low-frequency tem on the surrounding plasma. deployment boom continuously to measure the satellite's particle radio and plasma waves excited measures tether tension, while a and field environment. The booms by modulating the tether current. second sensor at the base of the remain at this first point for an In addition, several variations of boom measures the speed of the entire orbit, and then move further these configurations will be used tether. This information is fed to out to a second stopping point for particular experiments and the to repeat the process. The third overflight of ground stations and final measuring point is at looking for Tethered Satellite full extension. System-induced radio emissions. Instruments in the satellite and Approximately halfway through the payload bay stimulate the these operations, the satellite's ionosphere, measure the resulting rotation is reversed so that the response, determine the power tether will not be twisted when J generation properties of the entire retrieval begins. However, the tether system, and characterize the tether can be retrieved twisted surrounding environment at three if necessary. After Station 1operations, retrieval operations begin with the reel assembly winding in the tether. The satellite, under computer control, approaches to within 2.4 km of the orbiter, a position known as Station 2, where it stops for 5 hours to dampen dynamic perturbations t t ,.=f J and gather additional engineering and science data. Many of the same experiments conducted at Station1willberepeated,includ- Science instruments mounted Science Operations Center ingtheboommeasurementsat in the cargo bay may continue located at Johnson Space Center. threedifferentdistancesfromthe to take readings of the Shuttle In the operations center, they will satellite.Whilestopped,any environment after docking, be able to evaluate the quality of oscillationsthathavedeveloped When these final measurements ...... clata obtained, replan science inthesystemwillbedampedto are completed, the instruments activities as needed, and direct anacceptablelevel. are turned off, and the Tethered adjustments to the instruments. Retrievalresumessothatthe Satellite System enters a quiet After the flight, the Science finalstagesofretrievalanddock- state until the Shuttle returns Operations Center will support ingtakeplaceindaylight.When to Earth...... data distribution and analysis. thesatelliteis200mfromthe During the TSS-I mission, Deployer and satellite systems orbiter,crewmemberstakeover principal investigators and their will be monitored by the Payload tethercontrol.Usingradar, support teams will monitor and Operations Control Center at closed-circuittelevisionimages, direct science activities from the Johnson Space Center. computerdisplays,andlooking outtheorbiter'swindowsto monitorthesatellite'sposition andspeed,crewmembersgradu- allyeasethesatellitebackinto thedockingringontheboomby controllingthetetherreeltake-up rateandfiringtheShuttle's maneuveringthrusters.After docking,thedeployerboomis retractedintoitscanister,andthe satelliterelatchedtothesatellite supportstructure.Themission timelineprovidesforpost- retrievaloperationsatthistime, allowingscientiststomakefur- thermeasurementswiththesatel- liteinstruments.Oncethese operationsarecomplete,satellite electricalpoweristurnedoff.

\ Retrieval

Investigators in the Science Operations Center

2g The TSS-1 Crew

between ESA and NASA, he With a number of experi- The Science Grew an attempt to rescue a malfunc- Three scientists--Jeffrey A. tioning satellite. His research joined the NASA astronaut candi- ments sharing equipment, Hoffman, Franklin R. Chang-Diaz, interest lies in high-energy astro- dates selected in July 1980 for the crew of TSS-I will work and Claude Nicollier--will be physics and his second space- astronaut training as a mission closely with the principal the mission specialists for TSS- 1. flight was the Astro-1 ultraviolet specialist. He earned a B.S. Mission specialists are career and X-ray observatory mission. degree in physics from the investigators to monitor astronauts who have been trained Franklin R. Chang-Diaz was University of Lausanne, results, initiate changes, to operate orbiter hardware, selected in May 1980 as an astro- Switzerland, in 1970 and an M.S. and control satellite opera- as well as specific mission naut candidate and became a degree in astrophysics in 1975 mission specialist in August from the University of Geneva. tions. The crew member experiments. 1981. He earned his B.S. degree He has helped develop retrieval controlling this process will Jeffrey A. Hoffman, the in mechanical engineering in techniques for the Tethered Satellite System, taken part in have to rapidly analyze and Payload Commander, will be on 1973 from the University of his third mission. He was selected Connecticut and his Ph.D. in infrared astronomy programs, is synthesize data from such by NASA in January 1978 and applied plasma physics in 1977 a certified test pilot, and is a cap- sources as radar, computer became a mission specialist in from the Massachusetts Institute tain in the Swiss Air Force. This displays, and direct visual August 1979. He graduated from of Technology. He has been will be his first space mission. Amherst College in 1966 with heavily involved with the United observation. a B.A. degree in astronomy States controlled fusion program Two Italian scientists--Franco The crew for the first (summa cum laude), earned and has helped design new con- Malerba and Umberto Guidoni-- Tethered Satellite System a Ph.D. in 1971 from Harvard cepts in rocket propulsion based will be the prime and alternate University in astrophysics, and on high-temperature plasmas. His payload specialists for the mis- mission brings to it a vari- in 1988 earned an M.S. degree previous spaceflights were STS sion. Payload specialists are ety of experience which in materials science from Rice 61-C in January 1986 and STS 34 astronauts provided by a payload allow them to readily meet University. He made the first in October 1989. sponsor, who have been trained to Space Transportation System Claude Nicollier is a research perform specific science duties. these challenges. The TSS-I contingency spacewalk in 1985 in scientist selected in July 1978 by Franco Malerba earned his crew has trained extensively the European Space Agency B.S. in electronics engineering for the mission and will (ESA) to be one of three in 1970 (cure laude) and his Europeans to train as payload Ph.D. in physics, specializing work closely with the prin- specialists for the Spacelab 1 in biophysics, in 1974 from the cipal investigators during mission. Under an agreement University of Genoa, Italy. He the mission. was selected as one of the European payload specialist candidates for the first Spacelab mission and served as a staff member at the European Space Agency Technical Center Space

I

Dr. Jeffrey A. Hoffman Dr. Franklin R. Chang-Diaz Capt. Claude Nicollier Dr. Franco Malerba Ot_,, ,., PLGE 30 COLOR PHOTOGRAPH Science Department, where he The Orbiter Crew Col. Loren J. Shriver (USAF), the participated in a space plasma The commander, pilot, and flight Mission Commander, will be on experiment that flew on Spacelab engineer complete the TSS- 1 his third mission. He graduated 1. He has performed research in crew. Veteran NASA astronaut from the U.S. Air Force Academy membrane biophysics at the U.S. Loren J. Shriver serves as the in 1967 with a B.S. in aeronauti- National Institutes of Health and mission commander, Andrew cal engineering and earned an the Italian National Research M. Allen serves as the pilot, and M.S. in astronautical engineering Council (CNR) and served as a Marsha S. Ivins as the flight from Purdue in 1968. Selected as consultant to Digital Equipment engineer. The mission comman- an astronaut candidate in January Corporation, Europe, for more der has responsibility for all _i9:/8 and completing training as than a decade. He has also per- operations during the flight, a pilot in August 1979, Shriver formed research on signal detec- while the pilot and flight engineer served as pilot on STS-51C, a tion methodologies for sonar data assist in these efforts. Department of Defense Mission, systems. Dr. Malerba will be the and as mission commander on CoL Loren J. Shriver first Italian national in space. STS-31 for the deployment of the Umberto Guidoni is a co- Hubble Space Telescope. investigator on the Research on Major Andrew M. Allen Electrodynamic Tether Effects (USMC),the Pilot, will be on his experiment and was appointed first mission. He was selected as the Project Scientist for it in an astronaut candidate in June 1989. In this capacity, he was 1987 and qualified as a pilot in responsible for integration of the August 1988. He graduated from experiment into the TSS-1 satel- Villanova University in 1977 lite. He earned his Ph.D in astro- with a B.S. in mechanical engi- physics from the University of neering and graduated from the Rome, Italy, in 1978. He has Marine Weapons and Tactics served as a staff scientist in the Instructor Course, the U.S. Navy solar energy division of ENEA Test Pilot School and the Naval (National Council for Renewable Fighter Weapons School (Top Maj. Andrew M. Allen Energy) and became senior Gun). He has logged more than researcher at the CNR Space 3,000 flight hours in some 30 Physics Institute in 1984. He different aircraft. received a CNEN (the Italian Marsha S. Ivins, the flight Nuclear Energy National engineer, will be on her second Committee) post-doctoral fellow- mission. She was selected as an ship for 1979-80 in the thermonu- astronaut candidate in May 1984, clear fusion field. qualified as a mission specialist in June 1985 and served as a mission specialist on STS-32, which retrieved the Long Duration Exposure Facility. She graduated from the University of Colorado in 1973 with a B.S. in aerospace engineering and holds a multi-engine Airline Transport Marsha S. lvins Pilot License, a single engine airplane, land, sea and commer- cial licenses, and instrument, multi-engine and glider flight instructor ratings. She has logged more than 4,500 hours in civilian and NASA aircraft. Dr. Umberto Guidoni OR',Gi,..d_ PLGE COLOR P._OTOG.,APH 31 Atether cuts across magnetic maneuver. Still farther away, a Generating Spacecraft fields in low-Earth orbit, convert- tethered probe retrieves samples Electrical Power Propulsion ing some of the spacecraft's from the dusty, red Martian land- A tether system could supply Active Spacecraft Propulsion orbital energy into electrical scape and returns them to the power to an orbiting spacecraft, After TSS-I characterizes the power. Another tether is a giant parent spacecraft for analysis. supplementing solar arrays and electrodynamic properties of antenna, transmitting electromag- Tethers may make these sce- batteries or serving as a backup conductive tethers, future mis- netic waves that carry messages narios possible. Many ideas for emergency power system. The sions may be used to demonstrate to Earth. An instrumented, aero- using tethers in space are being longer the tether, the higher the tether propulsion. If the direction dynamic model is being towed by advanced, but before the scenar- electrical voltage it will produce. of the current in the tether is a tether through the only wind ios become realities, the concepts The 20-kin long tether used in the reversed, the force caused by its tunnel that can provide exact behind them must be proven. TSS-1 mission will generate up to interaction with Earth's magnetic high-altitude hypersonic flight Several steps are being taken to approximately 5,000 volts, while field changes from drag to conditions -- the upper atmo- bring the ideas to fruition. The a 96-kin long tether could gener- propulsion. If an onboard power sphere. At a space station, a robot TSS-1 mission is crucial for ate as much as 15,000 volts. The supply, such as a solar array, craft on its way to capture a demonstrating that satellites on total amount of power produced pumps electricity into the tether, satellite is released from a tether very long tethers can be success- by the system will depend on the current direction is reversed, and propelled into a higher orbit, fully deployed and retrieved conditions in the ionosphere and making the tether into an electric and later, the Shuttle is released in space. It may also determine the capabilities of the satellite to motor. The electrical energy on a tether from a remote docking whether conducting tethers can collect electrons. One of the flowing into the tether is trans- port and lowered to the right generate high electrical potentials questions TSS- 1 may help to formed into motional energy for altitude for return to Earth; no and drive currents, possibly lead- answer is how much current can the spacecraft, causing it to gain fuel is expended for either ing to the production of power for be extracted from the ionosphere. altitude; thus, the spacecraft's future spacecraft. Successful orbit is boosted without using Tethered Satellite System flights precious fuel. may lead to the following possi- ble uses for tethers.

32 COLOR PHOTOGRAPH Passive Spacecraft Propulsion Broadcasting Studying the measure chemical constituents, Non-conducting tethers can also from Space Atmosphere map global current systems and propel spacecraft. A tether trans- Wave generation and propagation In an atmospheric mission, the magnetic and electric fields, track fer system could place objects to are the focus of some TSS-1 Shuttle payload bay would face winds, and monitor pollution and higher or lower orbits without experiments. Travelling through Earth, and the satellite could be ozone depletion. Measurements excessive use of rocket engines the ionospheric plasma, the cur, lowered to a fringe area of the from this previously inaccessible and fuel consumption. For exam- rent-carrying tether radiates atmosphere about 130 km above region will improve models ple, if a satellite tethered above a electromagnetic waves from its Earth's surface on tethers up to of atmospheric chemistry space station is released, it gains whole length, and especially 100 km long. Sounding rockets and dynamics. momentum and moves into a from its two ends. By modulating have provided vertical profiles of The TSS-1 hardware can be higher orbit while the station's the current (turning it on and off this atmospheric region in a few reconfigured for follow-on atmo- orbit is lowered. Conversely, at desired frequencies in the same isolated spots, but it has not been spheric missions. The satellite can if the Shuttle is lowered from manner that a radio station oper- studied on a global basis because be outfitted with additional insu- a space station on a tether and ates), it may be possible to use atmospheric drag prevents satel- lation to control heating, atmo- released, it loses altitude and the waves for communicationS. : lites from orbiting below approxi- spheric instruments, and the station is boosted into a A 20- to 100-km long tether mately 180 km. aerodynamic stabilizers so that higher orbit. deployed from the Space Shuttle With the Tethered Satellite most instruments can face for- A tethered elevator could be could produce ultra-low- System, the region down to ward. Five times longer than used for many transportation frequency (ULF) waves from 130 km can be surveyed for days on TSS-1, the tether would be needs: moving payloads up and 3 to 30 hertz (Hz); extremely- at a time because the large inertial nonconducting. More advanced down between a space station and low- frequency (ELF) waves mass of the orbiter overcomes missions may string probes down- remote laboratories or platforms; from 30 to 300 Hz; and very-low- the satellite's relatively small ward to different points along a taking laboratories to different frequency (VLF) waves from drag. Satellite instruments tether to collect data simultane- gravity levels along a tether; 300 to 3,000 Hz. Ground-based immersed in the atmosphere can ously at different altitudes. and returning materials to Earth antennas, especially below for analysis. 15,000 Hz, are extremely ineffi- cient as most of the power pushed into them goes into heating the ground. Broadcasting from space in these bands could not only prove to be much more efficient but also extend the radio frequen- __ cies available.

0i_ii -\- _- ......

Movable platforms on an atmospheric tether could allow O_,r,,,','_1pP_.GE scientists to gather extensive, global data about the upper atmosphere simultaneously at a variety of altitudes, COLOR [sisOTOGP'A£ H possibly leading to an understanding of phenomena such as the ozone hole over the South Pole.

33 Using the Atmosphere Tether-Controlled as a Wind Tunnel Microgravity Wind tunnels on Earth are used When a tethered satellite is to test the effects of aerodynamic deployed from a spacecraft, the flow around objects, including center of mass for the total sys- the thermal stability of structures tem shifts to a point between the and materials. Tethers can give two objects. At some point near engineers access to the largest, this center of mass, an object open, continuous wind tunnel -- attached to the tether will experi- • \ \ the atmosphere. A tether ence no relative acceleration, or anchored to the Space Shuttle can zero-gravity. By changing the lower an instrumented aerody- object's position on the tether, namic model 100- to 150-km into different accelerations, or gravi- the outer atmosphere. Here, it can ties, can be obtained. A portable be exposed to ranges of condi- laboratory that can crawl to dif- tions that are impossible to repro- ferent positions along the tether duce in wind tunnels: heat can be exposed to various levels transfer, drag, strong air flows, of microgravity; experiments and turbulence. Data gathered exploring the effects of gravity on from these tests can be used to materials and biological samples improve spacecraft reentry and will benefit from such a facility. Wind tunnels can only partially simulate flight condi- develop aerobraking techniques Conversely, a tethered ballast tions in the upper atmosphere. By using tethers to place that take advantage of the atmo- could be used to "tune" a space instrumented models in this region, engineers could sphere to slow a spacecraft's station microgravity lab. By gather true performance data on proposed designs for changing the length of the tether, aerospace craft. speed. A Shuttle tethered aero- thermodynamic research facility the lab's center of gravity could is being studied for demonstra- be changed to account for such tion on a future mission. things as the use of consumables, area movement, and other factors affecting microgravity conditions. Tethers could also be used to simulate gravity in space. By attaching a tether between two objects, such as a living module and an automated processing facility, and then rotating the two = around a common point at the center of the tether, the "artificial gravity" of centrifugal force can be created. = i

COLOR p:-:OT,-,n-,_ ^ P_.,J A movable laboratory on a tether could be positioned at J I ,J I '._'_Mgl_l&l r] the exact level of gra_qty required by an experimenter.

34 Quick Reference ToExperiments

Acronym Title Investigator/Organization PageNo. EMET Investigationof ElectromagneticEmissionsby the ElectrodynamicTether R. Estes,PI/SAO p. 26 IMDN InvestigationandMeasurementof DynamicNoisein theTSS G.Gullahorn,PI/SAO p. 27 OESEE Observationsat the Earth'sSurfaceof ElectromagneticEmissionsby TSS G.Tacconi,PI/U.of Genoa p. 26 RETE ResearchonElectrodynamicTetherEffects M Dobrowolny,PI/CNR p. 24 ROPE ResearchonOrbitalPlasmaElectrodynamics N. Stone,PI/MSFC p. 23 SETS ShuttleElectrodynamicTetherSystem P.Banks,PI/U.of Michigan p. 25 SPREE ShuttlePotentialandElectronReturnExperiment M.Oberhardt,N/Phillips Laboratory p. 25 TEiD TheoreticalandExperimentalInvestigationof TSSDynamics S. Bergamaschi,PI/Inst.of AppliedMechanics p. 27 TEMAG MagneticFieldExperimentfor TSSMissions F.Mariani,PI/U.of Rome p. 24 TMST TheoryandModellingin Supportof Tether A. Drobot,PI/SAIC p. 27 TOP TetherOpticalPhenomenaExperiment S. Mende,AI/Lockheed p. 26

DCORE DeployerCoreEquipment C.Bonifazi,PI/ASI p. 23 SCORE SatelliteCoreEquipment C.Bonifazi,PI/ASI p. 23

35 Further Reading

1. "Applicationsof TethersinSpace,"Proceedingsof firstworkshopon 17. Moore,R.D., "TheGeomagneticThruster- A HighPerformance applicationsof tethersin space,NASACP-2364,2365,2366, March 'Alfv_nWave'PropulsionSystemUtilizingPlasmaContacts." 1985. AIAAPaperNo.66-257. 2. "TheProcessof SpaceStationDevelopmentUsingExternalTanks," 18.Moore,R.D., "TheSolarWind Engine,ASystemUtilizingthe Energy Reportby the ExternalTankWorkingGroupof the CaliforniaSpace in the SolarWindfor Powerand Propulsion." Institute,LaJolla,California,11 March1983. AIAAPaperNo.66-596. 3. "ShuttleTetheredSatelliteSystemDesignStudy," 19. Moravec,Hans,"A Non-SynchronousOrbitalSkyhook."Journalof NASATM X-73365,MarshallSpaceFlightCenter,December1976. theAstronauticalSciences,XXV,No.4, pp.307-322,1977. 4. "TheTetheredSatelliteSystem,"FinalReportfromthe Facility 20. Pearson,Jerome,"AnchoredLunarSatellitesfor Cislunar RequirementsDefinitionTeam;sponsoredby MSFCunderNASA transportationandCommunication."Journalof the Astronautical ContractNAS8-33383to theCenterfor AtmosphericandSpace Sciences,XXVII,No.1, pp. 39-62, 1979. Sciences,UtahStateUniversity,May1980. 21. Pearson,Jerome,"TheOrbitalTower;A SpacecraftLauncherUsing 5. Alfv_n,H.,"SpacecraftPropulsion;NewMethods."Science, the Earth'sRotationalEnergy."ActaAstronautica2 (9/10), Vol. 176,pp. 167-168, 14April 1972. pp. 785-799,1975. 6. Artsutanov,Y.,"V KosmosBezRaket(Into SpaceWithout Rockets)." 22. Polyakov,G.,"Kosmicheskoye'Ozherel'ye'Zemli(A Space ReportNo.ADA084507,Air ForceSystemsCommand,Wright 'Necklace'Aboutthe Earth)."TeknikaMolodezhi,No.4, PattersonAFB,Ohio,lp69. pp.41-43, 1977.Translation:NASATM-75174. 7. Artsutanov,Y.,"V kosmosnaelektrovoze."KomsomolskayaPravda, 23. Rupp,C.C.,andJ. H. Laue,"Shuttle/TetheredSatelliteSystem." 31, July 1960. Journalof the AstronauticalSciences,XXVI-I,January-March1978. 8. Banks,PeterM, P.R.Williamson,andK. L. Oyama,"ShuttleOrbiter 24. Rupp,C.C.,"A TetherTensionControlLawfor TetheredSubsatellites TetheredSubsatellitefor ExploringandTappingSpacePlasmas." DeployedAlongthe LocalVertical."NASATMX-64963, AeronauticsandAstronautics,February1981. September1975. 9. Clarke,Arthur C.,"TheSpaceElevator;'ThoughtExperiment,'or Key 25.Shoddy,W.C.,"ScientificandTechnicalApplicationsof aTethered to the Universe?"AdvancedEarthOrientedApplicationsof Space SatelliteSystem."175thAIAAAerospaceSciencesMeeting, Technology,Vol. 1, pp. 39-48,1981. NewOrleans,Louisiana,15-17January1979. 10. Collar,A. R.,andJ. W.Flower,"A (Relatively)LowAltitude24-Hour 26. Tsiolkovsky,KonstantinE.,"Grezio zemlei nebe(Speculations Satellite."Journalof the BritishInterplanetarySociety,Vol. 22, pp. betweenEarthandSky)." Moscow,Isd-voANSSSR,1959. 785-799,1969. First publishedin 1895. 11. Colombo,Giuseppe,E.M.Gaposchkin,M D.Grossi,"Shuttle-Borne 27. vonTeisenhausen,Georg,"Tethersin Space- BirthandGrowthof a 'Skyhook;'A NewToolfor Low-Orbital-AltitudeResearch." NewAvenueto SpaceUtilization.NASATM-82571,February1984. SmithsonianInstitutionAstrophysicalObservatory,1974. 28. Williamson,P.Roger,P.M. Banks,andK. Oyama, 12. Colombo,Giuseppe,et al.,"Useof tethersfor PayloadOrbitaltrans- "TheElectrodynamicTether."NASAContractNAS5-23837, fer." SmithsonianAstrophysicalObservatory,NAS8-33691,March UtahStateUniversity,1978. 1982. 13. Dobrowolny,M., G.ColombolandM. D,Grossi,"Electrodynamicsof LongConductingTethersin theNear-EarthEnvironment." Suggested Terms for Database Searches SmithsonianInstitutionAstrophysicalObservatory,NAS8-31678 October1976. AdvancedPlanetaryExploration AdvancedPropulsion;AdvancedLaunchSystems 14. Drell,S. D., H.M. Foley,andM.A. Ruderman,"DragandPropulsion Alfv_n of LargeSatellitesin the Ionosphere:AnAIfv6nPropulsionEngine Beanstalk inSpace."Journalof GeophysicalResearch,Vol.70, no. 13, ElectrodynamicInteractions pp.313!-3145, July1965. ElectrodynamicTethers 15. Hunter,MaxwellW.,"AdvancedSpaceTransportationOptions." Funiculars Lockheed,August1982. OrbiterMonitorTransfer Skyhook 16. Isaacs,John D.,et al.,"SatelliteElongationIntoaTrue'Skyhook'." SolarSails Science,Vol. 151,pp. 682-683,1966. Tether(s):History,Constellations,andSpace

36 Glossary of Abbreviations and Acronyms

A: Amperes NASA: NationalAeronautics ac; AlternatingCurrent andSpaceAdministration Ah: Amperehours nT: Nanotesla AI: AssociateInvestigator OESEE: Observationsat the Earth'sSurface AMPS: Atmospheresand of ElectromagneticEmissions MagnetospheresandPlasmas by TSS (NASAworkinggroup) PI: PrincipalInvestigator bps: Bitspersecond POCC: PayloadOperationsControlCenter CEA: CoreElectronAccelerator PSN: PianoSpazialeNazionale- cm: Centimeters ItalianNationalSpacePlan CNR: ConsiglioNazionaledelleRicerche RETE: ResearchonElectrodynamic -- ItalianNationalResearchCouncil TetherEffects dc: DirectCurrent ROPE: ResearchonOrbitalPlasma DCORE: DeployerCoreEquipment Electrodynamics deg: Degrees SAO: SmithsonianAstrophysical degC: DegreesCentigrade Observatory deg/sec: Degreespersecond (Cambridge,Massachusetts) ELF: ExtremelyLow Frequency SCORE: SatelliteCoreEquipment EMET: Investigationof SETS: ShuttleElectrodynamic ElectromagneticEmissions TetherSystem bythe ElectrodynamicTether SPREE: ShuttlePotentialandReturn eV: ElectronVolt ElectronExperiment FPEA: FastPulseElectronAccelerator STS: SpaceTransportationSystem g: Gravity (Numericdesignationindicates Hz: Hertz specificmission) IMDN: InvestigationandMeasurement T: Tesla(unit of measurefor of DynamicNoisein theTSS magneticflux density) IWG: InvestigatorWorkingGroup TAG: Three-axisAccelerometerGyro JSC: JohnsonSpaceCenter TEMAG: MagneticFieldExperimentfor K: DegreeKelvin TSSMissions kbps: Kilobitspersecond TEID: TheoreticalandExperimental keV: Thousand(Kilo) ElectronVolts InvestigationonTSSDynamics kg: Kilogram TMST: TheoryandModelingin Support kHz: Kilohertz of Tether KSC: KennedySpaceCenter TOP: TetherOpticalPhenomena kV: Kilovolt Experiment kW: Kilowatt TSS: TetheredSatelliteSystem m: Meter TSS-I: FirstTetheredSatelliteSystem mA: Milliamperes Mission.TSSdeployedspaceward MHz: Megahertz andelectrodynamictests conducted MOU: MemorandumOfUnderstanding MPESS: Multi-PurposeEquipment ULF: UltraLow Frequency SupportStructure VLF: VeryLow Frequency MSFC: MarshallSpaceFlightCenter W: Watt

37 Acknowledgements

ThisbrochurewasdevelopedbytheTetheredSatelliteSystemProjectOffice, NASA/MarshallSpaceFlightCenter(MSFC),Huntsville,Alabama.

Authors: C.BlakePowers,CharlotteShea,andTracyMcMahan, allof EssexCorporation Editor: C.BlakePowers,EssexCorporation

EditorialAssistants:ChrisScantland,JulieCoolidge,ValerieNeal, SandraMurphree,LynnFinger,SarahMorgan,andDeniseAccardi, allof EssexCorporation

SPREEwrite-upby CaptainWilliamE.Slutter,U.S.Air Force,PhillipsLaboratory

EditorialReviewTeam Mr.BillyW. Nunley,TSS-1ProjectManager,MSFC Mr.MurrayCastleman,TSS-I DeputyProjectManager,MSFC Dr.NobieStone,TSS-1MissionScientist,MSFC Mr.TomShaner,TSS-1ChiefEngineer,MSFC Mr.TomStuart,TSS-1ProgramManager,NASAHeadquarters Mr. RickHoward,TSS-1SciencePayloadProgramManager,NASAHeadquarters Ms. PaulaCleggett-Haleim,PublicAffairsOffice,NASAHeadquarters Ms. DebraRahn,PublicAffairsOffice,NASAHeadquarters Mr. MarkHess,PublicAffairsOffice,NASAHeadquarters Dr.JeffreyA.Hoffman,TSS-1PayloadCommander,JSC Dr.FranklinChang-Diaz,TSS-1MissionSpecialist,JSC Mr.ClaudeNicollier,TSS-1MissionSpecialist,JSC Dr.GianfrancoManarini,TSSProgramManager,AgenziaSpazialeItaliana

Withappreciationfor theirContributions:theTSS'i principalinvestigators,the payloadexperimentdevelopers,andtheengineersandscientistson theirteams; theTSS-I crew;MartinMariettaAstronauticsGroupandAleniaSpaceSystems Group,thedevelopersof thedeployerandsatellitehardware;andotherpartici- pantsintheTSS-1missionwho providedinformationandillustrationsand/or reviewedthis document.

GraphicDesigner:BrienO'Brien,O'BrienGraphicDesign,Huntsville,Alabama

Coverpaintingandcenterfoldartby DavidW. Johnston,Huntsville,Alabama Illustrationson pagesiv,2,4, 10,tl, 12,13,28,& 29 byDavidW.Johnston Illustrationson pages33 & 34 courtesyofAlenia Illustrationson pages1 & 6 courtesyof MartinMarietta Photographson page7 by PatCorkery,MartinMarietta Photographof cometon page22 courtesyof R.RoyerandS.Padilla Photographon page14 courtesyof ChristianoCosmovici,CNR

All otherphotographsandillustrationscourtesyof NASA

'_ U.S. GOVERNMENT PRINTING OFFICE: 1992-324-999

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