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AUTHOR Froehlich, Walter TITLE The Tracking & Data Relay Satellite System. The New Space Network. INSTITUTION National Aeronautics and Space Administration, Washington, D.C. REPORT NO NASA-EP-251 PUB DATE 89 NOTE 33p.; Colored photographs may not reproduce well. AVAILABLE FROMSuperintendent of Documents, U.S. Government Printing Office, Washington, DC 20402 ($2.75). PUB TYPE Reports - Descriptive (141)

EDRS PRICE MF01/PCO2 Plus Postage. DESCRIPTORS *Aerospace Technology; *Communications Satellites; *Satellites (Aerospace); Science Materials; Science Programs; *Scientific Research; Space Exploration; *Space Sciences; *Telecommunications IDENTIFIERS National Aeronautics and Space Administration; Tracking (Science)

ABSTRACT This publication describes the giant-capacity space communications installation called the "Tracking and Data Relay Satellite System" (TDRSS). Chapters include: (1) "A New Communications Bridge to Orbit" (illustrating what it is and how it looks); (2) "TDRSS Goes to Work" (describing how it functions); (3) "The Ground Segment" (discussing the system's link with Earth); (4) "Why TDRSS is Needed" (its history and rationale); and (5) "The Space Network Today and Tomorrow." The technical information on the TDRSS, including frequency bands and ground terminal equipment, is appended. (YP)

* Reproductions supplied by EDRS are the best that can be made * * from the original document. * U DEPARTMENT OF EDUCATION Office of Educational Research c no improvemerit EDUCATIONAL RESOURCES INFORMATION CENTER ;ERIC) *This document has been reproduced as received frorr the person or organization originating it E Minor L.nanges have been made to improve reproduction guaiity

Points of view or opinions stated n this docu- men: do not necessarily represent official OERI positfon or policy I- When it_is fully operational, NASA's new Tracking and BOW* Satellite System (TD ) will provide almoSt ous communicationsfrgm th te Shuttle while in

ascorn have shrunk the gi wilt bring e oft to pek aiLdist,.

As we- era, and teChnol capabilities marl the commercial, in scievitific potential r The New Space Network

The king &

By Walter Froehlich

NASA

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For site by Ow tipurintrndeni ol Do( urntnt limcriltricnt ()Ith c.14',1,,hrtuitun, In the larger context of the U.S. space program, the TDRSS is the equivalent of a superhighway for voice, video, and data streams.

Like the multilane parkways, turnpikes, freeways, and beltways, r which have changed our lifestyles and our concept of motor transportation in the last 30 years, so the new NASA Space Network is profoundly altering our rception, as well,as the realities, bit-Earth

44 Contents

Introduction 2

Chapter I: A New Communications Bridge To Orbit What It Is and How It Looks

Chapter 2: TDRSS Goes To Work How the f"ieW.Spacie l'icturtak function

Chapter The Ground Segment II The f.arth-Msed Links

Chapter Why TDRSS Is Needed I Its History and Rationdle

Chapter The Space Network Today and Tomorrow 171 Present and future

IC( 11111(

In November 1983, five men system augmented the services of The new Tracking and Data aboard the U.S. Shuttle the 15 traditional ground-based Relay Satellite System is became the first space crew to communications stations. When the the key element in NASA's enjoy nearly continuous three-satellite TDRSS is completed evolving Space Network. communications with people on the with the launching of two more In writing, such as in press ground while flying in a low Earth satellites, the TDRSS will replace releases and technical publications, orbit. most of these ground stat.)ns. NASA refers to the new system by That mission was the ninth Even though only one of the its5breviation, "TDRSS," and to orbital flight for the Shuttle. During TDRSS satellites is in orbit, the each component satellite as "TDRS" it, unprecedented quantities of space segment of the TDRSS, (with only one "S"). information were generated by together with it.s associated ground But when talkingin casual instruments aboard Spacelab, the facilities, has already significantly conversation as well as at meetings European-built orbital research influenced U.S. space research and in formal speechesNASA module then on its first flight in and operations. officials and others either spell out the Shuttle cargo bay. The system, which is expected to the letters "T-D-R-S-S" or "T-D-R-S" Much of Space lab's data was exert momentous impact on U.S. or pronounce the letters as an instantaneously transmitted to space projects in the immediate acronym that sounds like "Tea scientists on Earth. They were able future, is explained in this Dress." to analyze and respond to these publication. This pamphlet, like other NASA research results while many of these documents, refers to the new experiments were still underway system as the "TDRSS." In this in orbit. pamphlet the system's satellites are On that seven-day mission more called "TDRSS satellites" or simply data was retrieved through space- "satellites." All other Earth-orbiting to-ground communications than craft are called "spacecraft" to on all 39 previous U.S. manned avoid confusion. spaceflights combined! Readers may want to join NASA The nearly continuous two -way personnel in saying "Tea Dress" voice exchange and record data when referring to either the flows were made possible by the satellites or the system. first satellite of NASA's new giant- capacity space communications installation called the "Tracking and Data Relay Satellite System" (TDRSS). This partly completed

A SERVANT IN Mt SKI is this MR.SS .satellite shown here in orbit awaiting commands and instructions from Earth The satellite transmits communications to and from research and applications spacecraft.

1 6 Introduction

It seems as if the Earth and highest transmission rate, the new modern environmental and Earth nearby orbital regions are system can transfer :n a single resources observation satellites and moving closer to each other. second the contents of a 20-volume by the soon-to-be-launched large Voice and data transmissions encyclopedia with 1,200 pages in new Hubble Space Telescope that between the Earth and these each volume and 2,000 words on will conduct unprecedented regions are multiplying rapidly. each page. astronomical research. NASA is building a new Earth-to- With the TDRSS these exchanges The instantaneous availability of orbit and orbit-to-Earth can take place almost continuously information from orbit helps communications link named throughout an orbital mission. scientists on the Earth closely "TDRSS." The letters stand for Earlier spacecraft communications monitor their individual research hacking and Data Relay Satellite were limited to a few intermittent projects taking place in space. They System. When completed, the minutes on each orbit. To can adjust instruments by remote system, together with its various communicate with the Earth, a control in response to unexpected NASA support elements, will be spacecraft had to be ip "view" of a research results even while the known simply as the "Space ground station. The TDRSS research is underway. They can Network." It will substantially eliminates this restriction. instantly analyze information with increase information exchanges The large-capacity, near- equipment on the Earth and discuss between low-orbiting spacecraft and continuous exchanges achievable results with colleagues on board the the ground. with the TDRSS are essential for the Shuttle while the work in space is in So far only one of the system's expanded scientific research and progress. Such interchanges will be three planned communications the burgeoning commercial and essential when manufacturing and satellites has been in place in orbit. industrial operations envisioned for other industrial and commercial Nevertheless, TDRSS has been space in the late 1980s and early activities begin on a large scale in keeping the electronic uplink and 1990s. Facilities for carrying out the Space Station in the 1990s. downlink channels between the these modern research and Although the contributions of Earth and orbiting spacecraft commercial ventures are already in TDRSS are less obviously visible bristling with voices, video, and use. or will be shortly. than those of many other space data. When the system's other two Sophisticated instruments events, TDRSS constitutes a satellites are launched, the carried aboard the bus-size cargo valuable national resource. The completed Space Network will bay of a Shuttle generate huge advantages emerging from it and represent one of the biggest volumes of data. The data flow the benefits that will flow from it advances in space communications becomes even more abundant when are bound to add up in the years technology in the 1980s. the Shuttle carries Spacelab. In this ahead to a giant leap for So massive is the system's compact $1-billion research humankind. capacity that some knowledgeable laboratory built by the European observers say nearby orbital Space Agency (ESA), scientists and regions, in terms of communica- technicians can work in orbit on tions, will become nearly as complex projects in a shirt-sleeve accessible as any continent. In a environment almost as if they were communications sense these in their laboratories on Earth. regions will be part of the Earth. If this research harvest cou'd not Because of this and other advances, be promptly transmitted to Earth the unique resources of space, through TDRSS, the Shuttle and which were beyond reach by any many of the automated spacecraft IN ORBIT Vii IV was means until the middle of this of today and tomorrow would need (aptiiied moments before century, are gradually becoming to carry additional, often bulky, the election of the /list readily accessible for very complex data storage equipment. This would MKS', satellite from the scientific and routine commercial take away precious space, weight, shuttle ( hallengei s (dig() hay by a 35171111 and industrial uses. and power from research and camera through the So vast is the capacity of the new operational payloads. High-rate data .Shuttle s alt flight de( k flows are generated nowadays not system that it can transmit the window on April 4, 1983. contents of an average library from only by the Shuttle, but also by Ntei ejection the TIMS.S an orbiting spacecraft down to the automated orbiting craft such as temporanly floated in Earth in a few minutes. At its orbit. Then its attiched Inertial tipper Stag< i 'IN booster propelled it to a mu( h higher orbit. 2 3 11. OP . rilla 444ri,"" I " 46'4:4 lit 10P"' . ;.111i a 41 4 011.61.1. A New Communications Bridge To Orbit What It !s and flow It Looks

Chapter 1 If it could be seen from the The TDRSS travels in a During recent Shuttle flights the Earth's surface, it might look "geostationary orbit" (also called remaining Earth stations of the 25- like a giant X far up in the sky. geosynchronous orbit), meaning is year -old Spaceflight Tracking and Closer up, it would resemble a movements correspond with the Data Network (STDN) have been windmill. It is a TDRSS satellite and, Earth's rotation. Thus, if it could be augmenting the first TDRSS like a windmill, it has four arms or watched from the ground, the satellite so that together they have paddles. Two opposing paddles are satellite would appear to be provided the Shuttle with nearly flat, square solar panels, measuring hanging in almost motion-free continuous communications 3.8 meters (151 inches) on each suspension above the Eartt. service. side. The two other paddles look Weighing 21/2 tons and stretching to Spacecraft traveling to the Moon like upside-down umbrellas. They 17.4 meters (57 feet) between its and to planets are so distant from are parabolic dish antennas with most distant rims, it is the largest the Earth that they can "see" about diameters of 4.9 meters (16.3 feet). and heaviest satellite ever launched half of the Earth's surface at any They are adding new dimensions to into a geosynchronous orbit. time. Thus, even as the Earth space communications. The satellite di.fers from rotates, at least one of the three Holding these paddles in place conventional communications strategically located ground are booms of extruded Beryllium, satellites in a big way: Our conven- communication stations of NASA's which form the arms and legs of tional communications satellites Deep Space Network is within sight the X. At the X's center is a box (a connect points on the Earth. They of the spacecraft at all times. Com- six-sided structure or hexagon) to transmit communications between munications between the craft and which other antennas of various cities, countries, and continents. the Earth can be carried on at any shapes and sizes are attached. The TDRSS satellite connects the desired time or even continuously. Inside the hexagon are the Earth with low-orbiting spacecraft. Low-orbiting spacecraftthose subsystems that control When the TDRSS is completed at altitudes of up to only a few communications, electric power, with the two other satellites, almost hundred miles"see" only a small satellite attitude, and other uninterrupted voice and data portion of the Earth's surface at any essential functions. exchanges will be routinely possible one time. If no Earth station Three satellites like this one will between the Earth and orbiting U.S. happens to be in the craft's view, make up the orbital segment of Shuttlesall with only one Earth- communication with the Earth is NASA's new "hacking and Data based communications station. not possible. The lower an orbiting Relay Satellite System," or The system will also allow nearly spacecraft's altitude, the less "TDRSS" for short. It, in turn, is continuous command and communications time is available if part of the new NASA Space telemetry communications between the craft depends solely on ground Network. This first satellite has ground control centers and stations for its contacts. been in orbit since April 1983. unmanned, automated research and When launched, the other two applications spacecraft orbiting up satellites will complete the system. to several thousand miles above the The satellite currently in Earth. operation at an altitude of 35,680 Since the new system's first kilom'ters (22,300 miles) above the satellite has been in orbit, it alone equator, is too far away to be visible (without the help of the remaining from the Earth's surface. But its Earth stations) has stretched 4 MU/ TRA in presence is felt by the communications between the Earth communications unprecedented services it provides. and the Shuttle from about 15 between Loth and orbit percent of the time during each is being ushered in by orbit to about 50 percent. this first of three satellites, which will make up the space segment of NASA s new Tracking and Data Relay Satellite System (1DRSS). The system, a virtual superhighway for space communications, is opening new opportun- ities for the uses of space.

415 1

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t All manned spacecraftexcept EachTDRSSsatellite is launched Maneuvering a satellite into its for Apollo flights to the Moon in the from the Shuttle. The satellite's proper orb'tal slot requires cardul late 1960c 'nd early 1970shave solar panels and antennas are and close coordination between been in such low Earth orbits. compaCtly olded as it is stowed in ground-based tracking systems and On these flights, including the the Shuttle's cargo bay. After the the satellite control center. These early Shuttle flights, voice and data Shuttle attains orbit at an altitude facilities ,nonitor the satellite's tnuismissions between the of about 280 kilometers (175 position and movements and send spacecraft and Firth were limited, miles), its cargo bay doors open up radio kommands to activate the averaging less than 15 minutes on and the satellite is ejected. At satellite's p opulsion system until each 90-minute orbit. On a typical launch, each satellite weighs about the satellite is properly aligned in orbit, the craft and crew were out of 2,270 kilograms (5,000 pounds). the desired position and attitude. communications reach for some After the Shuttle moves a safe The new Space Network's first 75 minutes. distance away, the satellite's satellitethe "East Satellite"has The new Space Network greatly attached booster rocket, known as been on station since 1983 above a expands these communications an "Inertial Upper Stage" (IUS), point at the equator near the city of windows. The threeTDRSSsatellites ignites and lifts the satellite to its Fortaleza on the northeast coast of will orbit more than 150 times as geosynchronous orbit. There, the Brazil (41 degrees west longitude). high as the Shuttle, which usually satellite detaches itself from its The system's second satellite remains below 480 kilometers (300 booster and then the solar panels the "West Satellite"is to be miles), and many times as high as and antennas unfold. positioned above the equator north most other low-orbiting U.S. When unfolded, the satellite of the Phoenix Islands in the mid- research and applications craft. measures 17.4 meters (57 feet) Pacific Ocean (171 degrees west Looking down from their lofty from the outer edge of one solar longitude). perch, these newTDRSSsatellites panel to the outer edge of the can accommodate nearly all U.S. other, and 14 meters (46 feet) from low-orbit communications traffic. the outermost edge of one dish antenna to the outermost edge of the other. The satellite is allowed to driftassisted by its attitude control thrustersto the position assigned to it in orbit.

1UKSN-LYE VIEW At its altitude of 35,680 kilometers (22,300 miles) above the equator, the IDFiSS ,satellite can 'see half of the Earth and thus can keep in communica- tions contact with low- orbiting spacecraft for at least half of the time during each of their orbits. The new space communications system requires only one ground terminal in coattast to the earlier systems

J The third satellite is to be used In the larger context of the U.S. as a spare, and will be positioned space program, the new Space between the others. Its precise Network is the equivalent of a location has not yet been selected, superhighway for voice, video, and but it will be above the equator, data streams. Like the multilane probably close to the border of parkways, turnpikes, freeways, and northwestern Brazil and Venezuela. beltways, which have changed our There it will be kept largely inactive lifestyles and our concept of motor as a backup, but ready to be moved transportation in the last 30 years, in the place of either of the two so the new MASA Space Network is active satellites if one of these profoundly altering our perception, should malfunction. as well as the realities, of Earth- The three TDRSS satellites make orbit communications. up the space segment of the new Most treasures from space have Space Network. Together with its so far been in the form of ground-based segments, the information and observations. Network will be able to support the These are leading to knowledge and complex advanced scientific, understanding perhaps more commercial, and industrial projects precious than material returns. The planned in low Earth orbits in this three TDRSS satellites and their decade and through the 19905. associated facilities substantially increase the quantities of information and observations that can be transmitted to the Earth.

RLADY FOR LAUNCH C-band Antenna a folded TDRSS satellite SOL Antenna is a compact package tiirked neatly into the cargo bay ')f the Shuttle (illustrations A and After having been injected into its 35 mo kilometer -high orbit Orbit: (223(X miles) the 28.5'1150 TIM SA Drive Cage satellite unfolds Single Access Solar Panel (illustration Cl until its Antenna Compartment antennas and solar panels .strehhlu dimensions that make it larger Than a house. TDRSS Goes To Work Now the New Space Network Functions

Chapter 2 Emergency! Odd digits are appearing on a monitor screen. Unintelligible responses are returning from orbit. The on-board memory is falling on one of our most valuable automated scientific research spacecraft There is danger we may lose the services of this still young space machine worth tens of millions of dollars. Using the lone operating TDRSS satellite, controllers extend their allotted communications time with the ailing spacecraft from 20 minutes to .50 minutes during each of the craft's next four orbits. In these 200 minutes, the controllers "dump" (recall to Earth) the contents of the craft's memory and analyze them. They then reload the craft's memory and send along the necessary commands to restore the craft to "In its two years of operations its normal working condition. (the system's first satellite) has achieved an outstanding record of success.... If one considers the Shuttle and Spacelab support Mims has giverij and the an-going support of the unianned spacecraft, even with only one satellite in the spacesegment, TDRSS has already validated the operational concepts which led to the initial approval of the program."

Robert 0. Aller NASA Associate Administrator For Space Tracking & Data Systems (in speech at 36th Meeting of the International Astronautical Federation, October 1985, Stockholm)

DEPLOYMENT OF TDRSS in a parking orbit satellite depicted in this awaiting ignition of its drawing shows the attached booster rocket satellite after its ejection for lifting it to its from the Shuttle s cargo required much higher bay. The satellite floats orbit.

8 In earlier days, before the TDRSS In its "downlink" or "return" The two parabolic "inverted satellite was available, controllers mode, the new satellite receives umbrella" antennas are called had to analyze spacecraft problems transmissions from a spacecraft, "single access antennas" because and make repairs by remote control amplifies them, am retransmits each of them can be used by only during the few intermittent them to the ground terminal. one spacecraft at a time for minutes a spacecraft was within Engineers say the new satellites sending or receiving transmissions. communications range of an Earth work in a "bent-pipe mode." The 30 cylindrical antenna elements station. Communications pass through on the hexagon can handle The emergency described above these satellites much the way fluids communications traffic to and from and its happy ending, which flow through an L-shaped or V- up to 20 spacecraft simultaneously. occurred in November 1985, is one shaped pipe. Signals are not They are called "multiple access of scores of events which have changed, merely redirected. antennas." dramatically Illustrated the virtues All communications between a The single access antennas are of the new system since its first TDRSS satellite from or to the Earthsteerable. They can be mechanically satellite began service in 1983. The pass through the satellite's 2-meter-turned by remote control to face expanded communications times diameter (6.7-foot) dish antenna. toward a spacecraft and receive or with TDRSS have been credited with That antenna, near the satellite's transmit at very high rates. At their making possible adjustments and hexagon central structure, is best performance, these antennas repairs that have kept several dedicated to Earth-to-space and can receive or transmit in each faltering spacecraft in operation. space-to-Earth traffic. second up to 300 megabits (300 The new satellitelike its two When the satellite receives million electrical impulses companions which are to join itis transmissions from the ground designating ones (1) or zeroes (0), a "repeater." It neither processes terminal, it instantaneously from which letters and numerals or nor alters any communications. It is retransmits them through one of itsimages can be derived). almost like an echo in the sky. It two parabolic "inverted umbrella" It is this high rate of data flow functions like a mirror, or more antennas or through the array of 30 through these high-gain antennas accurately, like a switchboard in cylindrical antenna elements that makes possible the system's orbit: mounted on the satellite's hexagon capacity of transmitting the Its "uplink" or "forward" central structure. The parabolic equivalent of the contents of a channels receive transmissions antennas and the array elements multiple-volume encyclopedia each from the ground, amplify them, are used exclusively for communica- second. These antennas are and retransmit them on another tions with orbiting spacecraft. especially designed for use by frequency to the orbiting spacecraft that generate and spacecraft to which they are transmit large quantities of data addressed. to Earth.

COMMIIIN101 1 IWis at high speeds (an take place between the Shuttle 5110001 uIits typical low altitude orbit) and Earth through the single-access' antennas of the TDRSS satellites. At the highest transmission rate, each umbrella like antenna can trans /et the equivalent of a small library, word for word and page by page, be tween a spacectaft and the Earth station within a few minutes.

9 16 In contrast, the array antennas, (2) The COMMUNICATIONS PAYLOAD That gap exists on the side of the while able to accommodate up to MODULE in the upper part of Earth opposite the midpoint 20 spacecraft simultaneously, can the hexagon (just below the between the two satellites. Thus, a receive or transmit at only much multiple access antenna region over the Indian Ocean slower ratesup to 50 kilobits a elements) contains electronic stretching from the Earth's surface second. That is still a large quantity equipment that regulates the up to an altitude of 1,200 of transmissions, the equivalent of flow of transmissions between kilometers (750 miles) is not within about 20 typewritten pages of 200 the various antennas and other view of either satellite. The words each per second. Yet, even communications functions. curvature of the Earth blocks the when the second active TDRSS This module's electronic view. Spacecraft passing through satellite goes into operation, the communications equipment that zone at altitudes of less man combined capacity of the multiple forms, in a way, the "elbow" of 750 miles will not be atie to have access system will remain at 20 the "bent pipe." communications contact via the simultaneous transmissions. (3) The ANTENNA MODULE consists Space Network. Thus, the limit for the entire of a platform holding various That relatively riarn,s "Zone of TDRSS system using two active antennas including the 30 Exclusion" (ZOE` stretches for satellites will be four simultaneous helices of the multiple access slightly less than 350 kilometers high-data transmissions and 20 at phased array system. (200 miles) on the Earth's surface, the lower data rates. When the Space Network is but shrinks with increasing altitude. Each Tr 7SS satellite is made up complete, it will provide global Spacecraft in orbits above 1,200 of three modules: coverage except for one remaining kilometers art unaffected. TDRSS (1) The EQUIPMENT MODULE, also gap. Even the strategic placement provides them with 100-percent called the "Spacecraft Module," of two satellites cannot give 100 around-the-Eirth coverage. ZONE Of EXCLUSION The satellites are only part of the is in the lower part of the percent coverage for low-orbit is depicted by the dark satellite's core hexagon. This spacecraft. Space Network Its other parts are triangular area on the module encompasses sub- on the Earth. The TDRSS ground bottom of the globe systems that control the station and a variety of other indicating regionnot thrusters to keep the satellite ground facilities also are essential visible from the1DRSt. on station and in the desired for the voice, command, telemetry, satellites. That relatirely attitude. The module also television, and data transmissions small region is the only houses equipment that stores and tracking services the Space place at which low-orbLing spacecraft and manages the power supply, POSITIONS Of the West Network is designed to pi'vide. are out of contact with and the machinery that oper- and East1DRSSsatellites the new space-based ates telemetry and tracking are shown on this map communications system. equipment. ,n relation to their New Mexico Ground Terminal. Spacecraft at altitude of 1,200 kilometers (750 miles) or higher have 100-percent coverage through1DRSS.

MRSS fast Satellite TDRSS West Satellite

1111111r200Km (black area denotes "Zone of Exclusion")

10 The Ground Segment The Earth-Based Links

he Space Network's link The large dishes, designated the Downlink traffic through the with the Earth is the North, Central, and South antennas, TDRSS satellites consists primarily TDRSS White Sands dispatch transmissions to, and of telemetry data. Spacecraft report Ground Terminal in New receive transmissions from, the their current physical condition Mexico. satellites. These dishes are the links such as their operating tempera- Three giant 18.3-meter-diameter between the TDRSS satellites and ture, fuel levels, and power supply (60-foot) dish antennas reach the Earth. and the results of their observa- skyward above a desert plain Smaller antennas are used for tions or experiments. Shuttle crews surrounded by mountains. Several related functions such as testing use TDRSS voice channels for smaller antennas are nearby. So are spacecraft for their compatibility conversations with Mission Control. office and equipment buildings. with the Network before their The New Mexico site was chosen Here, in this southwestern state, launch. These antennas can as the TDRSS ground focus partly not far from the U.S. bonier with simulate transmissions to and from because the region's dry climate Mexico, is the hub of the Space a spacecraft while it is still on and sparse rainfall is favorable for Network The White Sands antennas the ground. the heavy electronic traffic. Heavy connect the Earth with the TDRSS Through the TDRSS satellites rains and even high humidity can satellites and through them with pass commands to spacecraft to seriously interfere with communi-za- the growing community of low- adjust their positions by firing a tions at the system's frequencies. orbiting U.S. spacecraft. thruster, to turn a camera or heater This could become particular'y The White Sands Ground or other on-board equipment on or detrimental because the two active Terminal acts like the neck of an off, to start or stop observations, satellites are not directly overhead, hourglass or the tube of a funnel. and to begin or stop transmissions but on near opposite horizons from All transmissions from Earth to the tc the Earth. Also passing through the White Sands Terminal. Although TDRSS satellites, or from them to the uplinks are instructions or data both satellites are continuously in Earth, pass through this station. for storage in a spacecraft's the line of sight of the White Sands Since the Space Network will memory. Later the spacecraft can Ground Terminal for uninterrupted eventually serve nearly all low- draw on this information for communications contact, their orbiting U.S. spacecraft, virtually all guidance in automated operations. lines of sight to the station pass U.S. communications traffic through the atmosphere over a long between the Earth and nearby diagonal route. Heavy atmospheric spaceuplink and downlinkwill moisture could rause severe ultimately pass through the White absorption and degradation of Sands facility. transmissions.

GROUND TERMINAL Nestled on a desert plain surrounded by mountains, is the 1DRSS White Sands Ground Terminal in New MeAico in the southwestern United States. Since nearly all communica- tions to and from low- orbiting U.S. spacecraft, including Shuttle communications, will in the future be passing through the 1DRSS satellites, this terminal will be the hub for contact between the Wr Earth and near-Earth 4StViAlrj.7Rir space for the United .f. 4t . '114 k." States. The New Mexico station is Typically, telemetry from a low- One kind of receiving location is responsible for operating the orbiting spacecraft may follow a called a "Payload Operations antennas and the equipment for zigzag route to its ultimate Control Center" (POCC), and it is at processing the radio-frequency destination into the hands of these POCCs where researchers signals and for maintaining the researchers. Transmissions from a obtain the instantaneous results quality of theNetwork'sspace low-orbiting spacecraft are first from their research equipment services. But the White Sands directed upward to aTDRSS aboard a spacecraft. This allows Ground Terminal is only a part of satellite, which instantaneously researchers to order adjustments to the Network'sground segment. relays them down to the White on-board instruments as indicated TheNetworkControl Center is at Sands Ground Terminal. From there by the early feedbacl; so as to the Goddard Space Flight Center in the transmissions may be sent up obtain the best scientific results Greenbelt Maryland, a few miles to a commercial communications from their experiments. from Washington, D.C. Here, at the satellite, which relays them to the Most detailed analysis is done at main control room, technicians Goddard Space Flight Center. There the laboratories of the researchers, work at 19 dual monitor consoles data is processed into forms useful and some of the POCCs are located 24 hours a day, seven days a week. for research and applications. at their home laboratories on len other consoles are nearby for From the Goddard Center the university campuses and in supervisory personnel, for service data may move up again to another research centers. scheduling, and for emergency commercial satellite that will relay backup. The Center monitors, it to the appropriate data handling manages, controls, and coordinates center where it will be analyzed by theNetwork researchers and archived for future Technicians here draw up the recall. Less urgent transmissions THREE ANTENNAS, will be the main corn- schedules for the times and are recorded on magnetic tape each 18.3 meters (60 inunications links for duration theTDRSSsatellites are to and mailed. feet) in diameter, a; ,,early all low-orbiting be used for transmissions to and White Sands, are the i'.S. spacecraft. from any particular spacecraft. main communications Control Center personnel also links between the Earth schedule the routing for and the 1DRSS satellites. transmissions received from each The satellites, in turn, spacecraft. These transmissions are distributed to NASA project operations control centers and to each experiment's data analysis laboratory and through them to the individual researchers. These " project operations control centers analyze the incoming telemetry and often respond with requests that theNetworkControl Center forward commands to adjust a craft and its equipment. The distribution of spacecraft telemetry is made through the global NASA Communications Network (NASCOM), which also has ti. Its headquarters at the Goddard Center. NASCOM uses land lines, ocean cables, microwave links, and commercial satellites as appropriate for each particular communication.

1 12 For example, the Pocc for a COMPLEX ZIGZAGGING research spacecraft known as the communications links of Solar Mesosphere Explorer is NASA's modern TDRSS are located at the University of depicted in this diagram. Colorado, Boulder, Colorado. For The sequences Shuttle flights, the Mission Control demonstrate the central role of the 1DRSS Center is at the Johnson Space satellites. Shown here is Center in Houston, Texas. For a Landsat Earth resources Spacelab, dual POCCs are at the observation craft (big Marshall Space Might Center, craft in center) Huntsville, Alabama, and at a establishing its position European Space Agency facility in through references to West Germany. POCCs for several four other craft (dotted spacecraft are located at the lines), then scanning the Goddard Space night Center, Earth (depicted here as a Greenbelt, Maryland. beam on large arrow on Earth). The craft then Also received at the Goddard transmits its Center is information gathered by observations to the special instruments on Earth from 1DRSS (top center). The which the precise location of the TDRSS also receives TDRSS satellites can be deter mined. transmissions fro,, the These instrumentsa Bilateration Shuttle and the Space (monitoring from two sides) Telescope (lower and Ranging Transponder System middle right). The 1DRSS obtain ranging data which are satellite returns all of transmitted to the Goddard these transmissions to Center's Might Dynamics Facility. the White Sands Ground Terminal in New Mexico There, powerful computers calculate (bottom left antenna) the precise location of each TDRSS which, in turn, sends the satellite. transmissions up to a While a spacecraft communicates commercial satellite with a TDRSS satellite, the TDRSS (upper left corner). That simultaneously gathers ranging satellite returns the information on that spacecraft and transmissions to the transmits this information to the Goddard Space flight ground. The same Goddard Center (antenna at computers use this data to bottom right). There, calculate the precise position of transmissions are processed and each of the various spacecraft. distributed to researchers Thus, the Space Network and other users of the involves substantial installations on information. the ground as well as in space.

13 Why TDRSS Is Needed Its Rationale and History

Chapter 4 Staccato beeps and In those early days of the space These spacecraft, at altitudes of wavering whining tones age, communication with orbiting up to only a few hundred were the first sounds the craft was made possible by kilometers, were typically able to public came to know from strategically played Earth stations. communicate with the ground no satellites in space. They were scattered across more than about 15 percent of the The sounds, which were often continents beneath the typical time. For 85 percent of each orbit, replayed on radio newscasts in the orbital paths of early spacecraft. they were beyond any communica- late 1950s, were part of the The construction, maintenance, tion contact. telemetry through which these repair, and operation of these Earth This was true even though the satellites made known their stations required negotiations with ground network was supplemented presence, their orbital paths, and the governments of the various during many of the flights by the findings of their scientific nations on whose territories these tracking ships and communications observation instruments. staions were built. Entry permission aircraft to provide coverage at Much has changed in space had to be obtained for U.S. locations where ground stations operations since then, but personnel and equipment. Access were unavailable or impractical. communication is still essential could not always be readily gained In the U.S. Mercury, Gemini, today. When the beeps or whines even though many of these coun- Apollo, and Skylab programs of the stop and the telemetry ceases tries took great pride and satisfac- 1960s and 1970s and the first when a spacecraft can no longer tion in the role the stations gave several Shuttle flights in the 1980s, communicateit becomes them in early space explorations. the combined communication time worthless no matter how well its Although these stations served with all Earth stations averaged less remaining instruments work. If it the early U.S. space program well, than 15 minutes during each 90- cannot transmit its findings, a they demonstrated severe disadvan- minute orbit. Unmanned, satellite instantly turns into "space tages. Spacecraft in orbits of up to automated spacecraft in low orbits junk," a useless artifact racing only a few hundred kilometers fared no better, and some ground purposely through the sky. above the Earth's surface could stations could monitor only two The first U.S. spacecraft communicate with these stations spacecraft at a time. Explorer Ileft its imprint on only sporadically. By the early 1970s U.S. space history not merely by its Communications was possible planners knew that the network of spectacular launch on January 31, only frvin the time a spacecraft Earth stations would be inadequate 1958, but even more so by the rose above a station's horizon until for the ambitious projects of the scientific observations it it disappeared below the opposite Shuttle era. A fleet of Space communicated. Its transmissions horizon. Such overhead passes were Shuttles, each with a bus-sized from orbit led to the important typically only a few minutes long, cargo bay, then on the drawing discovery of previously unknown and on most orbits a craft rarely boards, would carry 1,:to space a radiation zones surrounding the passed more than a few stations. All series of research instruments Earth. These zones were named the U.S. manned spacecraft, except equal to a small research center. "Van Allen Belts" after the flights to the Moon, were in such With crews of up to eight persons University of Iowa physicist who low orbits. working in shifts around the clock had designed the experiments on throughout a Shuttle flight of up to board Explorer I. eight days or longer, voice and data communications would take on giant dimensions.

1.1ht A Cd AnT BLasson the unfolded 4.9-meter diameter (16.3 -loot) antenna of a 1DRSS mtellite makes a startling sight during ground test,,

14 15 :,--:,: Similarly, unmanned, automated Many more ground stations Preliminary studies of a possible science and applications spacecraft would be needed. The capacity of space-based tracking and data relay were growing in size and weight. the existing stations would have to system had been underway within They carried more instruments, and be significantly enhanced. Studies NASA for several years. In one many of these instruments were showed that even with these costly experiment the ATS-6 Earth more complex than those carried by improvements the network of synchronous spacecraft successfully their predecessors. Their commun- ground stations would still fall far relayed commands from Earth to a ications needs would multiply many short of the nearly continuous Nimbus weather and environmental times. coverage desired for the Shuttle spacecraft. ATS-6 then gathered For example, environmental and and other spacecraft at low orbital data transmissions from the resources observation satellites altitudes. Nimbus and relayed them to Earth. were about to add sophisticated Furthermore, quick retrieval of These experiments demonstrated new equipment. The Hubble Space telemetry data collected at the that a space-based system was Telescope, which is expected to ground stations scattered around feasible with available technologies. provide unprecedented the world would be needed. These The envisioned system could meet astronomical observations, will call data would have to be sent to all expected new requirements for for complex transmissions for central collection points at high- communications, data acquisition, remote control of its instruments volume transmission rates. Costs of and tracking. Its projected costs, and, in turn, should yield such a service would be very high. when amortized over 10 years, voluminous observational data for compared favorably with the conveyance to the Earth. estimated expenses of upgrading and operating the ground station system. Moreover, only one ground

'I' ANTENNAS and solar panels snugly folded, a TDRSSsatellite is being readied for mating to its booster rocket.

%al

THRUSTER ENGINES, thruster was also used to like this one -pound moue the firstTURSS model, are used 11 keep satellite to its proper TDRSSsatellites from orbit after a malfunction dnfting from the precise in its booster rocket had positions they must inserted it into an retain for their work. This unsatisfactory orbit.

0 r..) 16 terminal would be needed for global The first satellite was launched When the new system is coverage with obvious savings in on April 4, 1983, in what was then complete, only a few ground construction and maintenance, and the sixth orbital flight of a Shuttle. stations will be retained. Among administrative costs. A malfunction in the Inertial Upper them will be the stations at Merritt In its financial analysis, NASA Stage, to which the satellite was Island, Florida, and '.nose in found that it would be advanta- attached, placed the satellite into Bermuda. They are used by the geous to lease the new system an unsatisfactory egg-shaped orbit Shuttle during its launches and rather than to own it. This would in which its communications landings when the flight position of allow NASA to use its current coverage was very limited. the Shuttle antennas makes budget resources for space research Specialists from the Goddard communication through the TDRSS and Shuttle development rather Center, TRW, and SPACECOM satellites impossible. Also to be than tying up large capital developed plans to correct the orbit retained are stations needed to expenditures for the new system. by commanding the satellite to fire service spacecraft whose orbits are NASA would then pay for the system its thrusters in a carefully times incompatible with the TDRSS. as it was being used over 10 years series of bursts. The maneuvers When the Space Network begins through annual service fees. were successful, and on June 29, full operations NASA will be Thus, in December 1976, NASA 1983, the satellite reached its prepared to give low-orbiting contracted with the Space Commun- intended circular synchronous spacecraft tti communications ications Company (SPACECOM), now orbit. support needed for the exciting headquartered at Gaithersburg, While awaiting the completion of space projects planned for the Maryland, to develop the system the TDRSS with the launches of the remaining years of this century. and lease it to NASA. system's other two satellites, the Subcontractors were the Harris 25-year-old network of ground Government Communications stations has continued to serve, System Division, Melbourne, augmenting the single TDRSS Florida, and TRW Defense & Space satellite. Systems Group, Redondo Beach, California. Harris furnished the

White Sands Ground Terminal 11,..rmImailm. equipment and the single access antennas. TRW designed, built, and tested the three satellites and integrated the ground terminal equipment. Funds were borrowed from the U.S. Treasury Department's Federal Financing Bank.

TOMS SATELLITE perched on its booster rocket is ready for stowage into the Shuttle cargo bay for launch. The booster, called an Inertial Upper Stage (IUS), lifts USA the 1DRSS satellite from the Shuttle's low orbit to the high orbit the1DRSS requires. Note worker at lower left for comparison with IUS-satellite size.

I

17 4-, Pri The Space Network Today and Tomorrow Fresent and Future Uses

Chapter 5 The regions above the Earth's dense layer of atmosphere, which were beyond reach by any means until the middle of this century, are gradually becoming sites for routine scientific research and commercial and industrial operations. NASA's fleet of Space StilIles has made frequent flights of up to eight days or longer into these regions with up to eight-member crews. Dozens of complex tomated craft in low-altitude its are also showing that these areas offer unique, extremely useful attributes. These once forbidding regions are turning into familiar, beneficial zones.

"The c .tinuous THL HUBBLE SPACE Landsat 4, nght, is one of communications contacts, the TELESCOPE, left, is the biggest 1DRSS users fulltime data retrieval, and the expected to become one for applications. The very high data rate capacity of the heaviest users of Landsat s 'Thematic the 1DRSS satellites for Mapper" and its other have which TDRSS affords, transmission of images observation instruments introduced a new dimension of astronomical objects require voluminous into the mission planning and and other communications conduct of complex space communications of its channels to Earth. missions." scientific findings.

Robert Cc Aller NASA Associate Administrator For Space Tracking and DataSystems in a speech at 36t1. Meting of International Astronautical Federation, October 1985, Stockholm, Sweden

18 Accordingly, the demand for spacecraft. asp.; the retrieval and The Space Station is expected to Earth-to-orbit and orbit-to-Earth in-orbit repairs of malfunctioning become a hub for scientific, communication channels is spacecraft. As the costs and industrial, and commercial research multiplying rapidly. High-volume, complexity of automated spacecraftand, eventually, a manufacturing continuous communications continue to rise, in-orbit servicing racility for products with qualities channels are needed by Shuttle and maintenance of these craft by that can be achieved only in the crews, research scientists, users of Shuttle crews becomes more and prolonged low gravity or high weather and Earth resources space- more economically attractive. vacuum of space. craft, and even by entrepreneurs Shuttle crews working in two Materials processing experi- looking into incipient investment shifts of 12 hours each need nearly ments, which began in early U.S. opportunities for commercial and around-the-clock communciations manned space flights in the 1960s industrial high-technology ventures channels. These needs and wants and 1970s, have been expanded on in space. The new TDRSS is are bound to multiply when Shuttle Shuttle flights. Early candidates for designed to till these growing crews begin to assemble in orbit manufacturing in orbit are communications needs and wants. the planned U.S. Space Station, and medicines and pharmaceutical Shuttle crews, who are the when that Space Station begins its products on which many people primary users of the new Space own operations in the 1990s. The may come to depend for then Network, require nearly continuous station will be a permanent, well-being: crystals and other voice, television, data, and continuously inhabited research electronic components for faster telemetry channels to and from and work facility requiring nearly and "smarter" computers than any Mission Control. They rued to relay continuous voice, television, data, now available; and alloys with current research and operational and telemetry channels to Earth. unprecedented strength and information and to obtain expert Astronauts, scientists, engineers, conductivity. input for their work from specialists and other specialists will be living NASA's Office of Commercial on the ground. and working in the Space Station Programs was established in 1984 That work nowadays involves for periods of up to several months to encourage and help businessmen complicated scientific experiments until new crews replace them. The invest in and establish commercial with sophisticated on-board regions in near-Earth orbit will enterprises in space. President instruments, the launching from never again be uninhabited at Reagan has predicted that "before the Shuttle's cargo bay of costly any time. the end of this century, many commercial and scientific billions of dollars of commercial activity will be taking place in and because of space." Studies indicate that some 500 materials may be advantageously produced in space. Among these are glasses with until now unachievable optical qualities, lighter and stronger alloys from metals which cannot be uniformly mixed on Earth because of their widely varying weights, and biological substances which cannot be separated within the pull of Earth's gravity. As raw materials and manufactur- ing equipment are transported to the Space Station and finished products are returned to Earth, and as production and research crews are rotated, the demands for voice and data communications channels are bound to intensify.

26 Similarly, the demand for Experience over a quarter of a From these observations communications by unmanned century of manned space opera- researchers expect to learn much applications spacecraft is growing. tions has shown that lengthy dia- about still mysterious celestial For example, two Earth resources logue between Mission Control and entities and processes taking place observation satellites, Landsat 4 spacecraft crews can become at nearly incredible distances and and 5, are equipped with "Thematic essential for survival in emergen- about the evolution and possible Mappers," powerful remote sensing cies. Life-threatening damage to future of the universe. About 30 instruments which gather valuable the Apollo 13 craft from an minutes of extensive transmissions observations about conditions on on-board explosion during a flight throagh the TDRSS satellites are the Earth. These instruments to the Moon in 1970 was overcome expected to be needed on each of required high-rate communications mainly because experts on the the telescope's orbits. These channels to relay their huge ground were able to discuss at transmissions are needed for volumes of findings. Until the first length with the crew how best to operating the telescope's ,DRSSsatellite began its opera- compensate for the impaired instruments, for tracking the craft, tions, the Thematic Mappers' equipment. and for relaying to Earth its large observations could not be trans- One of the chief science users of quantities of measurements and mitted to Earth because of the the new Space Network will be the images gatherer' on each orbit. limited ground station capabilities. Hubble Space Telescope. The new These transmissions will be The single TDRSS satellite in telescope's optics will see objects channeled to the Space Telescope orbit since '983 has already proven 50 times fainter than today's best Science Institute Facility at the it can provide the stringen instruments can discern. It will look Johns Hopkins University, Balti- communciations needs of space back in time, viewing radiations more, Maryland. There, all of the recovery operations. The satellite's from the edge of the universe that telescope's observations will be ability to communicate with the have been traveling at the speed of analyzed and arcnived for continu- Shuttle for almost half of each orbit light for billions of years. ing studies by scientists. greatly aided Mission Control in monitoring the successful in-orbit repairs by astronauts of the malfunctioning Solar Maxir. Im Mission scientific spacecraft in 1984. Similarly, the TDRSS played a crucial role in the retrieval of two < crynmunications satellites in improper orbits in that same year, and in the repair of the failing Syncom IV -3 in 1985.

SPACUAB, the orbital European built sesean h ., module that fits into the Shuttle cargo bay, generates colossal quantities of scientific data, which need to be quickly transmitted to Earth. Spacelab has been one of the heaviest users of ID RSS.

27 20 Other major science users of the Eventually most U.S. spacecraft TDRSS are expected to be a variety in low-Earth orbits are expected to of low-orbiting spacecraft studying be serviced by the new Network, physical and chemical processes of substantially enhancing their the upper atmosphere, measuring performance through more flexible Earth's gravitational and magnetic operations and high data rate properties, and examining and capacity. In these and other ways mapping aspects of the galaxy and the Space Network is expected to the distant universe. have profound impact on the future Materials Science Among these is the "Solar of the U.S. space program. Mesosphere Explorer," a spacecraft On the Earth, the growth in the instrumented for examining certain quality and quantity of communica- constituents of the upper atmo- tions facilities has changed our way sphere such as ozone and nitric of life. With the nearly universal acid concentations. The craft has availability of telephones, radio, and been communicating up to now television, which has come about in through the Earth stations of the this century, instantaneous access current Spaceflight Tracking and to news, information, Space Plasma Physics Data Network (STDN), but is entertainment, and to expected to change to the new person-to-person electronic Space Network. communication is taken for Also expected to be served by the granted. new Network are the "Cosmic The communications revolution Background Explorer' through of the last several decades has which scientists are gradually brought people on the Earth closer, assembling a full-sky map of diffuse shrinking or wiping out many of the cosmic background radiations; the once formidable barriers between "Gamma Ray Astronomy them. Modern communication has Ouservatory," which is examining had significant impact on the structure of our galaxy; the commerce, industry, education, "Earth Radiation Bue,et medicine, and almost every other Astronomy and Solar Experiment," measuring the human activity. Physics absorption and reflection of solar The new Space Network is an radiations by the Earth; the extension of that communications "Geopotential Research Mission," revolution into space. The Network accumulating gravity and magnetic will open unprecedented new Earth data; and the "Upper possibilities and opportunities for Atmosphere Research Satellite." making use of the unique attributes of space for science, industry, and numerous other valuable purposes. The end of total dependence on Earth-based stations for space SMITTLL CAHOOLS are usually extensive users communications closes an of the TDKSS satellites. important chapter in the history of Scientific instruments in the U.S. space program. The Space the Shuttle 5 cargo bay Network is designed for service require communications now and in the future. A fully for monitoring and functioning Space Network is the control from Earth and beginning of what might be called for quick analysis of the Space Communications Age. instrument outputs so that instrument adjustments can be made. Shown here are various configurations of Spacelab scientific and applications research Atmospheric Physics and payloads. 21 faith Observations 2 Technical Information

TheTDRS5operates at both TheSingle Access Service (SA)is Each antenna responds indepen- S-band (2025-2300 mHz) divided into two frequency bands, dently to steering commands from and at Ku-Band (13700- the S-band (SSA) and the K-band theTDRSSWhite Sands Ground 5115 mHz). (KSA), and uses very sensitive steer- Terminal. To reach the maximum The Multiple Access Service (MA) able 4.9-meter (16.3-foot) parabolic data relay capacity a spacecraft also ono-ates in the S-band communica- dish antennas to communicate with needs to be equipped with a -as frequency and uses a fixed one spacecraft at a time. Each steerable high-gain antenna. antenna on theTDRSSsatellite to TDRSSsatellite has two such (For example, Landsat 5 is communicate with many spacecraft antennas. The SSA and KSA services equipped with 1.8-meter para- at the same time. This service is are available simultaneously. The SA bolic antenna and transmits its designed for low-rate, long-duration service is designed for spacecraft Thematic Mapper data toTDRSSat users. Precise location of the which require large quantities of 84 megabits per second. The Space spacecraft can be determined, but data to be relayed. Telescope will have a 1.3-meter is not required for use of the MA Communication through these antenna with a data rate of 1.024 services. The amount of data antennas requires precise informa- megabits per second on the (band-width) which can be relayed tion about the location of a S-band.) to the Earth is limited to 50 spacecraft so as to point the steer- The space-to-ground link (SGL) kilobits per second. able satellite antenna to that space- antenna is a gimballed 2-meter craft. Transmissions up to 6 (6.6-foot) parabolic reflector on the megabits per second can be made end of a fixed arm. It provides at the S-band frequencies and up to high-power K-band SGL communica- 300 megabits per second in the tions between theTDRSSsatellite Solar Array K-band frequencies. Stepping and the White Sands Ground motors in the arm and base of each Terminal. All data to and from antenna move them to follow the spacecraft serviced by theTDRSS motion of the spacecraft with which flows through this antenna. they are communicating.

2.0 Meter K-band K-band Antenna Antenna (1DRS Space/ (Conune Ida! Ground Link) Coverage)

MINIM.611116. 4.9 Meter Antenna (2) (MRS K/S band Single Access Service and Commercial K-band Spot Ream)

Stand Phased Array (1DRS Multiple Access C-band Antenna DISH AP TENIYAS of the Service) S-band (Commercial Coverage) Omni TDRSS satellite, seen Antenna from above, look like two long folded umbrellas as Solar Sall technicians inspect the hinges and deployment mechanisms prior to loading the satellite into the Shuttle cargo bay for launch. The White Sands Ground Equipment is maintained to Computer software to receive Terminal provides the following separate up to 20 signals from service requests from NASA and equipment and services: the MA phased array outputs and to convert these into equipment Three 18-meter (60-foot) K-band to properly prepare MA forward allocations and configurations antennas serving the space-to- commands for transmission to through which these requests can ground link for the two active specific spacecraft communi- be executed. TDRSSsatellites and the backup cating through the MA system. Computer capability to monitor satellite. An S-band telemetry and The software to determine range TDRSSsatellite operations and to command antenna for commun- and range rate tracking data warn system controllers when ications with the spare satellite. measurements from spacecraft action may be necessary. Several other antennas for communications signals. These Instruments for these functions simulation and calibration of measurements are required for are housed in the equipment and spacecraft to test and adjust the determination of spacecraft office buildings at White Sands, their compatibility with the locations and orbit parameters. New Mexico. TDRSSnetwork. The information is used to steer Central radio frequency receivers, the TDRSS satellite's SA antennas For additional information contact: transmitters and associated RF for communication with these National Aeronautics and Space signal processing equipment spacecraft. Administration necessary to receive and process Washington, D.C. 20546 data streams from spacecraft and to prepare forward signals for transmission to these spacecraft.

TDRSS MRSS Service Service (fast) (West)

TDRSS Uplink and Downlink Return forward K-band Link Link

Multiple K-band Access Single S-band K-band Multiple Access Access S- and S-Band K-band

Single Access S- and K-band

TDRSS around Terminal

User Spacecraft User 23 Spacecraft 30 THESt/LITTLE is 7 u the TDRS ti satellitesIn to s Shuttle,in thehe most os Rse xt of the Mun S communicationscomm services.Shuttle use DI transmission of videu.mi data.1DRSS is vast expandingthe Shlul as well for low-orbitingtutinnnigasnPanspacec Most treasures which have come fran space to Earth so far have been in the form of information and observations. These are leading to knowledge and understanding perhaps more precious than material returns. The three TDRSS satellites and their associated ground facilities substantially increase the quantities of information and observations which can be transmitted to the Earth.

3.2