STS 15-L
TRACKING AND DATA RELAY SATELLITE SYSTEM (TDRSS) AND TDRS-B 
The Tracking and Data Relay Satellite (TDRS-B) is the second TDRSS advanced communications spacecraft to be launched from the orbiter Challenger. The first was launched during Challengers maiden flight in April 1983. TDRS-1 is now in geosynchronous orbit over the Atlantic Ocean just east of Brazil (41 degrees west longitude). It initially failed to reach its desired orbit following successful Shuttle deployment because of booster rocket failure. A NASA-industry team conducted a series of delicate spacecraft maneuvers over a 2- month period to place TDRS-1 into the desired 22,300-mile altitude. Following its deployment from the orbiter, TDRS-B will undergo a series of tests prior to being moved to its operational geosynchronous position over the Pacific Ocean south of Hawaii (171 degrees W. longitude). A third TDRSS satellite is scheduled for launch in July 1986, providing the Tracking and Data Relay Satellite System with an on-orbit spare located between the two operational satellites. TDRS-B will be identical to its sister satellite and the two-satellite configuration will support up to 23 user spacecraft simultaneously, providing two basic types of service: a multiple access service which can relay data from as many as 19 low-data-rate user spacecraft at the same time and a single access service which will provide two high-data-rate communications relays from each satellite. TDRS-B will be deployed from the orbiter approximately 10 hours after launch. Transfer to geosynchronous orbit will be provided by the solid propellant Boeing/U.S. Air Force Inertial Upper Stage (IUS). Separation from the IUS occurs approximately 17 hours after launch. The concept of using advanced communication satellites was developed following studies in the early 1970s which showed that a system of communication satellites operated from a single ground terminal could support Space Shuttle and other low Earth-orbit space missions more effectively than a world-wide network of ground stations. NASAs Space Tracking and Data Network ground stations eventually will be phased out. Three of the networks present 12 ground stations ñ Madrid, Spain; Canberra, Australia; and Goldstone, CA ñ have been transferred to the Deep Space Network managed by the Jet Propulsion Laboratory in Pasadena, CA, and the remainder ñ except for two stations considered necessary for Shuttle launch operations ñ will be closed or transferred to other agencies after the successful launch and checkout of the next two TDRS satellites. The ground station network, managed by the Goddard Space Flight Center, Greenbelt, MD, provides communications support for only a small fraction (typically 15-20 percent) of a spacecrafts orbital period. The TDRSS network of satellites, when established, will provide coverage for almost the entire orbital period of user spacecraft (about 85 percent). A TDRSS ground terminal has been built at White Sands, NM, a location that provides a clear view to the TDRSS satellites and weather conditions generally good for communications. The NASA Ground Terminal at White Sands provides the interface between the TDRSS and its network elements, which have their primary tracking and communication facilities at Goddard. Also located at Goddard is the Network Control Center, which provides system scheduling and is the focal point for NASA communications with the TDRSS satellites and network elements. The TDRSS satellites are the largest privately-owned telecommunications spacecraft ever built, each weighing about 5,000 lb. Each satellite spans more than 57 ft., measured across its solar panels. The single access antennas, fabricated of molybdenum and plated with 14k gold, each measure 16 ft. in diameter, and when deployed, span more than 42 ft. from tip to top.
The satellite consists of two modules. The equipment module houses the subsystems that operate the satellite. The telecommunications payload module has electronic equipment for linking the user spacecraft with the ground terminal. The spacecraft has seven antennas. The TDRS spacecraft are the first designed to handle communications through S, Ku and C frequency bands. Under contract, NASA has leased the TDRSS service from the Space Communications Co. (Space com), Gaithersburg, MD, the owner, operator and prime contractor for the system. TRW Space and Technology Group, Redondo Beach, CA, and the Harris Government Communications System Division, Melbourne, Fl, are the two primary subcontractors to Space com for spacecraft and ground terminal equipment, respectively. TRW also provided the total software for the ground segment operation and did the integration and testing for the ground terminal and the TDRSS, as well as the systems engineering. Primary users of the TDRSS satellite have been the Space Shuttle, Landsat Earth resources satellites, the Solar Mesosphere Explorer, the Earth Radiation Budget Satellite, the Solar Maximum Mission satellite and Spacelab. Future users include the Hubble Space Telescope, scheduled for launch Oct. 27, 1986; the Gamma Ray Observatory, due to be launched in 1988; and the Upper Atmosphere Research Satellite in 1989

INERTIAL UPPER STAGE 
The Inertial Upper Stage (IUS) will be used to place NASAs second Tracking and Data Relay Satellite (TDRS-B) into geosynchronous orbit. The first TDRS was launched by an IUS aboard Challenger in April 1983 during mission STS-6. The 51-L crew will deploy IUS/TDRS-B approximately 10 hours after liftoff from a low-Earth orbit of 153.5 nautical miles. Upper stage airborne support equipment, located in the orbiter payload bay, positions the combined IUS/TDRS-B into the proper deployment attitude ñ an angle of 59 degrees ñ and ejects it into low-Earth orbit. Deployment from the orbiter will be by a spring eject system. Following deployment from the payload bay, the orbiter will move away from the IUS/TDRS-B to a safe distance. The first stage will fire about 55 minutes after deployment. Following the aft (first) stage burn of two minutes, 26 seconds, the solid fuel motor will shut down and the two stages will separate. After coasting for several hours, the forward (second) stage motor will ignite at six hours, 14 minutes after deployment to place the spacecraft into its desired orbit. Following a one-minute, 49-second burn, the forward stage will shut down as the IUS/TDRS-B reaches the predetermined geosynchronous orbit position. Six hours, 54 minutes after deployment from Challenger, the forward stage will separate from TDRS-B and perform an anti-collision maneuver with its onboard reaction control system. After the IUS reaches a safe distance from TDRS-B, the upper stage will relay performance data back to a NASA tracking station and then shut itself down seven hours, five minutes after deployment from the payload bay. As wit the first NASA IUS launched in 1983, the second has a number of features which distinguish it from other previous upper stages. It has the first completely redundant avionics system ever developed for an unmanned space vehicle. The system has the capability to correct in-flight features within milliseconds. Other advanced features include a carbon composite nozzle throat that makes possible the high-temperature, long-duration firing of the IUS motors and a redundant computer system in which the second computer is capable of taking over functions from the primary computer if necessary. The IUS is 17 ft. long, 9 ft. in diameter and weights more than 32,000 lb., including 27,000 lb. of solid fuel propellant. The IUS consists of an aft skirt; an aft stage containing 21,000 lb. of solid propellant fuel, generating 45,000 lb. of thrust; an interstage; a forward stage containing 6,000 lb. of propellant, generating 18,500 lb. of thrust; and an equipment support section. The equipment support section contains the avionics which provide guidance, navigation, telemetry, command and data management, reaction control and electrical power. Solid propellant rocket motors were selected in the design of the IUS because of their compactness, simplicity, inherent safety, reliability and lower cost. The IUS is built by Boeing Aerospace Corp, Seattle, under contract to the U.S. Air Force Systems Command. Marshall Space Flight Center, Huntsville, AL, is NASAs lead center for IUS development and program management of NASA-configured IUSs procured from the Air Force. 
SPARTAN-HALLEY MISSION 
For the Spartan-Halley mission, NASAs Goddard Space Flight Center and the University of Colorados laboratory for Atmospheric and Space Physics (LASP) have recycled several instruments and designs to produce a low-cost, high-yield spacecraft to watch Halleys Comet when it is too close to the sun for other observatories to do so. IT will record ultraviolet light emitted by the comets chemistry when it is closest to the sun and most active so that scientists may determine how fast water is broken down by sunlight, search for carbon and sulfur atoms and related compounds, and understand how the tail evolves. Principal investigator is Dr. Charles Barth of the University of Colorado LASP. Mission manager is Morgan Windsor of Goddard Space Flight Center. The Instruments Two spectrometers, derived from backups for a Mariner 9 instrument which studied the Martian atmosphere in 1971, have been rebuilt to survey Halley’s Comet in ultraviolet light from 128 to 340 nanometers (nm) wavelength, stopping just above the human eyes limit of about 400 nm. Each spectrometer uses the Ebert-Fastie design: an off-axis reflector telescope, with magnesium fluoride coatings to enhance transmission which focuses light from Halley, via s spherical mirror and a spectral grating, on a coded anode converter with 1,024 detectors in a straight line. The grating is ruled at 2,400 lines per millimeter. The detectors are made of cesium iodide (CsI) for the G-spectrometer (128-168 nm) and cesium telluride (CsTe) for the F-spectrometer (180-340 nm). The system has a focal length of 250 mm and an aperture of 50 mm. The F-spectrometer grating can be rotated to cover its wider range in six 40 nm sections. A slit limits its field of view to a strip of sky 1 by 80 arc-minutes (the apparent diameter of the moon is about 30 arcminutes). The G-spectrometer has a 3 x 80 arc-minute slit because emissions are fainter at shorter wavelengths. With Halley as little as 10 degrees away from the sun, two sets of baffles must be used to reduce stray light. An internal set is part of the Mariner design. A new external set serves both instruments. It has two knife-edge baffles 38.5 inches away from the spectrometer entrances, and 20 secondary baffles to stop earthlight. Together, the two baffle sets reduce stray light by a factor of a trillion. It is this system that will make it possible for Spartan-Halley to observe the comet while so close to the sun. In addition, internal filters reduce solar Lyman-alpha light (121.6 nm), scattered by the Earthís hydrogen corona, which would saturate the instruments. Two film cameras, boresighted with the spectrometers, will photograph Halley to assure pointing accuracy in post-flight analysis and to match changes in the tail with spectral changes. The 35 mm Nikon F3 cameras have 105 mm and 135 mm lenses and are loaded with 65-frame rolls of QX-851 thin-base color film. The cameras will capture large-scale activity such as the separation angle between the dust and ion tails, bursts from the nucleus, and asymmetries in the shape of the coma. The whole instrument package is mounted on a n aluminum optical bench ñ 35 by 37 inches and weighing 175 lb. ñ attached to the Spartan carrier. This provides a clean interface with the carrier and aligns the spectrometers with the Spartan attitude control sensors. A 15-inch-high housing covers the spectrometers and the cameras. The instrument package is controlled by a LASP-developed microprocessor which stores the comet Halley ephemeris and directs the Spartan carrier attitude control system.


MISSION OPERATIONS 
Halley’s Comet will be of greatest scientific interest from Jan. 20 to Feb. 22; perihelion is on Feb. 9. At that time, Halley will be 139.5 million miles from Earth and 59.5 million mi. from the sun. The Shuttle will go into an orbit 176 miles high and inclined 28.5 degrees to the equator. This will have Halley visible for more than 3,000 seconds per orbit (about 56 percent of the orbit), including more than 90 seconds with the sun occulted by the Earth. After a pre-deployment health check of Spartan voltages and currents, the Shuttle robot arm will pick up the spacecraft and hold it over the side. Upon release, Spartan will perform a 90-second pirouette to confirm that it is working and the Shuttle will back away to at least five miles so light reflected from the Shuttle does not confuse Spartan’s sensors. After two orbits of preparation, the 40-hour science mission will begin. A backup timer will ensure that the spectrometer doors open 70 minutes after release. Spartan-Halley will conduct 20 orbits of science observations interspersed with five orbits of attitude control updates. A typical science orbit will start with four 100-second calibration scans of Earthís atmosphere, followed by a 900-second tail scan. Observing will be interrupted for 15 minutes of pointing updates and housekeeping. It then resumes with four 200-second scans of the coma, followed by sunset and four coma scans while the sun is occulted. At the end of the mission Spartan-Halley will be retrieved by the Shuttle robot arm and placed in the payload bay. After the mission, the processed film and data tapes will be returned to the University of Colorado team for scientific analysis. 
The Science 
Current theories hold that comets are dirty snowballs made up largely of water ice and lightweight elements and compounds left over from the creation of the solar system. Remote sensing of the chemistry of Halley’s Comet, by measuring how sunlight is reflected, will help in assaying the comet. The dirt in the snowball is detectable in visible light, and the snow (water ice) and other gases are detectable, indirectly, in ultraviolet. The most important objective of the Spartan-Halley mission is to obtain ultraviolet spectra of comet Halley when it is less than 67 million miles from the sun. As Halley nears the sun, temperatures rise, releasing ices and clathrates, compounds trapped in ice crystals. The highest science priority for Spartan is to determine the rate at which water is broken down (dissociated) by sunlight. This must be measured indirectly from the spectra of hydroxyl radicals (OH) and atomic oxygen which are the primary and secondary products. The hydroxyl coma of the comet will be more compact than the atomic oxygen coma because of its short life when exposed to sunlight. Hydrogen, the other product, will not be detectable because of the Lyman-alpha filters in the spectrometers. Heavier compounds will be sought by measuring spectral lines unique to carbon, carbon monoxide (CO), carbon dioxide (CO2), sulfur, carbon sulfide (CS) molecular sulfur (S2), nitric oxide (NO) and cyanogen (CN), among others. Spartan-Halley’s spectrometers will not produce images, but will reveal the comet’s chemistry thought the ultraviolet spectral lines they record. With these data, scientists will gain a better understanding of how: # Chemical structure of the comet evolves from the coma and proceeds down the tail; # Species change with relation to sunlight and dynamic processes within the comet; and # Dominant atmospheric activities at perihelion relate to the comets long-term evolution. Other observatories will be studying Halley’s comet, but only Spartan can observe near perihelion.