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Release No. 91-41 June 7, 1991 Current Status and History The Tracking and Data Relay Satellite (TDRS)-E is the fifth in a series of communications spacecraft planned for the Tracking and Data Relay Satellite System (TDRSS). TDRS-A, now is orbit and known as TDRS-1, was deployed from the Space Shuttle Challenger on April 5, 1983 on Space Transportation System (STS)-6. TDRS-B was destroyed during the Challenger accident in January 1986. TDRS-C, known as TDRS 3 in orbit, was launched from Discovery on September 29, 1988 on STS-26. TDRS-D, known as TDRS-4 in orbit, was launched from Discovery on March 13, 1990 on STS-29. Currently, TDRS-4 is located at 41 degrees West longitude, over the Atlantic Ocean off Brazil, TDRS-3 is located at 174 degrees West longitude, and TDRS-1 is located at 171 degrees West longitude. Both TDRS-3 and TDRS-1 are over the Pacific, East of the Gilbert Islands and South of Hawaii. TDRS-4 is also known as TDRS-East and the combination of TDRS-1 and TDRS-4 provide the TDRS Western satellite capability. The satellite communications system was initiated following studies in the early 1970s which showed that a system of telecommunication satellites operated from a single ground station could better support the space shuttle and scientific application mission requirements planned for the Nation's space program. In addition, the system was seen as a means of halting the spiralling costs of upgrading and operating a network of tracking and communications ground stations located around the world. Deployment Sequence TDRS-E will be deployed from Atlantis approximately six hours after launch on orbit five (over the Pacific south of Hawaii). Injection burn to geosynchronous orbit will be initiated at 77 degrees East Longitude (Indian Ocean, south of India), placing the satellite in orbit at 178 degrees West Longitude (over the Pacific near the Gilbert Islands). The STS-43 crew elevates the Inertial Upper State (IUS)/TDRS to 29 degrees in the payload bay for preliminary tests and then raises it to 58 degrees for deployment. A spring-loaded ejection system is used for deploying the IUS/TDRS. The first burn of the IUS booster will take place an hour after deployment, or about seven hours after launch. The second and final burn (to circularize the orbit) will take place five and one half hours after the first burn, approximately 12 and one half hours into the mission. Separation of the booster and satellite will occur at 13 hours after launch. Upon reaching geosynchronous orbit, the deployment of antennas and appendages is started. The deployment sequence is: 1. Deploy solar arrays. 2. Deploy space-ground link boom. 3. Deploy C-band boom. 4. Separation of IUS and TDRS. 5. Release single access booms. 6. Position single access antennas. 7. Open single access antennas. During steps five, six and seven, Earth acquisition is taking place concurrently. The TDRS is three-axis stabilized with the multiple access body fixed antennas pointing constantly at the Earth while the solar arrays track the Sun. Communication System The TDRSs do no processing of user traffic in either direction. Rather, they operate as "bent pipe" repeaters, relaying signals and data between the user spacecraft and the ground terminal and vice versa without processing. The TDRSS is equipped to support up to 26 user spacecraft, including the space shuttle, simultaneously. It will provide two types of service: (1) multiple access which can relay data from as many as 20 low data rate (100 bits per second to 50 kilobits per second) user satellites simultaneously and (2) single access which will provide two high data rate channels (to 300 megabits per second) from both the East and West locations. The TDRSS ground terminal is located at White Sands, NM. It provides a location with a clear line-of-sight to the TDRSs and a place where rain conditions have limited interference with the availability of the Ku-band uplink and downlink channels. The White Sands Ground Terminal (WSGT) is operated for NASA by Contel Federal Systems under a contract that expires in 1995. Co-located at White Sands is the NASA Ground Terminal (NGT), which is operated for NASA by Bendix Field Engineering and provides the interface between WSGT and other primary network elements located at NASA's Goddard Space Flight Center, Greenbelt, MD. Those facilities at Goddard include the Network Control Center (NCC), which provides system scheduling and is the focal point for NASA communications and the WSGT and TDRSS users; the Flight Dynamics Facility (FDF), which provides the network with antenna pointing information for user spacecraft and the TDRSs; and the NASA Communications Network (NASCOM), which provides ground to ground communications through Earth terminals at Goddard, White Sands and the Johnson Space Center in Houston, TX. The Network Control Center console operators monitor the network performances, schedule emergency interfaces, isolate faults in the system, account for system use, test the system and conduct simulations. The user services available from the Space Network, which includes TDRSS and its supporting Goddard Space Flight Center elements, are provided through NASCOM, a global system which provides operational communications support to all NASA projects. NASCOM offers voice, data and teletype links with the Space Network, the Ground Spaceflight Tracking and Data Network (GSTDN), and the user spacecraft control centers. TDRS Components The TDRSs are composed of three distinct modules: an equipment module, a communications payload module and an antenna module. The modular design reduces the cost of individual design and construction efforts that, in turn, lower the cost of each satellite. The equipment module housing the subsystems that operate the satellite is located in the lower hexagon of the spacecraft. The attitude control subsystem stabilizes the satellite to provide accurate antenna pointing and proper orientation of the solar panels to the Sun. The electrical power subsystems consists of two solar panels that provide a 10-year power supply of approximately 1,700 watts. The thermal control subsystem consists of surface coatings and controlled electric heaters. The payload module is composed of the electronic equipment required to provide communications between the user spacecraft and the ground. The receivers and transmitters for single access services are mounted in compartments on the back of the single- access antennas. The antenna module is composed of seven antenna systems: two single-access, the multiple access array, and space-to-ground link and the S-band omni for satellite heath and housekeeping. Commercial K-band and C-band antennas round out the complement. For single-access service, the TDRSs have dual-feed S-band, Ku-band parabolic (umbrella-like) antennas. These antennas are free to be positioned in two axes directing the radio beam to orbiting user spacecraft below. These antennas are used primarily to relay communications to and from user spacecraft. The high data rates provided by these antennas is available to users on a time- shared basis. Each antenna is capable of supporting two user spacecraft services simultaneously--one at S-band and one at Ku- band--provided both users are within the beam width of the antenna. The multiple access antenna array is hard-mounted in one position on the surface of the antenna module facing the Earth. Another antenna, a 6.5 foot (two meter) parabolic reflector, provides the prime link for relaying transmissions to and from the ground terminal at Ku-band. Project Support and Staff TRW Space and Technology Group in Redondo Beach, CA, is the prime spacecraft contractor. Ground operations at the White Sands complex are conducted by Contel Federal Systems and Bendix Field Engineering. The Project Manager for the Advanced Tracking and Data Relay Satellite Project is Charles Vanek; Nicholas G. Chrissotimos is TDRS Manager for the spacecraft project; Daniel A. Spintman is Chief, Networks Division; Wesley J. Bodin is Associate Chief for Ground Network; Phillip Liebrecht is Assistant Chief for TDRSS and Gary A. Morse is Goddard Network Director.