(68K)NASA has had many ground-based tracking and data acquisition systems over the years to receive data from spacecraft and keep track of their location. With satellites traveling in many orbits, it was necessary to have ground stations all over the globe in order to stay in continuous contact. To replace these costly oversees ground stations NASA developed the Tracking and Data Relay Satellite System (TDRSS). TDRSS uses spacecraft in synchronous orbits to relay data from satellites below to a single ground station at White Sands, NM.
Goddard Space Flight Center had been studying the idea of a relay satellite network since the 1960's. During the budget squeeze of the early 1970's following the end of the Apollo program, NASA decided to lease a TDRS system for a period of 10 years. A contract for TDRSS was awarded to Western Union Space Communications, Inc., with TRW and Harris as subcontractors, at the end of 1976. The TDRS spacecraft was to have been shared by NASA and Western Union. The spacecraft carried Advanced Westar commercial communications equipment as well as TDRSS hardware.
Problems and delays plagued TDRSS. Both NASA and Western Union decided that separate satellites would better suit their needs. Western Union sold their share in 1983 and Continental Telephone eventually wound up owning and running the system. NASA bought the system in 1990 and retained GTE (who merged with Contel) as the operator. NASA leases TDRS-3 and TDRS-4 C-band transponders to the commercial communications industry.
TDRSS was originally to have been operational by the end of 1979 at a cost of $800 million. The first two spacecraft were planned for launch on Atlas-Centaur vehicles. Delays hit the program when it was decided to switch to the Space Shuttle/IUS. Cost estimates more than doubled to over $2 billion. The first TDRS made it to synchronous orbit using its own hydrazine thrusters after the IUS failed to get it all the way there. The second TDRS was lost in the Challenger disaster.
The 2200kg spacecraft has a hexagonal body with two sun-tracking solar array panels that provide 2kW at the beginning of life. The three-axis stabilized design uses reaction wheels and 24 monopropellant hydrazine thrusters. The antenna farm includes two 4.9m parabolic antennas, a 30-element phased array, a 2m parabolic for the K-band ground link, a 1m steerable K-band antenna, an S-band omni, and a C-band antenna. The phased array can receive S-band signals from up to 20 spacecraft.
In February 1995, NASA awarded a $482M contract to Hughes to build three additional TDRS spacecraft for the system. Launch dates: