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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 Challenger's 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 worldwide network of ground stations.

NASA's Space Tracking and Data Network ground stations eventually will be phased out. Three of the network's present 12 ground stations -- Madrid, Spain; Canberra, Australia; and Goldstone, Calif. -- have been transferred to the Deep Space Network managed by the Jet Propulsion Laboratory in Pasadena, Calif., and the remainder -- except for two stations considered necessary for Shuttle launch operations -- will be closed or transferred to other agencies after the successful launch and checkout of the next two TDRS satellites.

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