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A tracking and data relay satellite (TDRS) is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System (TDRSS) used by NASA and other United States government agencies for communications to and from independent "User Platforms" such as satellites, balloons, aircraft, and the International Space Station. This system was designed to replace an existing worldwide network of ground stations that had supported all of NASA's manned flight missions and unmanned satellites in low-Earth orbits. The primary system design goal was to increase the amount of time that these spacecraft were in communication with the ground and improve the amount of data that could be transferred. These TDRSS satellites are all designed and built to be launched to and function in geosynchronous orbit, above the surface of the Earth. The first seven TDRSS satellites were built by the TRW corporation. The three later versions have been manufactured by the Boeing corporation's Satellite Systems division. Ten satellites have been launched; however, one was destroyed in a launch failure (the Challenger disaster). TDRS-1 was decommissioned in October 2009. TDRS-4 was decommissioned in December 2011. Seven TDRSS satellites are still in service. All of the TDRSS satellites have been managed by NASA's Goddard Space Flight Center. The contract for TDRS versions L & K was awarded to Boeing on December 20, 2007. On November 30, 2011, NASA announced the decision to order an additional third-generation TDRS satellite, TDRS M.〔 ==Operations== The first tracking and data relay satellite was launched in 1983 on the Space Shuttle ''Challenger's'' first flight, STS-6. The Boeing-built Inertial Upper Stage that was to take the satellite from Challenger's orbit to its ultimate geosynchronous orbit suffered a failure that caused it not to deliver the TDRS to the correct orbit. As a result, it was necessary to command the satellite to use its onboard rocket thrusters to move it into its correct orbit. This expenditure of fuel reduced its capability to remain in a geostationary orbit; by late 1997 the orbit had changed to the point that the satellite was able to see the South Pole, and an uplink/downlink station was installed at Amundsen–Scott South Pole Station in January 1998;〔(【引用サイトリンク】title=TDRS history )〕 TDRS-1 was an important communication uplink for Antarctic research until 2009. The second tracking and data relay satellite was destroyed along with ''Challenger'' shortly after launch during the STS-51-L mission in January 1986. The next five TRW-built TDRSS satellites were successfully launched on other Space Shuttles. Three follow-up Boeing-built satellites were launched by Atlas rockets in 2000 and 2002. A NASA Press Release summarized the capabilities of the system as a whole: "Working solo, TDRS-1 provided more communication coverage, in support of the September 1983 Shuttle mission, than the entire network of NASA tracking stations had provided in all previous Shuttle missions." The first generation of TDRS are planned to be retired in 2015. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tracking and data relay satellite」の詳細全文を読む スポンサード リンク
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