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The Tracking and Data Relay Satellite System (TDRSS) is a network of American communications satellites (each called a Tracking and Data Relay Satellite (TDRS)) and ground stations used by NASA for space communications. The system was designed to replace an existing network of ground stations that had supported all of NASA's manned flight missions. The prime design goal was to increase the time spacecraft were in communication with the ground and improve the amount of data that could be transferred. Many Tracking and Data Relay Satellites were launched in the 1980s and 1990s with the Space Shuttle and made use of the Inertial Upper Stage, a two-stage solid rocket booster developed for the shuttle. Other TDRS were launched by Atlas IIa and Atlas V rockets. The most recent generation of satellites provides ground reception rates of 300 Mbit/s in the Ku- and Ka-bands and 800 Mbit/s in the S-band.〔http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=2002-011A〕 ==Origins== To satisfy the requirement for long-duration, highly-available space-to-ground communications, NASA created the Spacecraft Tracking and Data Acquisition Network (STADAN). Consisting of parabolic dish antennas and telephone switching equipment deployed around the world, the STADAN provided space-to-ground communications for approximately 15 minutes of a 90-minute orbit period. This limited contact-period sufficed for unmanned spacecraft, but manned spacecraft require a much higher data collection time. The follow-on network, called the Manned Space Flight Network (MSFN), interacted with manned craft in Earth orbit. Another network, the Deep Space Network (DSN), interacted with manned craft higher than 10,000 miles from Earth, such as the Apollo missions, in addition to its primary mission of data collection from deep space probes. With the creation of the Space Shuttle in the mid-1970s, a requirement for a higher performance space-based communication system arose. At the end of the Apollo program, NASA realized that MSFN and STADAN had evolved to have similar capabilities and decided to merge the two networks to create the Spacecraft Tracking and Data Network (STDN). Even after consolidation, STDN had some drawbacks. Since the entire network consisted of ground stations spread around the globe, these sites were vulnerable to the political whims of the host country. In order to maintain a high-reliability rate coupled with higher data transfer speeds, NASA began a study to augment the system with a space-based communication nodes. The space segment of the new system would rely upon satellites in geostationary orbit. These satellites, by virtue of their position, could transmit and receive data to lower orbiting satellites and still stay within sight of the ground station. The operational TDRSS constellation would use two satellites, designated TDE and TDW (for East and West), and one on-orbit spare. After the study was completed, NASA realized that a minor system modification was needed to achieve 100% global coverage. A small area would not be within line-of-sight of any satellites – a so-called Zone of Exclusion (ZOE). With the ZOE, neither TDRS satellite could contact a spacecraft under a certain altitude (646 nautical miles). With the addition of another satellite to cover the ZOE and ground station nearby, 100% coverage could exist. The space-based network study created a system that became the plan for the present-day TDRSS network design. As early as the 1960s, NASA's Application Technology Satellite (ATS) and Advanced Communications Technology Satellite (ACTS) programs prototyped many of the technologies used on TDRSS and other commercial communications satellites, including frequency division multiple-access (FDMA), three-axis spacecraft stabilization and high-performance communications technologies. , TDRSS project manager is Jeff J. Gramling, NASA Goddard Space Flight Center. Boeing is responsible for the construction of TDRS K. 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 System」の詳細全文を読む スポンサード リンク
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