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Telstar is the name of various communications satellites. The first two Telstar satellites were experimental and nearly identical. Telstar 1 launched on top of a Thor-Delta rocket on July 10, 1962. It successfully relayed through space the first television pictures, telephone calls, and fax images, and provided the first live transatlantic television feed. Telstar 2 launched May 7, 1963. Telstar 1 and 2—though no longer functional—still orbit the Earth. ==Description== Belonging to AT&T, the original Telstar was part of a multi-national agreement among AT&T (US), Bell Telephone Laboratories (US), NASA (US), GPO (UK) and the National PTT (France) to develop experimental satellite communications over the Atlantic Ocean. Bell Labs held a contract with NASA, paying the agency for each launch, independent of success. The US ground station—built by Bell Labs—was Andover Earth Station, in Andover, Maine. The main British ground station was at Goonhilly Downs in southwestern England. The BBC, as international coordinator, used this location. The standards 525/405 conversion equipment (filling a large room) was researched and developed by the BBC and located in the BBC Television Centre, London. The French ground station was at Pleumeur-Bodou () in north-western France. The satellite was built by a team at Bell Telephone Laboratories that included John Robinson Pierce, who created the project; Rudy Kompfner, who invented the traveling wave tube transponder that the satellite used;〔 and James M. Early, who designed its transistors and solar panels. The satellite is roughly spherical, measures in length, and weighs about . Its dimensions were limited by what would fit on one of NASA's Delta rockets. Telstar was spin-stabilized, and its outer surface was covered with solar cells capable of generating 14 watts of electrical power. The original Telstar had a single innovative transponder that could relay data, a single television channel, or multiplexed telephone circuits. Since the spacecraft spun, it required an array of antennas around its "equator" for uninterrupted microwave communication with Earth. An omnidirectional array of small cavity antenna elements around the satellite's "equator" received 6 GHz microwave signals to relay back to ground stations. The transponder converted the frequency to 4 GHz, amplified the signals in a traveling-wave tube, and retransmitted them omnidirectionally via the adjacent array of larger box-shaped cavities. The prominent helical antenna received telecommands from a ground station. Launched by NASA aboard a Delta rocket from Cape Canaveral on July 10, 1962, Telstar 1 was the first privately sponsored space launch. A medium-altitude satellite, Telstar was placed in an elliptical orbit completed once every 2 hours and 37 minutes, inclined at an angle of approximately 45 degrees to the equator, with perigee about from Earth and apogee about from Earth〔 This is in contrast to most of today's communications satellites, which travel in circular geostationary orbits.〔(''An Introduction to Satellite Communications'' ), page 3, D. I. Dalgleish, 1989〕 Due to its non-geosynchronous orbit, Telstar's availability for transatlantic signals was limited to the 20 minutes in each 2.5 hour orbit when the satellite passed over the Atlantic Ocean. Ground antennas had to track the satellite with a pointing error of less than 0.06 degrees as it moved across the sky at up to 1.5 degrees per second. Since the transmitters and receivers on Telstar were not powerful, ground antennas had to be huge. Bell Laboratory engineers designed a large horizontal conical horn antenna with a parabolic reflector at its mouth that re-directed the beam. This particular design had very low sidelobes, and thus made very low receiving system noise temperatures possible. The aperture of the antennas was . The antennas were long and weighed . Morimi Iwama and Jan Norton of Bell Laboratories were in charge of designing and building the electrical portions of the azimuth-elevation system that steered the antennas.The antennas were housed in radomes the size of a 14-story office building. Two of these antennas were used, one in Andover, Maine, and the other in France at Pleumeur-Bodou. The GPO antenna at Goonhilly Downs in Great Britain was a conventional 26-meter-diameter paraboloid. 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「telstar」の詳細全文を読む スポンサード リンク
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