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A GPS satellite is a satellite used by the NAVSTAR Global Positioning System (GPS). The first satellite in the system, Navstar 1, was launched February 29, 1978. The GPS satellite constellation is operated by the 50th Space Wing of the United States Air Force. The GPS satellites circle the Earth at an altitude of about 20,000 km (12,427 miles) and complete two full orbits every day.〔(【引用サイトリンク】title=The Global Positioning System )〕 == Block I satellites == Rockwell International was awarded a contract in 1974 to build the first eight Block I satellites. In 1978 the contract was extended to build an additional three Block I satellites. Beginning with Navstar 1 in 1978, ten "Block I" GPS satellites were successfully launched. One satellite, "Navstar 7", was lost due to an unsuccessful launch on 18 December 1981.〔 (【引用サイトリンク】 BLOCK I SATELLITE INFORMATION )〕 The Block I satellites were launched from Vandenberg Air Force Base using Atlas rockets that were converted intercontinental ballistic missiles. The satellites were built by Rockwell International at the same plant in Seal Beach, CA where the S-II second stages of the Saturn V rockets had been built.〔 (【引用サイトリンク】 Site: Boeing North American, Inc. )〕 The Block I series consisted of the concept validation satellites and reflected various stages of system development. Lessons learned from the 11 satellites in the series were incorporated into the fully operational Block II series. Dual solar arrays supplied over 400 watts of power, charging NiCd batteries for operations in Earth's shadow. S-band communications were used for control and telemetry, while a UHF channel provided cross-links between spacecraft. A hydrazine propulsion system was used for orbital correction. The payload included two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). The final Block I launch was conducted on 9 October 1985, but the last Block I satellite was not taken out of service until 18 November 1995, well past its 5 year design life.〔(【引用サイトリンク】title=GPS (Navstar) )〕 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「GPS satellite blocks」の詳細全文を読む スポンサード リンク
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