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Delta is an American versatile family of expendable launch systems that has provided space launch capability in the United States since 1960. There have been more than 300 Delta rockets launched, with a 95% success rate. Two Delta launch systems – Delta II and Delta IV – are still in use, though the Delta II will soon be retired. Delta rockets are currently manufactured and launched by the United Launch Alliance. ==Delta origins== The original Delta rockets used a modified version of the PGM-17 Thor, the first ballistic missile deployed by the United States Air Force, as their first stage. The Thor had been designed in the mid-1950s to reach Moscow from bases in Britain or similar allied nations, and the first wholly successful Thor launch had occurred in September 1957. Subsequent satellite and space probe flights soon followed, using a Thor first stage with several different upper stages. The fourth upper stage used on the Thor was the Thor "Delta," delta being the fourth letter of the Greek alphabet. Eventually the entire Thor-Delta launch vehicle came to be called simply, "Delta."〔 〕 The Delta name stems from its position as the fourth, or D version, of the Thor based rocket combination. The vehicle has been known both as Thor-Delta and simply Delta. NASA intended Delta as "an interim general purpose vehicle" to be "used for communication, meteorological, and scientific satellites and lunar probes during '60 and '61". The plan was to replace Delta with other rocket designs when they came on-line. The Delta design emphasized reliability rather than performance by replacing components which had caused problems on earlier Thor flights. NASA let the original Delta contract to the Douglas Aircraft Company in April 1959 for 12 vehicles of this design: *Stage 1: Modified Thor IRBM with a Block I MB-3 engine producing thrust. (LOX/RP1 turbopump, gimbal mounted engine, two verniers for roll control) *Stage 2: Modified Able. Pressure fed UDMH/nitric acid powered Aerojet AJ-10-118 engine producing . This reliable engine cost $4 million to build and is still flying in modified form today. Gas jet attitude control system. *Stage 3: Altair. A spin stabilized (via a turntable on top of the Able) at 100 rpm by two solid rocket motors before separation. One ABL X-248 solid rocket motor provided of thrust for 28 seconds. The stage weighed and was largely constructed of wound fiberglass. These vehicles would be able to place into a LEO or into GTO. Eleven of the twelve initial Delta flights were successful. The total project development and launch cost came to $43 million, $3 million over budget. An order for 14 more vehicles was let before 1962. 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「Delta (rocket family)」の詳細全文を読む スポンサード リンク
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