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The S-III (pronounced "ess three") was a proposed third stage of the early Saturn C designs for a five-stage Saturn launch vehicle. The Saturn C configurations were based on a "building block" approach, in which the upper stages would be test-flown before the intermediate stages. The S-III was to have been a LOX-Hydrogen fueled stage powered by two J-2 engines. The original Saturn C-2 design would have been a three or four stage launch vehicle using the S-I plus S-III plus S-IV stages plus, and for some missions, S-V. So, the very first Saturn (SA-1) consisted of an S-I stage and dummy S-IV and S-V stages. Before a live S-IV was ever flown (as the second stage of SA-5, the first of the Block II series), the idea of an S-V stage was dropped. The Saturn I series gave way to the Saturn IB. The first stage of this rocket was modified and renamed to the S-IB. The second stage of this rocket was an uprated version of the S-IV, the S-IVB; this stage was considered sufficiently similar to the S-IV stage that it was sole-sourced to Douglas without the usual bidding process. Of course, the S-IVB would also be used as the third stage of the Saturn V. Its first stage was the S-IC. Since no stage initially designed to be a second stage had ever been manufactured (remember, the second stage of the Saturn IB was still an evolved version of the initially-envisioned fourth stage), it received the S-II designation. With the Saturn S-IC, S-II, and S-IVB stages already in development, there was no need for another stage to be designed as a third stage, so the S-III stage was dropped. ==Evolution of Five Stage Saturn== A number of Saturn stage configurations (A, B, C) were considered between 1958 and 1960. One early version was the Saturn A-1, which had the familiar S-I stage plus a Titan I 1st stage as a 2nd stage and a Centaur as a 3rd stage. The Saturn A-2 was the same except that the 2nd stage consisted of a cluster of 4 Jupiters rather than a Titan 1st stage. In the Saturn B-1, the 2nd stage was a custom-developed LOX/RP-1 stage powered by 4 H-1 engines. Again, the Centaur was to be the 3rd stage. Then there was the Saturn C-1: S-I stage plus S-IV plus Centaur, known in this application as the S-V. This is the Saturn I which actually flew, except that the S-V stage was never live. The original Saturn C-2 design would have been S-I stage plus S-III plus S-IV plus, for some missions, S-V. The S-III was to have been a LOX-Hydrogen stage powered by two J-2 engines. The original Saturn C-3 configuration was S-I plus S-II plus S-III plus, for some missions, the S-IV and even S-V. The S-II was to have had four J-2 engines and the S-I would have been upgraded either by increasing the thrust of its eight H-1 engines to 250,000 lb or by replacing the center four H-1 engines with a single F-1 engine. In December 1959, the Silverstein committee (formally known as the "Saturn Vehicle Evaluation Committee") decided to skip development of the Saturn A and B configurations and go straight to the Saturn C configurations, which provided greater payload lifting power. NASA HQ accepted the recommendations of the Silverstein Committee and forwarded them to MSFC in Hunstville. Huntsville concurred, but dropped the S-III stage. So, by end of 1960 the S-III stage disappeared from the developing Saturn C configurations. In the Saturn C-2, the S-III stage was replaced by the S-II stage, with 4 J-2 engines. The upgraded S-I in the C-3 was replaced by a new stage powered by two F-1s. By 1962, consideration of the Saturn C-2 and C-3 vehicles were dropped entirely. The Saturn C-4 was briefly considered (4xF-1 plus 4xJ-2 plus 1xJ-2) before being replaced by the Saturn C-5, which provided a greater payload margin for lunar missions. The S-II designation was now applied to the 2nd stage of the C-5.〔 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「S-III」の詳細全文を読む スポンサード リンク
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