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Douglas Aircraft's SASSTO, short for "Saturn Application Single Stage to Orbit", was a single-stage-to-orbit (SSTO) reusable launch system designed by Philip Bono's team in 1967. SASSTO was a study in minimalist designs, a launcher with the specific intent of repeatedly placing a Gemini capsule in orbit for the lowest possible cost. The SASSTO booster was based on the layout of the S-IVB upper stage from the Saturn family, modified with a plug nozzle. Although the SASSTO design was never followed up at Douglas, it is widely referred to in newer studies for SSTO launchers, notably the MBB "Beta" design, which was largely an updated version of SASSTO. ==History== In 1962 NASA sent out a series of studies on post-Apollo launch needs, which generally assumed very large launchers for a manned mission to Mars. At Douglas, makers of the S-IVB, Philip Bono led a team that studied a number of very large liquid-fueled boosters as a way to lower the cost of space exploration. His designs were based on an economy of scale which makes larger rockets more economical than smaller ones as the structure accounts for less and less of the overall weight of the launcher.〔("OOST" )〕 At some point the dry weight of the launcher becomes lower than the payload it can launch, after which increases in payload fraction are essentially free. However, this point is crossed at relatively large vehicle sizes - Bono's original OOST study from 1963 was over long - and this path to lower costs only makes sense if there is an enormous amount of payload that needs to be launched. After designing a number of such vehicles, including ROOST and the ROMBUS/Ithacus/Pegasus series, Bono noticed that the S-IVB stage, then just starting to be used operationally, was very close to being able to reach orbit on its own if launched from the ground. Intrigued, Bono started looking at what missions a small S-IVB-based SSTO could accomplish, realizing that it would be able to launch a manned Gemini capsule if it was equipped with some upgrades, notably an aerospike engine that would improve the specific impulse and provide altitude compensation.〔Bono〕 He called the design "SASSTO", short for "Saturn Application Single-Stage To Orbit". These same upgrades would also have the side-effect of lowering the weight of the SASSTO compared to the original S-IVB, while at the same time increasing its performance. Thus the study also outlined a number of ways that it could be used in place of the S-IV in existing Saturn IB and Saturn V stacks, increasing their performance. When used with the existing Saturn I lower stage, it would improve payload to low earth orbit from 35,000 to , or if the landing gear were removed and it was expended like the S-IVB. SASSTO would thus give NASA a short-term inexpensive manned launch capability, while also offering improved heavy-launch capability on the existing Saturn infrastructure. SASSTO required a number of new technologies, however, which made development risky. In particular, the performance of the aerospike engine had to be considerably higher than the J-2 it would replace, yet also offer the ability to be restarted multiple times as the single engine was used for launch, de-orbit and landing. Of particular note was the final landing burn, which required the engines to be restarted at during the descent. The vehicle's weight was also greatly reduced, almost by half, which would not have been trivial considering the relatively good performance of the S-IVB design. 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「Douglas SASSTO」の詳細全文を読む スポンサード リンク
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