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Lunar orbit rendezvous (LOR) is a key concept for landing humans on the Moon and returning them to Earth and was first utilized for the Project Apollo missions in the 1960s and 1970s. In a LOR mission, a main spacecraft (such as the Apollo CSM) and a smaller lunar lander (such as the Apollo LM) travel together into lunar orbit. The lunar lander then independently descends to the surface of the Moon, while the main spacecraft remains in lunar orbit. After completion of the mission there, the lander returns to lunar orbit to rendezvous and re-dock with the main spacecraft, then is discarded after transfer of crew and payload. Only the main spacecraft returns to Earth. LOR is first known to have been proposed in 1916 by Ukrainian rocket theoretician Yuri Kondratyuk, as the most economical way of landing humans on the Moon. When NASA began actual work in 1961 on President John F. Kennedy's goal to achieve the first such landing by the end of the 1960s, LOR was proposed by Tom Dolan and championed by John C. Houbolt, but considered controversial, impractical, and possibly dangerous, because space rendezvous had never been done. However, Houbolt's persistence paid off, convincing NASA's management, and Administrator James E. Webb publicly announced in July 1962 that Apollo would utilize this method. Even then, Kennedy's Science Advisor Jerome Wiesner remained opposed to the method, and publicly criticized Webb. As history has shown, the method worked, and allowed NASA to use only one Saturn V per lunar landing mission, something other landing options did not offer. == Apollo Mission mode selection == Lunar orbit rendezvous was first known to be proposed in 1919 by Ukrainian and Soviet engineer Yuri Kondratyuk, as the most economical way of landing a human on the Moon. When the Apollo Moon landing program was started in 1961, it was assumed that the three-man Command and Service Module combination (CSM) would be used for takeoff from the lunar surface, and return to Earth. It would therefore have to be landed on the Moon by a larger rocket stage with landing gear legs, resulting in a very large spacecraft (in excess of ) to be sent to the Moon. If this were done by direct ascent (on a single launch vehicle), the rocket required would have to be extremely large, in the Nova class. The alternative to this would have been Earth orbit rendezvous, in which two or more rockets in the Saturn class would launch parts of the complete spacecraft, which would rendezvous in Earth orbit before departing for the Moon. This would possibly include a separately launched Earth departure stage, or require on-orbit refueling of the empty departure stage. Tom Dolan proposed the alternative of lunar orbit rendezvous, which had been studied and promoted by Jim Chamberlin and Owen Maynard at the Space Task Group in 1960 early Apollo feasibility studies. This mode allowed a single Saturn V to launch the CSM to the Moon with a smaller Lunar Excursion Module (LEM). When the combined spacecraft reaches lunar orbit, one of the three astronauts remains with the CSM, while the other two enter the LEM, undock and descend to the surface of the Moon. They then use the ascent stage of the LEM to rejoin the CSM in lunar orbit, then discard the LEM and use the CSM for the return to Earth. This method was brought to the attention of NASA Associate Administrator Robert Seamans by Langley Research Center engineer John C. Houbolt, who led a team to develop it. 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「Lunar orbit rendezvous」の詳細全文を読む スポンサード リンク
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