Lunar orbit rendezvous
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.
[1] Lunar orbit rendezvous was first proposed in 1919 by Ukrainian engineer Yuri Kondratyuk,[2] as the most economical way of sending a human on a round-trip journey to the Moon.
[Note 2] 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.
Wernher von Braun and Heinz-Hermann Koelle of the Army Ballistic Missile Agency presented lunar orbit rendezvous, as an option for reaching the Moon efficiently, to the heads of NASA, including Abe Silverstein, in December 1958.
[6] During 1959 Conrad Lau of the Chance-Vought Astronautics Division supervised a complete mission plan using lunar orbit rendezvous which was then sent to Silverstein at NASA in January 1960.
[Note 3] 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.
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.
As it turned out, this capability proved invaluable in 1970, saving the lives of the Apollo 13 astronauts when an oxygen tank explosion disabled the Service Module.
As a member of Lunar Mission Steering Group, Houbolt had been studying various technical aspects of space rendezvous since 1959 and was convinced, like several others at Langley Research Center, that LOR was not only the most feasible way to make it to the Moon before the decade was out, it was the only way.
He had reported his findings to NASA on various occasions but felt strongly that the internal task forces (to which he made presentations) were following arbitrarily established "ground rules."
[10] In November 1961, Houbolt took the bold step of skipping proper channels and writing a nine-page private letter directly to associate administrator Robert C. Seamans.
These two powerful groups, along with the engineers who had originally developed the plan at Langley, persuaded key officials at NASA Headquarters, notably Administrator James Webb, who had been holding out for direct ascent, that LOR was the only way to land on the Moon by 1969.
