was successfully demonstrated in 1965 and 1966 on six Project Gemini missions with the aid of radar and on-board computers. It was also successfully done each of the eight times it was tried on Apollo missions. Apollo Mission mode selection 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. 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. 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. Tom Dolan, who worked for Lau, was sent to explain the company's proposal to NASA engineers and management in February 1960. This alternative was then studied and promoted by Jim Chamberlin and Owen Maynard at the Space Task Group in the 1960 early Apollo feasibility studies. This mode allowed a single Saturn V to launch the CSM to the Moon with a smaller 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