Apollo 11 the CMP on the Apollo 8 crew, began experiencing trouble with his legs. Doctors diagnosed the problem as a bony growth between his fifth and sixth vertebrae, requiring surgery. Lovell took his place on the Apollo 8 crew, and, when Collins recovered, he joined Armstrong's crew as CMP. In the meantime, Fred Haise filled in as backup LMP, and Aldrin as backup CMP for Apollo 8. Apollo 11 was the second all-veteran crew on an American mission, the first being that of Apollo 10. The next was STS-26 in 1988. The backup crew consisted of Lovell as Commander, William Anders
Canceled Apollo missions 1963, and replaced them with two manned Saturn IB missions, designated AS-204 and AS-205. These would be followed by the first unmanned flight of the Lunar Module (LM) on AS-206, then the third manned mission, designated AS-207/208, would use AS-207 to launch the crew in an improved Block II CSM, which would rendezvous and dock with the LM launched unmanned on AS-208. The crew selected on March 21, 1966, for AS-204 consisted of Command Pilot Virgil "Gus" Grissom, Senior Pilot Ed White, and Pilot Roger Chaffee, who named their mission Apollo 1. AS-205 was to be named Apollo 2, and