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
Apollo 7 for 21 months, while the cause of the accident was investigated and improvements made to the spacecraft and safety procedures, and unmanned test flights of the Saturn V rocket and Apollo Lunar Module were made. Apollo 7 fulfilled Apollo 1's mission of testing the Apollo command and service module (CSM) in low Earth orbit. The Apollo 7 crew was commanded by Walter M. Schirra, with senior pilot / navigator Donn F. Eisele, and pilot / systems engineer R. Walter Cunningham. Official crew titles were made consistent with those that would be used for the manned lunar landing missions: Eisele was