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 program Block II space suits, and would be designated by the Block II titles, regardless of whether a LM was present on the flight or not. On April 24, 1967, Mueller published an official Apollo mission numbering scheme, using sequential numbers for all flights, manned or unmanned. The sequence would start with Apollo 4 to cover the first three unmanned flights while retiring the Apollo 1 designation to honor the crew, per their widows' wishes. In September 1967, Mueller approved a sequence of mission types which had to be successfully accomplished in order to achieve the manned lunar landing. Each step