Canceled Apollo missions Schirra's crew would fly the C mission, first manned CSM (Block II CSM-101, retrofitted with the cabin safety improvements) as Apollo 7 in October 1968. McDivitt's crew and mission were kept as the first manned development LM flight (D mission); this was planned to be Apollo 8 in December 1968, now using a single Saturn V launch vehicle instead of two separate Saturn IB launches. The E mission was planned as an elliptical medium Earth orbit test of the operational LM with the CSM in a simulated lunar mission to an apogee of , to be commanded by Frank Borman
Apollo 15 to Apollo 12, and since Apollo 11's backup crew had been designated for Apollo 13 (which did not land on the Moon), they were the first Apollo crew for a successful lunar landing mission to have backed up another such mission. Having had the opportunity to familiarize themselves with the Apollo spacecraft, they could devote more of their training time as prime crew for Apollo 15 to geology and sampling techniques. The astronauts at NASA who were scientists, such as geologist Harrison Schmitt, pushed though the early Apollo missions for a greater place for science as part of the mission,