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
Canceled Apollo missions to Apollo 17 under pressure from the scientific community, replacing Joe Engle. Schmitt, a geologist, became the only professional scientist and the twelfth man to walk on the Moon. Slayton's intention for the Apollo 19 crew was the original (prior to cancellation) Apollo 16 backup crew: For Apollo 20 there is even more uncertainty. Based on normal crew rotation, the crew would likely have been: Another possibility would have been: One of the surplus CSMs, CSM-119, was modified to carry two additional crew and kept on standby for a potential rescue mission in case of issues on-board Skylab. During Skylab