Canceled Apollo missions planning their own circumlunar flight for December to upstage the Americans once again (see Zond program). McDivitt's crew—who had grown accustomed to working with LM-3 and preparing for its flight—was kept on the D mission which now became Apollo 9, while Borman's crew would fly the CSM lunar orbit mission on Apollo 8, and the E mission was canceled. The swap of crews was also decisive in who would be the first man to walk on the Moon. Pete Conrad was backup Commander for McDivitt's crew, and by the process of crew rotation, would have been in line for Commander
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