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
Apollo 15 the same time, Command Module Pilot Alfred Worden orbited the Moon, using a scientific instrument module (SIM) in the service module (SM) to study the lunar surface and environment in great detail with a panoramic camera, a gamma-ray spectrometer, a mapping camera, a laser altimeter, a mass spectrometer, and a lunar subsatellite deployed at the end of Apollo 15's stay in lunar orbit (an Apollo program first). The mission successfully accomplished its objectives, but was marred by negative publicity that accompanied disclosure of the crew carrying unauthorized postage covers to the Moon, some of which were sold by a West