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
Journey of Apollo 15 to the Moon fuel on the LM, allowing it to land with more equipment and consumables on board. A major issue for all lunar orbiting spacecraft are mass concentrations or "mascons". These are regional areas where denser material is under the surface. Apollo 15 travelled over regions that had never been covered on previous flights, so it was unknown how its orbit would be affected by them. Mission Control predicted that by the time the crew awoke the next "morning", the lowest point of their orbit, perilune, would have dropped to about 8.6 nm (16.1 km) but this turned out to be an