Apollo 9 in early 1969. However, LM problems again prevented it from being ready for the D mission by December, so NASA officials created another mission for Apollo 8 using the Saturn V to launch only the CSM on the first crewed flight to orbit the Moon, and the E mission was cancelled as unnecessary. Slayton asked McDivitt and Borman which mission they preferred to fly; McDivitt wanted to fly the LM, while Borman volunteered for the pioneering lunar flight. Therefore, Slayton swapped the crews, and McDivitt's crew flew Apollo 9. The crew swap also affected who would be the first crew
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