Apollo 11 the CMP on the Apollo 8 crew, began experiencing trouble with his legs. Doctors diagnosed the problem as a bony growth between his fifth and sixth vertebrae, requiring surgery. Lovell took his place on the Apollo 8 crew, and, when Collins recovered, he joined Armstrong's crew as CMP. In the meantime, Fred Haise filled in as backup LMP, and Aldrin as backup CMP for Apollo 8. Apollo 11 was the second all-veteran crew on an American mission, the first being that of Apollo 10. The next was STS-26 in 1988. The backup crew consisted of Lovell as Commander, William Anders
Apollo 15 operations on the Lunar surface inside it to sample, but found most of the rocks to be too large. Mission Control called up and said they would like the crew to dig a trench to study the soil mechanics and take a core sample. Irwin dug the trench, which Scott photographed. Then the core sample was taken from inside the crater. Returning to the Rover, they drove 650 ft (200 m) to a large boulder. Even walking short distances on the slope was time consuming so it was easier to just have the crew use the Rover to get there. The boulder was 10 ft