Apollo LM and CSM spacecraft. Exterior (top) and cutaway (bottom) illustrations of the Apollo Lunar Module (LM, right, gold) and the Apollo Command/Service Module (CSM, left, grey). Each Apollo mission was crewed by three astronauts, sitting in the Command Module (CM, conical section of the CSM). The cylindrical Service Module section contained scientific instruments, propulsion systems, fuel cells and life support systems. Once at the Moon, two astronauts used the LM to descend to the Moon and return to the CSM, which was piloted by the third astronaut. The CM was then used to re-enter the Earth's atmosphere, with the other sections being jettisoned.