Illustration of the Command/Service Module (CSM) spacecraft, used during the Apollo programme which landed astronauts on the Moon. The Command Module (CM, conical section) housed a crew of three astronauts. The cylindrical Service Module (SM) contained scientific instruments, fuel cells, gas tanks, and propulsion systems. These included four sets of Reaction Control System thrusters which allowed control of the spacecraft's orientation. Once at the Moon, two astronauts used the Lunar Module (not shown) to descend to the Moon's surface and return to the CSM. The CM was then used to re-enter the Earth's atmosphere, with the other sections being jettisoned.