The time available for operations on the Moon was limited by supplies that could be carried on the LEM. Apollo 11's Buzz Aldrin and Neil Armstrong spent about 22 hours on the lunar surface. Once the Moon business was completed, the upper stage of the LEM went off, separating from the descent stage and meeting with the CSM (the possibility of something going wrong at that point that might cause the CSM to perform unexpected maneuvers) one of the reasons why a pilot had to stay in orbit). After the two spaceships were docked, the two astronauts in the LEM joined the pilot in the CSM and the LEM was dropped, eventually collapsing on the lunar surface. With all three astronauts aboard, the main engine of the CSM would fire and send the spaceship home. The Apollo missions all ended with the detachment of the cone-shaped command module from the service module, and the CM would reenter the earth's atmosphere, its heat shield absorbing the tremendous heat of reentry created by atmospheric friction. Eventually, the parachute-slowed spaceship would "splash down" in the ocean, with the crew and the spaceship retrieved by helicopter and taken to a waiting aircraft carrier.