The amount of time available for operations on the moon was limited by assets that could be transported on LEM; Apollo 11's Buzz Aldrin and Neil Armstrong spent about 22 hours on the moon surface. When business on the moon was complicated, the upper stage of LEM would burst, differ from the descent stage and rendezvous with CSM (the possibility that something goes wrong at this point, which may require CSM to make unexpected maneuvers in order to make rendezvous was one of the reasons why a pilot needed to stay in orbit). When the two spacecraft had ended up, the two astronauts went inside the LEM in the CSM pilot, and LEM was jettisoned to eventually crash on the moon surface. With all three astronauts aboard, CSM's main engine would fire and send the spacecraft home. The Apollo missions all ended with the separation of the conformational command module from the service module, and the CM would re-enter the Earth's atmosphere, with its heat shield absorbing the enormous reheat heat generated by atmospheric friction. Finally, the spacecraft, sunk by parachutes, splashed into the sea, with the crew and spacecraft recovered by helicopter and taken to a waiting aircraft.