This lunar module (LM), one of 12 built for Project Apollo, was meant to be used in low Earth orbit to test the techniques of separation, rendezvous, and docking with the command and service module. The second of two such test vehicles, its mission was cancelled because of the complete success of the first flight. The lunar module had two stages. The descent (lower) stage was equipped with a rocket motor to slow the rate of descent to the lunar surface. It contained exploration equipment and remained on the Moon when the astronauts left. The ascent (upper) stage contained the crew compartment and a rocket motor to return the astronauts to the orbiting command module. After the crew entered the command module for the trip back to Earth, the lunar module was released and eventually crashed into the Moon.