The Lunar Module (LM) - originally called the Lunar Excursion Module (LEM) and still pronounced "lem" after the name was changed - was the spacecraft that allowed the Apollo astronauts to land on the Moon.
Built by Grumman Aerospace on Long Island, N.Y., the spacecraft had two major parts: the descent stage and the ascent stage, which were carried to lunar orbit by the companion Command Service Module (CSM), a separate spacecraft of approximately twice the mass of the LM that carried the astronauts to and from Earth.
The LM model on exhibit is one quarter the size of the actual LM, which was 17.9 ft. (5.5 m) tall and approximately 14.0 ft. (4.3 m) in diameter with a landing gear span of 29.75 ft. (9.07 m).
Before Apollo 11 was allowed to land its LM in July 1969, the LM was flight-tested in Earth orbit during Apollo 9 and in lunar orbit during Apollo 10. Altogether, six LMs touched down and hosted 12 Moonwalkers between 1969 and 1972. The final three landers were more advanced versions of the original, carried a Lunar Rover Vehicle - nicknamed the Moon Buggy - and enabled longer stays on the surface.
Discarded after use, the LM was the world's first true spacecraft in that it could operate only in outer space; it was structurally and aerodynamically incapable of flight through the Earth's atmosphere. The most reliable component of the Apollo/Saturn system, no LM ever suffered a failure that significantly affected a mission. During the Apollo 13 crisis, the LM Aquarius greatly exceeded its design requirements by maintaining life support for astronauts after an explosion damaged the Apollo Service Module.
At launch, the LM sat directly beneath the CSM with legs folded, inside the Spacecraft-to-LM Adapter (SLA) attached to the third stage of the Saturn V rocket, where it remained through Earth parking orbit and the rocket burn that sent it toward the Moon. Then, the SLA opened and the CSM separated, turned around and came back to dock with the LM.
During the flight to the Moon, the docking hatches were opened and the LM pilot entered to temporarily power up and test systems. (interior, shown right) After achieving a lunar parking orbit, the commander and LM pilot powered up the LM, replaced the hatches and docking equipment, unfolded and locked the landing legs and separated from the CSM, flying independently.
After the command module pilot visually inspected the LM landing gear from the CSM, the LM was withdrawn to a safe distance and the descent engine performed a 30-second burn to reduce speed and drop close to the surface. Then, the engine was started again and, with the crew flying on their backs, the computer slowed the LM's forward and vertical velocity to near zero. During final approach, the LM pitched over to a near-vertical position, allowing the crew to look forward and down to see the lunar surface. At this point, the commander took over control and, with just enough fuel reserve, hovered for about two minutes to make any corrections before landing. Finally, three-foot-long probes extending from three footpads of the lander touched the surface, the descent engine cut off and the LM settled on the surface.
To leave the Moon, the LM would use the descent stage as a launch platform and fire the ascent engine to climb back into orbit. After a few course correction burns, the LM would dock with the CSM for transfer of the crew and rock samples. Then, the LM separated and went into solar orbit or crashed into the Moon.