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The lunar module(LM) is the part of some spacecraft that is used to land a crew on the surface of the Moon. To date, only one space program has had a successful Moon landing, so this article will describe that module.
The only lunar module that has successfully settled on the Moon’s surface is the LM associated with the Apollo space program. This module was built from 1969 through 1972 and six of them landed on the Moon. Each carried a crew of two, so 12 humans have walked on the lunar surface.
The LM consists of two parts: the ascent stage and the descent stage. During launch the Lunar Module sat directly beneath the CSM(command/service module), its legs folded inside the spacecraft to LM adapter(SLA) which was attached to the third stage of the Saturn V rocket. It stayed in place through the trans lunar injection burn. Once in a lunar parking orbit, the Commander and LM Pilot powered up the LM, unfolded and locked its landing legs, and separated from the CSM. The Commander operated the flight controls and engine throttle, while the Lunar Module Pilot operated other spacecraft systems and kept the Commander informed on systems status and navigational information. After inspection of the landing gear, the LM was moved to a safe distance and the descent engine was pointed forward into the direction of travel to perform the 30 second descent orbit insertion(DOI) burn to reduce speed and drop the LM’s perilune to within approximately 15 km of the surface about 480 km uprange of the landing site.
After each successful landing the LM left the surface and docked with the CSM. After the crew transferred back to the CSM, the LM was discarded. A few of them reentered Earth atmosphere and are on display, but the majority of them were sent into solar orbit, left on the Moon, or crashed back into the lunar surface. They were designed to be disposable, so were used accordingly. The crew of Apollo 13 used the LM as a safe haven after systems failures made the CSM unusable. Hopefully, with the right budget, there will be a new version of the lunar module to write about in the next few years.
We’ve also recorded an entire episode of Astronomy Cast all about Moon Exploration. Listen here, Episode 114: The Moon, Part 2: Exploration of the Moon.
NASA: Apollo 11 Lunar Module