Designed solely for the one-sixth gravity and vacuum of the Moon, it had to be a new type of spacecraft, unlike anything that had every been built.The design went through several configurations over the years to save weight and consider unknown Lunar conditions and kept evolving through each successive mission. It had to be small enough to fit inside the Saturn V rocket and light enough to be launched into space. It had four widely-spaced legs so it couldn’t tip over and big footpads so it wouldn’t sink.
Each LM consisted of an ascent stage and a descent stage, with both stages functioning as a single unit after separation from the Command Module through descent, landing, and stay on the lunar surface. The descent stage then served as the launch platform from which the ascent stage lifted off the moon. Interstage fittings were severed by explosives, so that the ascent stage then operated as an independent spacecraft during liftoff, ascent, rendezvous, and docking with the Command Module in lunar orbit. Thermal and micrometeroid shields also covered the decent stage. This shield, of aluminized Mylar, agave the craft a fragile, almost flimsy appearance. The ascent stage was the control center of the LM, with position for two astronauts. It contained the systems required for navigation, control, communications, life support, electrical power, and propulsion. The descent stage, the unmanned portion of the LM, carried the scientific equipment and experiments that were used on the lunar surface, as well as the descent propulsion. system.
The Lunar Module was the first true spacecraft, performing its mission only in the vacuum of space. Because of this, it could be designed to be purely functional, without streamlining-no aerodynamic qualities were necessary.