The lunar module actually consists of two separate sections. The lower section is the descent stage. Its primary function was to house the fuel and engine necessary for a controlled, powered decent to the lunar surface. Obviously, it also contains the landing gear, which cushioned the lunar module as it landed on the surface and supported the vehicle upright. (It's interesting to note that LM1 and 2 originally did not have landing gear because they were to be used in unmanned, Earth orbital test flights, so landing gear was not needed. However, landing gear was added to LM2 for use in the drop tests, which simulated the speeds and possible impact angles that the astronauts would experience on actual landings.) The decent stage is large because not only does it have to "fly" its own weight but the weight of the ascent stage too, which is the upper section of the lunar module. The decent stage housed the equipment the astronauts would use to explore the Moon and the TV camera used to send back the images of Neil Armstrong as he descended the ladder into history. 1 Apollo 11 Lunar Module in space 20k jpg 2 Lunar Module descent stage diagram 87k jpg 3 TV image of Neil Armstrong's first step 39k jpg Not pictured: Apollo Lunar Module diagram 149k jpg Photo credits: NASA Apollo 11 Audio/Video (requires free Real Player ) Apollo 11 landing on the Moon Audio/Video credits: NASA