This is the Lunar Module Ascent Engine, one of the most important in the manned Apollo missions. It was used to lift up the ascent stage of the Lunar Excursion Module (LEM) from the surface of the Moon after the completion of a manned Lunar-landing mission. The LEM then docked with the Command Module (CM) orbiting the Moon. Once the astronauts were safely aboard the CM, the LEM was ejected and allowed to crash on the surface of the Moon while the CM escaped its lunar orbit and heading back to Earth. The LEM Ascent Engine engine produced 3,500 pounds of thrust and was developed and built by the Bell Aerosystems Company. This engine was transferred to the Smithsonian from the NASA Johnson Space Flight Center in 1974.