This is the liquid propellant Lunar Module Ascent Engine. It was one of the most important in the manned Project Apollo missions since it was used to lift up the ascent stage of the Lunar Excursion Module (LEM) from the surface of the Moon which was then to dock with the Command Module (CM) orbiting the Moon. In the event of a too fast approach to the Moon, the engine could also be used to slow down the descent. It produced 3,500 pounds of thrust. The engine was developed and built by Rocketdyne.
Gift of Rocketdyne Division, Rockwell International Corporation