English: Neil Armstrong shown with NASA Langley Research Center's Lunar Excursion Module (LEM) Simulator. Training with the simulator, part of Langleys Lunar Research Facility, allowed the Apollo astronauts to study and safely overcome problems that could have occurred during the final 150-foot descent to the surface of the moon. NASA needed such a facility in order to explore and develop techniques for landing the LEM on the moons surface, where gravity is only one-sixth as strong as on the Earth, as well as to determine the limits of human piloting capabilities in the new surroundings. This unique facility, completed in 1965 and now a National Historic Landmark, effectively canceled all but one-sixth of Earths gravitational force by using an overhead cable system.