Colonization of the Moon the Apollo 12 mission landed next to the Surveyor 3 spacecraft, demonstrating precision landing capability. The use of a manned vehicle on the Moon's surface was demonstrated in 1971 with the Lunar Rover during Apollo 15. Apollo 16 made the first landing within the rugged lunar highlands. However, interest in further exploration of the Moon was beginning to wane among the American public. In 1972, Apollo 17 was the final Apollo lunar mission, and further planned missions were scrapped at the directive of President Nixon. Instead, focus was turned to the Space Shuttle and crewed missions in near Earth orbit.
Gravitation of the Moon mascons, which are large positive gravity anomalies associated with some of the giant impact basins. These anomalies significantly influence the orbit of spacecraft around the Moon, and an accurate gravitational model is necessary in the planning of both manned and unmanned missions. They were initially discovered by the analysis of Lunar Orbiter tracking data: navigation tests prior to the Apollo program showed positioning errors much larger than mission specifications. Mascons are in part due to the presence of dense mare basaltic lava flows that fill some of the impact basins. However, lava flows by themselves cannot fully explain the gravitational