The History of Lunar Exploration

Throughout the 19th and 20th centuries, visual exploration with powerful telescopes yielded fairly comprehensive knowledge of the geography of the visible side of the Moon. The previously unseen far side of the Moon was first revealed to the world in October 1959 through photographs made by the Soviet Luna 3 spacecraft. These photographs showed that the far side of the Moon is similar to the near side except for the absence of large maria. Craters are now known to cover the entire Moon. In 1964 and 1966 photographs from U.S. spacecraft—Ranger 7 through 9 and Lunar Orbiter 1 through 5—further supported these conclusions. The entire Moon has about 3 trillion craters larger than 1 m in diameter.

The successful landings of the robotic U.S. Surveyor series spacecraft and the USSR Luna series in the 1960s, and then the manned landings on the lunar surface as part of the U.S. Apollo program, made direct measurement of the physical and chemical properties of the lunar surface a reality. The Apollo astronauts collected rocks, took thousands of photographs, and set up instruments on the Moon that radioed information back to Earth even after the astronauts departed. These instruments measured temperature and gas pressure at the lunar surface; heat flow from the Moon’s interior; molecules and ions of hot gases, called the solar wind, that stream out from the atmosphere of the Sun; the Moon’s magnetic field and gravity; seismic vibrations of the lunar surface caused by landslides, meteorite impacts, and so-called moonquakes; and the precise distance between Earth and the Moon.

All six manned landings on the Moon—Apollo 11, 12, 14, 15, 16, and 17 returned samples of rock and soil to Earth. These samples weighed a total of 384 kg. The astronauts explored increasingly wider areas on the Moon with each successive flight, culminating with the 35 km explored using a lunar roving vehicle by the Apollo 17 crew. This final mission included the only geologist ever to walk on the Moon, Harrison Jack Schmitt. The total cost of Apollo program was about $25.4 billion.

Originally three additional lunar landing missions had been planned, as Apollos 18 through 20. In light of the drastically shrinking NASA budget and the decision not to produce a second batch of Saturn Vs. These missions were cancelled to make funds available for the development of the Space Shuttle, and to make their Apollo spacecraft and Saturn V launch vehicles available to the Skylab program. Only one of the Saturn Vs was actually used; the others became museum exhibits.

Hiten (originally called Muses-A) was built and launched by ISAS , the Japanese Space Agency on January 4, 1990, as an Earth orbiting satellite designed primarily to test and verify technologies for future lunar and planetary missions. The spacecraft carried a small satellite named Hagoromo which was released into orbit around the Moon. Hiten itself was put into a highly elliptical Earth orbit which passed by the Moon ten times during the mission, which ended when Hiten was intentionally crashed into the Moon on 10 April 1993. Hiten was named after a flying, music-playing Buddhist angel. Hagoromo was named for the veil worn by Hiten. This mission included Japan\'s first-ever lunar flyby, lunar orbiter, and lunar surface impact.

In 1994, the joint Defense Department/NASA spacecraft Clementine orbited the Moon for 71 days, mapping the color and precise altitude of the lunar surface. From Clementine data, astronomers obtained their first global look at the topography and mineralogy of the Moon, finding that the Moon’s crust is indeed made of a low-iron, low-density rock called anorthosite and mapping the large, ancient basins that make up the structural framework of the Moon. Clementine also discovered ice on the Moon in the permanently dark areas near the south pole.

NASA sent a spacecraft of its own, an orbiter called Lunar Prospector, to the Moon in 1998. Lunar Prospector orbited around the Moon’s north and south poles and returned data until July 1999. The spacecraft mapped the gravitational field of the Moon, determined the distribution of radioactive elements in its crust, and confirmed the presence of ice at the lunar poles. Scientists used the spacecraft right up to its final moments. They ended Prospector’s mission by programming it to crash into the Moon’s surface and then observed