Exploration Of The Moon

Since 1959, there have been 52 missions12 to the lunar surface or to cislunar space, of which 48 were at least a partial success in terms of mission objectives and data return. On 31 January 1966, the Russian Luna 9 spacecraft made the first soft landing of a spacecraft on the Moon. Since that time, substantial in-situ analysis of the lunar surface has been made. The bulk of lunar rock samples that were returned to Earth were from the Apollo manned missions. Recent missions have indicated the possible presence of water (hydrogen concentrations) - an unexpected resource that will substantially increase the opportunity for the permanent return of humans to the Moon.

1.3.1 The Apollo experiments

On 11 December 1972, the sixth and final lunar surface mission of the Apollo Program (Apollo 17) landed in a valley near the edge of Mare Serenitatis (Figure 1.13). Astronauts Eugene Cernan and Harrison Schmitt spent 72 hours at the site, named Taurus-Littrow (after the mountains to the north). The site was geologically diverse, with the mountain ring of the Serenitatis Basin nearby, and lava

12 Missions to the lunar surface or cislunar space from 1959 to 2006: 27 Russian spacecraft (24 Luna and 3 Zond), 23 American spacecraft (5 Ranger, 6 Surveyor, 9 Apollo, 1 Pioneer, 1 Galileo, 1 Clementine, and 1 Lunar Prospector), 1 Japanese spacecraft (Muses A), and the European Space Agency's SMART-1 orbiter.

Landing Sites

I I Highlands L = Luna

Figure 1.13. Apollo landing sites.

I I Highlands L = Luna

Figure 1.13. Apollo landing sites.

filling in the valley lowlands. The main objective of the mission was to collect samples of these different types of rock.

The crew spent more than 22 hours on the lunar surface, using the rover to traverse the mare plains. The traverses totaled more than 30 km, and nearly 120 kg of rock and soil were collected - the largest total sample mass of any Apollo mission. Many of the rock samples have since been studied in detail.

A mass spectrometer was placed on the lunar surface during the Apollo 17 mission. It provided data on the distribution of many types of rarefied gases, including argon-40 and helium-4, and very small amounts of argon-36, methane, ammonia, and carbon dioxide at sunrise, as well as neon-20, neon-22, and molecular hydrogen. Essentially, all the argon-40 on the Moon comes from the decay of potassium-40 in the lunar interior. Variability in the amount of atmospheric argon (a 6- to 7-month periodicity was observed) suggests the presence of a partially molten core, which is interesting from both scientific and resource utilization standpoints. If deep vents that periodically release gases onto the surface are found, these gases could be trapped and used for manufacturing, as carrier gases in pneumatic conveyor systems, and for other uses.

A similar instrument, the suprathermal ion detector, had, on an earlier mission, documented the presence of a cloud of hot solar-wind electrons near the terminator. This cloud was found to vary with changes in the solar wind and extreme ultraviolet flux. In addition, one other interesting event was found. This event, principally water vapor, must remain suspect because of its proximity to the Apollo 14 mission. However, the large magnitude and the long time duration of the event argue against a mission-related source.

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