In May 1961 Pres. John F. Kennedy committed America to landing astronauts on the Moon by 1970. The choice among competing techniques for achieving a Moon landing and return was not resolved until considerable further study. Three methods were considered. In direct ascent, one vehicle would lift off from Earth, land on the Moon, and return. However, the proposed Nova rocket would not be ready by 1970. In Earth orbit rendezvous, a spacecraft carrying the crew would dock in Earth orbit with the propulsion unit that would carry enough fuel to go to the Moon. However, this method required two separate launches.
In the method ultimately employed, lunar orbit rendezvous, a powerful launch vehicle (Saturn V rocket) placed a 50-ton spacecraft in a lunar trajectory. The spacecraft had three parts. The conical command module (CM) carried three astronauts. The service module (SM) was attached to the back of the CM and carried its fuel and power to form the command/service module (CSM). Docked to the front of the CSM was the lunar module (LM). One astronaut stayed in the CSM while the other two landed on the Moon in the LM. The LM had a descent stage and an ascent stage. The descent stage was left on the Moon, and the astronauts returned to the CSM in the ascent stage, which was discarded in lunar orbit. The LM was flown only in the vacuum of space, so aerodynamic considerations did not affect its design. (Thus, the LM has been called the first “true” spacecraft.) Before reentering Earth’s atmosphere, the SM was jettisoned to burn up. The CM splashed down in the ocean. The lunar orbit rendezvous had the advantages of requiring only one rocket and of saving fuel and mass since the LM did not need to return to Earth.
In October 1968, following several uncrewed Earth-orbit flights, Apollo 7 made a 163-orbit flight carrying a full crew of three astronauts. Apollo 8 carried out the first step of crewed lunar exploration: from Earth orbit it was injected into a lunar trajectory, completed lunar orbit, and returned safely to Earth. Apollo 9 carried out a prolonged mission in Earth orbit to check out the LM. Apollo 10 journeyed to lunar orbit and tested the LM to within 15.2 km (9.4 miles) of the Moon’s surface. Apollo 11, in July 1969, climaxed the step-by-step procedure with a lunar landing; on July 20 astronaut Neil Armstrong and then Edwin (“Buzz”) Aldrin became the first humans to set foot on the Moon’s surface.
Cohesiveness of lunar soil, demonstrated qualitatively in a crisply defined boot print left on the Moon by U.S. astronaut Edwin Aldrin during the Apollo 11 mission, July 1969. Aldrin photographed the print as part of a study of the nature of the soil and its compaction behaviour. This image has also become an icon of the first visit by humans to another world.
Scientists and space planners have long acknowledged that extended human residence on the Moon would be greatly aided by the use of local resources. This would avoid the high cost of lifting payloads against Earth’s strong gravity. Certainly, lunar soil could be used for shielding habitats against the radiation environment. More advanced uses of lunar resources are clearly possible, but how advantageous they would be is presently unknown. For example, most lunar rocks are about 40 percent oxygen, and chemical and electrochemical methods for extracting it have been demonstrated in laboratories. Nevertheless, significant engineering advances would be needed before the cost and difficulty of operating an industrial-scale mining and oxygen-production facility on the Moon could be estimated and its advantages over transporting oxygen from Earth could be evaluated. In the long run, however, some form of extractive industry on the Moon is likely, in part because launching fleets of large rockets continuously from Earth would be too costly and too polluting of the atmosphere.
The solar wind has implanted hydrogen, helium, and other elements in the surfaces of fine grains of lunar soil. Though their amounts are small—they constitute about 100 parts per million in the soil—they may someday serve as a resource. They are easily released by moderate heating, but large volumes of soil would need to be processed to obtain useful amounts of the desired materials. Helium-3, a helium isotope that is rare on Earth and that has been deposited on the Moon by the solar wind, has been proposed as a fuel for nuclear fusion reactors in the future.
One natural resource uniquely available on the Moon is its polar environment. Because the Moon’s axis is nearly perpendicular to the plane of the ecliptic, sunlight is always horizontal at the lunar poles, and certain areas, such as crater bottoms, exist in perpetual shadow. Under these conditions the surface may reach temperatures as low as 40 K (−388 °F, −233 °C). Water molecules are found in their strongest concentrations at the lunar poles. These cold traps have collected volatile substances, including water ice, over geologic time.
The Lunar Prospector spacecraft, which orbited the Moon for a year and a half, carried a neutron spectrometer to investigate the composition of the regolith within about a metre (three feet) of the surface. Neutrons originating underground owing to radioactivity and cosmic-ray bombardment interact with the nuclei of elements in the regolith en route to space, where they can be detected from orbit. A neutron loses more energy in an interaction with a light nucleus than with a heavy one, so the observed neutron spectrum can reveal whether light elements are present in the regolith. Lunar Prospector gave clear indications of light-element concentrations at both poles, interpreted as proof of excess hydrogen atoms. The existence of water ice at the Moon’s south pole was confirmed by the LCROSS spacecraft.
The lunar ice can serve as a source of rocket propellants when split into its hydrogen and oxygen components. From a longer-term perspective, however, the ice would better be regarded as a limited, recyclable resource for life support (in the form of drinking water and perhaps breathable oxygen).
Aside from the existence of water, the lunar polar regions still represent an important resource. Only there can be found not only continuous darkness but also continuous sunlight. A solar collector tracking the Sun from a high peak near a lunar pole could provide essentially uninterrupted heat and electric power. Also, the radiators required for eliminating waste heat could be positioned in areas of continuous darkness, where the heat could be dissipated into space.
The lunar poles also could serve as good sites for certain astronomical observations. To observe objects in the cosmos that radiate in the infrared and millimetre-wavelength regions of the spectrum, astronomers need telescopes and detectors that are cold enough to limit the interference generated by the instruments’ own heat (see infrared astronomy). To date, such telescopes launched into space have carried cryogenic coolants, which eventually run out. A telescope permanently sited in a lunar polar cold region and insulated from local heat sources might cool on its own to 40 K (−388 °F, −233 °C) or lower. Although such an instrument could observe less than half the sky—ideally, one would be placed at each lunar pole—it would enable uninterrupted viewing of any object above its horizon. James D. Burke
How many countries have been to the moon? The United States, the Soviet Union and China are the three nations which have successfully landed their spacecraft on the moon. And, the US is the only country to have ever put people on the moon. Russia (the USSR), Japan, China, the European Space Agency (ESA), and India have all made visits to the moon via probes.
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