Polar Regions
There are two reasons why the lunar poles might be attractive as locations for a human colony. First, there is evidence that water is present in some continuously shaded areas near the poles. Water be found to be equally distributed at both poles, or it may exist only in select craters. Second, because the Moon's axis of rotation is almost perfectly perpendicular to the ecliptic plane, it may be possible to power polar colonies exclusively with solar energy. Power collection stations can be located so that at least one is in sunlight at all times, yet all are close enough to each other to be connected in an electrical grid. Some sites have nearly continuous sunlight.
Which pole is selected for the moon base will be determined by which pole provides the optimal combination of water and sunlight. Right now the betting appears to be on the south pole region.
The European Space Agency's SMART-1 craft shed light on lunar topography, particularly the south polar region before ending its existence with an impact on the moon in September 2006. Japan’s SELENE launched in September 2007 studied the Moon's geologic evolution, the surface environment and the moon's gravity field before purposely crashing into the moon in June 2009 near the south pole. Both impacts hoped to provide evidence of water on the moon. The results were not determinative.
NASA's Lunar Reconnaissance Orbiter (LRO) launched in June 2009 will spend at least a year in a low polar orbit approximately 50 kilometers (31 miles) above the lunar surface, while its seven instruments search for safe landing sites, locate potential resources (including water), characterize the radiation environment and test new technology.
India's first mission to the Moon (Chandrayaan-1), launched in October 2008, possessed a U.S.-made radar instrument designed to pin down the locations of water ice. However, an experiment (in conjunction with NASA's LRO) to locate water in a crater near the north pole failed in August 2009 just before all contact was lost with the orbiter.
Some specific advantages of polar locations are as follows:
- Water ice - Probably located here and may in addition contain frozen ammonia, methane, and other ices deposited by comets.
- Areas of near constant sunlight - Most places on the moon receive 14 terrestrial days of sunlight followed by 14 terrestrial days of darkness, but at the south pole there are areas of near-constant sunlight which receive sunlight up to 90 percent of the time, making them excellent sites for solar power systems. The sun is seen to perpetually revolve near the horizon, similar to the "midnight sun" effect on Earth. By placing a solar power system on this spot, year round electrical power can be generated to support a lunar colony.
- Cold & shadowed crater bottoms - Extensive areas of permanently shadowed crater bottoms with temperatures as low as -230° Celsius - good sites for infrared telescopes. They also provide sheltered storage areas for essential cryogenic liquids such as liquid oxygen, cryogenic fuels, and liquid nitrogen. Protection from solar flares is also provided.
- Relatively constant temperature - The poles have few dramatic temperature shifts. Surface temperature remains close to -30° C. It provide a constant temperature environment leading to a more simplified environmental control system. For example, a habitat cooling system will not be required. Outside the polar regions surface temperature spans about 400 degrees over the course of the 28-terrestrial-day lunar day. The constant extreme cold at these polar sites will eliminate the heat dissipation problems associated with equatorial sites
South Pole
The south pole has peaks as high as Mt. McKinley and crater floors four times deeper than the Grand Canyon. NASA in a September 2009 report displayed the highest resolution view to date of the moon's rugged south polar region. The mapping data collected indicate that the region of the moon's south pole near Shackleton Crater is much more rugged than previously understood.
Two locations of interest at the lunar south pole have been examined extensively:
Malapert Mountain & Shackleton Crater
Malapert mountain, located near the Shackleton crater at the lunar south pole, offers several advantages as a site. It is exposed to the sun most of the time; two closely spaced arrays of solar panels would receive continuous power. By contrast, sites near the lunar equator experience two weeks of day and two weeks of night each month.
Its proximity to Shackleton Crater (slightly over 100 kilometers) means that it could provide power and communications to the crater. This crater is potentially valuable for astronomical observation. An infrared instrument would benefit from the very cold temperatures. A radio telescope would benefit from being shielded from Earth's broad spectrum radio interference. Preliminary data indicates the presence of water at this location. Placing the habitat within the crater will also provide protection from solar radiation. In the shadow of the crater, cryogenic storage facilities can also be set up for the storage of liquid oxygen, liquid nitrogen, liquid silane, and liquid hydrogen. The nearby Shoemaker and other craters are in constant deep shadow, and might contain valuable concentrations of hydrogen and other volatiles.
At around 5,000 meters (16,500 feet) elevation, the mountain offers line of sight communications over a large area, as well as to Earth. Malapert's height and position on the lunar prime meridian (the longitude line running from north pole to south pole through the center of the Nearside hemisphere) mean that Earth is always visible from its summit. This permits continuous radio contact with the homeworld.
Japan’s SELENE (also known as Kaguya) lunar orbiter in early 2009 determined that a ‘Peak of Eternal Light‘ at either of the lunar poles does not exist.
The possibility of a Peak of Eternal Light at the rim of Shackleton Crater or on Malapert, made those locations prime candidates for early lunar bases. Having eternal sunlight is an advantage for any outpost relying largely on solar power. Nevertheless, some points at the lunar poles do have solar illuminationas as much as 89% of the time, so they remain very strong candidates for near-constant solar power.
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Less lofty lunar polar sites experience periodic radio blackouts when Earth dips below the horizon for hours or days at a time. Many such sites are visible from Malapert's summit, so a facility there could serve as a radio relay to link them with Earth. In particular, Malapert could relay signals to and from a base at the lunar south pole, 120 kilometers away on the rim of Shackleton crater. A south pole base could be the hub of an eventual lunar railway/solar power distribution network [read]. With a six-degree, 40-kilometer slope, Malapert's northwest flank is not too steep for robot rovers to negotiate.
Aitken Basin
The Aitken Basin is the largest known impact crater in the solar system (2600-kilometer-wide, 12-kilometer-deep). It stretches north from the south pole on the far side of the moon. The only impact basin close to SPA in size is the Chryse Basin on Mars. It is darker and richer in iron than the rest of the lunar highlands.
A hole the size of the Aiken Basin is especially exciting as it might have dug well into the mantle of the Moon. Mantles are important. They are deeper and compositionally different from the crust which forms the surface of a planet. Crusts are typically tens of kilometers thick (perhaps up to 100 km on the lunar farside). Mantles contain information about a planet's total composition, a key parameter in understanding planet formation and how the planets vary in composition with distance from the Sun.
North Pole
Unlike Earth, whose extreme tilt causes seasons, the Moon's rotational axis is almost perfectly upright, deviating just 1.5 percent from the main plane of the solar system that extends outward from the Sun's belly. On Earth, summer means constant sunlight at the North Pole, and winter plunges the Arctic into permanent darkness. But on the Moon, theorists have long suspected there might be high points from which the Sun is always visible.
Peary Crater
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Percent of time various locations on Peary Crater are sunlit
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At the north pole, the rim of Peary crater has been proposed as a favorable location for a base. The Peary crater, created long ago by the impact of an asteroid, is about 45 miles (73 kilometers) wide. Examination of images from the Clementine mission appear to show that parts of the crater rim are permanently illuminated by sunlight. The temperature conditions are expected to remain very stable at this location, comparable to winter conditions in parts of earth's polar regions. Such sites would also have resort-like temperatures compared with other lunar locations that fluctuate between blistering heat and unfathomable cold.
The crater is not far from suspected stores of water ice. Melted, it would be vital for drinking. Broken into hydrogen and oxygen, the water could provide breathable air and be used to make rocket fuel for a trip to Mars. The Peary crater interior may also harbor hydrogen deposits.
Although hydrogen appears to be concentrated at the poles, the presence of water ice has not yet been confirmed. Data from the Clementine mission suggested the presence of water ice in the large Shackleton crater near the Moon's South pole. The Lunar Prospector spacecraft detected possible water ice not only at the south pole, but also at the north pole - actually more so. On the other hand, Cornell News reported the results of a radar experiment (using the Arecibo radio telescope) that did not show any hints of water on the Moon.
Nearside
Equatorial Lunar Base locations are considered less desirable initially since solar power would only be available there two weeks per Lunar month. During the two week nights at these locations, a heavy battery system or nuclear power system would be required to produce power. In addition, water would have to be transported to these locations from the Poles.
Perhaps later, when an infrastructure is developed to bring water and power, these equatorial sites will be utilized. The lunar equatorial regions are likely to have higher concentrations of Helium-3 because the solar wind has a higher angle of incidence. They also enjoy an advantage in launching material from the Moon, but the advantage is slight due to the Moon's slow rotation.
Aristarchus
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View of Aristarchus and Herodotus craters taken from orbit during the Apollo 15 mission. The view is toward the south. Aristarchus crater is near the center of the image, and the flooded Herodotus is to the right.
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The Human Lunar Return (HLR) study occupied NASA exploration planners during 1995 and the first half of 1996. Aristarchus emerged as the prime landing region for the HLR expedition. Aristarchus "is one of the most geologically diverse regions for its size on the lunar surface," and thus has great science potential. Situated in central north-eastern Oceanus Procellarium, it includes:
- Aristarchus Plateau - revealed by Clementine to be tectonically uplifted along its northwest fringe nearly 100 meters above the surrounding terrain;
- Cobra Head - "the largest and most conspicuous volcanic source crater" on the moon;
- Schroter’s Valley - a 100-kilometer-long lava channel ;
- Herodotus crater - 35-kilometer-wide and partially submerged by ancient lava flows;
- Aristarchus crater - The crater is 26 miles (42 kilometers) in diameter and approximately 2 miles (3.2 kilometers) in depth, and sits at the southeastern edge of the Aristarchus Plateau. Aristarchus is one of the youngest and largest craters on the Moon. The crater formed between 100 and 900 million years ago;
- Sundry rilles, scarps, and volcanic domes and vents; and
- Deposits of iron-rich glassy material spewed from ancient volcanic fire fountains. This last, which may resemble similar deposits found by the Apollo 17 astronauts in 1972, is a potentially rich source of lunar oxygen for rocket propellant.
Farside
The lunar far side lacks direct communication with Earth, though a communication satellite at the L2 Lagrangian point would cover the far side. Farside is an excellent place for radio telescopes because the moon's body shields them from interfering natural and artificial radio signals from Earth.
The moon would be an excellent location for SETI (search for extraterrestrial intelligence) activity. With a rarer vacuum, the view would be clearer than near-earth orbital space. Raw materials abundant on the moon, like silicon and aluminum, can be used in construction of giant telescopes. The farside is the best place in the solar system for sensitive SETI radio searches. It is insulated by 3,500 feet of rock and is always turned away from the earth and its myriad of radio frequency sources. When the sun is down for the two week night, there is no quieter radio environment.
Scientists have estimated that the highest concentrations of He-3 will be found on the marias on the far side, as well as near side areas containing concentrations of the titanium-based mineral ilmenite. On the near side the Earth partially shields the surface from the solar wind during each orbit. But the far side is fully exposed, and thus should receive a greater proportion of the ion stream.
In-between / Orientale Basin
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The concentric, circular Orientale basin, 600 miles across, is near the center; the nearside is to the right, the far side to the left. At the upper right is the large, dark Oceanus Procellarum; below it is the smaller Mare Humorum. These, like the small dark Mare Orientale in the center of the basin, formed over 3 billion years ago as basaltic lava flows. At the lower left, among the southern cratered highlands of the far side, is the South-Pole-Aitken basin, similar to Orientale but twice as great in diameter and much older and more degraded by cratering and weathering. The cratered highlands of the near and far sides and the Maria are covered with scattered bright, young ray craters.
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The Orientale Basin is the most prominent asteroid impact feature on the moon, yet its existence went unsuspected until the mid-1960s, when Lunar Orbiter spacecraft began photographing regions not directly observable from Earth. Orientale straddles the line between the moon's nearside and farside hemispheres. At its center is dark, flat Mare Orientale, which is entirely surrounded by the rugged Rook Mountains. The Cordillera Mountains surround the Rook Mountains in turn, forming Orientale's outer rim. Interspersed between Mare Orientale, the Cordilleras, and the Rooks are irregular, dark-floored flat areas designated Lacus Veris and Lacus Autumni. The northern edge of Orientale's jumbled ejecta blanket spills across the lunar equator.
It has been proposed locating a staffed lunar observatory on the northern Orientale ejecta blanket, on the equator at 80 degrees west longitude. Reasons given for this proposal are as follows:
- Access to the celestial sphere - On a spherical world like the Earth or moon, a minimum of five observatories are needed to permit continuous observation of the entire sky: one at each pole and three spaced 120 degrees apart along the equator. The single northeast Orientale site is thus a compromise. It's equatorial location allows observation of nearly the entire northern and southern sky visible from the moon's western hemisphere. Over a few months, as the moon orbits the Earth and the Earth orbits the Sun, its western hemisphere points at new areas of sky; this permits observation of the entire celestial sphere.
- Uninterrupted line of sight to Earth: Locating the base on the moon's nearside enables direct radio communication with Earth with no need for a satellite relay; the prospective observatory site can be checked out using Earth-based instruments before final selection; the observatory can study the Earth.
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Lunar Orbiter 4 image of the Mare Orientale basin on the Moon. The basin forms a giant "bulls-eye" on the western limb of the Moon. Three distinct circular rings can be seen. The outer most is the Cordillera Mountain scarp, almost 900 km in diameter. The basin was formed by a giant impact early in the Moon's history.
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Proximity to farside - Nearly all astronomical observations can be made from the lunar nearside. Some forms of radio astronomy (including the search for radio signals from extraterrestrial civilizations) demand a farside site where the moon's bulk can block Earthly radio noise. Teleoperated robot rovers could be based at the Orientale Basin to establish and maintain a radio observatory in the farside hemisphere. Radio communication over the lunar horizon is impossible because the moon lacks an ionosphere, so small radio repeaters (akin to those in cell phone networks) would link rovers and radio observatory with the base.
- Driveable and workable terrain - Driveability refers to how easily surface vehicles can move through a terrain, while workability refers primarily to how easily construction equipment can dig. United States Geological Survey studies from the 1960s indicate the Orientale Basin should be driveable with careful planning. Seismic data collected at Fra Mauro indicates that the surface is made up of "relatively young impact ejecta" tens of meters deep, and thus should be relatively easy to excavate.
- Proximity to geologically important features - A lunar observatory by itself will not be the only justification for a lunar outpost. The Orientale Basin has the important advantage of being on and near many geologically important features. In addition to the large and young Mare Orientale impact basin, there is western Oceanus Procellarum, which is characterized by an unusually large number of apparently volcanic features, including the Marius Hills and the Aristarchus Plateau. Volcanic areas are much more promising for lunar resources, water in particular, than non-volcanic ones.
