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The colonization of the Moon is the proposed establishment of permanent human communities on the Moon. Advocates of space exploration have seen settlement of the Moon as a logical step in the expansion of humanity beyond the Earth. National claims to the best locations on the moon may eventually lead to another space race. Polar colonies would be ideal for avoiding long cold nights and to take full advantage of the sun. Nations first to arrive at the poles might lay claim to them, similar to claims made at the Earth's north pole.

Permanent human habitation on a planetary body other than the Earth is one of science fiction's most prevalent themes. As technology has advanced, and concerns about the future of humanity on Earth have increased, the argument that space colonization is an achievable and worthwhile goal has gained momentum.^[1][2] Because of its proximity to Earth, the Moon has been seen as a prime candidate for the location of humanity's first permanently occupied extraterrestrial base.

Should attempts at colonization go ahead, economic concerns are likely to lead to settlements being created near mines and processing centers, or near the poles where a continuous source of solar energy can be harnessed. While it would be relatively easy to resupply a lunar base from Earth, in comparison to a Martian base, the Moon is likely to play a large role in the development of long-duration closed-loop life support systems. Duplicating the ecology of Earth so that wastes can be recycled is essential to any long term effort of space exploration^{[citation needed]}. The wealth of knowledge gained by extracting and refining resources on the Moon would positively affect efforts to build colonies elsewhere in the Solar System.

Contents 1 History 1.1 Exploration phase 2 Advantages and disadvantages 2.1 Advantages 2.2 Disadvantages 3 Locations 3.1 Polar regions 3.2 Equatorial regions 3.3 Far side 4 Structure 4.1 Habitat 5 Energy 5.1 Nuclear power 5.2 Solar energy 5.3 Energy storage 6 Transport 6.1 Earth to Moon 6.2 On the surface 6.3 Surface to space 6.4 Surface to and from cislunar space 7 Economic development 7.1 Space based materials processing 7.2 Exporting material to Earth 7.3 Tourism and research 7.4 Technology spin off 7.5 Solar power satellites 8 See also 9 References 10 External links

[edit] History

Space colonization

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The notion of siting a colony on the Moon originated before the space age; Konstantin Tsiolkovsky (1857-1935), among others, suggested such a step. ^[3] From the 1950s onwards, a number of concepts and designs have been suggested by scientists, engineers and others.

Noted science fiction author Arthur C. Clarke proposed a lunar base of inflatable modules covered in lunar dust for insulation in 1954.^[4] A spaceship, assembled in low Earth orbit, would be launched towards the Moon, and astronauts would set up the igloo-like modules and an inflatable radio mast. Subsequent steps would include the establishment of a larger, permanent dome; an algae-based air purifier; a nuclear reactor for the provision of power; and electromagnetic cannons to launch cargo and fuel to interplanetary vessels in space.

In 1959, John S. Rinehart suggested that the safest design would be a structure that could "[float] in a stationary ocean of dust," since there were, at the time this concept was outlined, theories that there could be mile-deep dust oceans on the Moon.^[5] The design proposed consisted of a half-cylinder with half-domes at both ends, with a micrometeoroid shield placed above the base.

The Project Horizon was a 1959 study regarding the U.S. Army's plan to establish a fort on the Moon by 1967.^[6] H. H. Koelle, a German rocket engineer of the Army Ballistic Missile Agency (ABMA) was leading the Project Horizon study. The first landing would be carried out by two "soldier-astronauts" in 1965 and more construction workers would soon follow. Through numerous launches (61 Saturn I and 88 Saturn V), 245 tons of cargo would be transported to the outpost by 1966.

[edit] Exploration phase

Exploration of the lunar surface by spacecraft began in 1959 when the Soviet Luna 2 mission crash-landed into the surface. The same year, the Luna 3 mission radioed photographs to Earth of the Moon's hitherto unseen far side, marking the beginning of a decade-long series of unmanned lunar explorations.

Responding to the Soviet program of space exploration, US President John F. Kennedy in 1961 told the U.S. Congress on May 25: "I believe that this nation should commit itself to achieving the goal before this decade is out of landing a man on the moon and returning him safely to the Earth." The same year the Soviet leadership made some of its first public pronouncements about landing a man on the Moon and establishing a lunar base.

In 1962, John DeNike and Stanley Zahn published their idea of a sub-surface base located at the Sea of Tranquility.^[4] This base would house a crew of 21, in modules placed 4 meters below the surface, which was believed to provide radiation shielding as well as the Earth's atmosphere does. They favored nuclear reactors for energy production, because they are more efficient than solar panels, and would also overcome the problems with the long lunar nights. For life support system, an algae-based gas exchanger was proposed.

Manned exploration of the lunar surface began in 1968 when the Apollo 8 spacecraft orbited the Moon with three astronauts on board. This was mankind's first direct view of the far side. The following year, the Apollo 11 lunar module landed two astronauts on the Moon, proving the ability of humans to travel to the Moon, perform scientific research work and bring back sample materials.

Additional missions to the Moon continued this exploration phase. In 1969 the Apollo 12 mission landed next to the Surveyor 3 spacecraft, demonstrating precision landing capability. Following the near-disaster of Apollo 13, Apollo 14 was the last mission on which astronauts were quarantined on their return from the Moon. The use of a manned vehicle 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 manned missions in near Earth orbit.

The Soviet Luna program failed to send a manned mission to the Moon. However, in 1966 Luna 9 was the first probe to achieve a soft landing and return close-up shots of the lunar surface. Luna 16 in 1970 returned the first Soviet lunar soil samples, while in 1970 and 1973 during the Lunokhod program two robotic rovers landed on the Moon. Lunokhod 1 explored the lunar surface for 322 days, but the contact with Lunokhod 2 was lost after about 4 months of its operation. 1974 saw the end of the Soviet Moonshot, two years after the last American manned landing.

In the decades following, interest in exploring the Moon faded considerably, and only a few dedicated enthusiasts supported a return. However, evidence of lunar ice at the poles gathered by NASA's Clementine and Lunar Prospector missions rekindled some discussion,^[7][8] as did the potential growth of a Chinese space program that contemplated its own mission to the Moon.^[9] Subsequent research suggested that there was far less ice present (if any) than had originally been thought, but that there may still be some usable deposits of hydrogen in other forms.^[10]

In 2004, U.S. President George W. Bush called for a plan to return manned missions to the Moon by 2020. Propelled by this new initiative, NASA issued a new long-range plan that includes building a base on the Moon as a staging point to Mars. This plan envisions a Lunar outpost at one of the moon's poles by 2024 which, if well-sited, might be able to continually harness solar power; at the poles, temperature changes over the course of a lunar day are also less extreme,^[11] and reserves of water and useful minerals may be found nearby.^[11] In addition, the European Space Agency has a plan for a permanently manned lunar base by 2025.^[12][13] Russia has also announced similar plans to send a man to the moon by 2025 and establish a permanent base there several years later.^[2]

A Chinese space scientist has said that the People's Republic of China could be capable of landing a human on the moon by 2022 (see Chinese Lunar Exploration Program),^[14] and Japan and India also have plans for a lunar base by 2030.^[15] Neither of these plans involves permanent residents on the Moon. Instead they call for sortie missions, in some cases followed by extended expeditions to the lunar base using rotating crew members, as is currently done for the International Space Station.

[edit] Advantages and disadvantages

Putting aside the general questions of whether a human colony beyond the Earth is feasible or scientifically desirable in light of cost-efficiency, proponents of space colonization point out that the Moon offers both advantages and disadvantages as a site for such a colony.

[edit] Advantages

Placing a colony on a natural body would provide an ample source of material for construction and other uses, including shielding from radiation. The energy required to send objects from the Moon to space is much less than from Earth to space. This could allow the Moon to serve as a construction site or fueling station for spacecraft.^[4] Some proposals include using electric acceleration devices (mass drivers) to propel objects off the Moon without building rockets. Others have proposed momentum exchange tethers (see below). Furthermore, the Moon does have some gravity, which, experience to date indicates, may be vital for fetal development and long-term human health.^[16][17] Whether the Moon's gravity (roughly one sixth of Earth's) is adequate for this purpose, however, is uncertain.

In addition, the Moon is the closest large body in the solar system to Earth. While some Earth-crosser asteroids occasionally pass closer, the Moon's distance is consistently within a small range close to 384,400 km. This proximity has several benefits:

• Monetary (space tourism), security, and technological gains.
• The energy required to send objects from Earth to the Moon is lower than for most other bodies.
• Transit time is short. The Apollo astronauts made the trip in three days. Other chemical rockets such as would be used for any Moon missions in the next one to two decades at least, would take a similar length of time to make the trip.
• If the Moon were colonized then it could be tested if humans can survive in microgravity. Those results could be utilized for a viable Mars colony as well.
• The short transit time would also allow emergency supplies to quickly reach a Moon colony from Earth, or allow a human crew to evacuate relatively quickly from the Moon to Earth in case of emergency. This could be an important consideration when establishing the first human colony.

Wikiversity has learning materials about Lunar Boom Town

• The round trip communication delay to Earth is less than three seconds, allowing near-normal voice and video conversation. The delay for other solar system bodies is minutes or hours; for example, round trip communication time between Earth and Mars ranges from about eight minutes to about forty minutes. This again would be of particular value in an early colony, where life-threatening problems requiring Earth's assistance could occur. (See, for example, Apollo 13.)
• On the lunar near side, the Earth appears large and is always visible as an object 60 times brighter than the Moon appears from Earth, unlike more distant locations where the Earth would be seen merely as a star-like object, much as the planets appear from Earth. As a result, a lunar colony might feel less remote to humans living there. The Apollo 8 astronauts, when behind the Moon, were the first humans to have no view of the Earth.
• A lunar base would provide an excellent site for any kind of observatory.^[1] As the Moon's rotation is so slow, visible light observatories could perform observations for days at a time. It is possible to maintain near-constant observations on a specific target with a string of such observatories spanning the circumference of the Moon. The fact that the Moon is geologically inactive along with the lack of widespread human activity results in a remarkable lack of mechanical disturbance, making it far easier to set up interferometric telescopes on the lunar surface, even at relatively high frequencies such as visible light.^[18]

[edit] Disadvantages

There are several disadvantages to the Moon as a colony site:

• The long lunar night would impede reliance on solar power and require a colony to be designed that could withstand large temperature extremes. An exception to this restriction are the so-called "peaks of eternal light" located at the lunar north pole that are constantly bathed in sunlight. The rim of Shackleton Crater, towards the lunar south pole, also has a near-constant solar illumination. Other areas near the poles that get light most of the time could be linked in a power grid.
• The Moon lacks light elements (volatiles), such as carbon and nitrogen, although there is some evidence of hydrogen near the north and south poles. Additionally, oxygen, though one of the most common elements in the regolith constituting the Moon's surface, is only found bound up in minerals that would require complex industrial infrastructure using very high energy to isolate. Some or all of these volatiles are needed to generate breathable air, water, food, and rocket fuel, all of which would need to be imported from Earth until other cheaper sources are developed. This would limit the colony's rate of growth and keep it dependent on Earth. The cost of volatiles could be reduced by constructing the upper stage of supply ships using materials high in volatiles, such as carbon fiber and other plastics, although converting these into forms useful for life would involve substantial difficulty. The 2006 announcement by the Keck Observatory that the binary Trojan asteroid 617 Patroclus,^[19] and possibly large numbers of other Trojan objects in Jupiter's orbit, are likely composed of water ice, with a layer of dust, and the hypothesized large amounts of water ice on the closer, main-belt asteroid 1 Ceres, suggest that importing volatiles from this region via the Interplanetary Transport Network may be practical in the not-so-distant future. However, these possibilities are dependent on complicated and expensive resource utilization from the mid to outer solar system, which are not likely to become available to a Moon colony for a significant period of time.
• There is continuing uncertainty over whether the low (one-sixth g) gravity on the Moon is strong enough to prevent detrimental effects to human health in the long term. Exposure to weightlessness over month-long periods has been demonstrated to cause deterioration of physiological systems, such as loss of bone and muscle mass and a depressed immune system. Similar effects could occur in a low-gravity environment, although virtually all research into the health effects of low gravity has been limited to zero gravity. Countermeasures such as an aggressive routine of daily exercise have proven at least partially effective in preventing the deleterious effects of low gravity.
• The lack of a substantial atmosphere for insulation results in temperature extremes and makes the Moon's surface conditions somewhat like a deep space vacuum. It also leaves the lunar surface exposed to half as much radiation as in interplanetary space (with the other half blocked by the moon itself underneath the colony). Although lunar materials would potentially be useful as a simple radiation shield for living quarters, shielding against solar flares during expeditions outside is more problematic.
• Also, the lack of an atmosphere increases the chances of the colonial site being hit by meteors, which would impact upon the surface directly, as they have done throughout the Moon's history. Even small pebbles and dust have the potential to damage or destroy insufficiently protected structures.
• Moon dust is an extremely abrasive glassy substance formed by micrometeorites and unrounded due to the lack of weathering. It sticks to everything, can damage equipment, and it may be toxic.^[20]
• Growing crops on the moon faces many difficult challenges due to the long lunar night (nearly 15 earth days), extreme variation in surface temperature, exposure to solar flares, and lack of bees for pollination. (Due to the lack of any atmosphere on the Moon, plants would need to be grown in sealed chambers, though experiments have shown that plants can thrive at pressures much lower than those on Earth.^[21]) The use of electric lighting to compensate for the 28 day/night might be difficult: a single acre of plants on Earth enjoys a peak 4 megawatts of sunlight power at noon. Experiments conducted by the Soviet space program in the 1970s suggest it is possible to grow conventional crops with the 15 day light, 15 day dark cycle.^[22] A variety of concepts for lunar agriculture have been proposed,^[23] including the use of minimal artificial light to maintain plants during the night and the use of fast growing crops that might be started as seedlings with artificial light and be harvestable at the end of one lunar day.^[24] Placing the farm at the constantly lit North Pole would be a way of escaping from this problem. One estimate suggested a 0.5 hectare space farm could feed 100 people.^[25]

[edit] Locations

Three criteria that a lunar outpost should meet are:

• good conditions for transport operations;
• a great number of different types of natural objects and features on the Moon of scientific interest; and
• natural resources, such as oxygen. The abundance of certain minerals, such as iron oxide, varies dramatically over the lunar surface.^[26]

While a colony might be located anywhere, potential locations for a lunar colony fall into three broad categories.

[edit] 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 may be present in some continuously shaded areas near the poles.^[27] 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. Some sites have nearly continuous sunlight. For example, 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 nearly continuous power.^[28]
• Its proximity to Shackleton Crater (116 km, or 69.8 mi) 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.^[28]
• The nearby Shoemaker and other craters are in constant deep shadow, and might contain valuable concentrations of hydrogen and other volatiles.^[28]
• At around 5,000 meters (16,500 ft) elevation, it offers line of sight communications over a large area, as well as to Earth.^[28]
• The South Pole-Aitken basin is located at the south lunar pole. This is the largest known impact basin in the solar system, and should provide geologists access to deeper layers of the Moon's crust.

NASA chose to use a south-polar site for the lunar outpost reference design in the Exploration Systems Architecture Study chapter on Lunar Architecture.^[29]

At the north pole, the rim of Peary crater has been proposed as a favorable location for a base.^[30] Examination of images from the Clementine mission appear to show that parts of the crater rim are permanently illuminated by sunlight (except during lunar eclipses).^[30] As a result, the temperature conditions are expected to remain very stable at this location, averaging −50 °C (−58 °F).^[30] This is comparable to winter conditions in Earth's the Poles of Cold in Siberia and Antarctica. The Peary crater interior may also harbor hydrogen deposits.^[30]

Although hydrogen appears to be concentrated at the poles, the presence of lunar ice has not yet been confirmed. A bistatic radar experiment performed during the Clementine mission suggested the presence of water ice around the south pole.^[31][32] The Lunar Prospector spacecraft reported enhanced hydrogen abundances not only at the south pole, but also at the north pole — actually more so.^[33] On the other hand, results reported using the Arecibo radio telescope have been interpreted by some to indicate that the anomalous Clementine radar signatures are not indicative of ice, but surface roughness.^[34] This interpretation, however, is not universally agreed upon.^[35]

[edit] Equatorial regions

The lunar equatorial regions are likely to have higher concentrations of helium-3 (rare on Earth but much sought after for use in nuclear fusion research) because the solar wind has a higher angle of incidence.^[36] They also enjoy an advantage in launching material from the Moon, but the advantage is slight due to the Moon's slow rotation.

Several probes have landed in the Oceanus Procellarum area. There are many areas and features that could be subject to long-term study, such as the Reiner Gamma anomaly and the dark-floored Grimaldi crater.

[edit] Far side

The lunar far side lacks direct communication with Earth, though a communication satellite at the L2 Lagrangian point, or a network of orbiting satellites, could enable communication between the far side of the Moon and Earth.^[37] The far side is also a good location for a large radio telescope because it is well shielded from the Earth.^[38] Due to the lack of atmosphere, the location is also suitable for an array of optical telescopes, similar to the Very Large Telescope in Chile.^[39] To date, there has been no ground exploration of the far side.

Scientists have estimated that the highest concentrations of helium-3 will be found in the maria on the far side, as well as near side areas containing concentrations of the titanium-based mineral ilmenite. On the near side the Earth and its magnetic field partially shields the surface from the solar wind during each orbit. But the far side is fully exposed, and thus should receive a somewhat greater proportion of the ion stream.^[40]

[edit] Structure

[edit] Habitat

There have been numerous proposals regarding habitat modules. The designs have evolved throughout the years as mankind's knowledge about the Moon has grown, and as the technological possibilities have changed. The proposed habitats range from the actual spacecraft landers or their used fuel tanks, to inflatable modules of various shapes. Early on, some hazards of the lunar environment such as sharp temperature shifts, lack of atmosphere or magnetic field (which means higher levels of radiation and micrometeoroids) and long nights, were recognized and taken into consideration.

Some suggest building the lunar colony underground, which would give protection from radiation and micrometeoroids. This is not the only advantage to this option. The average temperature on the moon is about −5 °C. The day period (two weeks) has an average temperature of about 107 °C (225 F), although it can rise as high as 123 °C (253 F). The night period (also two weeks) has an average temperature of about −153 °C (−243 F). ^[41] Underground, both periods would be around 24 °C (75 F), and humans could install ordinary air conditioners. ^[42] The construction of such a base would probably be more complex; one of the first machines from Earth might be a remote controlled boring machine to excavate living quarters. Once created, some sort of hardening would be necessary to avoid collapse, possibly a spray-on concrete-like substance made from available materials.^[43] A more porous insulating material also made in situ could then be applied. Inflatable self-sealing fabric habitats might then be put in place to retain air. As an alternative to excavating, it is possible that large underground extinct lava tubes might exist on the Moon.^[44]

A possibly easier solution would be to build the lunar base on the surface, and cover the modules with lunar soil. The lunar regolith is composed of a unique blend of silica and iron-containing compounds that may be fused into a glass-like solid using microwave energy. ^[45] This may allow for the use of "lunar bricks" in structural designs, or the "glassing" of loose dirt to form a hard, ceramic crust. Others have put forward the idea that the lunar base could be built on the surface and protected by other means, such as improved radiation and micrometeoroid shielding. Artificial magnetic fields have been proposed as a means to provide radiation shielding for long range deep space manned missions, and it might be possible to use similar technology on a lunar colony. Some regions on the Moon possess strong local magnetic fields that might partially mitigate against exposure to charged solar and galactic particles.^[46]

[edit] Energy

A lunar base would need power for its operations — from fuel production and communications to life support systems and scientific research.

[edit] Nuclear power

A nuclear fission reactor might fulfill most of the base's power requirements. The advantage of a fission reactor over a fusion reactor is that the technology already exists. A fusion reactor has the advantage that helium-3, which is required for a certain type of fusion reaction, is abundant on the Moon. However, fusion reactors are far from being a practical power source at present and may not be available at the time of lunar colonization. Radioisotope thermoelectric generators could be used as backup and emergency power sources for solar powered colonies.

[edit] Solar energy

Solar energy is a strong candidate. It could prove to be a relatively cheap source of power for a lunar base, especially since many of the raw materials needed for solar panel production can be extracted on site. However, the long lunar night (14 Earth days) is a drawback for solar power on the Moon's surface. This might be solved by building several power plants, so that at least one of them is always in daylight. Another possibility would be to build such a power plant where there is constant or near-constant sunlight, such as at the Malapert mountain near the lunar south pole, or on the rim of Peary crater near the north pole. A third possibility would be to leave the panels in orbit, and beam the power down as microwaves.

The solar energy converters need not be silicon solar panels. It may be more advantageous to use the larger temperature difference between sun and shade to run heat engine generators. Concentrated sunlight could also be relayed via mirrors and used in Stirling engines or solar trough generators, or it could be used directly for lighting, agriculture and process heat. The focused heat might also be employed in materials processing to extract various elements from lunar surface materials.

[edit] Energy storage

In the early days, a combination of solar panels for 'day-time' operation and fuel cells for 'night-time' operation could be used.

Fuel cells on the Space Shuttle have operated reliably for up to 17 days at a time. On the Moon, they would only be needed for 13.7 days — the length of the lunar night. Fuel cells produce water directly as a waste product. Current fuel cell technology is more advanced than the Shuttle's cells — PEM (Proton Exchange Membrane) cells produce considerably less heat (though their waste heat would likely be useful during the lunar night) and are physically lighter, not to mention the reduced mass of the smaller heat-disapating radiators. This makes PEMs more economical to launch from Earth than the shuttle's cells, but PEMs have not yet been proven in space.

Combining fuel cells with electrolysis would provide a 'perpetual' source of electricity - solar energy could be used to provide power during the Lunar 'day', and fuel cells at night. During the Lunar 'day', solar energy would also be used to electrolise the water created in the fuel cells - although there would be small losses of gases that would have to be replaced.

[edit] Transport

[edit] Earth to Moon

Conventional rockets have been used for most lunar exploration to date. The ESA's SMART-1 mission from 2003 to 2006 used Hall effect thrusters. NASA will use chemical rockets on its Ares V booster and Lunar Surface Access Module, being developed for a planned return to the Moon around 2019. The construction workers, location finders, and other astronauts vital to building, will be taken in NASA's Orion spacecraft.

[edit] On the surface

Lunar colonists will want the ability to move over long distances, to transport cargo and people to and from modules and spacecraft, and to carry out scientific study of a larger area of the lunar surface for long periods of time. Proposed concepts include a variety of vehicle designs, from small open rovers to large pressurised modules with lab equipment, and also a few flying or hopping vehicles.

Rovers could be useful if the terrain is not too steep or hilly. The only rovers to have operated on the surface of the Moon (as of 2008) are the Apollo Lunar Roving Vehicle (LRV), developed by Boeing, and the robotic Soviet Lunokhod. The LRV was an open rover for a crew of two, and a range of 92 km during one lunar day. One NASA study resulted in the Mobile Lunar Laboratory concept, a manned pressurised rover for a crew of two, with a range of 396 km. The Soviet Union developed different rover concepts in the Lunokhod series and the L5 for possible use on future manned missions to the Moon or Mars. These rover designs were all pressurised for longer sorties.^[47]

If multiple bases were established on the lunar surface, they could be linked together by permanent railway systems. Both conventional and magnetic levitation (Mag-Lev) systems have been proposed for the transport lines. Mag-Lev systems are particularly attractive as there is no atmosphere on the surface to slow down the train, so the vehicles could achieve velocities comparable to aircraft on the Earth. One significant difference with lunar trains, however, is that the cars would need to be individually sealed and possess their own life support systems. The trains would also need to be highly resistant to derailment, as a punctured car could lead to rapid loss of life.

For difficult areas, a flying vehicle may be more suitable. Bell Aerosystems proposed their design for the Lunar Flying Vehicle as part of a study for NASA. Bell also developed the Manned Flying System, a similar concept.

[edit] Surface to space

A lunar base will need efficient ways to transport people and goods of various kinds between the Earth and the Moon and, later, to and from various locations in interplanetary space. One advantage of the Moon is its relatively weak gravity field, making it easier to launch goods from the Moon than from the Earth. The lack of a lunar atmosphere is both an advantage and a disadvantage; while it is easier to launch from the Moon because there is no drag, aerobraking is not possible, which makes it necessary to bring extra fuel in order to land. An alternative, which may work for supplies, is to surround the payload with impact-absorbing materials, something that was tried in the Ranger program. This can be efficient if the impact protection is made of needed lighter elements that are absent from the Moon (Ranger used balsa wood)^[48]

One way to get materials and products from the Moon to an interplanetary waystation might be with a mass driver, a magnetically accelerated projectile launcher. Cargo would be picked up from orbit or an Earth-Moon Lagrangian point by a shuttle craft using ion propulsion, solar sails or other means and delivered to Earth orbit or other destinations such as near-Earth asteroids, Mars or other planets, perhaps using the Interplanetary Transport Network. If a lunar space elevator is ever built, it could transport people, raw materials and products to and from an orbital station at Lagrangian points L1 or L2.

[edit] Surface to and from cislunar space

A cislunar transport system has been proposed using tethers to achieve momentum exchange.^[49] This system requires zero net energy input, and could not only retrieve payloads from the lunar surface and transport them to Earth, but could also soft land payloads on to the lunar surface.

[edit] Economic development

For long term sustainability, a space colony should be close to self sufficient. On site mining and refining of the Moon's materials could provide an advantage over deliveries from Earth – for use both on the Moon and elsewhere in the solar system – as they can be launched into space at a much lower energy cost than from Earth. It is possible that vast sums of money will be spent in interplanetary exploration in the 21st century, and the cost of providing goods from the Moon might be attractive.^[43]

[edit] Space based materials processing

In the long term, the Moon is likely to be very important in supplying space-based construction facilities with raw materials. ^[47] Zero gravity allows materials to be processed in ways impossible or difficult on Earth, such as 'foaming' metals, where a gas is injected into a molten metal, and then the metal is annealed slowly. On Earth, the gas bubbles rise and burst, but in a zero gravity environment, that does not happen. Annealing is a process that requires large amounts of energy, as a material is kept very hot for an extended period of time. This allows the molecular structure to align in the strongest possible way. Materials which cannot be alloyed or mixed on Earth because of the gravity field effects on density differences could be combined in space, resulting in composites which could have exceptional qualities. No one knows, because no one has been able to experiment along these lines on any scale. However, it is possible that a material or process will be identified which will be highly valuable on Earth, but impossible to make here.

[edit] Exporting material to Earth

Exporting material to Earth in trade from the Moon is more problematic due to the high cost of transportation. One suggested candidate is Helium-3 from the solar wind, which has accumulated on the Moon's surface over billions of years, and which is rare on Earth. Helium is present in the lunar regolith in quantities of ten to a hundred (weight) parts per million, and 0.003 to 1 percent of this amount (depending on soil). 2006 market price for He-3 was about $46,500 per troy ounce ($1500/gram, $1.5M/kg), more than 120 times the value per unit weight of Gold and over eight times the value of Rhodium.

In the long term future He-3 may prove to be a desirable fuel in thermonuclear fusion reactors.

[edit] Tourism and research

Other economic possibilities include the tourism industry; manufacturing that requires a sterile, low-gravity environment in a vacuum; research and processing of potentially dangerous life forms or nanotechnology, and long-term storage of radioactive materials. The low gravity may find health uses such as allowing the physically disabled to continue to enjoy an active lifestyle. Large, pressurized domes or caverns would permit human-powered flight, which may result in new sports activities.

[edit] Technology spin off

Technology developed for a Lunar colony would likely have application to other potential space venues, including near-Earth asteroids and Mercury, which has many similarities to the Moon.

[edit] Solar power satellites

Gerard O'Neill, noting the problem of high launch costs in the early 1970s, came up with the idea of building Solar Power Satellites in orbit with materials from the Moon.^[50] Launch costs from the Moon are about 100 times lower than from Earth, due to the lower gravity and lack of atmosphere. This 1970s proposal was predicated on the then advertised future launch costs of NASA's space shuttle.

On 30 April 1979 the Final Report "Lunar Resources Utilization for Space Construction" by General Dynamics Convair Division under NASA contract NAS9-15560 concluded that use of lunar resources would be cheaper than terrestrial materials for a system comprising as few as thirty Solar Power Satellites of 10 GW capacity each.^[51]

In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al published another route to manufacturing using lunar materials with much lower startup costs.^[52] This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under telepresence control of workers stationed on Earth.

[edit] See also

[edit] References

[edit] External links

• Science Magazine The Clementine Bistatic Radar Experiment. Retrieved December 18, 2004.
• Space Daily Lunar Polar Ice Not Found With Arecibo Radar. Retrieved December 18, 2004.
• NASA Ames Research Center EUREKA! ICE FOUND AT LUNAR POLES. Retrieved December 18, 2004.
• Cornell News Arecibo radar shows no evidence of thick ice at lunar poles (...). Retrieved December 18, 2004.
• NASA Johnson Space Centre Liftoff! Moon Base Alpha. Last checked January 20, 2005.
• Encyclopedia Astronautica Subcategory: - Manned - Lunar rover - . Retrieved December 20, 2004.
• DigitalSpace Concepts A Multi-Function "Service Station" for Lunar Telerobotic Base Preparation. Checked January 29, 2006.
• The vision for space exploration, NASA.
• How Stuff Works - What if we lived on the moon? Retrieved 15 March 2007.
• Wiki devoted to the return to the moon- Lunarpedia

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