Colonization of the Moon

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. Recent indication that water might be present in quantities at the lunar poles have increased interest in the Moon. Polar colonies could also avoid the problem of long lunar nights (about 14.77 Earth days, a little more than two weeks) and take advantage of the sun continuously.

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.

Proposals

The notion of siting a colony on the Moon originated before the space age. In 1638 Bishop John Wilkins wrote A Discourse Concerning a New World and Another Planet, in which he predicted a human colony on the Moon.[3] Konstantin Tsiolkovsky (1857–1935), among others, also suggested such a step.[4] From the 1950s onwards, a number of concepts and designs have been suggested by scientists, engineers and others.

In 1954 the noted science-fiction author Arthur C. Clarke proposed a lunar base of inflatable modules covered in lunar dust for insulation .[5] A spaceship, assembled in low Earth orbit, would launch to 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.[6] The proposed design consisted of a half-cylinder with half-domes at both ends, with a micrometeoroid shield placed above the base.

Project Horizon

Project Horizon was a 1959 study regarding the U.S. Army's plan to establish a fort on the Moon by 1967.[7] H. H. Koelle, a German rocket engineer of the Army Ballistic Missile Agency (ABMA) led 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 II), 245 tons of cargo would be transported to the outpost by 1966.

Lunar ark

A Lunar ark was proposed at a February 2008 conference held by the International Space University in Strasbourg, France. Subsequent planning may be taken up by the International Lunar Exploration Working Group (ILEWG).[8][9][10]

Moon exploration
Main articles: Exploration of the Moon and List of current and future lunar missions

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.[5] 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 (1994) and Lunar Prospector (1998) missions rekindled some discussion,[11][12] as did the potential growth of a Chinese space program that contemplated its own mission to the Moon.[13] 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.[14] However, in September 2009, the Chandrayaan probe, carrying a NASA instrument, discovered that the Lunar regolith contains 0.1% water by weight, overturning theories that had stood for 40 years.[15]

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,[16] and reserves of water and useful minerals may be found nearby.[16] In addition, the European Space Agency has a plan for a permanently manned lunar base by 2025.[17][18] 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),[19] and Japan and India also have plans for a lunar base by 2030.[20] 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.

NASA’s LCROSS/LRO mission had been scheduled to launch in October 2008.[21] The launch was delayed until the 18th of June 2009,[22] resulting in LCROSS's impact with the Moon at 11:30 UT on the 9th of October, 2009.[23][24] The purpose is preparing for future lunar exploration.

Water discovered on moon

In September 2009 it was announced that NASA's Moon Mineralogy Mapper on India's Chandrayaan-1 had detected water on the moon.[25][26]
On November 13, 2009 NASA announced that the LCROSS mission had discovered large quantities of water ice on the moon around the LCROSS impact site at Cabeus. "Large" is a relative term. The amount of water discovered is put in perspective by this comment from Robert Zubrin: "The 30 m crater ejected by the probe contained 10 million kilograms of regolith. Within this ejecta, an estimated 100 kg of water was detected. That represents a proportion of 10 parts per million, which is a lower water concentration than that found in the soil of the driest deserts of the Earth. In contrast, we have found continent sized regions on Mars, which are 600,000 parts per million, or 60% water by weight."[27]

Advantages and disadvantages
For more details on this topic, see space colonization.

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.

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.[5] 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.[28][29] 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 (including 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 and future technologies could improve on this time.
* 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.

* The round trip communication delay to Earth is less than three seconds, allowing near-normal voice and video conversation, and allowing some kinds of remote control of machines from Earth that are not possible for any other celestial body. 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.
* A lunar base would provide an excellent site for any kind of observatory.[1] Particular advantages arise from building observatory facilities on the Moon from lunar materials. 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.[30]
* A lunar base could also hold a future site for launching rockets, to distant planets such as Mars. Launching rockets from the Moon would be an easier prospect than on Earth due to the Moon's lower gravity requiring a lower escape velocity. A lower escape velocity would require less propellant, and so less money is required.
* A farm at the lunar North Pole could provide eight hours of sunlight per day for rotating crops, a beneficial temperature, radiation protection, insects for pollination, and all other plant needs artificially during the local summer for a cost. One estimate suggested a 0.5 hectare space farm could feed 100 people.[31]
* A moon colony provides us with most of the experiments, skills, and knowledge we need to colonize another planet.[citation needed]
* A moon colony can easily be seen from the Earth, and might inspire many more humans to seriously consider the advantages and future of colonization. A clear sign or signal can be made to remind humans on Earth, inspiring future leaders, astronauts, and scientists.

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 is highly depleted in light elements (volatiles), such as carbon, nitrogen and hydrogen. A number of robot probes including Lunar Prospector gathered evidence of hydrogen generally in the Moon's crust consistent with what would be expected from implantation from the solar wind, and higher concentrations near the poles.[32] There had been some disagreement whether the hydrogen must necessarily be in the form of water. The LCROSS mission has definitely found evidence of water.[33] This water would be in ice form perhaps mixed in small crystals in the regolith in a colder landscape than people have ever mined. Other volatiles containing carbon and nitrogen could conceivably also be in the same cold traps as the ice. If sufficient means of recovering these volatiles on the Moon to support life and industrial processes is not found, they would need to be imported from some other source, and stringently recycled. This would limit the colony's rate of growth and keep it dependent on Earth. The transportation cost of importing volatiles from Earth could be reduced by constructing the upper stage of supply ships using materials high in volatiles, such as carbon fiber and other plastics. The 2006 announcement by the Keck Observatory that the binary Trojan asteroid 617 Patroclus,[34] 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.
* It is uncertain 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 health deterioration that is caused by low gravity.[citation needed]
* 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) raising the issues of the health threat from cosmic rays and the risk of proton exposure from the solar wind, especially since two-thirds of the Moon's orbit is outside the protection of the Earth's magnetosphere. 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 (micrometeoroids) 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.[35]
* 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 insects 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.[36]) The use of electric lighting to compensate for the 15-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.[37] A variety of concepts for lunar agriculture have been proposed,[38] 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.[39]

Locations
For more details on this topic, see Geology of the Moon.

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.[40]

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

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.[41] 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 (see Peak of Eternal Light for further discussion); two closely spaced arrays of solar panels would receive nearly continuous power.[42]
* 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.[42]
* The nearby Shoemaker and other craters are in constant deep shadow, and might contain valuable concentrations of hydrogen and other volatiles.[42]
* At around 5,000 meters (16,500 ft) elevation, it offers line of sight communications over a large area, as well as to Earth.[42]
* The South Pole-Aitken basin is located at the south lunar pole. This is the second largest known impact basin in the solar system, as well as the oldest and biggest impact feature on the Moon[43], 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.[43]

At the north pole, the rim of Peary crater has been proposed as a favorable location for a base.[44] 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).[44] As a result, the temperature conditions are expected to remain very stable at this location, averaging −50 °C (−58 °F).[44] This is comparable to winter conditions in Earth's Poles of Cold in Siberia and Antarctica. The Peary crater interior may also harbor hydrogen deposits.[44]

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.[11][45] The Lunar Prospector spacecraft reported enhanced hydrogen abundances not only at the south pole, but also at the north pole — actually more so.[46] 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.[47] This interpretation, however, is not universally agreed upon.[48]

A potential limitation of the polar regions is that the inflow of solar wind can create an electrical charge on the leeward side of crater rims. The resulting voltage difference can affect electrical equipment, change surface chemistry, erode surfaces and levitate lunar dust.[49]

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.[50] They also enjoy an advantage in extra-lunar traffic: The rotation advantage for launching material is slight due to the Moon's slow rotation, but the corresponding orbit coincides with the ecliptic, nearly coincides with the lunar orbit around Earth and nearly coincides with the equatorial plane of Earth.

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.

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.[51] The far side is also a good location for a large radio telescope because it is well shielded from the Earth.[52] 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.[53] 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.[54]

Lunar lava tubes

Lunar lava tubes form a potentially important location for constructing a future lunar base, which may be used for local exploration and development, or as a human outpost to serve exploration beyond the Moon. Any intact lava tube on the moon could serve as a shelter from the severe environment of the lunar surface, with its frequent meteorite impacts, high-energy Ultra-Violet radiation and energetic particles, and extreme diurnal temperature variations.[55][56]; March 5, 2010; Discover Magazine; Phil Plait Astronomy [1] The second lunar lava tube was discovered by LRO.

Structure

Habitat
A NASA model of a proposed inflatable module

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 also greatly reduce the risk of air leakage, as the colony will be fully sealed from the outside except for a few exits to the surface. This is not the only advantage to this option. The average temperature on the moon is about −5 °C. The day period (about 15 days) 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 15 Earth days) has an average temperature of about −153 °C (−243 °F).[57] Underground, both periods would be around -23 °C (-9 °F), and humans could install ordinary air conditioners.[58]

The construction of such a base would probably be more complex; one of the first machines from Earth might be a remote controlled excavating 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.[59] A more porous insulating material also made in-situ could then be applied. Mining methods such as the room and pillar might also be used. Inflatable self-sealing fabric habitats might then be put in place to retain air. Eventually an underground city similar to the The Forum Shops at Caesars and Underground City, Montreal can be constructed. Farms setup underground would need artificial sunlight. As an alternative to excavating, a lava tube could be covered and insulated, thus solving the problem of radiation exposure. One such lava tube has been discovered in early 2009.[60]

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.[61] 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. Building the lunar base inside a deep crater would provide at least partial shielding against radiation and micrometeoroids. Artificial magnetic fields have been proposed[citation needed] 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 exposure to charged solar and galactic particles.[62]

Energy

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

Nuclear power

A nuclear fission reactor might fulfill most of the base's power requirements. Fission reactors can also overcome the difficulty of the 15-day lunar night. Radioisotope thermoelectric generators could be used as backup and emergency power sources for solar powered colonies.

Solar energy
For more details on this topic, see Peak of Eternal Light.

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 (15 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.

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 15 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-dissipating 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 electrolyze the water created in the fuel cells - although there would be small losses of gases that would have to be replaced.

Transport

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.

On the surface
A lunar rover being unloaded from a cargo spacecraft. Conceptual drawing.

Within the colony it will be difficult to set up a public transport system. However a system of Escalators, moving walkways and elevator can be used to quickly transport people and cargo around.

Lunar colonists will also 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[update]) are the three Apollo Lunar Roving Vehicles (LRV), developed by Boeing, and the two robotic Soviet Lunokhods. 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.[63]

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. In addition achieving the extremely cold temperatures necessary for the superconducting magnets that levitate and drive the Mag-Lev trains would be much easier to achieve than on Earth due to the lack of an atmosphere. 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.

Surface to space

Launch technology
A lunar base with a mass driver (the long structure that goes toward the horizon.) NASA conceptual illustration.

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)[64]

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.

Launch costs

* Estimates of the cost per pound of launching cargo or people from the Moon vary and the cost impacts of future technological improvements are difficult to predict. An upper bound on the cost of launching material from the Moon might be about $40,000,000 per kilogram, based on dividing the Apollo program costs by the amount of material returned.[65][66][67] At the other extreme, the incremental cost of launching material from the moon using an electromagnetic accelerator could be quite low. The efficiency of launching material from the Moon with a proposed electric accelerator is suggested to be about 50%.[68] If the carriage of a mass driver weighs the same as the cargo, two kilograms must be accelerated to orbital velocity for each kilogram put into orbit. The overall system efficiency would then drop to 25%. So 1.4 kilowatt-hours would be needed to launch an incremental kilogram of cargo to low orbit from the Moon.[69] At $0.1/kilowatt-hour, a typical cost for electrical power on Earth, that amounts to $0.16 for the energy to launch a kilogram of cargo into orbit. For the actual cost of an operating system, energy loss for power conditioning, the cost of radiating waste heat, the cost of maintaining all systems, and the interest cost of the capital investment are considerations. David R. Criswell believes that there is a potential for the cost of electrical power on the Moon to become enough less than the cost on Earth for electrical power to be exported from the Moon to Earth by microwave.[70]
* Passengers cannot be divided into the parcel size suggested for the cargo of a mass driver, nor subjected to hundreds of gravities acceleration. However, technical developments could also affect the cost of launching passengers to orbit from the Moon. Instead of bringing all fuel and oxidizer from Earth, liquid oxygen could be produced from lunar materials and hydrogen should be available from the lunar poles. The cost of producing these on the Moon is yet unknown, but they will be more expensive than on Earth. The situation of the local hydrogen is most open to speculation. As a rocket fuel, hydrogen could be extended by combining it chemically with silicon to form silane,[71] which has yet to be demonstrated in an actual rocket engine. In the absence of more technical developments, the cost of transporting people from the Moon will be an impediment to colonization.

Surface to and from cislunar space

A cislunar transport system has been proposed using tethers to achieve momentum exchange.[72] 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.

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.[59]

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.[63] 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. This is the foundation of the free MoonBaseOne game made by a non-profit that teaches kids about space.

Exporting material to Earth

Exporting material to Earth in trade from the Moon is more problematic due to the cost of transportation which will vary greatly if the Moon is industrially developed (see above). 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.

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.[73] Launch costs from the Moon will vary greatly if the Moon is industrially developed (see above). 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.[74]

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.[75] 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.

See also

* Apollo program
* Aurora programme
* Google Lunar X Prize
* In-Situ Resource Utilization
* Space architecture
* Lunar Architecture (NASA)
* Lunar Government
* Lunar outpost (NASA)
* Lunar space elevator
* Moon in art and literature
* Moon Society
* OpenLuna
* Lunar Explorers Society
* National Space Society
* Planetary habitability
* Soviet Moonshot
* Space Frontier Foundation
* Federation of Galaxy Explorers
* Human outpost (artificially created controlled human habitat)

References

Notes

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7. ^ Dept. of the Army, Project Horizon, A U.S. Army Study for the Establishment of a Lunar Military Outpost, I, Summary (Redstone Arsenal, AL, 8 June 1959). See also: Moonport: A History of Apollo Launch Facilities and Operations
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General references

* Peter Eckart (2006). The Lunar Base Handbook, 2nd edition. McGraw-Hill. pp. 820 pp. ISBN 978-0073294445.
* Wendell Mendell (editor) (1986). Lunar bases and space activities of the 21st century. Lunar and Planetary Institute. pp. 865 pp. ISBN 0942862023.
* G. Jeffrey Taylor (December 23, 2004). "Cosmochemistry and Human Exploration". Planetary Science Research Discoveries. http://www.psrd.hawaii.edu/Dec04/spaceResources.html.
* G. Jeffrey Taylor (November 21, 2000). "Mining the Moon, Mars, and Asteroids". Planetary Science Research Discoveries. http://www.psrd.hawaii.edu/Nov00/mining.html.