Colonization of the Moon

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Because of its proximity to Earth and the early telescopic observation of familiar land forms, such as mountains and plains, the Moon has long been seen as a candidate for the first human colony in space. The Apollo program, while demonstrating the feasibility of travel to the Moon (albeit at a high cost), dampened enthusiasm for a lunar colony because the rock and dirt Apollo astronauts brought back proved to be extremely low in the lighter weight elements needed for life. Many space colonization advocates now prefer Mars, which has a more Earth-like environment, but others believe the Moon is still the logical first step. NASA's long range Vision for Space Exploration plan includes a return to the Moon.

History

Siting a colony on the Moon is an idea that goes back to a time before the space age; Konstantin Tsiolkovsky, among others, suggested this. During the 1950's there were many concepts put forward by scientists and engineers, and since then there have been several concepts and designs put forward.

1954 - Arthur C. Clarke proposed a lunar base of inflatable modules covered in lunar dust for insulation. The spaceship itself would be assembled in low Earth orbit, and then launched towards the Moon. It lands on Mare Imbrium, near Mt. Piton. The astronauts then set up the igloo structures as well as an inflatable radio mast. The next step is then to build a larger, permanent dome. An algae-based air purifier is set up as well. A nuclear reactor is used to provide power. Electromagnetic cannons are used to launch cargo and fuel to interplanetary ships which never lands. [1]
1959 - John S. Rinehart suggested that the safest design would be a structure that could "[float] in a stationary ocean of dust," since there was, at the time this concept was outlined, theories that there could be mile-deep dust oceans on the Moon. The design proposed consisted of a half-cylinder with half-domes at both ends. A micrometeoroid shield is then placed above the base. [2]
1959 - The Project Horizon was a study regarding the U.S. Army's plan to establish a fort on the moon by 1967. 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. [3]
1962 - John DeNike and Stanley Zahn published their idea of a sub-surface base located at the Sea of Tranquility. This base would house a crew of 21, in modules placed 4 metres below the surface, which was believed to provide radiation shielding as good as the Earth's atmosphere does. They favoured nuclear reactors for energy production, because they are more efficient than solar panels, and it would also overcome the problems with the long lunar nights. For life support system, an algae-based gas exchanger could be useful. [4]
1968 - Apollo 8 orbits the moon proving the ability to send humans to the moon.
1969 - the Apollo 11 lunar module lands on the moon proving the ability to land on the moon, Apollo 11 also proves that astronauts can work on the moon.

2004 NASA's long range plan includes building a base on the Moon as a staging point to Mars.

Advantages and disadvantages

Putting aside the general questions of whether a human colony beyond the Earth is feasible or desirable (see: space colonization for a discussion), the Moon offers advantages and disadvantages as a site for such a colony.

Advantages

Placing a colony on a natural body provides an ample source of material for construction and other uses, including shielding from radiation. A large body also has gravity, which, experience to date indicates, may be vital for long term human health. 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 of 384 400 km. This proximity has several benefits:

the energy or delta V 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. Earth crosser asteroids require somewhat less delta V, but the months of travel needed will demand a safe habitat for humans during the journey that can more than offset any savings.
the short transit time also allows emergency supplies to reach a Moon colony from earth in a couple of days. This could be a very important consideration when establishing the first human colony.
the round trip communication delay to Earth is only a few seconds, allowing direct voice and video communications. The delay for other solar system bodies is minutes to hours. This again may be of particular value in a first colony, where life threatening problems requiring Earth's assistance can be expected to occur. (See: Apollo 13)

Disadvantages

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

the long Lunar night prevents reliance on solar power (except, perhaps, at the polar regions) and requires a colony to be designed to withstand large temperature excursions.
the Moon lacks light elements (volatiles) needed for life, though there is some evidence of water near the north and south poles. Light elements would have to be imported, perhaps eventually from the outer planets, but from Earth initially. This limits the colony's rate of growth and keeps it dependent on Earth. The cost of volatiles can be reduced by constructing the upper stage of supply ships using materials high in volatiles, such as carbon fiber and plastics.
there is a question, at least, of whether the 1/6 g gravity on the Moon is strong enough for human health long term.

Locations

V. V. Shevchenko proposed in 1988 three criteria that a lunar outpost should meet:

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

While a colony might be located anywhere, locations for a Lunar colony fall into a few broad categories.

Polar regions

There are two reasons why the lunar poles might be attractive as locations for a lunar colony. First, there is evidence that water is present in some continuously shaded areas near the poles. 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 sun light at all times, yet close enough to be connected in an electrical grid. Some sites have nearly continuous sunlight. For exampe, there is a mountain (Malapert) near the Shackleton crater at the lunar south pole which offers several advantages as a site:

It is exposed to the sun most of the time; two closely spaced arrays would receive continuous power.
Its proximity to Shackleton Crater (116 kilometres) means that it could provide power and communications to the crater where the valuable water ice is potentially located, and ice could provide liquid water, oxygen, and rocket fuel, among many other things.
The surrounding areas that are in constant deep shadow may be valuable not only for ice, but 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.
At around 5000 metres elevation, it offers line of sight communications over a large area, as well as to Earth.

The presence of water ice at the Moon's poles is not settled yet, though. Data from the Clementine mission suggested the presence of water ice around the south pole. [5] [6] This would have been detected in the large Shackleton Crater near the Moon's South pole. [7]

The Lunar Prospector spacecraft detected possible water ice not only at the south pole, but also at the north pole - actually more so. [8] 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. [9]

Equatorial regions

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.

One site mentioned by Shevchenko as meeting his criteria is Oceanus Procellarum. Several probes have landed in that area. There are many areas and features that should be subject to long-term study, such as the Reiner Gamma anomaly and the dark-floored Grimaldi crater. Furthermore, measurements from ground-based telescopes as well as from the Zond 6 spacecraft, reveal the presence of oxygen-bearing mineral in the area.

Far side

The lunar far side lacks direct communication with Earth, though a communication satellite at the L2 Lagrangian point would cover the far side. It might be a good ___location for a large radio telescope because it is well shielded from the Earth. Its topography differs from the near side and there had been no ground exploration of the far side to date.

Structure

Habitat

There have been numerous proposals regarding the habitat modules. The designs have evolved throughout the years as humankind's knowledge about the moon have grown, and as the technological possibilities have changed. The proposed habitats range from the actual spacecraft landers or the 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. 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. 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.

A possibly easier solution might be to build the lunar base on the surface, and then cover the modules with lunar soil. 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.

As an alternative to excavating, it is possible that large underground extinct Lava tubes might exist on the Moon. As of 2004, existence of lava tubes on the Moon has not been confirmed.

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 could possibly be able to fill most of the need for power. The advantage it has against a fusion reactor is that it is an already existing technology. One advantage of using a fusion reactor is that Helium-3 which is required for a type of fusion reactions is abundant on the moon. However, it's possible that reliable, efficient fusion reactors will not be availible at the time of lunar colonization.

Radioisotope thermoelectric generators could be used as backup and emergency power sources for solar powered colonies.

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 in situ. However, the long lunar night (14 Earth days) is a drawback for solar power on the Moon. This could be solved by building several power plants so that at least one of them is always in daylight. Another possibility could 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.

The solar energy converters need not be silicon solar panels. It may be more feasible 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 directly for lighting, agriculture and process heat.

Transport

On the surface

Lunar colonists will want the ability to move over long distances, to transport cargo and people to and from modules and spacecrafts, and to be able 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 that operated on the surface of the Moon as of 2004 were the Apollo Lunar Roving Vehicle (LRV), developed by Boeing and the unmanned 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, range would be 396 km. The Soviet Union developed different rover concepts in the Lunokhod series (DLB Lunokhod 1-3/LEK) and the L5 for possible use on future manned missions to the Moon or Mars. These rover designs were all pressurised for longer missions.

For difficult areas, it could be a good idea to use a flying vehicle. 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

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 realtively 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's easier to launch from the Moon because there is no drag, there is no way to use aerobraking, 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).

One way to get materials and products from the Moon to an interplanetary waystation might be with a mass driver, a magnetically accelerated rail. 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. If a lunar space elevator ever proves practical, it could transport people, raw materials and products to an orbital station at Lagrangian points L1 or L2.

Economic development

For long term sustainability, a space colony should be close to self sufficient. In situ 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 lower 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 could be attractive.

Exporting material to Earth in trade is more problematic due to the high cost of transportation. One suggested candidate is Helium-3 from the solar wind, which may have accumulated on the Moon's surface over billions of years, which may prove to be a desirable fuel in fusion reactors, and which is rare on Earth. Neither the abundance of Helium-3 on the lunar surface nor the feasibility of its use in fusion power plants have been established, however.

Moon colonies in fiction and film

Moon colonies are found in many novels, short stories and films. This is an incomplete list with some of them. Not all have the Moon colony itself as central to the plot.

The short story People Came From Earth by Stephen Baxter. It can be found in The Year's Best Fantasy and Horror: Thirteenth Annual Collection.
2001: A Space Odyssey by Arthur C. Clarke
In the novel Rendezvous with Rama by Arthur C. Clarke, a meeting is held at a lunar colony, to decide how to deal with the Rama object.