A colony dome built over a lake-sized deposit of comet ice in a deep crater, turning it into a water reservoir as well as a future colony site. Sunlight is redirected to the dome via a series of advaced mirrors. Image courtesy NASA.

Buried Lunar Colony
Tech Level: 14
Lava Tube Lunar Colony
Tech Level: 14
Lunar City
Tech Level: 15
Domed Surface City
Tech level: 16

Decades after being first established, the site of the first moonbase may look very crowded. Dozens of habitat modules linked to specialized structures such as hydroponic farms, maintenance shacks, laboratories, processing plants, factories, machine shops, lunar hotels, flier domes, souvenir shops, and more, both above and below ground. A few hundred meters away, the primary Electromagnetic Launcher shoots off cargo payloads of Helium-3 to Earth every twenty minutes. The permanent population of the lunar outpost could be anywhere from several hundred to several thousand, with over thousands of tourists passing through every year. The base is slowly but surely earning back its huge initial investment.

Like the frontier towns of the old West, most of the infrastructure of the outpost is somewhat haphazard, added on as things went along and dictated by sheer necessity of the moment. But there will eventually come a time when both the planners on Earth and the local residents decide its time to get serious about long-term lunar residency, and build a true colony that can handle the burgeoning population.

The old moonbase(s) would not be abandoned, of course. It would continue on as a center of operations for profitable industries like it always has. But if people are going to spend years of their lives on the moon, they need actual long-term homes, perhaps even places where they can raise families.

The big, transparent-domed moon cities so beloved of classic science fiction are unfortunately highly impractical until relatively high tech levels, and even then be expensive and troublesome. Radiation will always be a hazard on an airless world like the moon. Most lunar colonies would by necessity be primarily underground affairs to protect its inhabitants from this danger.

One of the major technical differences between a moonbase and a full-fledged colony is that the colony will need to be pretty much completely self-sustaining. The colony will have to be able to supply its own power, air, water, food and other essentials indefinitely even if all contact was cut off from Earth. If the personnel on the moon intend to raise families there, ensuring the population’s long-range viability in the environment would be essential.

The question, is long-range sustainability possible for lunar colonies? Even discounting deposits of lunar ice, there is plenty of needed elements in the lunar regolith, such as oxygen, nitrogen, and hydrogen to produce breathable air and water. Solar power and large amounts of Helium-3 are present to take care of energy needs. Advanced, high-efficiency recycling systems as well as an active mining and industrial infrastructure would have to be in place and constantly maintained to keep a colony going.

Food production might prove trickier, however. Lunar "soil" is sterile and pretty much just hard rock and abrasive dust. In order to produce soil that one could raise crops in, the soil would have to be processed built up from scratch or imported from Earth, both of which could prove costly and resource-draining. Also, food plants would have to be specially engineered to both be compatible with their new environment (probably requiring them to get by on less water, less gravity, more environmental radiation, etc) and to yield as much usable produce as possible per plant. Soil-grown crops could be grown in dome facilities on the surface and tended mostly by robots. The plants could be genetically engineered to withstand more radiation than their Earth-bound cousins in order to make this particular system work.

Hydroponic farms may be a more desirable alternative, but would probably require both more water and power than the surface-dome soil-grown farms. Another alternative is to use vats of genetically-engineered algae, yeast, and fungi grown with the help of the colony’s waste products. The microorganisms would be sifted from the waste, processed, and used to fortify the diets of the colonists. Very advanced colonies could of course just directly break the waste down into its component chemicals and turn that back into consumable processed food. Such communities could also used specialized cloning facilities to clone the cells from earth-based animals in order to produce muscle tissue without reproducing the whole animal, giving them a potential supply of meat. Traditional livestock-raising in the lunar environment would probably be too problematic and costly to b practical.

Lunar colonies, in order to meet their food needs, would mostly likely use a combination of some or all the above techniques. The plants would also help to add to the overall recycling system of the colony, and if lunar farming is ambitious enough it could even handle the bulk of the air recycling. Estimates indicate that 226 cubic meters of greenhouse volume and 40 square meters of planted area per lunar resident would be needed to supply a moon colony’s air and food.

Like with all enclosed life-sustaining environments, waste management and efficient recycling would be an absolute necessity, and would have to operate at close to 100% efficiency to make the colony viable. For a colony that could hold thousands of residents, that is no easy task.

Vehicles and transportation systems would have to be maintained expertly. Even though oxygen and other consumables lay in the lunar regolith, its a sure bet that most of it is not evenly distributed. This would necessitate mining and processing operations to roam far and wide over the lunar surface to find and properly exploit needed deposits.

The ability to expand without outside help would be needed to handle potential expansions of the population. This means the colony’s industrial capacity must at least potentially stay above a certain level for the colony to stay viable, in order to produce new vehicles, habitats, and tools as needed.

Tech Level: 14
Moonbase Alpha, from the British sci-fi series Space:1999, is a prime example of a buried lunar colony with over 20 subsurface levels. Image copyright Carlton Communications.

The most straight-forward way to build a lunar colony is to use the same techniques used to build the first moonbases, scaled up.

Like with a moonbase, location would be important. Locating the colony near an exploitable ice deposit would be desirable, as would a location that has easy access to necessary mineral ores. The first lunar colonies might be constructed clustered around the old moonbase and each other, in order for one to lend support to others in case of emergencies. However, too many people in one location could also tax the area’s available mineral resources, forcing newer colonies to be established farther afield.

A large, deep pit would have to be excavated, probably with the help of explosives. The colony’s seed habitats, modules, and machinery would all be constructed or lowered inside. It would be covered over again, with a few surface facilities such as solar cells, motor pool, and communication equipment to mark the spot on the surface. Additional excavation can continue once the colony is established.

A popular architectural design for moon colonies uses radial symmetry. The colony would consist of a central vertical core of machinery and access elevators and tunnels, with different levels of habitats and spaces radiating out from it. The very bottom of the shaft would handle recycling systems and house any nuclear or geothermal power source if one is present.

The colony could expand by drilling and digging sideways on a level by level basis. Instead of using ready-made modules, they would line the newly exposed regolith walls with insulation and air tight seals and pressurize them when complete.

A buried lunar colony could expand beyond the rather rigid design constraints of early modular moonbases. Excavated chambers could be conformed to any size or design the colony planners could want. It is certainly possible that they could have large open parks, lake-like water reservoirs, auditoriums, and so on.

A buried lunar colony need not always dig down. Lunar cliffs and crater walls could also be tunneled into and utilized.

An idea for fast lunar excavation bandied about at times by science fiction authors is to use small-scale "clean" nuclear explosives, five kilotons or less in yield, to excavate large pits for new colonies quickly. The moon has no ecology that could be harmed by released radiation, most of the rock made radioactive by the blast would be removed by robots, and since the colony’s seed modules would be heavily insulated and armored anyway, there would be little residue that could get through to harm a future colony’s population. This option would be difficult to implement in today’s political climate, but this may not always remain so.

Tech Level: 14

Would-be colonists might prospect for natural locations that could fit their needs, such as lava tubes. The moon was once much more volcanically active than it is today, and its lighter gravity means that lava chambers could form much larger (up to ten times wider) there than on Earth.

If a large and readily-accessible series of such tubes can be found, they can make an excellent foundation for the start of a colony. Engineers would work on reinforcing and bracing the tunnels, and afterwards install modules or use insulating material that can conform to the tube’s shape. Interconnecting chambers can slowly be built up for the entire volume of the lava chambers present, and excavation of additional spaces can be undertaken after the colony is established.

Depending on the exact location, size, and configuration of the tunnels, a lava tube colony may prove much easier and cheaper to establish than a normal buried colony. In fact, lava tubes, because they offer natural radiation protection and insulation, would be prime real estate on the moon. A skilled lunar spelunker--someone who specializes in exploring and mapping cave systems on the moon--would probably be in high demand by interests seeking to establish new colonies.

Tech Level: 15

Just as a colony is basically a scaled-up moonbase, in many ways a lunar city would be a scaled up colony, approaching the population and scale of cities on Earth. The first lunar cities may not be planned as such, but may be the natural result of repeated expansions by already established colonies. Colonies originally built close to one another may simply expand and consolidate into one.

Supplying everyday necessities to a population of many thousands is no easy task anywhere, but a vacuum world like the Moon present many unique challenges. There would be miles and miles of tunnels underneath the regolith, even though from the surface it may look only like an occasional outcropping of buildings and structures here and there among a miniature sea of solar panels.

Lunar cities would have to be set up in similar ways to an arcology on Earth; see the article on Arcologies in the Megastructures section. Like arcologies, they would be made as human-friendly as possible, with things like mirrors, windows, artworks, miniparks, and more all designed to give the illusion of more space than there is. The interior partitions of living quarters would be made modular and movable, in order to adapt the space for needs by residents, whether they be singles, couples, or families.

Advanced lunar cities may eventually get away from the modular tube and tunnel motif of the early moonbases and really open up their spaces, especially the ones deep underground that are completely insulated from radiation and have little chance of suffering decompression. Dome cities on the surface may be problematic, but underground they may blossom in order to foster a spirit of true community among its inhabitants. In fact, dome structures underground could even take advantage of advanced imaging technology and project scenes of an Earth-type sky on the inner surface of the dome.

Tech Level: 16
A park-like domed colony with its sunward side polarized to filter the light reaching its surface. Artist unknown.

Can the lunar "bubble cities" of golden age science fiction ever become a reality? Possibly, with the right advances in material sciences and life support systems.

The dome itself would have to be engineered similar to tank armor; several reinforced layers of translucent material sandwiched between many-centimeter thick sections of substances like stiffened aerogels. These aerogels would cushions and scatter fragments and shrapnel from anything hitting the dome and penetrating, such as meteorites or artillery shells. The foamed aerogel could be under a certain amount of pressure, so when a breach does form it would spread into it and clog the gap until real repairs could be made.

It has also been suggested that liquid water from ice deposits could be circulated through a dome’s cells to help mitigate potential radiation hazards.

The substance used for the dome itself would have to be transparent but as tough as possible. It does not only have to keep air in, but it must act effectively as armor against both radiation and physical threats as well as prove structurally light and strong enough to support its own weight. Interwoven carbon filaments similar to diamond could be a good candidate material.

The dome itself also would not be one huge integrated piece of material. Likely it would be constructed in small hexagonal or triangular sections for ease in repair and maintenance. Besides the dome material itself and its insulation, there would also be thermal reflective layers to help regulate the colony’s temperature as well as light polarizing layers that would filter how much sunlight engineers would let in. Advanced cities could even have "chandelier" structures, shops and community centers and restaurants and so on, hanging from the apex of the dome and accessed by elevators following the dome’s curve.

Unlike in some sci-fi sources, the designers of a bubble city would not be negligent of the possibility of a catastrophic breach in the dome. A random meteor is not very likely, but the possibility of war, acts of terrorism, or a major industrial accident can’t be ignored. Every building inside the dome would be made vacuum-proof and hooked up to both the city’s life support system as well as its own short-term emergency system. All entrances would be required to be airlocks. The air pressure inside the dome would normally be kept lower than normal to slow the outward rush of air, and its likely the populace would have to undergo "breach drills" every once in a while, just like schools and other buildings occasionally hold fire drills on Earth.

Even after surface dome cities become a viable option, most construction and habitats on the Moon will likely remain underground, as its assumed readily-available meters-thick rock will remain cheaper for radiation protection and insulation than manufactured high-tech materials. In fact, it is likely that any domed surface facility will only be the top layer of an extensive underground construction. Domes may also be constructed over craters of accommodating size, to use the crater walls to help support the dome.

Large surface "bubble" enclosures need not always contain cities either; they could be used for farmland, wildlife parks/reserves, or liquid water reservoirs.

Further Information

Article added 2006