William B Stoecker
November 18, 2013 | 4 comments
Image Credit: NASA
Having written about colonies in space (huge manned space stations in Earth or solar orbit, with spin-induced gravitation and farms, with plants supplying food and oxygen) and colonies floating on the sea, I think it is now time to consider the viability of colonies on Earth’s Moon. It will be difficult and prohibitively expensive to develop and support such colonies using conventional rocket technology to convey colonists and building materials to our Moon, so we will probably have to wait for more advanced propulsion systems. Perhaps fully reusable space planes, powered for part of their flight with scramjets, would be feasible for getting into Earth orbit, and some system combining ion rockets to get into Lunar orbit and chemical-fueled rockets to get down to the Lunar surface and back again will suffice, especially since many of the Moon landers could make one way trips (down but not up) bringing colonists and supplies to get the colony started. Mass drivers could be used on the airless Moon to lift payloads up again, into orbit, or even “space elevators” tethered to weights at a Lagrange point. But I suspect more advanced systems will be needed to make the concept truly practical; perhaps electrogravitic systems (discussed in one of my previous articles) can be made to work.
Our Moon has virtually no atmosphere, and just over one sixth Earth’s gravity. On average it is about 60% as dense as the Earth, and is believed to have a nickel-iron solid inner core about 480 kilometers in diameter, and a molten outer core surrounding it, a spherical shell about 60 kilometers thick. Then there is a mantle above that, and finally the crust, averaging about 50 kilometers in thickness. The maria, or “seas” on the Moon, are mostly made of mafic (rich in heavier elements) basalt, a volcanic rock believed to have been generated by the impact of asteroids billions of years ago. The oldest Lunar rocks yet found are from the highlands and have been dated at 4.4 billion years. The current theory to explain the Moon’s formation postulates that when the Earth was very young it was slightly smaller than now, and was impacted by a fairly high velocity planetesimal about the size and mass of Mars, which caused a mass of molten material to be thrown into Earth orbit. This material, it is believed, condensed and coalesced to form our satellite. A problem with this theory is the fact that the isotope ratios of Lunar rocks are virtually identical with those found on Earth, but perhaps if the planetesimal originated in the same orbit as Earth or in one very nearby it would have isotopes similar to Earth’s. Significantly, fairly large quantities of water ice have been detected in deep, cold craters near the Lunar poles; this would be an invaluable resource for colonists. The Moon has far less internal heat than Earth does, and little or no volcanism, although there is some evidence for outgassings from the interior.
Unlike a colony built in space, a colony on the Moon would have close access to raw materials. Metals are present, and silicates and other minerals that could be made into glasses and ceramics. The low gravity would make it easier to move heavy loads, and the lack of any real atmosphere would make high speed maglev trains practical for surface transportation. However, the lack of an atmosphere means that colonies would have to be sealed, and air to fill them at least partly shipped from Earth. While oxygen might be produced from the ice on the Moon, there is no real source for nitrogen, although a low pressure pure oxygen atmosphere might be feasible, provided that nitrogen fertilizers were brought from Earth to nourish plants. Meteor strikes are all too common on the Moon, and some shielding would be needed against them, as well as against the radiation from space, including deadly solar storms. One problem is the fact that most locations on the Moon experience two weeks of sunlight, which can cause a lethal thermal buildup, and two weeks of bitterly cold night, with no light to make plants grow.
Certainly before large, fully self-sustaining colonies are attempted, people would build smaller manned Lunar bases, both for further exploration of the Moon and to determine if larger colonies are even feasible. We need to find out if humans can thrive in low gravity…up until now, people have only spent a very short time on the Lunar surface, preceded and followed by several days of microgravity. We do know that microgravity, or “weightlessness” causes loss of bone mass and muscle strength along with other health risks, and no combination of diet and exercise has yet been discovered that will prevent these adverse effects. But no research has been done to determine the effects of low gravity…perhaps there is some minimum threshold above which human beings can maintain good health, aided by proper exercise. Conceivably, people might even be healthier and live longer in low gravity, avoiding many foot, back, hip, and knee problems…we simply don’t know. And could women carry healthy babies to term, and, once delivered, could they develop normally? Could domestic animals reproduce and thrive, or plants? All of these questions need to be answered, and most of them could be, with a Lunar base.
If the base was built in the polar regions, water would be available, in the form of ice. There are areas completely shielded from the Sun’s deadly radiation and safe from thermal buildup. The Moon’s axial tilt is only 1.54 degrees, and it is believed that at least four areas on the rim of the north polar Peary Crater are always lighted by the Sun from one direction or another, as are the summits of the Malapert Mountains next to Shackleton Crater near the south pole. A colony built near these locations, perhaps just within the rim of the Peary Crater, could use large mirrors to reflect sunlight into windows, with a twenty four hour cycle. Photovoltaic arrays, also high on the rim, could provide a continuous supply of electricity. The late science fiction writer, Arthur C. Clarke, suggested that inflatable modules could be erected on the Moon and then covered with a thick layer of Lunar regolith (a fancy name for dust and dirt). Four meters of regolith would protect the base from most small meteorites and would provide radiation protection equivalent to Earth’s atmosphere, but, in the weak Lunar gravity, would weigh only as much as a layer just over two thirds of a meter thick. But the Lunar dust, which, as our astronauts discovered, gets into spacecraft when people exit and return, would be a problem. It could damage electronic equipment, and may be slightly toxic over long periods, or at least be able to cause silicosis if continually inhaled.
If people and plants are able to thrive in the low gravity, and if research with small animals suggests that human reproduction could be accomplished safely, then we may move on to full scale colonies. Anywhere away from the polar regions some energy source would be needed, or at least some efficient way to store solar power for the two week Lunar night, to power indoor lights strong enough to permit photosynthesis and allow plants to grow. Perhaps cold fusion can be made to work reliably on a large scale, or some exotic form of “free” energy. The colonies could be built underground; one way would be the cut and fill technique for building tunnels. A long trough could be excavated into the Lunar surface, or a circular depression, and a long, vaulted structure (or a dome) could be erected within and then covered with four meters of regolith. In the low gravity, arched or domed structures could be quite large; the colonists might eventually construct domes with a diameter of, say, a thousand feet and a height of five hundred feet, or a vault just as high and wide and many miles in length. A smaller scale might be more practical, like a vault four hundred feet wide and half as high; even this would allow some fairly tall trees to grow. There may be lava tubes on the Moon, natural caves left behind when lava flows cooled and hardened, that could be used to save the effort and expense of excavation. In fact, cave entrances have been spotted on the Moon, looking like natural skylights that might be caused by a cave in of part of the roof of a lava tube. On the other hand, some of these, as well as identical ones on Mars, appear perfectly circular and look suspiciously artificial.
For greater efficiency, the long vaults, for example, might include two low-ceilinged levels at the bottom, one for human habitation and perhaps some industry, and one for intensive farming. With perfect lighting conditions and temperatures, a year round growing season, good soil, and an absence of pests, plant diseases, and extreme weather conditions, yields could be very, very high. The entire vault might be filled with such multiple levels, or, if the colonists could afford it, at least some vaults might be left open and filled with parks and gardens, and even forests. Full spectrum lighting would be needed, bright enough to power photosynthesis, and thermal buildup might then be a problem, although, a few meters below the surface, the regolith has an average temperature of nine degrees Fahrenheit below zero.
The Moon’s total surface area is 14,600,000 square miles. If, due to difficult terrain (high mountains, deep craters, and extremely hard or extremely unstable rock) only half of that could be used, and if the vaults were placed as far apart as their width, over a long period of time the colonies might still be expanded to occupy over 3,600,000 square miles. With a human population averaging, say, 100 people per square mile, the Moon could support some 360 million colonists…provided that the problems of energy, thermal buildup, and finding sufficient oxygen and nitrogen for an atmosphere could be solved. Perhaps, given exotic propulsion systems for spacecraft carrying large amounts of cargo, most of the needed raw materials might be brought in from comets and from the moons of the outer planets in our Solar System. And this is assuming only one level of the long vaults, just below the surface. A second, staggered layer of vaults might eventually be constructed, say, 200 feet below the first layer. Twenty such layers, extending less than a mile down, could accommodate a human population of over seven billion…roughly the present population of Earth. Given the Moon’s low density, low gravity, and low internal heat (compared to Earth) such layers might extend several miles down.
Life there would seem very, very strange to us. Claustrophobia would probably not be a problem with spaces two hundred feet high, four hundred feet wide, and extending for many, many miles in length. Moonquakes are rare and normally very weak, and the habitats would probably be safer from natural calamities than any place on Earth. Parks and gardens, bright (albeit artificial) sunlight, and a mild climate would not be likely to cause depression. In the low gravity, just over one sixth of Earth’s, people could leap to heights of twenty feet or more, and man-powered flight would be practical, even easy.
But, on the other hand, there might be one small additional problem with all of this. Given the rectilinear structures and tall towers discovered on the Moon, it looks as if someone, whether from Mars, another solar system, or even, long ago, from Earth, may have already been there. And, given the mysterious transient lunar phenomena and the UFOs that have followed Apollo spacecraft, they may still be there. This particular piece of real estate may already be taken.