A Great Step Forward: Suggestions on the Construction of a Permanent Base on the Moon

by Benjamin Brothers, 1998

The space program has existed for less than fifty years, but in that time it has changed forever the place we imagined for ourselves in the universe. Seeing a tiny blue planet suspended against a starry sky, we began to think of Earth not as an infinite resource but as a small cradle of mankind. And in the words of the turn-of-the-century rocket pioneer Konstantin Tsiolkovsky, "One cannot live in the cradle forever."

Colonizing the solar system is our next step, the first of our tentative journey into a larger world. There is a spirit in man that rises to the challenge; there is a yearning for adventure and discovery. Building a permanent space station is that challenge; it is the adventure. It is a beginning in the settlement of the final frontier.

In order to construct a space station, we must first determine its size, location, and function. There are three feasible locations where a station could be built: low-earth orbit, a libration point in the same orbit as the Moon, and on the lunar surface. By building in low-earth orbit, we can cut down on fuel and transportation. The proximity to earth also allows for emergency escapes. The International Space Station (ISSA) will be constructed here. However, despite the benefits, low-earth orbit is not suited for a permanent construction. The gravitational pull of the Earth is great, and the orbits of satellites, including ISSA, will degenerate over time. Constructed in low-earth orbit, a space station would eventually crash to Earth. The ISSA has a predicted lifetime of 12-15 years.

Equidistant from the Earth and the Moon, and following the orbit of the Moon are two stable libration points. They occur because the gravitational pulls of the earth and moon balance with the centrifugal force one would feel by being in the rotating coordinate system of the earth and moon. Thus, a space station placed at one of these points would remain fixed with respect to the Earth and the Moon as the entire system revolved around the Sun (R. Johnson & Holbrow, 1977).

Finally, a space station could be located on the surface of the Moon itself. The gravity on the Moon is only 1/6 that of the Earth's (and 1/6 of that which could be generated by rotating a free-floating space station). This, and the distance from Earth, are the two major disadvantages to locating a base on the Moon. But the advantages are many.

A lunar base would have access to the materials and resources of the Moon. Metals can be extracted from the lunar soil; oxygen is a very useful by-product of the process. This provides invaluable material for construction, life-support, and rocket fuel. More importantly, significant deposits of water have recently been found on the Moon. NASA's Clementine Lunar Explorer found between 110 million to 1.1 billion tons of water ice at the lunar poles (National Aeronautics and Space Administration [NASA], 1998a). This is enough to sustain thousands of people for several centuries without recycling, and would make the construction and habitation of a lunar base much easier.

Additionally, the Moon would provide a stable platform on which to build any structures. In space, everything must be done in zero gravity under perilous conditions. On the surface, engineers can dig foundations for added support, and could work in relative safety. Buildings on the surface can also be expanded very easily, allowing room for future growth.

Despite the inconvenience of weakened gravity, it seems clear that our space station should be a lunar base. The desire for permanence rules out a low-earth orbit, and it would be prudent to benefit from the resources of the Moon.

The Moon is a big place. We must specify where on the surface we are going to build our space station. The polar regions are the most desirable, even though a more difficult trajectory is needed to reach them instead of the equatorial areas (S. Johnson, 1964). First, the polar regions, especially the North Pole, contain most of the ice found on the surface (NASA, 1998a). Prudence would indicate that we should build as close to the resources as possible. Second, the sunlight received at the poles is less direct than at the equator. This would minimize the tremendous temperature swings at the lower latitudes. Finally, there are mountain peaks at the poles which are in continuous sunlight (S. Johnson, 1964). Solar arrays placed here would result in an uninterrupted flow of electricity.

After lunar surveyors have determined the best location for the lunar base, we must decide on its design features. The first question is size; how big should the lunar base be? Although a large-scale colony will probably be designed later, the first effort should be small-scale. A scientific research lab is preferable to a small city. The short-term residence of scientists and engineers (perhaps a two-year stay) would assure that there are no lasting effects from the low gravity.

Additionally, a small station would be cheaper than a large one, and the information gathered in the construction of the first lunar base would be invaluable in the construction of a larger second base.

There are other requirements for a lunar base. It must emphasize redundancy, for there is no room for failure. In addition, it must be compartmentalized, to keep small failures small, and prevent disasters. There must be abundant energy, since it is required at all times by life-support systems. And it seems wise to assure that, in emergencies, there is human control over all processes, even those which are normally automatic.

Defenses are needed in four major areas: seismic instability, solar radiation, thermal fluctuation, and meteoroids. The safety of the base depends on protection from these dangers; the first three are critical.

Seismic activity is a cause of major concern in the construction of buildings on Earth, and we must have similar concern on the Moon. An Apollo seismic detection network operated for eight years, and indicated relatively low seismicity (Taylor & Spudis, 1990). But low seismicity is not the same as no seismicity, and we cannot afford to ignore the possibility of earthquakes (moonquakes?). Fortunately, we can take the same precautions on the Moon that we do here. Framed structures should be reinforced with cross-bracing, keeping in mind the need for both strength and flexibility. Any structures must have a low center of gravity to prevent overturning and collapse.

Another area of concern is solar radiation. The sun continually emits into space a wide range of electromagnetic radiation, including deadly low-wavelength, high-energy gamma rays and X-rays. Low-wavelength radiation is blocked by the Earth's atmosphere, but reaches the lunar surface unimpeded. Gamma rays would kill an unprotected human within minutes, and any space station needs shielding to protect the inhabitants. One option is to bury the structures. Although this is feasible and likely desirable in some cases, there will have to be some structures above ground. The magnificent views and vistas of the surface and the stars add romanticism to space travel, and it would be a shame if we could not engineer a station to allow access to them.

If the shell of the structure consisted of multiple shells of very high strength glass and beryllium (S. Johnson, 1964), fluids could be placed between the shells. The multiple shells would add redundancy to the station, while the fluids block radiation. Another worry is the proton-type radiation of solar flares. Elements with low atomic numbers are most effective at blocking this (S. Johnson, 1964); some spaces between shells could be filled with helium and hydrogen. Although support systems and sleeping quarters would likely be located beneath the surface, precautions against radiation will allow the astronauts to work and live under the stars.

In space, the energy received from the sun is directly received by the surface. The temperature skyrockets during the day, and plummets during the night, when there is no atmosphere to trap the escaping radiation. The temperature on the lunar equator varies from -150 to 130 degrees Celsius (R. Johnson & Holbrow, 1977). It is necessary, as much as possible, to protect the lunar base from these fluctuations. It is hard on the systems, and the structures. They must be designed to deal with thermal expansion. All materials expand when heated to some degree. The design must account for this. We must also remember that the surface soils and the structure have different emissive and absorptive capacities (S. Johnson, 1964). They expand at different rates, and a structure that doesn't plan for this could soon collapse.

Planning for thermal variance was one reason we chose to site our base at the pole. This will reduce the severity of the problem. Another solution is to distribute the energy received over the entire structure instead of allowing it to be concentrated on the area in direct sunlight. This could be accomplished by building the outside structure with a heat-conductive metal. In order to protect the comfort of the residents, the inner shells could be built with an insulating material.

Finally, our base should be protected from small meteoroids. Large meteors (like those depicted in certain bad movies) are not the concern. The concern is over the smaller meteoroids which are far more numerous. On Earth, these merely burn up in the atmosphere, producing shooting stars. On the Moon, however, there is no atmosphere to slow and destroy them. They reach the surface intact. The base shell must be strong enough that it will not crack upon the impact of a meteoroid weighing up to several grams. And if a wall does crack, it must be designed in such a way that the crack will not expand or rupture.

We must also consider the construction of the base. Because transportation into space is expensive. NASA (1998b) estimates that it spends between $1,000 and $10,000 per pound to put a payload into orbit, so every effort must be made to use materials already located on the lunar surface.

Surface samples returned by the Apollo missions found that the lunar soil contained approximately 45% oxygen, 10-15% iron, 20-25% silicon, 5-10% aluminum and 2-7% titanium (R. Johnson and Holbrow, 1977). Titanium and aluminum can both be extracted from the soil by electrochemical means, with the addition of solar energy (For a detailed explanation of the chemistry, see pp. 74-77 of R. Johnson and Holbrow, 1977.). Oxygen is released in both of these processes, and can supply the outpost with both atmosphere and rocket fuel. Refining the silica found in the soil will allow the station to produce glass. The use of these metals and products, will add to the commercial and industrial potential of a lunar base, and will save a great deal on construction costs.

The reduced gravity of the Moon will also allow for more economical construction. As a beam is increased in length, it eventually bends under its own weight, an event known as buckling. This is a limiting factor on the length of the beam. Because the weight of an object depends on the gravitational field around it, beams in a lunar structure can be 1.82 times as long as they can on Earth (S. Johnson, 1964). The cross-sectional area of a statically loaded beam can also be reduced by a factor of 0.17 over a similar beam on Earth (S. Johnson, 1964). And with the single exception of seismic activity, all the loads on a lunar structure will be static. There is no wind shear to consider, and no snow loads to analyze.

We can get significant savings in the amount of material used by designing structures with long, slender beams. It would of course be unwise to push the design to its limit by reducing the beams by the maximum possible amount, since all the structures need to be quake-proof, and have a high factor of safety. Nevertheless, the potential for conservation is considerable. The reduced material consumption per area will cut costs and allow for larger structures.

Developing a permanent lunar base is more complicated than designing an inhabitable structure on the Moon. That structure must be made self-sufficient. It must be able to support itself without aid from Earth. This requires a paradigm shift in thinking. Until now, every man launched into space was completely dependent on Earth, whether for food or fuel or atmosphere. In time, dependent colonies become sovereign nations. In the same way, a lunar base should aim to be a viable, self-contained ecosystem. There are two immediate goals which must be realized if this dream is to be met: the base must feed itself, and maintain a stable atmosphere.

If a lunar base is to be the first step to the settlement of the solar system, it must be able to feed itself. It is important, therefore, to grow the food consumed by the lunar base on the Moon, even at the cost of reducing the number of residents. The technology is available to raise crops in space. Hydroponics would be the most likely choice, since it relies not on soil but on chemicals suspended in water-based solutions. This would also save space by allowing farmers to stack rows of crops. It also has the obvious benefit of not relying on soils not present on the Moon.

We must devise a nutritional plan concurrently with an agricultural design. What will the crew eat? It is not unreasonable that the crew of the lunar base be able to eat an American diet. No one should be expected to eat the same space-efficient legume every day. The diet must be varied and satisfying. Vegetarian grains and plants may be the easiest to grow with hydroponics, but the diet is not palatable. We need to raise meat and fish as well. This decision will increase the cost of feeding the inhabitants. It will also increase the agricultural area needed per person, as well as the area of the structure. Some grains that are raised will be used as cattle fodder. A large aquarium system can be used to raise trout, catfish, and other fish. Livestock can be housed in a structure conceived for this purpose. This livestock can provide the residents with milk and dairy products as well as meat. Along with the fruits and vegetables the inhabitants will grow, these will provide a complete diet.

There are other advantages. Plant life will help maintain a natural balance to the ecosystem in the base. Photosynthesis will convert carbon dioxide back into oxygen. If the correct number of plants are grown, the ratio will be self-sustaining. Condensation and transpiration will help recycle the water used (Space Science Board, 1979). And we cannot ignore the psychological comfort that a botanical "garden" would provide to those who live there.

A lunar base will also have to provide its own atmosphere. The composition should be relatively similar to that on Earth. The oxygen content should be slightly higher to prevent an insufficient supply, and a higher carbon dioxide content will help heat the station, and increase the productivity of the agriculture. Just as on Earth, the inert gas nitrogen will be present to prevent chemical reactions. There is also evidence that nitrogen is necessary to prevent respiratory disease (R. Johnson & Holbrow, 1977). The nitrogen content should be around 50-60% by volume, while carbon dioxide should be no more than 0.5% by volume. It is important to insure that the partial pressure of carbon dioxide is no more than 3.8 millimeters mercury (Kammermeyer, 1966). The remainder would be oxygen.

Because the atmosphere is so critical to the survival of the base, the system that maintains it must be fail-proof. Airlocks should be maintained between compartments to prevent evacuation, and a computer should monitor the levels of all the gases at all times, and maintain the atmosphere at the correct levels. There should be three of these computers, so that one is always in reserve. Finally, there should be a "shelter" that runs its own system, and which could be accessed in an emergency. It would be able to maintain the astronauts until they could return to Earth.

The Moon has been completely surveyed. This task began in the 1960s during the Apollo program, and was completed this year with the mission of the lunar surveyor Clementine. From these maps, it should be possible to select the location of the base.

The next step is the construction of a spaceport. At present, a shuttle cannot land on the Moon; it requires a craft capable of landing vertically, like the LEM used during the Apollo landings. A new larger craft of this kind would need to be constructed. This would travel to the Moon, carrying with it the supplies and fuel needed to build a landing strip for the shuttle. Fuel would need to be stockpiled for use on the return trip, although the lunar base would be able to create its own fuel later on. A vertical take-off should be unnecessary, since the escape velocity is only 2.4 km/sec (as opposed to 11.3 km/sec on the Earth). The space shuttle should be able to function as an airplane for this leg of the trip.

Once we have the ability to transport supplies to the Moon in larger quantities, we can begin the construction of the actual station. The first step would be the construction of living quarters for the workers, and the construction of the life-support systems. The materials for this will have to be brought from Earth, so it should be as small as is reasonable. At this stage, the food will be supplied as well. Once the workers are situated, the goal should be to construct the plants necessary to fabricate the metals used in the rest of the construction. When this is done, the entire structure can begin to take shape. Of the two cornerstones of self-sufficiency, agriculture and atmosphere, atmosphere must come first. One can eat imported food for as long as necessary, but supplying oxygen is far more cumbersome and expensive. The full sleeping quarters should be built underground, and the living quarters and laboratories constructed above ground, along with the agricultural complex.

At this stage, the first scientists and agriculture experts will arrive. They will begin the task of making the lunar base fully functional. As the complexes are finished, the full crew complement will move in, and the station will begin its operational life.

And at a later date, the station can begin to recoup its investment. A lunar spaceport would be an efficient launching pad for satellites and probes to the far reaches of the solar system and beyond. The fuel needed to send a man to Mars would be reduced, saving space for the supplies needed for a longer stay on the red planet. The astronomical observations taken from the Moon would be far better than those from the Hubble Space Telescope. We could examine the far edges of the Universe with more accuracy than ever before.

And for the first time, ordinary people could visit the Moon, as commercial space travel became feasible. Tourists could spend time in space, in a section of the lunar base newly constructed for that purpose by private business. Entrepreneurs would see the potential and begin the construction of larger and larger colonies, as a few thousand brave adventurers decide to live on the Moon.

The opportunities are infinite. What is required is a catalyst, an initiator. That initiator must be us.

It is possible to construct a lunar base today. The engineering can be done with today's technology. The costs would be high, but certainly not exorbitant. Critics often imagine that the space program is a money drain. However, all of the money goes to people. Engineers, miners, construction workers, scientists, and everyone else who is a part of the project benefits. All of the money spent on the development of a lunar base is returned to the economy. In addition, large engineering projects develop new technologies and manufacturing techniques that benefit all mankind.

Although possible, it will not be easy to build a permanent station on the Moon. It will be the greatest engineering challenge in history. It will unite disciplines from civil engineering to electrical engineering, to computer science, to metallurgy, to agricultural science. We should remember that nothing worth doing is effortless. The more difficult the road that must be traveled, the greater the reward at the end of the day.

Works Cited and References

Bernert, R.E. and Z.J.J. Stekly. (1965) "Magnetic Radiation Shielding using Superconducting Coils." Symposium on Protection against Radiations in Space. Washington, DC: Scientific and Technical Information Division, National Aeronautics and Space Administration.

von Braun, Wernher. (1965) "Man-made radiation in space." Symposium on Protection against Radiations in Space. Washington, DC: Scientific and Technical Information Division, National Aeronautics and Space Administration.

Fitzgerald, A.E. et al (Eds.) (1981) Basic Electrical Engineering: Circuits, Electronics, Machines, Controls. Taipei, Taiwan: McGraw-Hill Book Company.

Haffner, James W. (1967) Radiation and Shielding in Space. New York, NY: Academic Press.

Johnson, Richard and Charles Holbrow (Eds.). (1977) Space Settlement: A Design Study. Washington, DC: Scientific and Technical Information Office, National Aeronautics and Space Administration.

Johnson, Steward Willard. (1964) Criteria for the Design of Structures for a Permanent Lunar Base. Urbana: University of Illinois Press.

Kammermeyer, Karl (Ed.). (1966) Atmosphere in Space Cabins and Closed Environments. New York: Appleton Century Crofts.

Kaplan, M.F. (1989) Concrete Radiation Shielding: Nuclear Physics, Concrete Properties, Design and Construction. New York, NY: John Wiley and Sons.

Levy, Richard H. and G. Sargent Janey. (1965) "Plasma Radiation Shielding." Symposium on Protection against Radiations in Space. Washington, DC: Scientific and Technical Information Division, National Aeronautics and Space Administration.

MacElroy, R.D. and D.T. Smernoff (Eds.). (1987) Controlled Ecological Life Support Systems: Proceedings of Workshop II of the COSPAR Twenty-Sixth Plenary Meeting Held in Toulouse, France, 30th June-11th July 1986. Oxford, UK: The Committee on Space Research, Pergamon Press.

National Aeronautics and Space Administration. (1998a) NASA NEWS Release: H98-38: Lunar Prospector Finds Evidence of Ice at Moon's Poles. http://tommy.jsc.nasa.gov/~woodfill/SPACEED/SEHHTML/ moonh2O.html.

---. (1998b) Official Nasa Website. http://www.nasa.gov.

Pain, H.J. (1993) The Physics of Vibrations and Waves. Chichester, UK: John Wiley and Sons.

Space Science Board, National Research Council. (1979) Life Beyond the Earth's Atmosphere: The Biology of Living Organisms in Space. Washington, DC: National Academy of Sciences.

Taylor, G. Jeffrey and Paul D. Spudis. (1990) Geoscience and a Lunar Base: A Comprehensive Plan for Lunar Exploration. Washington, DC: Science and Technical Information Division, National Aeronautics and Space Administration.

This page was last modified on July 20, 1998. Send any comments to ben@gwaihir.org or return to my homepage.