Almost two generations ago, a dozen men walked the moon's surface. Soon afterward, political priorities shifted and the world's attention turned elsewhere for decades. But now, with new players joining the community of space-capable nations, the moon is again being discussed as a serious destination for future explorers. The notion this time is not just to plant a flag, but to set up a long-term manned presence on our planet's closest neighbor.
This article will examine possible strategies for how a future lunar base may come about, and what benefits could be reaped from it.
The Lunar Fleet
Saturn V rocket; photo courtesy of NASA
It still costs over ten thousand dollars per pound to put a payload into low earth orbit. Breaking out of Earth's gravity entirely consumes even more resources and fuel, requiring very large and powerful rockets such as the Apollo program's Saturn V. The Saturn V remains the largest space vehicle ever built, capable of sending fifty-ton payloads onto a lunar-bound trajectory.
In order to return to the moon, the various space agencies involved would have to reinvest in such powerful launch vehicles once again. The heaviest rocket currently in use, Russia's Energia rocket, is capable of inserting a 32 ton payload into a lunar transfer orbit. Not surprisingly, it is the vehicle of choice for a number of private and international interests looking to launch a new wave of probes at Earth's natural satellite in the near future.
However, the U.S. may not be content with relying on foreign launch vehicles for its would-be return to the moon. Harrison Schmitt, one of the last astronauts on the moon and a leading advocate for its commercial development, predicted in a recent Popular Mechanics article that a modern Saturn V-style booster could be developed for about $5 billion dollars. Using improved technologies, these new, larger Saturn-like rockets would be capable of delivering one-hundred-ton payloads to the lunar surface for a per-pound cost cheaper than the Energia.
China, with ambitious plans to land taikonauts on the moon in the next generation, is also developing a large, Energia-like rocket for just such a purpose.
The Scouts
The European Space Agency, National Aeronautics and Space Administration, Japan, India, and China are all planning on launching new spacecraft to the moon in the next few years.
The ESA already has SMART-1, an orbital surveyor, circling and mapping the moon. SMART-1 was meant primarily as a testbed for experimental technology, particularly its miniaturized ion rocket engine.
India is planning on launching its first lunar probe, Chandrayaan-1, in late 2007. Meant primarily as a means of pushing the limits of Indian technical capability, the Chandrayaan probe will map the moon and send back high-resolution images of its surface.
Around the same time, China will launch the first of its Chang'e series of lunar surveyor craft, named after the legendary Chinese goddess who flew to the moon. It is also designed to produce high-resolution maps of the moon.
A year later, in late 2008, NASA will follow up with its Lunar Reconnaissance Orbiter. It is designed to scout for potential landing sites for future manned missions using, among other sensors, an advanced synthetic-aperture radar.
The launch of Japan's LUNAR-A probe has been repeatedly delayed because of technical problems and is currently under review by the country's space agency. The LUNAR-A carries instruments to monitor moonquakes, measure near-surface heat flux, and study the lunar core and interior structure.
The Japanese are also planning to launch a general mapping mission of the moon with their SELENE (SELenological and ENgineering Explorer) probe, scheduled for a 2007 launch.
There are also plans by NASA and some private interests to deploy small rovers to more closely examine areas of interest on the moon's surface.
Location, Location, Location
If all probes mentioned carry out their missions as planned, the moon will be far more extensively mapped by the dawn of the next decade. Using these data, future mission planners will decide on the monumental next step: where and how to send the first manned missions back to the moon.
NASA and other space agencies are especially interested in the polar regions, where earlier survey satellites detected the presence of water ice lurking deep in the eternal shadows of ancient craters. The presence of what may be thousands of tons of water ice could be crucial to a future manned presence on the moon. This ice could not only provide drinking water, but by separating its basic elements, it would allow a moonbase to extract oxygen for breathing and hydrogen for fuel.
However, not everyone is confident the ice will be able to be harvested as a useful resource. The temperature in the perpetual dark of those craters is hundreds of degrees below zero, making the ice steel-hard and razor-sharp. This is in addition to the dangers of astronauts working in hazardous super-frigid temperatures for extended periods of time, hundreds of meters down in pitch-blackness. Even using advanced autonomous vehicles may not be enough to overcome the extreme conditions in order to bring significant amounts of ice back for use by a lunar base.
Assuming the ice-gathering problem can be overcome, however, the northern lunar pole looks especially attractive to NASA. Unlike Earth, the moon has very little axial tilt, and rotates about a near-vertical axis with respect to the sun. At certain points near the northern lunar pole, particularly around the rim of Peary Crater, the sun never sets; it forever skims just above the horizon. This could greatly ease energy-gathering requirements through the use of solar cells, and should maintain most of the landscape at a steady temperature of -50 degrees Centigrade.
The First Moonbase
The first few manned missions back to Luna will probably closely resemble the Apollo landings in character: a handful of astronauts in small landers, a ceremonial planting of the flag, and many surveys and scientific experiments. However, it is beyond these that the true challenge lies: setting up long-term facilities on a barren, airless rock over 230,000 miles away.
The specific spot chosen will likely be a wide, level area near one or more of the previously discovered repositories of ice. A flat area would make spacecraft landing much easier, as well as facilitate setting up solar-cell arrays for energy gathering. Ideally, such an area would also be relatively free of obstructions such as large boulders, and have a minimum of lunar dust astronauts would have to contend with.
It is likely that unmanned predecessor missions will carry many supplies and equipment well ahead of the astronauts to the site previously chosen for the base. Everything the first moonbase astronauts may need will already be there waiting for them, including construction materials, tools, vehicles, batteries, and so on. The moon is close enough to allow slow but reliable teleoperations from Earth, meaning ground control could use remote-controlled maintenance drones to handle much of the preliminary construction. These construction robots could also handle such tasks as removing potential obstructions such as rocks and large amounts of lunar dust.
One proposal is to send an unmanned back-up return vehicle to the site ahead of the first manned crew, so that when the astronauts arrive they will have an extra vehicle at their disposal. This would not only provide them with a means to return home should their primary vehicle run into problems, but would also give them extra living space during those first few crucial weeks they may be setting up the primary base habitat.
SMART-1 orbital surveyor; artist's rendering courtesy of NASA
The most important structure to be built will be the first surface habitat, meant to serve the astronauts' long-range living needs outside their ship. The exact design will depend on a great many factors, including weight, cost, configuration, and a slew of others. The first habitat might be wholly constructed on Earth like a Space Station module and landed on the moon already fully assembled. The first crew would just have to warm it up, do a systems check, and move in.
The primary surface habitat might also be an inflatable structure. Such a module would be potentially lighter, less bulky, and cheaper than a wholly constructed hard-frame module. A far cry from thin-skinned balloons, an inflatable module would have a dozen or more layers of reinforced and insulating material around a solid core of interior walls, and would be slowly inflated by attached gas canisters.
A third method for building a primary habitat is simple modular construction, like many military advance bases use today. This would be the cheapest kind of habitat material-wise. However, this also would require a much greater human presence on the surface to construct, increasing the amount of time astronauts would have to spend on potentially hazardous extravehicular activity.
A radical proposal, from NASA's John Mankins, a human and robotic technology specialist, is to use a "Habot"—a lunar-base module constructed on an ambulatory chassis, using legs or wheels to slowly move about on its own. This would greatly facilitate the quick construction or reconfiguration of a moonbase, but with foreseeable technology it would also be the most expensive and difficult type of habitat module to construct.
This first habitat, no matter how it is built, is usually envisioned as being a long cylinder or half cylinder (to better fit into launch vehicles), usually no longer or wider than a modern mobile home. Many of the life-support systems used would be similar to those first pioneered on the International Space Station.
After the first shelter, astronauts would need to establish a power source. Modular solar-cell arrays would be set up on the surface to take advantage of the unfiltered sunlight the moon receives. These would be deployed in large, tightly gridded "farms" close to the base. The lunar personnel would have to set up not only enough cells to power the base, but also enough to charge the batteries they will need to run their systems during the lunar night, should that be necessary.
Another option would be to bring along a small, fully operational nuclear reactor to the moonbase, and use the solar cells as a supplementary energy source. Reactors small and mobile enough to make the trip to the moon are easy enough to engineer with today's technology. The main obstacle to supplying a moonbase with one would be political. Even though there is no (native) ecology on the moon to contaminate, the reactor would still have to be launched from Earth, and rockets have a nasty habit of very occasionally exploding upon launch. It was concern over such an explosion spreading radioactive material that led to legal controversy surrounding the launches of the Gallileo and Cassini interplanetary probes, which used nuclear material for heating cells. A full-scale nuclear reactor aboard such a high-profile launch would likely draw even more controversy.
The third major necessity on the lunar surface is a storm shelter. The moon is outside both Earth's atmosphere and magnetic field, leaving its surface completely exposed to the harsh energies of space. During peak solar activity, astronauts may be exposed to potentially hazardous levels of radiation, even in their primary habitat or return vehicle. They will need a place where they can retreat in order to ride out these intense solar storms.
The simplest solution is to just dig one: a few meters of solid rock makes a very effective shield. Like Kansas residents a quarter million miles away, moonbase personnel may find themselves digging out a storm cellar. Excavation machinery could create the shelter, which would be lined with air- and temperature-tight walls and pressurized. Ideally, it would be attached to the main habitat for quick access. It would even be possible for autonomous construction machines to excavate a shelter ahead of time, and have the astronauts construct or place their main habitat right over it.
An alternate method is to build a surface storm bunker, a heavily reinforced structure covered over with a few meters of lunar rock or bags of moondust.
Auxiliary structures would need to be added afterward to make the base fully functional as an outpost. Storage tanks for water and rocket fuel. Communication dishes to facilitate contact with Earth and lunar-orbit satellites. Storage facilities for tools and parts.
Houston, we have a moonbase.
Expansion
A huge number of possibilities exist of how to expand a moonbase beyond the basic setup of lander, habitat, power source, and storm shelter. What exactly would be added would depend on what the base was designed for.
Like the International Space Station, the lunar outpost will most likely be built up in separate but interconnecting modules to allow astronauts ease of access to all parts of the base. And as solar and cosmic radiation are constant hazards on the airless world, setting up half-buried or even fully underground modules may quickly become preferable. Construction rovers could excavate a hole for a new module, move it in via tractor or construct it inside, then cover it back over with lunar soil.
Almost certainly additional habitat units and solar cell farms will be added as simple redundancies and to expand capacity. As any moonbase's purpose at the very start will be primarily scientific in nature, an influx of mission specialists would be very likely. Dedicated laboratory modules may be the first auxiliary additions to the basic moonbase.
Robotic rovers and surface vehicles are increasingly assumed by planners to be part of the ongoing mission, so a pressurized motor pool, complete with vehicle-sized airlock, may be needed for the easy repair and upkeep of these machines.
One or more hydroponics modules may also be desirable for any type of expanded moonbase, for a number of reasons. The plants could help with air replenishment, supplement the food supply, and make for a generally pleasanter living environment at the base.
Even if the lunar ice proves harvestable, chances are limited initial resources would prevent astronauts from turning their attention to it right away. But once the moonbase is fully underway and a proven success, this would change. A secondary facility would be set up on the rim of an ice-bearing crater, perhaps with power and communication lines leading back to the main base. This secondary base would not actually be on or even near the ice; its purpose would be to maintain, supervise, and remotely operate the automatons which would probably do the actual dirty work.
Ancient ice is not the moon's only valuable natural resource. Of great interest to many scientists are the large quantities of helium-3 found in lunar soil, deposited there over millions of years by the solar wind. Helium-3 is a rare isotope of helium that is valuable in fusion reactions. All the energy needs in the United States circa 1990 could have been met by fusing about 28 tons of helium-3, with no toxic byproducts. Helium-3 is currently valued at $14,000 an ounce, roughly twenty-five times that of gold.
Lunar soil contains about thirteen parts per billion of helium-3, meaning very large amounts of rock and dust would have be processed to isolate the material. Some envision large autonomous vehicles roaming over the lunar surface, sucking in lunar dust and extracting the material through heating, cooling, and specialized membranes. The helium-3 would then be stored at the moonbase in specialized containers for transport back to Earth.
There are of course other elements in the dust and rock that could prove valuable. Helium-3 mining will produce large amounts of hydrogen as a byproduct, about one part per ten thousand. Oxygen is also present in abundance. Silicon and aluminum extracted from the soil can be used to build simple solar-power arrays. Iron, calcium, titanium, and other elements within the lunar regolith could also prove valuable. Centralized storage and support facilities at the moonbase would have to be set up to handle all this mining activity.
Oddly, one of the moon's most valuable resources may prove to be its low gravity. Once the mining infrastructure is set up, it would actually be cheaper to send material over two hundred thousand miles from the moon to low earth orbit than to send the same material into orbit from Earth's surface, a mere hundred miles away. In fact, practical large-scale construction in earth orbit may first have to wait for large-scale mining and fabrication operations on the moon to be established.
Luna's lower gravity and lack of an atmosphere also allow it to take advantage of launch technologies that are problematic on Earth, such as an electromagnetic cargo launcher (ECL). An ECL is a long, canted track of powerful electromagnets used to accelerate small payloads (up to 100 kg) to escape velocity. On Earth, ECLs require enormous power to overcome Earth's gravity, and payloads risk being ripped apart by the tremendous pressures their velocity creates in the lower atmosphere. On the moon, energy requirements are much less, and there is no atmosphere to worry about. An ECL combined with a small, modular maneuvering package for the payloads could deliver cargo anywhere in the Earth-Moon system for pennies a pound, and in much greater volume than standard rockets could ever achieve.
A profitable source of income for a moonbase that has been bandied about a lot in recent years is space tourism. Once all the bugs are shaken out of the lunar outpost and the basic habitats are expanded, tourists can become a very real possibility. At first only millionaires will be able to afford to go, but as access to the moon expands in succeeding years, people with more modest incomes will have a shot at it as well. A "Lunar Hotel" may be the first privately funded series of modules to be added to the moonbase.
A number of sources have made a point of mentioning that on the moon, the average person is light enough to fly under his own power, if given wings and air to fly in. Some space entrepreneurs envision enormous inflatable domes where people could strap on oversized, lightweight polymer wings and do just that.
A kind of lunar tourism that does not require any tourists to actually be present is for a company to pick a relatively small area of the lunar surface, far from where any damage to a moonbase could be done, and drop dozens of small, cheap, solar-powered rovers onto the surface. Patrons back on Earth, say at an amusement park, could plant themselves in a simplified remote-operations station and get to drive one of the rovers around for ten minutes at a time.
From Outpost to Colony
Decades after being first established, the site of the first moonbase may look very crowded, with 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 ECL shoots off cargo payloads of helium-3 to Earth every twenty minutes. The permanent population of the lunar outpost is now several hundred, with over a thousand tourists passing through every year. The base is slowly but surely earning back its huge initial investment.
SELENE probe; artist's rendering courtesy of NASA
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. But there will eventually come a time when both the planners on Earth and the local residents decide it is time to get serious about lunar residency, and build a true colony that can handle the burgeoning population.
The old moonbase would not be abandoned, of course. It would continue on as a center of operations for profitable industries like it always had. 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. Radiation will always be a hazard on an airless world like the moon. True lunar colonies would by necessity be primarily underground affairs to protect their inhabitants from this danger.
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 formed much larger there than on Earth.
If a large and readily accessible series of such tubes could be found, they could 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 could slowly be built up for the entire volume of the lava chambers present, and excavation of additional spaces could be undertaken after the colony was established.
Ice might also exist buried under the lunar surface beyond the permanently shaded craters, deposited there by ancient comet impacts. Ideally, a new colony could be built near such an impact crater to advantage of it.
Crater walls and mountain cliffs that are shaded from the sun for most or all of the lunar day could also make good colony locations for their radiation protection. There would be less need to build facilities underground, but the long-term extreme cold could create its own problems.
Another option is simply to excavate a hole for the new colony. This may take more time and money that scouting out a good natural location, but it has the advantage of being able to be done almost anywhere. This method might be preferable if planners want to keep the new colony close to the old moonbase. A large pit would be cleared, and the colony's 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 could continue once the colony is established.
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 quickly excavate large pits for colonies. The moon curently 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 modules would be heavily insulated and armored anyway, little residue could get through to harm a future colony's population. This option would be difficult to implement in today's political climate, but that may not always remain so.
...And Beyond
The moon offers both tremendous opportunities and daunting challenges. But perhaps the biggest obstacle to overcome in returning men to the moon is right here on Earth.
Finding the will as a nation not only to return to the moon, but stay there permanently is likely to be an uphill battle. The problem is one of long-term investments like manned space travel clashing with short-term economics and political expediency. The public needs to be made aware that space exploration is not just about PR stunts and political spin. New launch vehicles, future lunar missions, a moonbase, and beyond, are just steps on a ladder that could lead to a long and prosperous future for all nations involved.
If we ourselves in this generation cannot walk on the moon, what would we give to know that our children or grandchildren could wake up someday, look out the window with morning coffee in hand, and see a blue-white Earth above a steel gray horizon?
Further Information
In Print:
"Mining the Moon" by Harrison H. Schmitt, Popular Mechanics, October 2004.
On the Internet:
"Perfect Spot Found for Moon Base"
"Sunny spot picked out for future lunar base"