The cratered surface of the moon (top) and the
dusty regolith that makes up that surface (below).
Despite all its hazards, regolith may hold the answer, not just for blocking out radiation but also for providing building material for a self-sustaining outpost on the moon. The key lies in particles of glass and metallic iron in the lunar soil. In the 1990s the University of Tennessee’s Lawrence Taylor showed that finer samples of regolith contain enough of this material to make it useful. “One night I go downstairs and stick some of it [the regolith] in the microwave,” he recalls. “I had no reason to do it. It had been tried years ago and never worked. This time it just went zap! ”
Taylor found he could melt a pile of lunar soil in 10 to 20 seconds. Then he focused a single magnetron on another sample: “With 50 watts of energy I took a one-centimeter block of lunar soil to 1700 degrees Celsius (3100°F) in 10 seconds,” he says.
This result has tremendous implications. By microwaving lunar soil, astronauts could weld, or sinter, the particles together to form a serviceable foundation. If they raise the temperature, the top layers would melt and turn into a tough glass. Not only would the explorers have an instant highway, they would also mitigate the worst of the dust clouds. Regolith does not blow around by itself on the moon. Human feet or tire treads have to stir it up, and if they are traveling on pavement, the dust stops.
Taylor envisions a lunar microwave machine akin to a Zamboni that smooths the ice at a hockey game. “I can sinter the soil to a foot deep with the first set of magnetrons, then have a second set that melts the top two inches into glass,” he says.
Even more important, perhaps, is a plant being built by Larry Clark of Lockheed Martin that is designed to extract oxygen from regolith. Its significance is obvious to any space engineer. Liquid oxygen makes up 75 to 80 percent of a spacecraft’s fuel mass. If there is no need to bring spare oxygen from Earth, launch vehicles can be far lighter and cheaper to fly or can carry much more payload. “NASA wants us to look at making 8 metric tons [9 tons] of oxygen per year,” Clark says. “That’s 44 kilograms [97 pounds] per day during daylight. We could refuel two ascent vehicles per year.”
Clark pondered factories in space 15 years ago and kept his ideas alive for years on a shoestring research budget. Things are different now. What he is doing in Lockheed’s labs south of Denver “is not an experiment,” he says. “We’re taking it to the next level.”
Of the many ways to make oxygen from lunar soil, Clark has chosen hydrogen reduction. It operates at relatively cool temperatures, 1300 to 1500°F. The disadvantage is that it obtains oxygen almost exclusively from iron oxides, which make up just about 10 percent of the regolith. Other, hotter processes get much higher yields. Still, Clark calculates that 100 square yards of regolith excavated to a depth of only two inches will produce 660 pounds of oxygen, enough to sustain a four-member explorer team for 75 days.
Clark’s lab, with its gleaming tile floors and gentle sunlight, does not look like the moon, but his machinery is the real thing. The robot excavator is about the size of a power lawn mower, and it has steel drums with scoops mounted on them—like a steamroller with cups. When technicians punch the start button, the robot glides across the floor to a sandbox about 20 feet away. The drums lower and begin to rotate. The cups scoop up sand and feed it into a hopper on the back of the robot’s platform. When the hopper is full, the robot trundles over to a “lunar lander” and dumps the sand into a plastic receptacle. Leave it alone and the robot will dig and dump all day.
In the finished product, when the excavator has filled the reservoir next to the spacecraft, an elevator will lift the soil to the reactor, which will measure only 20 inches long and be shaped like a cement mixer. There the regolith will be heated and rotated under pressure while the hydrogen percolates through it. Above 1300 degrees, the iron oxides will begin to crack, and the oxygen will combine with the hydrogen, flashing off as water vapor.
If the astronauts needed water, the process would stop at that point. If not, the vapor would enter a second chamber for electrolysis. The oxygen would be siphoned off to the lunar habitat or to fuel storage tanks, while the hydrogen would return to the reactor for reuse.
Clark hopes to test his system in a few years aboard an unmanned lunar precursor mission. He has made each piece of his factory work and is in the process of integrating the parts into a seamless whole—a bona fide oxygen plant that could largely free future moon explorers from their ties to supply ships from Earth. “Every year the mission planners come around and say, ‘It’s real nice, but [the entire process] has never been done before,’ ” Clark says. “The next time I want to be able to say, ‘Well, here it is.’ ”
Apollo 15 commander Dave Scott taking pictures of the moon's surface (top). A lunar panorama,
assembled from Apollo 15 photographs, shows moon-buggy tracks on the dusty surface (below).
