When Neil Armstrong took “one giant leap for mankind” onto thesurface of the moon in 1969, his booted foot sank into a layer of finegray dust, leaving an imprint that would become the subject of one ofthe most famous photographs in history. Scientists called the dustlunar regolith, from the Greek rhegos for “blanket” and lithos for“stone.” Back then scientists regarded the regolith as simply part ofthe landscape, little more than the backdrop for the planting of theAmerican flag.
No more. Lunar scientists have learned a lot about the moon sincethen. They’ve found that one of the biggest challenges to lunarsettlement—as vexing as new rocketry or radiation—is how to live withregolith that covers virtually the entire lunar surface from a depth of7 feet to perhaps 100 feet or more. It includes everything from hugeboulders to particles only a few nanometers in diameter, but most of itis a puree created by uncountable high-speed micrometeorites that havebeen crashing into the moon unimpeded by atmosphere for more than 3billion years. A handful of regolith consists of bits of stone,minerals, particles of glass created by the heat from the tiny impacts,and accretions of glass, minerals, and stone welded together.
Eons of melting, cooling, and agglomerating have transformed theglass particles in the regolith into a jagged-edged, abrasive powderthat clings to anything it touches and packs together so densely thatit becomes extremely hard to work on at any depth below four inches.
For those who would explore the moon—whether to train for exploringMars, to mine resources, or to install high-precisionobservatories—regolith is a potentially crippling liability, anall-pervasive, pernicious threat to machinery and human tissue. Afterjust three days of moonwalks, regolith threatened to grind the jointsof the Apollo astronauts’ space suits to a halt, the same way rustcrippled Dorothy’s Tin Man. Special sample cases built to hold theApollo moon rocks lost their vacuum seals because of rims corrupted bydust. For a permanent lunar base, such mechanical failures could spelldisaster.
Regolith can play havoc with hydraulics, freeze on-off switches, andturn ball bearings into Grape Nuts. When moondust is disturbed, smallparticles float about, land, and glue themselves to everything.Regolith does not brush off easily, and breathing it can causepulmonary fibrosis, the lunar equivalent of black lung. There isnothing like it on Earth. “Here you have geological processes that tendto sort and separate,” says geologist Douglas Rickman of NASA’sMarshall Space Flight Center. “On the moon you have meteorite impactsthat mix everything together.”
But space planners also see a brighter side to the story. Forty-twopercent of regolith is oxygen by weight. Extract that and it will helpmake breathable air, rocket fuel, and, when mixed with hydrogen, water.Heat up regolith and it will harden into pavement, bricks, ceramic, oreven solar panels to provide electricity. Cloak a living area in athick enough blanket of it and it will enable astronauts to liveradiation-free. If regolith is the curse of lunar exploration, it mayalso prove to be a blessing.
These issues lay dormant for three decades until January 2004, whenPresident Bush announced his “Vision for Space Exploration” and gaveNASA a new mandate: Return humans to the moon by 2020 and eventuallysend them on to Mars. More details of this plan emerged last Decemberat a meeting of the American Institute of Aeronautics and Astronauticsin Houston. Scientists are now thinking about what is needed to makethe vision a reality. While there is debate about the political will tosustain lunar exploration (see “The Future of NASA,” DISCOVER,September 2006), the technical hurdles are beyond dispute. The nextperson to step on the moon again will be taking humanity where it hasnever gone before, because that person will be settling in to stay—andthat will be extremely hard to do.
NASA’s current plans call for a series of “precursor” robotic lunarmissions to test technologies and gather information. These will beginnext year, long before NASA’s new Orion spaceship is ready to loft itsfour-astronaut crew moonward. By the time that happens, perhaps around2018, planners hope to have resolved some key unknowns: whether thereare ice deposits at one of the lunar poles, whether a space suit can bemade that can survive multiple journeys across the dust-riddenlandscape, and whether the human body can survive dust, lengthy staysin reduced gravity, and prolonged exposure to cosmic radiation.
A sunlit crescent of Earth seen from the moon.
The first trips will be Apollo-like sorties, brief visits to testtechniques and equipment and to begin building the outpost. Eventuallythe base will include living quarters, a launchpad, a storage facilityfor fuel and supplies, and a power plant. By 2024, NASA experts expectto have enough infrastructure to support a permanent human presencewith four astronauts rotating every six months, the same length of astay as on the International Space Station.
Setting up a permanent outpost on the moon would, in many respects,be more daunting than putting an outpost on Mars. Like Earth, Mars hasan atmosphere, weather, and seasons, and its gravity is one-third ofEarth’s. The moon has one-sixth of Earth’s gravity, no atmosphere, anda merciless and unending barrage of radiation and micrometeorites. Somescientists argue that if going to Mars is the ultimate goal, there’s nopoint in going to the moon.
But if the goal is learning about long-term stays in space, going tothe moon provides excellent instruction. Space station astronauts arein low Earth orbit, only 224 miles from safety. Moon astronauts will bethree days from help, and Mars astronauts will, at best, be monthsaway—virtually alone after liftoff. The explorers will not only have tolearn to live in reduced gravity in cramped spaces for prolongedperiods, as in the carefully calibrated indoor environment of the spacestation, but they must also work outside for extended periods inpotentially lethal environments they cannot control. They must makeconsumables like oxygen, recycle them, and recycle waste. They must beable to maintain their equipment, knowing that not only theirscientific mission but their very lives may depend on their repairs.And they must be able to cope with sickness, set broken bones, performemergency appendectomies, and, in the worst of circumstances, watch acomrade die from injury or blood loss, knowing that he or she couldeasily have survived with timely treatment at a terrestrial hospital.
Coping with these challenges will require an attitude adjustment anda lot of practice, and screwups are better handled closer to home.Former astronaut and U.S. senator Harrison Schmitt, the last man towalk on the moon, told delegates at a NASA-sponsored moon conferencelast year that humanity needed to “redevelop a deep space operationalstructure and discipline.” Others describe the situation more bluntly.NASA, grown skittish because of the losses of space shuttles Challengerand Columbia, has become too risk-averse.
“There are things we have to decide,” says University of Tennesseegeochemist Lawrence Taylor, a leading moon scientist. “There’s going tobe a hazard, and if we think it’s dangerous to go to the moon, whatabout Mars? You just can’t bail out and go home.”
The abrasive regolith is just one aspect of the moon’s harshenvironment. The equator promises relatively happy landings onrelatively smooth surfaces, but it also guarantees temperatures thatexceed 250 degrees Fahrenheit during the day and plummet below –240°Fduring the night—and both day and night last 14 Earth days. The Apolloastronauts did most of what they did during the lunar equivalent ofearly morning and forenoon—light enough to see but not as hot.
Climate is the main reason NASA announced last December that itwould build its outpost near one of the lunar poles. The currentfavorite spot is the edge of Shackleton Crater at the moon’s southpole, which is expected to feature “moderate” temperatures, between–50°F and 50°F. Shackleton also has the important advantage of being insunlight—albeit weak sunlight—for up to 80 percent of the year.Abundant light will be crucial for generating electricity. If the basewere built at the lunar equator, it would be in darkness for half ofevery month. During that time, solar-collecting arrays would be useless.
Another important attraction of the moon’s poles is the possiblepresence of useful natural resources. Lunar orbiters in the 1990sdetected concentrations of hydrogen, a potential resource for rocketfuel. Currently no one knows how much there is or what form it takes.Some scientists suspect that a comet may have sideswiped the moon longago, leaving water ice buried in permanently shadowed craters.Identifying the source of the hydrogen is a key goal for the roboticmissions that will precede the next landing by humans. The downside ofa polar landing is that the landscape there is craggier and moreforbidding than at the moon’s midline, which makes landings morechallenging. Nonetheless, NASA officials believe the advantages at thesouth pole outweigh the risks.
No matter where the base is sited, astronauts on a prolonged lunarmission must contend with low gravity and radiation. Although themuscle- and bone-weakening effects of low gravity won’t be a problemduring the brief initial moon missions, shielding astronauts fromdamaging radiation exposure will be an immediate concern.
One idea is to wrap the lunar habitat in an envelope filled withradiation-absorbing water. Another is to rig an artificial magneticfield to deflect the worst rays. The easiest solution, however, willprobably be to put the regolith to work: Simply place the habitatmodules in a crater and bury them under a thick layer of moon dust.
How much regolith is necessary? Nobody knows. It is conceivable thatradiation will cause chain reactions below the surface of the lunarsoil, producing fission products from secondary reactions that are evenmore harmful to human tissue than unshielded bombardment. Taylorsuspects that it would take 10 feet of soil or more to insulate theastronauts.
So astronauts will have to dig into the regolith, and this will notbe as easy as it sounds. First there is the challenge of getting heavyequipment into space. “We can’t afford to send a 200,000-poundbulldozer to the moon,” says Middle Tennessee State University civilengineer Walter Wesley Boles, a longtime student of lunar construction.“And even if we did, it would perform very poorly.” Engineers will haveto think small. A lunar regolith mover will be “about the size of ariding lawn mower,” Boles says. NASA is holding a regolith-diggingcontest this May, offering a $250,000 prize to the team whose robotdigs the most regolith in 30 minutes—but the excavator must weigh lessthan 90 pounds.
Then there are even more fundamental physics problems. Heavymachinery on Earth depends on friction and gravity to provide a stableunderpinning while the machine’s business end cuts, pushes, pulls,digs, scrapes, or pounds. On the moon, inertia is the same—nudgesomething and it will move with the same vector it has on Earth—butgravity is different. Jab too hard and the machine will jump. Twist toohard and the machine tips over.
One solution is to build a bin on the back of the bulldozer and fillit with regolith to make a counterweight before serious digging begins.Another is to outfit the bulldozer with augers, so it can screw itselfinto the lunar surface. Boles suggests getting rid of the bladealtogether and mounting a brush or a construction sweeper that woulduse less force and skim the regolith one thin layer at a time.
As they excavate the moon, astronauts can count on being envelopedin clouds of dust, especially if they use a sweeper. The effects ofman-made regolith dust storms on tools and equipment have been knownsince the backwash from Apollo 12’s engines sandblasted the derelictold Surveyor 3 spacecraft lying nearby. “They found moondust in everynook and cranny,” says William Larson of the Kennedy Space Center, alead scientist and program manager in NASA’s efforts to developtechniques for using lunar resources. Every artist’s rendering of animagined lunar outpost features regolith mounds that would screen vitalequipment and habitat from rocket-induced dust clouds on the launchpad.
Moondust is also a major unresolved issue for NASA’snext-generation space suit. During the Apollo missions, three days ofabbreviated moonwalks was about the limit before zippers balked, jointsstiffened, and connectors began to clog. The new astronaut explorersmust have a solution that will enable them to work there. Johnson SpaceCenter space suit engineer Amy Ross says: “We’re going to have tomaintain ball bearings [in the joints] and replace seals. We can’t havezero tolerance, but we don’t want to suck up all the astronauts’ freetime doing maintenance.”
Space engineers are still debating whether to have astronauts donoveralls for dirty work or to build a “dust porch” where astronauts canclean up before entering their living quarters. They are also grapplingwith how to make a suit that will not easily cut or abrade yet willweigh no more than 200 pounds on Earth—33 pounds on the moon. “It’sfairly challenging,” Ross acknowledges.
Despite all its hazards, regolith may hold the answer, not just forblocking out radiation but also for providing building material for aself-sustaining outpost on the moon. The key lies in particles of glassand metallic iron in the lunar soil. In the 1990s the University ofTennessee’s Lawrence Taylor showed that finer samples of regolithcontain enough of this material to make it useful. “One night I godownstairs and stick some of it [the regolith] in the microwave,” herecalls. “I had no reason to do it. It had been tried years ago andnever 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 ofenergy I took a one-centimeter block of lunar soil to 1700 degreesCelsius (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 aserviceable foundation. If they raise the temperature, the top layerswould melt and turn into a tough glass. Not only would the explorershave an instant highway, they would also mitigate the worst of the dustclouds. Regolith does not blow around by itself on the moon. Human feetor tire treads have to stir it up, and if they are traveling onpavement, the dust stops.
Taylor envisions a lunar microwave machine akin to a Zamboni thatsmooths the ice at a hockey game. “I can sinter the soil to a foot deepwith the first set of magnetrons, then have a second set that melts thetop two inches into glass,” he says.
Even more important, perhaps, is a plant being built by Larry Clarkof Lockheed Martin that is designed to extract oxygen from regolith.Its significance is obvious to any space engineer. Liquid oxygen makesup 75 to 80 percent of a spacecraft’s fuel mass. If there is no need tobring spare oxygen from Earth, launch vehicles can be far lighter andcheaper to fly or can carry much more payload. “NASA wants us to lookat making 8 metric tons [9 tons] of oxygen per year,” Clark says.“That’s 44 kilograms [97 pounds] per day during daylight. We couldrefuel two ascent vehicles per year.”
Clark pondered factories in space 15 years ago and kept his ideasalive for years on a shoestring research budget. Things are differentnow. What he is doing in Lockheed’s labs south of Denver “is not anexperiment,” he says. “We’re taking it to the next level.”
Of the many ways to make oxygen from lunar soil, Clark has chosenhydrogen reduction. It operates at relatively cool temperatures, 1300to 1500°F. The disadvantage is that it obtains oxygen almostexclusively from iron oxides, which make up just about 10 percent ofthe regolith. Other, hotter processes get much higher yields. Still,Clark calculates that 100 square yards of regolith excavated to a depthof only two inches will produce 660 pounds of oxygen, enough to sustaina four-member explorer team for 75 days.
Clark’s lab, with its gleaming tile floors and gentle sunlight, doesnot look like the moon, but his machinery is the real thing. The robotexcavator is about the size of a power lawn mower, and it has steeldrums with scoops mounted on them—like a steamroller with cups. Whentechnicians punch the start button, the robot glides across the floorto 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 therobot’s platform. When the hopper is full, the robot trundles over to a“lunar lander” and dumps the sand into a plastic receptacle. Leave italone and the robot will dig and dump all day.
In the finished product, when the excavator has filled the reservoirnext to the spacecraft, an elevator will lift the soil to the reactor,which will measure only 20 inches long and be shaped like a cementmixer. There the regolith will be heated and rotated under pressurewhile the hydrogen percolates through it. Above 1300 degrees, the ironoxides will begin to crack, and the oxygen will combine with thehydrogen, flashing off as water vapor.
If the astronauts needed water, the process would stop at thatpoint. If not, the vapor would enter a second chamber for electrolysis.The oxygen would be siphoned off to the lunar habitat or to fuelstorage tanks, while the hydrogen would return to the reactor for reuse.
Clark hopes to test his system in a few years aboard an unmannedlunar precursor mission. He has made each piece of his factory work andis in the process of integrating the parts into a seamless whole—a bonafide oxygen plant that could largely free future moon explorers fromtheir ties to supply ships from Earth. “Every year the mission plannerscome around and say, ‘It’s real nice, but [the entire process] hasnever been done before,’ ” Clark says. “The next time I want to be ableto 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).