The $100 Billion Question: Why Go Back?
NASA has been silent on the cost of a moon base, but plausible estimates surpass $100 billion. To justify that expense, the agency has generated a list of 200 reasons to return to the moon. Some are purely scientific: Radio telescopes sited on the lunar farside, for instance, would operate unimpeded by atmosphere and shielded from Earth-based radio noise. Such telescopes could also track potentially dangerous near-Earth asteroids undetectable from observatories on Earth. Other potential benefits have a more far-out, commercial cast. Future astronauts might mine rare helium-3 for use in nuclear fusion reactors back home. Or lunar residents might host entertainment events like “micro-g human sports or a lunar rover race.”
Many reasons, however, are tautological. NASA notes that the moon is a good place to test how prolonged isolation and exposure to radiation and microgravity affect the human body. But why bother unless humankind plans to explore the moon and Mars in the first place? NASA administrator Michael Griffin adds a patriotic spin: “Space will be explored and exploited by humans,” he said in a 2005 speech. “The question is, which humans, from where, and what language will they speak? It is my goal that Americans will be always among them.” G. G.
No matter where the base is sited, astronauts on a prolonged lunar mission must contend with low gravity and radiation. Although the muscle- and bone-weakening effects of low gravity won’t be a problem during the brief initial moon missions, shielding astronauts from damaging radiation exposure will be an immediate concern.
One idea is to wrap the lunar habitat in an envelope filled with radiation-absorbing water. Another is to rig an artificial magnetic field to deflect the worst rays. The easiest solution, however, will probably be to put the regolith to work: Simply place the habitat modules in a crater and bury them under a thick layer of moon dust.
How much regolith is necessary? Nobody knows. It is conceivable that radiation will cause chain reactions below the surface of the lunar soil, producing fission products from secondary reactions that are even more harmful to human tissue than unshielded bombardment. Taylor suspects that it would take 10 feet of soil or more to insulate the astronauts.
So astronauts will have to dig into the regolith, and this will not be as easy as it sounds. First there is the challenge of getting heavy equipment into space. “We can’t afford to send a 200,000-pound bulldozer to the moon,” says Middle Tennessee State University civil engineer Walter Wesley Boles, a longtime student of lunar construction. “And even if we did, it would perform very poorly.” Engineers will have to think small. A lunar regolith mover will be “about the size of a riding lawn mower,” Boles says. NASA is holding a regolith-digging contest this May, offering a $250,000 prize to the team whose robot digs the most regolith in 30 minutes—but the excavator must weigh less than 90 pounds.
Then there are even more fundamental physics problems. Heavy machinery on Earth depends on friction and gravity to provide a stable underpinning while the machine’s business end cuts, pushes, pulls, digs, scrapes, or pounds. On the moon, inertia is the same—nudge something and it will move with the same vector it has on Earth—but gravity is different. Jab too hard and the machine will jump. Twist too hard and the machine tips over.
One solution is to build a bin on the back of the bulldozer and fill it with regolith to make a counterweight before serious digging begins. Another is to outfit the bulldozer with augers, so it can screw itself into the lunar surface. Boles suggests getting rid of the blade altogether and mounting a brush or a construction sweeper that would use less force and skim the regolith one thin layer at a time.
As they excavate the moon, astronauts can count on being enveloped in clouds of dust, especially if they use a sweeper. The effects of man-made regolith dust storms on tools and equipment have been known since the backwash from Apollo 12’s engines sandblasted the derelict old Surveyor 3 spacecraft lying nearby. “They found moondust in every nook and cranny,” says William Larson of the Kennedy Space Center, a lead scientist and program manager in NASA’s efforts to develop techniques for using lunar resources. Every artist’s rendering of an imagined lunar outpost features regolith mounds that would screen vital equipment and habitat from rocket-induced dust clouds on the launchpad.
Moondust is also a major unresolved issue for NASA’s next-generation space suit. During the Apollo missions, three days of abbreviated moonwalks was about the limit before zippers balked, joints stiffened, and connectors began to clog. The new astronaut explorers must have a solution that will enable them to work there. Johnson Space Center space suit engineer Amy Ross says: “We’re going to have to maintain ball bearings [in the joints] and replace seals. We can’t have zero tolerance, but we don’t want to suck up all the astronauts’ free time doing maintenance.”
Space engineers are still debating whether to have astronauts don overalls for dirty work or to build a “dust porch” where astronauts can clean up before entering their living quarters. They are also grappling with how to make a suit that will not easily cut or abrade yet will weigh no more than 200 pounds on Earth—33 pounds on the moon. “It’s fairly challenging,” Ross acknowledges.
