Solving Settlement Problems: Dealing with Moon Dust
As scientists and engineers figure out how to return astronauts to the Moon, set up habitats, and mine lunar soil to produce anything from building materials to rocket fuels, they are scratching their heads over what to do about Moon dust.
This troublesome material is every-where on the Moon's surface. The powdery grit gets into everything, jamming seals and abrading spacesuit fabric. It also readily picks up an electrostatic charge. This characteristic causes it to float or levitate off the lunar surface and stick to faceplates and camera lenses. The fine dust might even be toxic.
Larry Taylor, distinguished professor of planetary sciences at the University of Tennessee, has an idea about what to do with this troublesome dust. He suggests that it can be melted into a useful material. "I am one of those weird people who like to stick things in ordinary kitchen microwave ovens to see what happens," Taylor admitted to several hundred scientists at a recent Lunar Exploration Advisory Group (LEAG) conference at NASA Johnson. At home in Tennessee, his most famous experiment involves a bar of Irish Spring soap, which quickly turns into "an abominable monster" when the micro-wave's start button is hit.
However, the experiment he described at LEAG involved transforming Moon dust: He once put a small pile of lunar soil brought back by Apollo astronauts into a microwave oven. Taylor found that it melted rapidly, within 30 sec, at only 250 W.
The reason it melted so quickly has to do with its composition. Lunar regolith, or soil, is produced when micrometeorites plow into lunar rocks and sand at high-impact velocities, melting and creating glass. The glass contains nanometer-scale beads of pure iron--so-called "nanophase" iron. Those tiny iron beads efficiently concentrate microwave energy, causing the beads to "sinter," or fuse the loose soils into large clumps.
This observation has inspired Taylor to imagine all kinds of machinery that could be sent to the Moon and then used to fuse lunar dust into useful solids.
"Picture a buggy pulled behind a rover that is outfitted with a set of magnetrons," he suggests. (A magnetron is the heating element in a microwave oven.) "With the right power and microwave frequency, an astronaut could drive along, sintering the soil as he goes, making continuous brick down 0.5 m deep," Taylor points out. He adds that by changing the power settings the astronaut could melt the top inch or two of the soil to make a glass road.
"Or say that you want a radio telescope," he continues. "Find a round crater and run a little microwave 'lawnmower' up and down the crater's sides to sinter a smooth surface. Hang an antenna from the middle--voila, instant Arecibo!" he ex-claims, referring to the giant 305-m-diam radio telescope formed from a natural circular valley in Puerto Rico.
Technical challenges remain. Sintering Moon dust in a microwave oven on Earth is not the same as doing it on the airless Moon. Researchers still need to work out details of a process for producing strong, uniformly sintered material in the harsh lunar environment.
However, the idea has promise. It could result in useful products such as sintered rocket landing pads, roads, bricks for habitats, and radiation shielding, while at the same time providing a means for dust abatement. "The only limit," says Taylor, "is imagination."
NASA scientists are also concerned about health issues that may result from inhaling Moon dust. When astronauts return to the Moon and travel to Mars they will have to be careful about what they inhale. In 1972, when Apollo astronaut Harrison Schmitt sniffed the air in his lunar module, the Challenger, he said that it smelled like gunpowder. His commander Gene Cernan agreed.
The two astronauts had just returned from a long Moonwalk around the Taurus-Littrow Valley, near the Sea of Serenity. Dusty footprints marked their entry into the spaceship. That dust became air-borne--and smelly. Later, Schmitt felt congested and complained of "lunar dust hay fever." His symptoms went away the next day; no harm done. He soon returned to Earth and the anecdote faded into history.
However, Russell Kerschmann never forgot. He is a pathologist at NASA Ames studying the effects of mineral dust on human health. Both the Moon and Mars are extremely dusty worlds, and inhaling their dust could be bad for astronauts, says Kerschmann.
"The real problem is the lungs," he ex-plains. "In some ways, lunar dust resembles the silica dust on Earth that causes silicosis, a serious disease." Formerly known as "stone-grinder's disease," silicosis first came to idespread public attention during the Great Depression when hundreds of miners drilling the Hawk's Nest Tunnel through Gauley Mountain in West Virginia died within five years of breathing the fine quartz dust kicked into the air by dry drilling--even though they had been ex-posed for only a few months. "It was one of the biggest occupational health disasters in U.S. history," Kerschmann says.
Kerschmann says that this health condition would not necessarily occur in astronauts, but he believes NASA needs to be aware of the problem and guard against it.
Quartz, the main cause of silicosis, is not chemically poisonous. "You could eat it and not get sick," he continues. "But when quartz is freshly ground into dust particles smaller than 10 ?m (for comparison, a human hair is 50+ ?m wide) and breathed into the lungs, they can embed themselves deeply into the tiny alveolar sacs and ducts where oxygen and carbon dioxide gases are exchanged." There, the lungs cannot clear out the dust via mucus or coughing. Moreover, the immune system's white blood cells commit suicide when they try to engulf the sharp-edged particles to carry them away in the blood-stream. In the acute form of silicosis, the lungs can fill with proteins from the blood. He adds that it is as if the victim slowly suffocates from a pneumonia-like condition.
Lunar dust, which like quartz is a compound of silicon, is (to our current knowledge) also not poisonous. But like the quartz dust in the Hawk's Nest Tunnel, it is extremely fine and abrasive, almost like powdered glass. Astronauts on several Apollo missions found that it clung to everything and was almost impossible to remove. Once it was tracked inside the lunar module, some of the dust easily became airborne, irritating lungs and eyes.
Worse on Mars?
Martian dust could be even worse. It is not only a mechanical irritant but also perhaps a chemical poison. Mars is red because its surface consists largely of iron oxide and oxides of other minerals. Some scientists suspect that the dusty soil on Mars may be such a strong oxidizer that it will burn any organic compound, such as plastics, rubber, or human skin, as viciously as undiluted lye or laundry bleach.
"If you get Martian soil on your skin, it will leave burn marks," says University of Colorado engineering professor Stein Sture, who studies granular materials such as lunar and Martian dirt for NASA. Because no soil samples have ever been returned from Mars, "we do not know for sure how strong it is, but it could be pretty vicious," says Sture.
Moreover, according to data from the Pathfinder mission, Martian dust may also contain trace amounts of toxic metals, including arsenic and hexavalent chromium--a carcinogenic toxic waste. That was a surprising finding presented in a 2002 National Research Council report called "Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface."
The dust challenge would be especially acute during the windstorms that occasionally envelop Mars from pole to pole. Dust whips through the air, scouring every exposed surface and sifting into every crevice. There would be no place to hide.
To find ways of mitigating these hazards, NASA will soon begin funding Project Dust, a four-year study headed by Masami Nakagawa, associate professor in the mining engineering department of the Colorado School of Mines. The project will investigate such technologies as thin-film coatings that repel dust from tools and other surfaces, and electrostatic techniques for shaking or otherwise removing dust from spacesuits.
These technologies, which would be crucial on the Moon and Mars, might also help on Earth by protecting people from sharp-edged or toxic dust. Examples include alkaline dust blown from dry lakes in North American deserts, wood dust from sawmills and logging operations, and, of course, abrasive quartz dust in mines.
The road to the stars is surprisingly dusty. However, says Kerschmann, "I strongly believe it's a problem that can be controlled."
Edward Flinn writes about aerospace related technology developments. He is based in Scarsdale, NY. This article originally appeared in the January 2006 edition of Aerospace America. Reproduced with permission from AIAA
NOTE:The views of this article are the author's and do not reflect the policies of the National Space Society.
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