Settlements on Mars remain a long way off. Even after science figures out how to get there, making something light enough to carry to the Red Planet yet strong enough to withstand the perils of space is no picnic---just ask the folks making that inflatable habitat that didn't inflate. But perhaps everyone’s been approaching this the wrong way. Rather than schlepping stuff to Mars, why not use materials that are already there?
That’s exactly what Eugene Aquino, Richard Kiefer, and Robert Orwoll hope to do. The chemists are working on turning Martian regolith (aka dirt) into bricks astronauts could use as building materials and radiation shields.
People have proposed using planetary resources like ice before, but regolith has a lot to recommend it. It is plentiful, for one, and easy to work with. Kiefer worked on a NASA experiment with lunar regolith 16 years ago. "That proved that you could take regolith and a polymeric material and make something that you could turn into a habitat---using only a microwave oven," he says.
The basics for the current experiment are equally simple: Mix powdered polymer with regolith, dump it into a silicon mold, and apply heat. Just how much heat, and how it's applied, remains proprietary. Of course, the scientists don't have any Martian regolith, so they're using volcanic ash from Hawai'i. Orwoll calls it "a close cousin" with similar properties, like lots of silicate and iron.
Those properties are important, because everything depends upon identifying the chemical features of regolith and finding polymers that will form strong attractions to them. The three chemists are testing a number of polymers, from standards like polyethylene to things they're cooking up, to see what works best. "We'd like the percentage of polymer in the bricks [by weight] to be as low as possible," says Aquino. "We'd like it to be 5 percent, but it's too early to say if we'll be able to."
Complicating things, you want a polymer with lots of hydrogen because (perhaps surprisingly, given how scant the atoms are) it is a body's best defense against radiation. Radiation is really just high-energy particles, and when they come up against electrons, the electrons sap that energy. Even though hydrogen atoms are just one proton and one electron, that makes for a really high number of electrons per unit mass---1:1, the highest of any element. On top of that, its wee little nucleus makes it highly unlikely to break apart if irradiated. "Liquid hydrogen is the best radiation shield, but that's just not a constructible material," Kiefer says. Even if regolith brick isn't a viable construction material, it could provide a layer of radiation protection.
People tend to think of space exploration as the highest of high-tech, but that isn't always the case. Sometimes a simpler approach is best, and dirt bricks are pretty simple. "Being able to use what's sitting right there on the ground is what could make Martian exploration possible," Orwoll says."You could easily have robots build habitats as needed ahead of time, and by the time the astronauts arrived, they'd already have a place to hang their hats." With regolith bricks, all NASA would have to haul to Mars is enough polymer to constitute a measly 5 percent of the overall structure. And when it comes to space travel, it doesn’t pay to fight gravity---the lighter your cargo, the cheaper your trip.
