‘Mars Bars’ to Serve as Radiation Shield
WILLIAMSBURG, Va. — Ryan McGlothlin takes a sugar-like powder, stirs in a substance that resembles flour, pours the mix into a mold and bakes it.
The result is a small, shiny, black bar meant to shield against radiation. The powder is polyethylene, and the “flour” is a gray topsoil.
McGlothlin, a chemistry major at the College of William and Mary, and chemistry department chairman Richard Kiefer are using those ingredients to develop a material to make bricks that would protect astronauts against radiation on Mars. They are working with aerospace researcher Sheila Thibeault at NASA Langley Research Center in nearby Hampton.
“What we’re doing is the basic research, establishing that yes, you can do this,” Kiefer said. The work also could have applications on Earth, such as use in shields around nuclear reactors, he said.
NASA hopes to put people on Mars within the next several decades. Because of the different orbits of Earth and Mars, the window of opportunity for travel between the two planets occurs only once every two years. That means that anyone traveling to Mars would have to stay there for a long time.
The prospect of an extended stay on Mars prompts a number of concerns, among them the health effects of galactic cosmic radiation, found nearly everywhere in space. The magnetic field surrounding Earth deflects the radiation, but Mars does not have such a field.
Radiation can cause illness or even death, depending on the dosage and length of exposure. Therefore, astronauts will need a material they can use to build shelters and laboratories that also will shield against radiation.
The lighter the material is in terms of mass, the better its shielding properties, and research has shown that liquid hydrogen is the best possible shield, Kiefer said. “But that’s a little impractical to take to Mars,” he said.
So the next best thing is a solid polymer, or chemical compound, that contains a lot of hydrogen. And polyethylene, a very cheap plastic from which plastic bags are made, has more hydrogen than other polymers, said McGlothlin, 21, of Lebanon, Va.
Loading lots of building material onto the space shuttle would create a heavy weight at launch. So the researchers are trying to figure out how much polyethylene is needed to create bricks by mixing it with a material that astronauts can find in abundance once they get to Mars: regolith, or topsoil.
“We’re trying to find the most efficient way to get the least payload and the maximum payout,” Kiefer said.
Obviously, Mars topsoil isn’t easy to get on Earth. Chemical analysis of soil samples obtained by probes has shown that Mars topsoil is similar to that on the moon. But since that isn’t plentiful on Earth either, the researchers are using regolith from a quarry in Minnesota that is similar to lunar soil.
Regolith contains very little hydrogen, so it would not shield well against radiation without added polyethylene, Kiefer said.
At a NASA laboratory, McGlothlin experiments with mixing different concentrations of polyethylene and regolith to see what works best. He has created small “Mars bars” containing 10%, 15% and 20% polyethylene.
Once the polyethylene and regolith are blended, McGlothlin puts the mixture in a drying oven to remove moisture. The mixture then is poured into a stainless steel mold that creates a small sample bar, such as 3 1/2 inches by 3/4 inch. The mold is heated for half an hour at 245 degrees Fahrenheit.
Back at William and Mary’s chemistry labs, McGlothlin does thermal mechanical analyses on the samples to find out how the material reacts under extreme temperatures. The bricks also are tested to make sure they can withstand pressure, so bricks toward the bottom of a building would not crumble or crack.
Kiefer said another student who since has graduated began testing Mars bricks using a different polymer a year ago. McGlothlin picked up the project this summer and will continue until he graduates.
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On the Net:
College of William and Mary chemistry department:
https://www.chem.wm.edu/
NASA Langley Research Center: https://www.larc.nasa.gov/
