New Space Shield May Help Make Mars Mission Reality
Richard A. Lovett
for National Geographic News
|March 23, 2007|
Scientists working toward a manned Mars mission say they're closing in on a new, high-tech material that can shield astronauts from deadly deep-space radiation.
Known as graphite nanofiber, the new material would be much lighter than the dense materials used on Earth as radiation shielding in nuclear power plants.
That's good, because radiation is one of the biggest dangers to long-distance space travelers.
Intense bursts from solar flares can kill quickly. But even normal background radiation levels in interplanetary space are high enough to pose dangers, including an increased risk of cancer. (Related: "Space Weather Could Scrub Manned Mars Mission" [August 9, 2005].)
While adequate shielding can easily be made with existing technology—a few feet of concrete would work admirably—such materials are too heavy to launch into space.
"If we don't get off the ground, we are not in business," Ram Tripathi, a senior research scientist at NASA's Langley Research Center, said at a meeting of the American Physical Society in Denver, Colorado, earlier this month.
This thorny safety issue can't be solved the same way on a Mars mission as it was on the International Space Station or the Apollo expeditions to the moon, Tripathi added. (See a photo gallery of the top photos from the space station.)
The Apollo trips, he said, were "little hops," so there wasn't time for background exposures to reach dangerous levels.
And in the space station, astronauts are close enough to Earth for its magnetic field to protect them from the worst types of radiation.
On occasions when short-lived solar flares overpower that protection, the astronauts can huddle in a cramped radiation shelter that doesn't add vastly to the station's weight.
But in deep space the radiation takes the form of larger particles that are more difficult to stop.
Worse, the wrong type of shielding can actually increase the danger, Tripathi said.
That's because incoming particles doesn't simply plow into the shielding and stop, like bullets hitting a bucket of sand. Rather, the particles collide with atoms of the shielding material, like billiards cues hitting their targets.
The radiation can be so energetic that it shatters the shielding atoms. This microscopic "shrapnel," if it makes it completely through the shielding, is just as dangerous to the ship's crew as the original particles.
This is a big problem in shielding made of normal spaceship construction materials, such as aluminum, whose atoms are relatively heavy and produce powerful shrapnel.
"You need a new material," Tripathi said. "You do not want a heavy material that produces debris."
Tripathi believes that the best choice is the lightest of all atoms: hydrogen.
Of course, it's not possible to build spaceship walls from hydrogen. But it is possible to build superstrong materials from graphite nanofiber, then enrich them with trapped hydrogen.
Tripathi refused to speculate on how much of this material would be needed or how much it would weigh. That depends on the mission, he said.
On short trips, he pointed out, astronauts can put up with cramped conditions. But on longer ones, the travelers will need more room to work, sleep, and relax.
"Then you need a bigger shield and more weight," he said.
Other experts are also beginning to realize that new forms of radiation shielding are an important need for long-distance space flights.
Dealing with radiation will be "a major headache," said science fiction author Mary Rosenblum, who researched the topic extensively for her 2006 novel Horizons.
Humans are far more sensitive to radiation than NASA's robotic probes, so more powerful protection is needed.
Rosenblum is excited by Tripathi's research.
"Effective shielding," she said, "has to come first on the list of necessities."
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