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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