NASA researchers are working hard to find their way around space radiation, a hazard future astronauts can't avoid if they hope to fly on long missions to Mars and eventually set foot on its surface.
Much of their focus is on new and better shielding materials to slap on the outer surface of a spacecraft, since the traditional aluminum shells won't cut it during a multiyear mission.
But some scientists are also looking at alternative approaches to safeguard astronauts, ranging from the use of electric fields that create a protective shell around a spacecraft to basic ship design, and even new spacesuits for the exploration of the Martian landscape.
"I think NASA should always be considering these far-out concepts," said NASA's Robert Youngquist, a physicist who leads the Applied Physics Lab at Kennedy Space Center in Florida.
Youngquist and two colleagues are studying the feasibility of a radiation shield that relies on electrostatic charge to ward off harmful high-energy particles before they reach a crewed spacecraft.
Youngquist's team envisions a spacecraft equipped with what's called a multipole electrostatic radiation shield, a radiation guard made up of three electrically charged spheres set in a line along the axis of the ship. The center sphere, set close or even attached to the crew module, would be positively charged, while two outrigger spheres on either side would carry a negative charge. Together, the combination should be enough to repel both high-energy protons and electrons that would otherwise penetrate a spacecraft.
"The key technology [here] is going to be the power supply," NASA physicist Philip Metzger told Space.com. "The primary factor is the amount of charge available to drive into these outriggers." Metzger is one of Youngquist's colleagues in the electrostatic shield study, and NASA researcher John Lane is the other.
Project researchers said computer simulations have shown that an electrostatic shield could protect a spacecraft. The method, however, would not be useful on Mars, where the electrostatic field would ultimately start a current through the atmosphere and cause electrical arcs much like those that light up the gas in fluorescent lights on Earth.
"It's like the atmosphere acts like a short circuit," Metzger said.
Tanking up against cosmic rays
Spacecraft designers may also use a ship's own cryogenic fluids as a radiation screen by arranging the cargo tanks containing them around crew compartments.
"In most [mission] scenarios, you need liquid hydrogen for fuel, and you need water," explained Richard Wilkins, director of NASA's Center for Applied Radiation Research at Prairie View A&M University in Texas, who is conducting one study into liquid shield approaches. "And these are all considered materials that are particularly good for cosmic ray shielding."
The atoms of liquid hydrogen are particularly good as a screen for galactic cosmic rays because they don't fragment into secondary particles as much as heavier elements like lead do when bombarded by high-energy radiation. Those secondary particles, researchers said, could be just as harmful as space radiation itself.
Wilkins has been bombarding columns of water with a neutron beam to determine how the particles pass through the liquid and arrive at a tissue-equivalent proportion counter, a device that simulates what the final radiation dose would be on human tissue, on the other side.
"We saw pretty much what we expected," Wilkins said, adding that the neutrons were predictably scattered by the liquid medium. He's planning additional studies with higher-energy particles and liquid nitrogen during the upcoming summer.
There are still some challenges facing the potential use of cryogenic liquids as radiation shields, not the least of which is the safe handling of large quantities of cryogenic liquids. At the 15th Annual NASA Space Radiation Health Workshop, held recently in New York, researchers said they also need a better understanding of the basic physics of cosmic rays and solar radiation in order to develop proper engineering designs for future spacecraft.
"But we're all highly motivated to figure this out," added Wilkins, who attended the conference.
Walking around a planet
Space is not the only place astronauts have to worry about exposure to high-energy particles.
During a walkabout on Mars, for example, spacesuits will have to shield astronauts against radiation, because the planet does not have a protective magnetic field like the Earth. There is also the added need to withstand Martian sandstorms, yet still be light enough to work on a planet with a gravity one-third that of Earth.
"You need something that is not too heavy," said Barry Patchett, a materials engineering professor at the University of Alberta in Canada. "The mass restrictions in space or even the moon are nowhere near as much as on Mars."
Just as NASA researchers are currently working on EVA suits for future space exploration efforts, Patchett and his students conducted their own study into the specific needs for a Mars mission. The project ultimately yielded plans for a 46-pound (21-kilogram) spacesuit with 12 different layers of protective materials, including new polymers and an outer layer designed not to react with electrostatic dust kicked up in Martian sandstorm. The research appeared in the April issue of the Journal of Materials Engineering and Performance.
"The challenge is that there isn't a book that says, 'This is what your suit has to do on Mars,'" explained Matthew Yarmuch, who participated in the study.