A bubble of plasma could shield astronauts from radiation during long journeys through space, researchers are suggesting. If the idea proves viable, it means heavy metal protective panels could be replaced by a plasma shield of just a few grams.
Astronauts travelling beyond the Earth’s orbit would be at risk of cancer and other illnesses due to their long term exposure to cosmic rays. Some of these energetic particles are spewed forth during outbursts from the Sun. Others come from outside our solar system and are more mysterious in origin.
The Earth’s magnetic field protects spacecraft in low Earth orbits, such as the space shuttle and International Space Station. But astronauts journeying to Mars would benefit from no such protection. Thick metal shielding could absorb the rays, but the extra weight that would need to be launched into space might make this an impractical approach.
“There’s no really sensible solution in terms of materials,” says John Slough of the University of Washington, in Seattle, US, who is leading a study of the plasma shield idea. “It’s an Achilles heel of manned space travel.”
Slough says the problem could be solved with just a few grams of hydrogen in the form of a plasma surrounding the spacecraft. NASA’s Institute for Advanced Concepts (NIAC) recently awarded Slough’s team $75,000 to explore the feasibility of the idea.
The details still need to be worked out, but the basic approach is clear. A high voltage device on the spacecraft would tear the hydrogen into its constituent protons and electrons. This plasma would then be spewed out into space, creating a cloud around the spacecraft.
There would need to be a wire mesh outside the spacecraft and enclosing the plasma cloud. Electricity supplied to the mesh would keep an electrical current running in the plasma cloud and help confined it near the spacecraft.
The plasma’s magnetic field would be a powerful deflector of cosmic rays, equivalent to aluminium shielding several inches thick, Slough says.
The larger the cloud, the better it will deflect cosmic rays. But a larger cloud requires a bigger wire cage to contain it, and would therefore increase the mass of the spacecraft.
The researchers are now examining this trade-off to determine the optimum size of the plasma bubble. As a rough estimate, Slough says the cloud might need to be about 100 metres across. At that size, the mesh would have to be stowed for launch and deployed once the craft reached in space.
The wire mesh would need to be made of superconducting material and it would need to be able to operate at relatively high temperatures, since it would be heated by sunlight. This sort of superconducting wire is available commercially, Slough says.
Future spacecraft might be powered by advanced engines that use plasma as a propellant. In that case, the discarded plasma could be recycled for use as a radiation shield. “You’re protected by your own exhaust,” Slough says.