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Researchers
are reviving an old but wild idea to protect astronauts from
space radiation.
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June 24, 2005: Opposite charges attract. Like charges
repel. It's the first lesson of electromagnetism and, someday,
it could save the lives of astronauts.
NASA's
Vision for Space Exploration calls for a return to the Moon
as preparation for even longer journeys to Mars and beyond.
But there's a potential showstopper: radiation.
 Space
beyond low-Earth orbit is awash with intense radiation from
the Sun and from deep galactic sources such as supernovas.
Astronauts en route to the Moon and Mars are going to be exposed
to this radiation, increasing their risk of getting cancer
and other maladies. Finding a good shield is important.
Right:
Supernovas
produce dangerous radiation. [More]
The
most common way to deal with radiation is simply to physically
block it, as the thick concrete around a nuclear reactor does.
But making spaceships from concrete is not an option. (Interestingly,
it might be possible to build a moonbase from a concrete mixture
of moondust and water, if water can be found on the Moon,
but that's another story.) NASA scientists are investigating
many radiation-blocking materials such as aluminum, advanced
plastics and liquid hydrogen. Each has its own advantages
and disadvantages.
Those are all physical solutions. There is another possibility,
one with no physical substance but plenty of shielding power:
a force field.
Most
of the dangerous radiation in space consists of electrically
charged particles: high-speed electrons and protons from the
Sun, and massive, positively charged atomic nuclei from distant
supernovas.
Like charges
repel. So why not protect astronauts by surrounding them with
a powerful electric field that has the same charge as the
incoming radiation, thus deflecting the radiation away?
Many
experts are skeptical that electric fields can be made to
protect astronauts. But Charles Buhler and John Lane, both
scientists with ASRC Aerospace Corporation at NASA's Kennedy
Space Center, believe it can be done. They've received support
from the NASA Institute for Advanced Concepts, whose job is
to fund studies of far-out ideas, to investigate the possibility
of electric shields for lunar bases.
Above:
Artist’s
concept of an electrostatic radiation shield, consisting of
positively charged inner spheres and negatively charged outer
spheres. The screen net is connected to ground. Image courtesy
ASRC Aerospace.
"Using
electric fields to repel radiation was one of the first ideas
back in the 1950s, when scientists started to look at the
problem of protecting astronauts from radiation," Buhler
says. "They quickly dropped the idea, though, because
it seemed like the high voltages needed and the awkward designs
that they thought would be necessary (for example, putting
the astronauts inside two concentric metal spheres) would
make such an electric shield impractical."
Buhler
and Lane's approach is different. In their concept, a lunar
base would have a half dozen or so inflatable, conductive
spheres about 5 meters across mounted above the base. The
spheres would then be charged up to a very high static-electrical
potential: 100 megavolts or more. This voltage is very large
but because there would be very little current flowing (the
charge would sit statically on the spheres), not much power
would be needed to maintain the charge.
 The
spheres would be made of a thin, strong fabric (such as Vectran,
which was used for the landing balloons that cushioned the
impact for the Mars Exploration Rovers) and coated with a
very thin layer of a conductor such as gold. The fabric spheres
could be folded up for transport and then inflated by simply
loading them with an electric charge; the like charges of
the electrons in the gold layer repel each other and force
the sphere to expand outward.
Right:
How the voltage would vary above a lunar base for the sphere
configuration shown above. You can learn more about this and
other configurations in the report Analysis
of a Lunar Base Electrostatic Radiation Shield Concept.
Placing the spheres far overhead would reduce
the danger of astronauts touching them. By carefully choosing
the arrangement of the spheres, scientists can maximize their
effectiveness at repelling radiation while minimizing their
impact on astronauts and equipment at the ground. In some
designs, in fact, the net electric field at ground level is
zero, thus alleviating any potential health risks from these
strong electric fields.
Buhler
and Lane are still searching for the best arrangement: Part
of the challenge is that radiation comes as both positively
and negatively charged particles. The spheres must be arranged
so that the electric field is, say, negative far above the
base (to repel negative particles) and positive closer to
the ground (to repel the positive particles). "We've
already simulated three geometries that might work,"
says Buhler.
 Portable
designs might even be mounted onto "moon buggy"
lunar rovers to offer protection for astronauts as they explore
the surface, Buhler imagines.
Right:
One scenario for how an electrostatic radiation shield could be deployed
for mobile lunar exploration vehicles. Inverted green cones denote
regions of partial radiation protection. Image courtesy ASRC Aerospace.
It sounds
wonderful, but there are many scientific and engineering problems
yet to be solved. For example, skeptics note that an electrostatic
shield on the Moon is susceptible to being short circuited
by floating moondust, which is itself charged by solar ultraviolet
radiation. Solar wind blowing across the shield can cause
problems, too. Electrons and protons in the wind could become
trapped by the maze of forces that make up the shield, leading
to strong and unintended electrical currents right above the
heads of the astronauts.
The
research is still preliminary, Buhler stresses. Moondust,
solar wind and other problems are still being investigated.
It may be that a different kind of shield would work better,
for instance, a superconducting magnetic field. These wild
ideas have yet to sort themselves out.
But, who knows, perhaps one day astronauts
on the Moon and Mars will work safely, protected by a simple
principle of electromagnetism even a child can understand.
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Author: Patrick L. Barry
| Editor: Dr.
Tony Phillips | Credit: Science@NASA
|
