"Force Field" Could Keep Lunar Astronauts Safe From Solar
Radiation
Artists 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. See larger image.
by Patrick L. Barry for Science at NASA
Huntsville AL (SPX) Jun 27, 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.
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.
"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.
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.
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.