(Submitted June 30, 1997)
How is it possible for manned space flights to survive the effects of
the Van Allen Radiation Belt?
As you know, the Van Allen radiation belts are doughnut-shaped regions
encircling Earth and containing high-energy electrons and ions
trapped in the Earth's magnetic field. Explorer I, launched by NASA in 1958,
discovered these two regions of intense radiation surrounding the Earth. They
are referred to as the inner and outer Van Allen radiation belts, after
James Van Allen who designed Explorer I. The inner region is centered at about
3000 km above Earth and has a thickness of about 5000 km. The outer region is
centered at about 15,000 -- 20,000 km above the surface of the Earth and has a
thickness of 6,000 -- 10,000 km.
Typically, manned space flight (such as the Shuttle) stays well below the
altitude of the van Allen radiation belts. Safe flight can occur below
altitudes of 400 km or so.
SO ...what do we do when we have to fly through the radiation belts -- like
when we went to the Moon or send probes to other planets?
In the 1960s, NASA asked Oak Ridge National Laboratory to predict how
astronauts and other materials would be affected by exposure to both the
Earth's Van Allen radiation belts and the Sun's radiation. Oak Ridge
biologists sent bacteria and blood samples into space and exposed small
animals to radiation. They concluded that proper shielding would be key to
successful flight not only for living organisms, but for electronic
instrumentation as well. To develop shielding for the Apollo crews,
Oak Ridge researchers recycled the Lab's Tower Shielding Facility, which had
hoisted shielding experiments aloft for the 1950's nuclear-plane project.
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