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The Question
(Submitted January 19, 1998)
I am curious to know what the effects of solar radiation have on space
craft after they leave the protection of the Van Allen belt. How much
protection do they need and how long could an astronaut survive in and
out of his craft.
The Answer
Solar radiation and cosmic radiation are both things to worry about in space.
The ultraviolet (UV) radiation from the Sun (without our protective ozone
layer and atmosphere to protect us) would be enough to rapidly give you
sunburn, melanoma, etc. However, unless your spacesuit or spacecraft
windows are specifically designed to let UV pass through, enough will be
blocked that you don't have to worry about it too much. (If you are in
space without a spacesuit or spacecraft, then you've got bigger problems
than radiation.)
When the sun flares, it produces x-rays, gamma-rays, and energetic
particles. The energetic particles are the worst, but they are delayed
compared to the X-rays and gamma-rays, so you have some warning that they
are coming. This gives you time to get into a 'storm shelter', a
well-shielded area that you can live in for a few days until the particles
die down. A good place for a storm shelter would be in the center of the
ship, surrounded by the water tanks. If you don't have a storm shelter
(e.g. if you are out moonwalking in just your suit) a bad solar flare can
kill you by radiation sickness.
The hard radiation (particles and x/gamma rays) from the non-flaring sun is
small compared to the galactic cosmic ray exposure. These particles come
from deep space more or less continuously. Small amounts of shielding can
cut out the majority of this, but the remainder will give you a somewhat
increased risk of cancer. Using very conservative rules of thumb, a week
in space's cosmic ray environment will shorten your life expectancy by
about a day (statistically--it is very unlikely to give you cancer, but if
it does, it will shorten your life by more than a day). Since space is
inherently dangerous at the present state of the art, cancer due to cosmic
rays is relatively small additional risk.
David Palmer
for Ask a High-Energy Astronomer
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