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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 an Astrophysicist

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