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Cosmic Rays and Space Travel

I don't know if I was misinformed, or misinterpreted something, or whether it was nothing more than watching unscientific science fiction, but I've thought for some time now that we had solved the cosmic ray problem -- extended exposure to dangerous radiation faced by astronauts who venture outside the protection of Earth's atmosphere. As it turns out, I was wrong. From "Shielding Space Travelers" (fee required) in this month's issue of Scientific American:

Outside the atmosphere, the cosmic-ray bombardment is intense... A week or a month of this radiation should not have serious consequences, but a couple of years on a jaunt to Mars is a different story. One estimate from NASA is that about one third of the DNA is an astronaut's body would be cut by cosmic rays every year...

In a report published last August, [Wallace Friedberg of the Federal Aviation Administration's Civil Aerospace Medical Institute in Oklahoma City and his colleagues] estimated that Mars astronauts would receive a dose of more than 80 rems a year. By comparison, the legal dose limit for nuclear power plant workers in the U.S. is five rems a year. One in 10 male astronauts would eventually die from cancer, and one in six women (because of their greater vulnerability to breast cancer). What is more, the heavy nuclei could cause cataracts and brain damage.

The author describes three options for protecting against cosmic rays: material shields, magnetic shields, and electrostatic shields. Problems with the latter two would seem to make them impractical, leaving material shielding. A water shield would have to be five meters deep, meaning that a spherical water tank encasing a small capsule would weigh 500 tons -- in comparison to the space shuttle's lift capacity of 30 tons.


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