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Summer/Fall 2008 Vol. 8 No. 2

Table of Contents

Exploring the Final Frontier

The Danger of Deep Space Radiation

In 2004 President Bush proposed an ambitious space exploration plan that envisioned sending astronauts back to the moon and eventually to Mars. Such missions into deep space will involve risks not seen by astronauts in low Earth orbit, in particular increased radiation levels. A recent report from the National Research Council concludes that a better understanding of space radiation and improved protection is needed, or it's unlikely astronauts can make long stays on the moon or travel to Mars anytime soon.

The two main forms of radiation in space are galactic cosmic radiation (GCR) -- background radiation present at all times -- and solar particle events (SPEs), which are short bursts of solar radiation. GCR contains heavy, high-energy particles that penetrate spacecraft. SPEs generally involve low-energy particles that can be blocked using shielding. They can be sudden and intense, however, creating a danger for crewmembers working outside the spacecraft. To protect its astronauts, NASA monitors the amount of radiation to which they are exposed and imposes strict lifetime limits.

In the past, astronauts avoided reaching their radiation limits either by staying within the safety of Earth's atmosphere, which blocks most space radiation, or by keeping the amount of time spent outside Earth's atmosphere short. Longer stays on the moon, or eventual trips to distant destinations like Mars, will mean exposure to more radiation, though. If crews hit their lifetime limits midmission, they'd have to turn around and come home or else risk the possibility of radiation sickness or even cancer.

James van Hoften, a former crew member on Discovery and Challenger who chaired the study committee, encountered space radiation during a spacewalk outside Challenger. "I saw what looked like a white laser line go right through my eyes," he said. "I thought, 'Well this can't be good…having high-energy particles fly through your head.' "

The biological effects of radiation exposure vary and are not entirely understood. Much of what is known comes from the study of accidental occupational radiation exposure, and from atomic bomb survivors, who received massive doses of gamma rays instantaneously. An atomic bomb is very different than what astronauts would experience, although the committee pointed out that, despite years of study, we don't know exactly what to expect in deep space.

Safely pushing the boundaries of human space exploration, said the committee, will require a better understanding of the deep space environment and shielding that can protect against all possible forms of radiation exposure.   -- Rebecca Alvania

Managing Space Radiation Risk in the New Era of Space Exploration. Committee on the Evaluation of Radiation Shielding for Space Exploration, Aeronautics and Space Engineering Board, Division on Engineering and Physical Sciences (2008, 132 pp.; ISBN 0-309-11383-0; available from the National Academies Press, tel. 1-800-624-6242; $33.00 plus $4.50 shipping for single copies).

The committee was chaired by James van Hoften, former senior vice president and partner of the Bechtel Corp., San Francisco. The study was funded by NASA.

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Copyright 2008 by the National Academy of Sciences