Health threat from cosmic rays

The health threat from cosmic rays (termed space radiation by NASA in this context) is the danger posed by cosmic rays generated by the Sun and other stars to astronauts on interplanetary missions. Space radiation consists of high energy protons, iron nuclei, and other cosmic elements.

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The Earth's surface is protected from space radiation by the bulk of air above it. Human space missions in orbit around the Earth are protected by the planet's magnetic field. The amount of radiation in interplanetary space is estimated at 80 rems per year, while it is only 0.03 rem per year on the Earth's surface.

Space radiation is considered a potential hindrance for future manned missions to Mars: it can break down chemical bonds in DNA and other biological molecules, causing cancer, cataracts, and brain damage. NASA set up the Space Radiation Shielding Program to study the problem and investigate possible solutions.

Several experiments, both in space and on Earth, are being carried out to evaluate the exact degree of danger. The Mars Radiation Environment Experiment (MARIE) was launched in 2001 in order to measure the magnitude of the radiation. Experiments at Brookhaven National Laboratory's Booster accelerator revealed that the danger is actually about half what was previously estimated: specifically, it turns out that low energy protons cause more damage than high energy ones. This is explained by the fact that slower particles have more time to interact with molecules in the body. Therefore, very high energy particles seem to pose a lesser threat than previously thought.

Three main mechanisms have been proposed to shield a space vehicle from cosmic rays: a thick shell of material (water or ethylene) to provide protection similar to that of the Earth's atmosphere, a huge magnetic field to deflect incoming ions, or a powerful electrostatic field to repel positively charged particles. None of these ideas are feasible with modern-day technology: the water shell would be too heavy to be lifted into space; the magnetic field would have to be so intense as to represent a health risk itself; the electrostatic shield would attract enormous amounts of electrons produced by the sun, causing a problem very similar to the one it is supposed to solve.

Another line of research is the development of drugs that mimic and/or enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are retinoids, which are vitamins with antioxidant properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.

References

• Eugene N. Parker, Shielding Space Travellers, Scientific American, March 2006.
• John Dudley Miller, Radiation Redux, Scientific American, November 2007.

See also

• Space weather