ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Friday, December 20, 1996 TAG: 9612200009
SECTION: NATIONAL/INTERNATIONAL PAGE: A-7 EDITION: METRO
DATELINE: WASHINGTON
SOURCE: Associated Press|
NASA needs to do a great deal more research on protecting astronauts against dangerous cosmic rays if it is to send human beings where nobody has gone before, a new study finds.
A report by a committee of the National Research Council finds that NASA knows too little about the health effects of long-term exposure to space radiation and how best to build spacecraft that would shield astronauts during a years-long mission to Mars or other planets.
``They simply don't understand the effect of galactic cosmic rays on humans,'' said Richard Setlow of the Brookhaven National Laboratory. ``There are tremendous uncertainties.''
Space outside of the Earth's magnetosphere, which naturally shields the planet, is filled with energetic particles from deep space and from the sun. These microscopic particles zap through the body, damaging DNA and perhaps disrupting nerve cells in the brain.
But exactly how great the dangers are is not known, said Setlow, who was chairman of the National Research Council committee.
``We know these particles can kill cells, can mutate cells and, from preliminary experiments, it appears they can cause cancer in animals,'' Setlow said. ``It would not be a killer in a short term,'' but the long-term effects on human health are unknown.
Also, unknown, he said, is how a long exposure to space radiation would affect brain cells. Neurons could be disrupted, perhaps affecting the thought processes and memory, after months and months of exposure, Setlow said.
There's no question that astronauts on the way to Mars would be zapped millions of times by cosmic and solar rays, he said.
``The number of particles over a long mission is great enough that on the average every cell in the body is traversed (struck by a particle),'' Setlow said.
Spacecraft can be built with shielding against radiation, but Setlow said it is not clear how this can best be done, nor how much radiation a spacecraft is likely to encounter.
``In the absence of precise data and calculations, the shielding would have to protect crew members against the higher, but uncertain, estimated risk,'' the report said. Such shielding could add as much as $30billion to the cost of a mission, the study shows.
Some materials that would break up the speeding particles could actually aggravate the problem.
``When these heavy, high-energy particles hit shielding, they go splat and make a whole bunch of secondary particles,'' Setlow said. ``The problem is not just protecting against the heavy particles, but also against the cascade of small particles'' caused by the impact.
Lead makes a poor shield against the radiation because of the secondary particle problem, he said. Hydrogen would make the best material for shielding, but Setlow said it is impractical. An alternative may be some shielding material that is mixed with hydrogen.
Because shielding adds weight to a spacecraft, NASA keeps the shielding material to a minimum safe level. But to do this, the agency must have a precise idea of the health effects so that it can determine the minimum safe level.
LENGTH: Medium: 65 linesby CNB