Cosmic Rays Pose Huge Hurdle for Spaceflight

April 15, 2008 -- James "Ox" van Hoften was on his first space shuttle mission in 1984 when he saw what looked like a white laser shoot through his eyes.

"What the heck was that," he yelled out to his crew mate, George "Pinky" Nelson, who happened to be a space physicist.

"Oh, that's just a cosmic ray," van Hoften recalled Nelson as saying.

"The thought of extremely high-energy particles originating from a distant cosmic event passing easily through the space shuttle and subsequently through my head made me think that this cannot be all that healthy," van Hoften wrote in an upcoming National Research Council report on space radiation. "The truth of the matter is that it is not."

As NASA prepares to leave the relative safety of low-Earth orbit, radiation exposure is emerging as the single biggest technological problem to overcome before humans can safely attempt interplanetary travel.

"In free space, radiation comes from all directions," said Marcelo Vazquez, a space radiation expert working with the Houston-based National Space Biomedical Research Institute. "If you are on the surface of the moon, you are shielded by the planetary body, which reduces the exposure, but there is a chronic, low dose."

"It will be different to go to Mars because there is more exposure to cosmic rays," he added. "No matter what shielding you have, it will not make the cut alone. At the end of the day when we go to Mars it will be a combination of shielding, medical countermeasures and operational countermeasures."

The first step in solving the problem is understanding how radiation damages the body on a molecular level.

On Tuesday, researchers unveiled preliminary results of one of the first studies comparing damage from highly energetic heavy particles like iron with more conventional radiation exposure from gamma rays that astronauts -- and the non-space-traveling public -- are exposed to.

The studies, which were conducted on mice at NASA's Space Radiation Laboratory at Brookhaven National Laboratory, suggest that astronauts may be at increased risk of colon cancer due to the high-energy radiation found in space.

In an interview with Discovery News, Albert Fornace, chairman of molecular cancer research at Georgetown University's Lombardi Comprehensive Cancer Center, noted that while the two types of radiation did not yield an immediate difference in the number of animals who developed cancerous tumors, the mice exposed to the beams resembling cosmic rays showed increased and long-lasting inflammation in their intestines.

"When we looked at intestinal cells 30 and 60 days after exposure, we see evidence of cell stress that were not seen in similar doses of gamma rays," Fornace said. "Overall, we found that the (high-energy) radiation was somewhat more toxic, but not as much as people had expected."

That could change over time. The findings are based on the first year of a planned four-year study.

"We really won't know for one or two more years," he added.