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.
Oddly, the higher energy radiation also triggered premature graying in the mice, compared to mice exposed to gamma rays. Researchers plan follow-up studies to compare genetic and chromosomal changes from the two types of radiation.
In related developments, researchers report progress in developing countermeasures for lower-energy radiation damage. The findings have implications for the treatment of cancer.
University of California-Irvine researchers, for example, discussed a protocol involving a cancer-fighting agent called DFMO and a low dose of an anti-inflammatory drug that reduced the risk of reoccurring colorectal polyps, an early sign of colon cancer, by as much as 95 percent with fewer toxic side effects.
Colon cancer is the third leading cause of cancer in men and fourth in women in the United States.
Fornace said his team focused on colon cancer risks from spaceflight because the disease is already so prevalent in our society that even a slightly elevated risk from radiation exposure could be significant.
In finding ways to fight cancer, it is important to understand on a molecular level how different types of radiation damage the body.
For example, some compounds show promise in combating damage from conventional radiation but might actually promote malignant cell growth in tissues damaged by high-energy cosmic rays. That's because conventional radiation, like gamma rays or X-rays break down bonds in DNA, the cell's blueprint for reproduction, allowing for interaction with water, which produces free radicals.
Cosmic rays behave more like bullets that blast through cells or tissue, creating tracks, as well as surrounding penumbras around the holes that resemble damage from conventional radiation. Medicines and protocols to aid cell healing, such as what would be attempted to repair conventional radiation damage, might also then keep mutated cells alive, triggering tumors, Vazquez said.
"One of the main focuses of NASA's program is to attack this problem at different angles," he said.
In addition to biological studies, the U.S. space agency is flying instruments on its upcoming Lunar Reconnaissance Orbiter mission to the moon as well as the next Mars rover, slated for launch in 2009, to assess the radiation risks.
NASA plans to land astronauts on the moon by 2020. The agency is retiring the shuttle fleet in two years and intends to shift the country's human exploration program beyond the space station, which orbits about 200 miles above the planet, to the moon and beyond.
"The big issue is the uncertainty of radiation risks," Fornace said. "We know about Earth-type radiation. What we don't know is what happens in space."
Related Links:
Irene Klotz's blog: Free Space
National Space Biomedical Research Institute