Frank Cucinotta, a professor of health physics and diagnostic sciences, has been fascinated with space and space travel since he was a kid. And when he began his work with the National Aeronautics and Space Administration (NASA), that fascination morphed into studying how radiation in space, or cosmic radiation, affects astronauts.

All living things on the planet are protected from the intense radiation of space by a thick layer of shielding provided by the Earth's atmosphere, which is equal to 10 meters of water. Radiation does get through to the surface of the planet, but at significantly lower levels than people would be exposed to in space.

Outside that protective layer, the cosmic radiation is intense and the biological damage produced by cosmic rays may be alien to the body's natural defense mechanisms. One estimate is that a single day in space is equivalent to a year's worth of natural radiation on Earth. And the effect is cumulative -- it doesn't dissipate when the astronauts return home.

Cucinotta studies the biological risks of exposure and evaluates what constitutes a safe duration in space. Cosmic radiation increases the risks for cancers, and seems to produce more lethal tumors than other types of radiation. It also seems to increase the risks for heart disease and cognitive conditions such as loss of memory and dementia.

"To provide the level of protection we all receive from Earth's atmosphere would require surrounding astronauts in hundreds of centimeters of material, which is impractical," Cucinotta said. "Ships and suits typically have 10 to 20 centimeters of protection. To better protect these men and women, we have to accurately determine the risks of radiation exposure when they are in space. This will lead to methods for identifying individuals who have lower risks, and to the discovery of biological approaches that can protect them."

To calculate the exposure risks, or the chance that a person will be diagnosed with cancer, Cucinotta and others studying cosmic radiation examine and develop theoretical models. Tests are then conducted on human cells and mice to validate their hypotheses.

Typical missions to the International Space Station lasted about six months. When NASA retired its space shuttle program, Russia provided the crafts to deliver astronauts to the station. Now, with fewer available crafts and relations straining between the United States and Russia, missions lasting for a year or longer are planned.

The current acceptable risk for fatal cancer among astronauts on the space station is no more than a 3 percent probability of death, and the maximum duration of space missions to stay within this limit is about 18 months. However, the trend toward longer missions, coupled with greater exposure, could reduce the length and number of missions in which an astronaut can participate.

And then there's Mars. While at NASA, Cucinotta and his team also explored the potential for a manned mission to Mars. The cosmic radiation exposure during a voyage to the Red Planet is much higher than that on the space station. The estimated fatal risks for cancer and other diseases during that mission could be as high as 20 percent.

"A trip to Mars will take approximately 1,000 days using current technology," Cucinotta said. "Based on theoretical models, the cosmic radiation during that mission could also impact the crew's cognitive abilities or cause them not to remember the journey after they safely returned to Earth. And once back on Earth, the types of cancers, according to studies conducted on mice, will be more aggressive and likely to occur at much younger ages, compared to the cancers found on our planet."

As Cucinotta continues to uncover the actual risks of cosmic radiation, and the means for protecting astronauts, his work also determines safe limits for man-made radiation, especially from medical equipment like computed tomography (CT) scans.

"Most people don't understand radiation. My colleagues and I are working to teach them about it, and protect them from it."