CAPE CANAVERAL, Florida (Reuters) -- Experts in the effects of space travel on the human body told a presidential commission on Wednesday that there were challenges but no "showstoppers" in building a permanent moon base, then sending astronauts to Mars.

Aerospace medical experts Stanley Mohler and Mary Ann Frey, both longtime researchers in the field, identified a number of health risks future astronauts could face, from radiation poisoning to meteoroid collisions, but said NASA was developing plans for every known contingency.

"From the medical standpoint, there is further research to be done, but we don't see any showstoppers out there," Mohler told the President's Commission on Moon, Mars and Beyond.

The commission, chaired by former Air Force Secretary Edward "Pete" Aldredge, is charged with developing strategies for implementing the space goals announced by President George W. Bush in January.

"It should be a relatively straightforward program of establishing 90-day (crew) rotations on a colony on the moon," Mohler told the panel in hearings at Wright-Patterson Air Force Base in Ohio.

Radiation, whether from solar flares or cosmic rays, was the highest hurdle identified by the scientists.

While the moon has plenty of lunar soil to shield habitation modules, a Mars mission, which could last 15 months, most of that time in transit, presents special problems.