Impact of rocket propulsion technology on the radiation risk in missions to Mars

Exposure to cosmic radiation is today acknowledged as a major obstacle to human missions to Mars. In fact, in addition to the poor knowledge on the late effects of heavy ions in the cosmic rays, simple countermeasures are apparently not available. Shielding is indeed very problematic in space, because of mass problems and the high-energy of the cosmic rays, and radio-protective drugs or dietary supplements are not effective. However, the simplest countermeasure for reducing radiation risk is to shorten the duration time, particularly the transit time to Mars, where the dose rate is higher than on the planet surface. Here we show that using nuclear electric propulsion (NEP) rockets, the transit time could be substantially reduced to a point where radiation risk could be considered acceptable even with the current uncertainty on late effects.