Space missions subject human beings or any other target of a spacecraft to a radiation environment of an intensity and composition not available on earth. Whereas for missions in low earth orbit (LEO), such as those using the Space Shuttle or Space Station scenario, radiation exposure guidelines have been developed and have been adopted by spacefaring agencies, for exploratory class missions that will take the space travellers outside the protective confines of the geomagnetic field sufficient guidelines for radiation protection are still outstanding. For a piloted Mars mission, the whole...