RADIATION EXPOSURE IN MANNED SPACEFLIGHT

Space missions expose humans to a radiation environment of a particula te composition and intensity not encountered within our biosphere. The natural radiation environment encountered in Earth orbit is a complex mixture of charged particles of galactic and solar origin and of thos e trapped by the geomagnetic field. In addition, secondaries are produ ced by interaction of cosmic ray primaries with the spacecraft shieldi ng material. Among this large variety of radiation components in space , it is likely that the heavy ions are the significant species as far as radiobiological effects are concerned In addition, a synergistic in teraction of microgravity and radiation on living systems has been rep orted in some instances. Based on an admissible risk of 3 % mortality due to cancers induced during a working career, radiation protection g uidelines have been developed for this radiation environment.