Estimates of Maximum Solar Particle Event Proton Fluences That Do Not Exceed Permissible Radiation Exposure Limits

Human exposure to solar particle event radiation on deep space missions is a serious concern for mission planners and space crews. Numerous studies of potential exposures to crews from large events that have occurred during the space era have been made. In addition, recent studies have attempted to asses possible exposures from extremely large historical events that have occurred prior to the modern spaceflight era. In this work we investigate maximum proton fluence levels for different energy spectral distributions that would not exceed permissible exposure limits for effective dose or any organ dose. The spectral distributions selected for analyses are representative of two extreme events that have occurred during the past six decades, February 1956 and November 1960. The calculations use the HZETRN 2010 transport code, developed at NASA Langley Research Center to transport incident protons through various aluminum shield thicknesses and body self-shielding, for different mission scenarios, including transits to Mars, and surface operations on the surfaces of Mars and Earth’s moon.