Overview of energetic particle hazards during prospective manned missions to Mars

A scenario for an initial manned mission to Mars involves transits through the Van Allen Radiation Belts, a 30 day ‘short surface stay’ and a 400 day Cruise Phase (to/from the planet). The contribution to the total dose incurred through transiting the belts is relatively small and manageable. Estimates of the particle radiation hazard incurred during a 30 day stay on the surface (using ESA's Mars Energetic Radiation Environment Models dMEREM and e MEREM) indicate that the dose is not expected to be particularly challenging health-wise due to the shielding effect provided by the Martian atmosphere and the body of the planet. This is in accord with estimations obtained using the Langley HZETRN code. Estimates of GCR exposure in free space during the minimum phase of Solar Cycle 23 determined using the CREME2009 model are in reasonable agreement with published results obtained using HZETRN (which they exceed by about 10%). The Cruise Phase poses a significant radiation problem due to the cumulative effects of isotropic Galactic Cosmic Radiation over 400 days. The occurrence during this period of a large Solar Energetic Particle (SEP) event, especially if it has a hard energy spectrum, could be catastrophic health wise to the crew. Such particle events are rare but they are not currently predictable. An overview of mitigating strategies currently under development to meet the radiation challenge is provided and it is shown that the health problem posed by energetic particle radiation is presently unresolved.

► Energetic particle radiation exposure limits were tested for the Martian surface.
► ESA's MEREM and NASA's HZETRN models showed that these limits are not exceeded over 30d.
► GCR exposure in free space during solar cycle 23(minimum) was estimated using CREME2009.
► The dose incurred over 400d estimated by CREME2009 exceeds that using HZETRN by 10%.
► This dose approaches career limit values for some space personnel.
► A hard spectrum SEP during cruise could be catastrophic. This problem is unresolved.