NASA Evaluation Of Radiation Hazard for Manned Mars Trip

More detail with numbers

MARIE data at Wikipedia

Posted due to comments below. In short could be a big issue, but most likely is not. MARIE measured the levels in Mars orbit at a mere 2.5 times that on the ISS. Being on the surface cuts that level in half to being on a par with the ISS. That is based on total energy alone however. Different types of radiation have different health impacts relative to their energy level. This is where the uncertainty comes in. The biological impact of the exact mix at Mars has not been determined.

Some will grab the worst case estimates and call Zubrin unreasonable yet ignore that his numbers are within the range of the minimum to expected risk. Is it reasonable to assume these worst case scenarios are the most likely when that the basic energy level is not even an order of magnitude higher than what would be experienced on the ISS or the Moon for a similar duration? Even at the worst case level multiple mitigation strategies exist.

Regards,
Mark