Large Radiation Dose for Mars Astronauts

There are a whole list of risks involved in a manned trip to Mars and back, but I've always considered that prolonged exposure to cosmic radiation could be the proverbial 'show stopper.' This article from NewScientist gives a good overview.

There are potential work-arounds to this issue. Instead of taking 375 days to get from Earth to Mars, engineers at Ad Astra are working on the VASIMR ion engine that could get you there in 39 days. Testing will be done in the next year or so in earth orbit.

So if the VASIMR ion engine pans out, the radiation exposure issue may be manageable. There are still lots of other hurtles though.