Radiation on the way to Mars A study published in the journal Science in May 2013 calculates 662 +/ 108 millisieverts (mSv) of radiation exposure for a 360 day return trip, as measured by the Radiation Assessment Detector (RAD). The study shows that ninety five percent of the radiation received by the RAD instrument came from Galactic Cosmic Rays or GCRs, which are hard to shield against without use of prohibitive shielding mass (1). The 210-day journey Mars One settlers will take, amounts to radiation exposure of 386 +/- 63 mSv, considering these recent measurements as standard. This exposure is below the upper limits of accepted standards for an astronaut career: European Space Agency, Russian Space Agency and Canadian Space Agency limit is 1000 mSv; NASA limits are between 600-1200mSv, depending on sex and age (1)