Measurements with the MSL Radiation Assessment Detector (RAD) on NASA's Curiosity Mars rover during the flight to Mars and now on the surface of Mars enable an estimate of the radiation astronauts would be exposed to on an expedition to Mars. NASA reference missions reckon with durations of 180 days for the trip to Mars, a 500-day stay on Mars, and another 180-day trip back to Earth. RAD measurements inside shielding provided by the spacecraft show that such a mission would result in a radiation exposure of about 1 sievert, with roughly equal contributions from the three stages of the expedition. A Sievert is a measurement unit of radiation exposure to biological tissue. This graphic shows the estimated amounts for humans on a Mars mission and amounts for some other activities.
Image credit: NASA/JPL-Caltech/SwRI
Note: For more information, see PIA17600: Radiation Measurements on Mars.