When NASA's Curiosity rover made its 253-day journey to Mars, it carried the Radiation Assessment Detector, or RAD. What it measured gave mission planners both useful data and serious cause for thought.
The Numbers
During transit, RAD measured an average dose rate of approximately 1.84 millisieverts per day. Over a 180-day one-way journey, that accumulates to roughly 330 mSv. On the Martian surface, the thin atmosphere reduces the dose rate to approximately 0.67 mSv per day. A complete round trip totals approximately 1 sievert — associated with a roughly 5% increase in lifetime fatal cancer risk.
The Solar Maximum Paradox
Counterintuitively, the safest time to travel to Mars may be during solar maximum. The enhanced solar wind sweeps away galactic cosmic rays from the inner solar system. A well-timed mission could cut total radiation exposure nearly in half — though solar flares require a dedicated radiation storm shelter aboard the transit vehicle.
Countermeasures
Polyethylene shielding, water walls around sleeping quarters, underground habitats on the surface, and pharmaceutical countermeasures in development can all reduce exposure. No single solution is complete, but in combination they make the exposure manageable — a serious engineering challenge, but not a mission showstopper.
