Radiation levels on the International Space Station are as high as they were on the antiquated Russian space station Mir, in spite of NASA’s attempts to clad the ISS with better shielding. If NASA can’t protect astronauts, its vision of sending a crew into deep space may come to nothing. Data collected by NASA and a Russian-Austrian collaboration show that astronauts on the ISS are subjected to about 1 millisievert of radiation per day, about the same as someone would get from natural sources on Earth in a whole year. Spending three months in these conditions translates into about one-tenth the long-term cancer risk incurred by regular smokers.