Space radiation measurements during the Artemis I lunar mission

Space radiation is a notable hazard for long-duration human spaceflight¹. Associated risks include cancer, cataracts, degenerative diseases² and tissue reactions from large, acute exposures³. Space radiation originates from diverse sources, including galactic cosmic rays⁴, trapped-particle (Van Allen) belts⁵ and solar-particle events⁶. Previous radiation data are from the International Space Station and the Space Shuttle in low-Earth orbit protected by heavy shielding and Earth's magnetic field^7,8 and lightly shielded interplanetary robotic probes such as Mars Science Laboratory and Lunar Reconnaissance Orbiter^9,10. Limited data from the Apollo missions^11-13 and ground measurements with substantial caveats are also available¹⁴. Here we report radiation measurements from the heavily shielded Orion spacecraft on the uncrewed Artemis I lunar mission. At differing shielding locations inside the vehicle, a fourfold difference in dose rates was observed during proton-belt passes that are similar to large, reference solar-particle events. Interplanetary cosmic-ray dose equivalent rates in Orion were as much as 60% lower than previous observations⁹. Furthermore, a change in orientation of the spacecraft during the proton-belt transit resulted in a reduction of radiation dose rates of around 50%. These measurements validate the Orion for future crewed exploration and inform future human spaceflight mission design.