Jeremy Hansen has spent years preparing for the moment he will leave Earth behind—and become one of the first astronauts in more than 50 years to venture beyond low-Earth orbit. In case of mishaps in deep space, Hansen has simulated countless spacecraft accidents. To practice teamwork in a harsh environment, he lived for a week deep underground in an Italian cave. And to rehearse the mental strain of life in close confinement, he spent days submerged in a capsule off the coast of Florida.
But there is one hazard Hansen can’t prepare for: space radiation. With the planned launch next month of NASA’s Artemis II mission—the first crewed spaceflight to leave Earth’s protective magnetic cocoon since the Apollo 17 mission of 1972—he will expose himself to a barrage of atomic shrapnel.
Riding within the Orion capsule on top of a rocket called the Space Launch System, Hansen and three other astronauts will first plunge through the Van Allen belts: clouds of electrons and protons trapped near Earth. Farther out, beyond Earth’s magnetosphere, they will face the risk of solar storms that can push particle radiation to potentially lethal levels in a matter of hours. They will also be battered by a sparse but steady background of higher energy particles that pack the biggest biological punch of all. Born in supernova blasts and other violent astrophysical events, these galactic cosmic rays—a mix of protons and the nuclei of heavier elements—move at near–light-speed and can tear through the body’s tissues, shredding strands of DNA and creating “free radical” ions that cause biochemical chaos.
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