Why does NASA let male astronauts stay in space longer than females?

Every day, Earth is besieged by ionizing radiation, high-energy waves that can remove electrons from atoms in the body. High levels of ionizing-radiation exposure can lead to radiation sickness and cancer. 

Fortunately, our planet’s magnetosphere and atmosphere prevent almost all of this radiation — generated by the sun and galactic cosmic rays from exploding stars — from reaching life on Earth’s surface. But up on the International Space Station (ISS), which is still protected by the magnetosphere but not the atmosphere, astronauts are exposed to higher levels of ionizing radiation, which increases their risk of developing cancer over the course of their careers.

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