According to the limits set by NASA in 1989, the threshold for an astronaut’s career is based on a lifetime cancer death risk exceeding a maximum of 3%. This risk is assessed using a scoring system based on age and gender.
Every day, Earth is surrounded by ionizing radiation, high-energy waves that can strip electrons from the atoms in our bodies. Exposure to high levels of ionizing radiation can lead to radiation-related illnesses and cancer.
Female astronauts face a higher risk of radiation exposure or cancer if working long-term on the ISS.
Fortunately, the magnetic field and atmosphere of our planet block nearly all of this radiation—generated by the sun and cosmic rays from exploding stars—from reaching life on Earth’s surface.
However, on the International Space Station (ISS), which is protected by the magnetic field but not the atmosphere, astronauts are exposed to higher levels of ionizing radiation, increasing their risk of developing cancer throughout their careers.
Why is there a career limit on radiation exposure for male and female astronauts?
According to R. Julian Preston, a senior government official in the Radiation Protection Division of the U.S. Environmental Protection Agency, NASA’s lower radiation threshold for female astronauts is based on findings that women are at twice the risk of developing lung cancer compared to men.
In 2018, former NASA astronaut chief Peggy Whitson, who publicly expressed her frustration with the radiation limits for female astronauts, had to retire after reaching her career limit for radiation exposure at the age of 57.
However, NASA’s radiation threshold is expected to change in the near future. In 2021, NASA convened a panel of experts from the National Academy of Sciences, Engineering, and Medicine to evaluate the space agency’s plan to raise the occupational radiation limit to 600 mSv for all astronauts, regardless of age.
NASA determined that limit by applying a cancer risk model to the most vulnerable group: newly entered women. The agency calculated the average risk of death from exposure for this group and adjusted that risk, allowing for a much greater margin of error than before.
The 600 mSv limit is equivalent to the exposure an astronaut would receive over four six-month missions on the ISS.
Preston, vice chair of the expert panel from the National Academy assessing cancer risk for crewed space missions, stated: “The new limit will reduce exposure for some groups of men, particularly older men. This means women could have a longer career.”
Preston added: “To achieve equality, women might have higher limits than they currently can, with current exposure levels exceeding the allowable limits. We have discussed this as an ethical issue.”
The proposed NASA plan includes exemptions from occupational exposure limits for longer missions, such as a final trip to Mars, which would expose astronauts to an estimated 900 mSv. However, that limit is likely lower than the 1,000 mSv occupational exposure limit that European, Canadian, and Russian space agencies currently set for their astronauts.
