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

Ionizing radiation, high-energy waves, can remove electrons from atoms in the body. Ionizing-radiation exposure can cause radiation sickness and cancer.

Our planet's atmosphere and magnetosphere prevent most of the radiation from reaching Earth's surface. The International Space Station, which is protected by the magnetosphere but not the atmosphere, increases the risk of cancer for astronauts because they are exposed to higher levels of ionizing radiation.

The maximum lifetime excess risk of cancer mortality is the basis for the current limits set by NASA. A 30-year-old woman with a career limit of 180 mSv of radiation is at a lower risk than a 60-year-old man with a career limit of 700 mSv.

There is a lower career limit for female astronauts than for male astronauts.

NASA had a lower radiation threshold for female astronauts based on the finding that women and men were exposed to the same amount of radiation.

The shadows of people were left on sidewalks by the atomic bomb dropped on Hiroshima.

It has been generally considered that women are more sensitive to ionizing radiation than men because of the survivors from the atomic bombs in Japan.

The guidelines have had career consequences. The former chief of NASA's astronaut corps, who had publicly voiced her frustration with the radiation limits for female astronauts, had to retire after hitting her career limit on radiation exposure at age 57.

NASA's radiation thresholds are expected to change in the near future. NASA asked the National Academies of Sciences, Engineering and Medicine to assess the space agency's plan to change its career radiation limit to 600 mSv for all astronauts of all ages. Early-career women are the most susceptible to cancer, and NASA determined that limit by applying the agency's cancer risk model to them. NASA calculated the average risk for this group and converted it to a dose, which allows for a larger margin of error. The 600-mSv dose is equivalent to four months of exposure for an astronauts. The average annual dose of radiation received by a person on Earth is 3.6 mSv, according to NASA.

The new limit would reduce the dose for some groups of males, particularly older males.

The committee analyzed the risk assessment process, ethical issues and communication of the new recommendations in its report, which was published in June 2021.

We discussed that as an ethical issue. It is a question of balancing the impact of that slightly higher dose on the career opportunity of the person. We proposed that NASA could do that.

The career exposure limit for astronauts is 900 mSv, but NASA wants to allow them to go to Mars. European, Canadian and Russian space agencies have career exposure limits for their astronauts.

If NASA decided that this is a critical mission, and there are certain astronauts who are critical to that mission who would exceed their career exposure, NASA could apply a waiver to that.

It was originally published on Live Science.