Why is NASA leaving male astronauts in space longer than female ones?

– Dima Zel / Shutterstock.com

Is space an unequal conquest between men and women? The aviation sector is still very unequal, with only 10% of women entering the astronaut profession. So why do the few women who have succeeded in becoming astronauts stay in space for less time than their male counterparts?

Man or woman, time spent in space should be limited

On Earth, the magnetosphere and then the atmosphere prevent high-intensity wave radiation from damaging human bodies. Excessive exposure to this radiation would actually be harmful to health and could cause diseases such as cancer.

This is not the case on board the International Space Station (ISS), which only benefits from the protection of the magnetosphere. Astronauts are thus exposed to higher levels of ionizing radiation, which increases their risk of developing cancer during their careers.

According to current limits, set by NASA in 1989, the effective dose limit for an astronaut’s career is based on a maximum risk of 3% for life-threatening cancer mortality. This risk is assessed on a sliding scale based on age and gender, ranging from a lower limit of 180 millisieverts (mSv) of radiation for a 30-year-old woman to an upper limit of 700 mSv for a 60-year-old man …

However, NASA’s radiation threshold was lower for female astronauts due to the following findings: when women and men were exposed to high levels of radiation during similar periods, women were more than twice as likely to develop lung cancer than men.

© Alexander Mokletsov / Wikimedia Commons, Valentina Tereshkova, the first woman to travel in space

A constraint that frustrates female astronauts

These limitations have had real consequences for the career. In 2018, former NASA astronaut corps chief Peggy Whitson publicly expressed her frustrations over radiation limits for female astronauts. Surely, the astronaut had to retire after reaching the limit of his career in radiation exposure at the age of 57.

Upcoming changes for astronauts

However, NASA radiation thresholds are expected to change in the near future. In 2021, NASA asked a panel of experts convened by the National Academies of Sciences, Engineering and Medicine to assess the space agency’s plan to change the radiation exposure limit for the increase to 600 mSv for all astronauts of all ages, regardless of gender.

NASA determined this limit by applying the Agency’s cancer risk model to the most vulnerable: early career women. NASA calculated the average exposure-related death risk for this group and converted this risk, which allows for a much larger margin of error than before, into a dose. This dose of 600 mSv is equivalent to the exposure that an astronaut would receive during four six-month expeditions aboard the ISS. By comparison, the average annual radiation dose received by a person on Earth is about 3.6 mSv according to NASA compared to 300 mSv per year in the ISS.

The new limit “would reduce the dose for certain groups of men, especially older men,” said Preston, who was also vice president of the National Academies’ panel of experts on cancer risk assessment for men. “It would mean that women could have an extended career. »

The committee, which published its report in June 2021, was composed of three groups, which analyzed the risk assessment process, ethical issues and the dissemination of new recommendations, respectively.

NASA’s proposed plan includes a deviation from the occupational exposure limit for longer missions, such as a possible trip to Mars, which would expose astronauts to an estimated dose of 900 mSv. However, this dose is likely to be below the 1,000 mSv occupational exposure limits currently imposed on astronauts by European, Canadian and Russian space agencies.

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