Why NASA's women astronauts cannot fly as much as men

"Cancer-causing space radiation is to blame.

LIKE EARTH, space has struggled with equality. When Wally Funk finally made the journey into space aboard Jeff Bezos's New Shepard flight it was a milestone for female astronauts. As a young aviator she had excelled in her tests as part of the privately funded Women in Space programme. But, despite the competence of the programme's participants, in 1961 the scheme was cancelled. Ms Funk's voyage this year was the first time that any of the Mercury 13, as they have since been dubbed, have made it into space. In all 67 women have become astronauts. But they face some unique problems. Why can't female NASA astronauts fly as much as their male counterparts?

Earth's atmosphere is constantly being bombarded with charged particles, mainly from the Sun and galactic cosmic rays (heavy, high-energy ions stripped of their electrons as they travel across solar systems at close to the speed of light). But Earth has a magnetic field that stretches to around 65,000km above its surface on the side facing the Sun, and much farther than that on the other side. This acts as a shield against the harmful rays. Beyond it astronauts are exposed to high levels of ionising radiation. This raises the risk of cancer, cardiovascular disease and cognitive impairment caused by damage to the nervous system.

Studying the effect of space radiation is hard. NASA has largely based its models on a study that has periodically tracked survivors of the atomic bombs dropped on Japan during the second world war. This research found women to be at a higher risk of developing cancer than men when exposed to radiation, partly because they live longer and are more likely to suffer certain cancers, such as those of the breast and thyroid. To limit these dangers NASA imposes a career limit for radiation exposure. This is supposed to keep the chance of developing radiation-induced fatal cancer to just 3% above that of non-astronauts. This means a 30-year-old female would be limited to exposure equivalent to 180 millisieverts (mSv), compared to a 55-year-old male whose limit would be 400 mSv. (The average American is exposed to around 3 mSv a year.) Astronauts taking a 180-day trip to the International Space Station would face exposure of between 50-120 mSv. Peggy Whitson, a former chief of NASA's astronaut corps, has said that this ceiling means a female can fly only 45-50% of the number of missions that a male can." [1]

1. "Why NASA's women astronauts cannot fly as much as men; The Economist explains." The Economist, 9 Aug. 2021, p. NA.