News & Analysis Physics World  August 2021

Call for single standard for astronaut radiation risk

Level playing field A report from the US National Academies of Sciences, Engineering and Medicine calls for a single radiation standard for both male and female astronauts. (Courtesy: NASA)

NASA must embrace a single standard of radiation exposure for both male and female astronauts when sending astronauts to the Moon, Mars or for extended stays in outer space. That is according to a new report from the US National Academies of Sciences, Engineering and Medicine (NASEM), which states that having different male and female standards for radiation exposure unnecessarily limits women astronauts’ mission time, which can further widen inequities in space exploration.

The report notes that longer and more distant space travel will expose astronauts to a “complex radiation environment comprised of galactic cosmic rays and solar particle events”. Currently, NASA tailors its overarching 3% risk of exposure-induced death (REID) protective standard to age and gender. For example, the current NASA radiation exposure standard for the International Space Station has a lower limit of about 180 millisieverts (mSv) for a 30-year-old woman and 700 mSv for a 60-year-old man. 

The NASEM report supports NASA’s own proposed shift to a single standard for male and female astronauts that is centred on a 3% REID for cancer of a 35-year-old female, which NASA determined typically as the highest-risk individual. A further change in the standard is that the 3% risk be converted to a “career” dose limit that is equivalent to 600 mSv and that applies to both men and women. While the NASEM report backs the NASA REID changes, it recommends more explanation by NASA about the ethical balancing and considerations for the change. It also calls for NASA to look again at whether 3% is the appropriate REID standard, which dates back to 1989 and was established during the era of travel to low-Earth orbit. 

The report cites current estimates for Mars missions as having 1000 mSv exposure for astronauts – well above the limit – and highlights that higher radiation exposure risk for travel to Mars raises a “waiver” possibility, but emphasizes that any waiver programme must apply only for compelling, fully explained reasons. The report recommends that NASA develops a waiver protocol that is judicious, transparent and informed by ethics, and sticks to ethical considerations so that it is not a blank exception from the radiation standard. 

Jeffrey Kahn, director of Johns Hopkins Berman Institute of Bioethics and a member of the 18-strong committee that wrote the report, told Physics World that the new standard “creates equality of opportunity” for participation in space flight. “The waiver may be appropriate but only with very clear and urgent kinds of justification,” says Kahn. “And the caveat is not because it is too hard to engineer our way to safe space flight.” Kahn points out that the NASEM report builds on a 2014 publication by the Institute of Medicine (now the National Academy of Medicine) that offered an ethical framework for waivers for risky space flight. 

Richard Blaustein