Report Explores Proposed Updates to NASA’s Radiation Exposure Limits

The National Aeronautics and Space Administration (NASA) should proceed with proposed approaches to revise its space radiation health standard and improve its strategies for communicating cancer risks to astronauts, an ad hoc committee of the National Academies of Sciences, Engineering, and Medicine concludes in a new report. NASA’s health standard sets the allowable limit of space radiation exposure throughout the course of an astronaut's career. The current standard is for low Earth orbit missions only and sets astronauts’ career exposure to ionizing radiation to not exceed three percent risk of exposure-induced death (REID) for cancer mortality at a 95 percent confidence level.

“This means that a male astronaut’s career radiation exposure limit would be reached with a 211-day mission to the International Space Station (ISS), whereas a female astronaut’s exposure limit would limit her to a 43-day mission to the ISS,” a document summarizing highlights of the consensus study report (PDF) explains.

NASA has proposed an updated space radiation health standard conveyed as a dose-based limit for radiation exposure during spaceflight over the course of an astronaut’s career. According to the National Academies, the updated standard is needed for upcoming missions of longer duration extending to greater distances in the solar system. NASA’s proposed limit is approximately 600 millisieverts to be applied universally among astronauts of all ages and sexes. The proposed limit was determined “by applying NASA’s cancer risk model to the most susceptible individual (i.e., a 35-year-old female) to calculate the mean REID, which was then converted to an effective-dose value.” The National Academies committee supports NASA’s proposal to apply a single, dose-based standard to all astronauts using the most protective approach but recommends that the administration reexamine whether a three-percent REID is the best metric to use moving forward.

The National Academies report also outlines recommendations for NASA’s radiation risk communication strategies. The committee urges NASA to provide all astronauts with an individual radiation risk assessment and “communicate a comprehensive picture of an astronaut’s own cancer risk, including an explanation of the uncertainty associated with the risk calculation.” And for long-duration spaceflight missions that would likely expose astronauts to radiation levels significantly exceeding the new limit proposed by NASA, the report describes a process by which the administration should develop a protocol for waiver of the space radiation standard that is “judicious, transparent, and informed by ethics.”

The full report, Space Radiation and Astronaut Health: Managing and Communicating Cancer Risks, is available from the National Academies website.