Although meant to minimize risks to human health, the proposed new limits would still be exceeded by...
To address the situation, at NASA's request, a team of top scientists organized by the National Academies of Sciences, Engineering, and Medicine published a report in June recommending that the space agency adopt a maximum career-long limit of 600 millisieverts for the space radiation astronauts can receive.
The sievert is a unit that measures the amount of radiation absorbed by a person-while accounting for the type of radiation and its impact on particular organs and tissues in the body-and is equivalent to one joule of energy per kilogram of mass.
"Everybody is planning trips to the moon and Mars," and these missions could have high radiation exposures, says Hedvig Hricak, lead author of the report and a radiologist at Memorial Sloan Kettering Cancer Center in New York City.
NASA's current space radiation limit, which was developed in 2014, involves a complicated risk assessment for cancer mortality that depends on age and sex, yet more relevant data are necessary, Hricak argues.
NASA wants to update its standards now because the agency is on the cusp of sending so many astronauts well beyond low-Earth orbit, where greater amounts of space radiation seem destined to exceed previously mandated exposure limits.
The new radiation limit proposed by Hricak and her team is linked to the risks to all organs of a 35-year-old woman-a demographic deemed most vulnerable in light of gender differences in the atomic bomb survivor data and the fact that younger people have higher radiation risks, partly because they have more time for cancers to develop.
The goal of the radiation maximum is to keep an individual below a 3 percent risk of cancer mortality: in other words, with this radiation limit, at most three out of 100 astronauts would be expected to die of radiation-induced cancer in their lifetime.
"For a mission to Mars, a 35-year-old woman right at that limit could have an over 10 percent chance of dying in 15 to 20 years. To me, this is like playing Russian roulette with the crew," says Francis Cucinotta, a physicist at the University of Nevada, Las Vegas, and former radiation health officer at NASA. Despite the supposed benefits the new limits would have for female astronauts, he is concerned that the risks are particularly pronounced for younger women in space.
Unlike someone in the vicinity of a nuclear explosion, the risk to an astronaut exposed to space radiation is long-term rather than immediate.
In any case, considering how little is known about various health risks from different kinds of space radiation, compared with radiation we are familiar with on Earth, researchers will surely continue with more studies like these to protect astronauts as much as possible.