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Now that the The Biden administration has expressed support for NASA’s Artemis mission to the moon, perhaps we should consider the risks astronauts face when they get there, and what could happen on a longer trip to Mars.
Of all the things to worry about while traveling in space – faulty equipment, the weird effects of weightlessness, colliding with space debris, and just being far away – one of the hardest to deal with is the health effects of radiation from the sun or cosmic events. This radiation consists of atoms that have lost their electrons as they accelerate in interstellar space and approach the speed of light – something that happens, for example, right after a star explodes. It comes in three forms: particles trapped in the earth’s magnetic field; particles shot into space during solar flares; and galactic cosmic rays, which are high energy protons and heavy ions from outside our solar system.
It is also one of the “red risks” identified by a NASA study published last year on the highest priority health problems facing astronauts. Radiation damages DNA and can lead to mutations that can cause cancer. It can also cause cardiovascular health problems, such as heart damage, narrowing of arteries and blood vessels, and neurological problems that can lead to cognitive impairment, according to a NASA website.
On Earth, people are exposed to 3 to 4 millisieverts (mSv) of radiation per year, mostly from natural sources such as some types of rock and the little cosmic rays that pass through the atmosphere. On the International Space Station, astronauts receive about 300 mSv per year. Until now, a 55-year-old male NASA astronaut was limited to an effective dose of 400 mSv during his career, while a 35-year-old female astronaut could only be exposed to 120 mSv.
With NASA planning to send people on much longer missions, the agency is considering raising that threshold to 600 mSv for astronauts of any gender or age. Under the existing standard, some experienced astronauts may be excluded from longer-term space missions because they are reaching their lifelong radiation limits. Younger astronauts have less flight time in space and therefore less exposure, but the success of a major mission may require experience beyond the youth.
The new limit proposed by NASA would still be lower than that for other space agencies; European, Russian and Canadian astronauts can be exposed to up to 1,000 mSv before being grounded by their space officials. But NASA officials make no apologies for their more conservative stance. “It’s a different risk attitude in what we consider tolerable risk,” said David Francisco, human space standards technical fellow in the office of NASA’s Chief Medical Officer. “We chose 600 because we think it is more acceptable to our culture. It’s something we’re constantly working on and going back and forth. We debated going to 1,000, and that’s one of the questions: Are we still conservative at 600? “
To resolve that question, the space agency asked a panel of experts from the National Academy of Sciences to determine the best number to use. The panel met last month and is expected to complete its work this summer. The experts will look at how NASA calculated its new exposure limits and how they match existing clinical data and animal studies.
To understand the link between radiation and cancer, medical researchers have long been tracking survivors of Japan’s nuclear bombings during World War II (as well as the health of their children). Studies have also been conducted on medical workers exposed to X-rays and nuclear power plant workers who receive low doses of radiation throughout their careers. But NASA doesn’t have much data on the health effects of space radiation on its astronauts.