Innumberable dangers threaten human astronauts traveling into deep space. Some of these, like asteroids, are obvious and avoidable with some decent LIDAR. Others aren’t. At the top of the not-so-much list is space radiation, something NASA is in now way prepared to protect explorers from while ferrying them to Mars. The radiation environment beyond the magnetosphere is not conducive to life, meaning sending astronauts out there without protection is equivalent to sending them to their doom.
While we’ve sent astronauts into space for over half a century now, the vast majority of these missions have been limited to traveling into low Earth orbit — between 99 and 1,200 miles in altitude. The Earth’s magnetic field — which extends thousands of miles into space — protects the planet from being hit head-on by high-energy solar particles traveling over one million miles per hour.
There are three big sources of space radiation, and they all pose a certain amount of risk that can’t always be anticipated or protected against. The first is trapped radiation. Some particles don’t get deflected by the Earth’s magnetic field. Instead, they’re trapped in one of the big two magnetic rings surrounding the Earth, and accumulate together as part of the Van Allen radiation belts. NASA has only had to contend with the Van Allen belts during the Apollo missions.
The second source is galactic cosmic radiation, or GCR, which originates from outside the solar system. These ionized atoms travel at basically the speed of light, although Earth’s magnetic field is also able to protect the planet and objects in low Earth orbit from GCR.
The last source is from solar particle events, which are huge injections energetic particles produced by the sun. There’s a distinction between the solar winds normally emitted by the sun, which take about a day to get to the Earth, and these higher-intensity events that hit us within 10 minutes. Besides producing a potentially lethal amount of radiation for astronauts, SPE can sometimes be wildly unpredictable, making it difficult for NASA scientists and engineers to develop protective measures against them.
NASA examines space radiation the way employers determine acceptable risks for their employees — they will not subject astronauts to an occupational risk of developing cancer beyond a certain threshold. To develop this assessment, NASA looks into a bunch of different factors, from where a crew will go, how far from the sun they will be, what the solar cycle will look like during that time to what kind of a ship and shielding they’re working with. A team of biologists studies what the physiological effects might be on any given trip and uses computer models to spit out occupational risk assessments.
For NASA, acceptable risk means a three percent excess lifetime risk of cancer.
But mitigating cancer risk isn’t the only issue. The most common problem is nausea — not so bad if you’re in a spacecraft with barf bags close by, but pretty dangerous if you’re out on a space walk and all you have is a space suit to catch your vomit. One’s immune system might also take a hit for a few days or weeks, and catching an infection out there in the dead of everything is no bueno.
Right now, the biggest thing we have for protecting astronauts from space radiation — particularly GCR — is material shielding. This works fairly well, but we don’t know how thick the shielding needs to be on a Mars-bound ship. Too thick, and it’s cost prohibitive to get the ship out into space, let alone into the stratosphere. Too thin and the crew suffers. In fact, thin shields could actually result in an increased amount of secondary radiation. That’s why aluminum has been the material of choice — it’s robust enough to break cosmic ray particles apart, but light enough for spacecraft to travel efficiently with.
But NASA has sent astronauts to the moon and back — through the Van Allen belts, no less — and nobody died. Doesn’t that mean we’ve already got the whole cosmic ray thing figured out?
Not quite. The effects of space radiation are dependent on exposure — the longer you’re out in space, the more you’re at risk. The Apollo missions took about three days to get to the moon. The crew for Apollo 11 was back home eight days after liftoff. The timeframe for Mars missions is on a scale of years. “There are two different classes of Mars missions,” says Gregory Nelson, a researcher at Loma Linda University who specializes in the physiological effects of space radiation. “One of those will get to there faster so you can stay longer on the Mars surface. I think that’s 500 days and you come back quickly. In the other version, you’re gone for like 900-some days.” Nelson says a crew going to Mars would probably be exposed to about one gray of radiation — over 277 times the dose of normal year’s worth of radiation exposure on Earth.
The risks of developing cancer or being exposed to a lethal amount of radiation rises exponentially in that timeframe. Simple aluminum shielding won’t cut it. There are some emerging technologies scientists are studying and testing that may prove helpful, however.
One is a concept called “active shielding” in which you create an artificial magnetic field through superconducting magnets. Unfortunately, as Nelson says, those technologies required way too much power. “You’d have to fly a whole other heavy space craft and power supply to make it work,” he says. There are scientists looking at generating smaller fields to protect individuals or ground vehicles. But according to Nelson, active shielding is “unproven.”
“The problem,” he says, “is the particles come in all directions at the same time, so it’s not like putting your hand out and blocking your view of the sun will be enough.”
Another idea is to actually intervene at the biological level itself. An idea currently being studied and tested is the use of antioxidants in large concentrations that might be administered after a bad solar event. Nelson cites studies into harnessing vitamin E compounds, or nutrients found in blueberries, strawberries, or red wine. Dorit Donoviel, deputy chief scientist at the National Space Biomedical Research Institute, is working on something similar by identifying potential compounds that may be able to prevent local tumor formation due to specific radiation events, through clinical trials on late-stage cancer patients.
Unfortunately, most of these studies rely on mouse models or humans who don’t represent the healthy, fit physique that defines nearly all astronauts. Overall, Nelson thinks these methods are so far inefficient, due to the high amounts of charged particles found in cosmic radiation. This is compounded by the fact that biological interventions can create horrible side effects — and you’d want to keep astronauts from having to inject something horrible into their bodies on a weekly basis.
Both Nelson and Donoviel reiterate that at present, NASA is unable to send people to Mars and still confidently stick to a three percent risk of developing cancer later in life. That certainly doesn’t mean the research will stop — but if the agency intends to put boots on the red planet by the end of the 2030s, they have a lot more work to do to solve the space radiation puzzle.