NASA’s biggest obstacle to sending humans to Mars may not be related to line items in budgets, but to the safety of the astronauts themselves. Despite having sent humans into space for nearly 55 years, NASA doesn’t quite understand what risks the radiation out there poses. More importantly, the agency doesn’t know exactly how to manage those risks—and it might not be able to.

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Space radiation presents the tallest hurdle to NASA’s future travel plans that extend beyond low-Earth orbit and for periods longer than a year. On the International Space Station, astronauts are bombarded with 10 times as much radiation as they experience on Earth in a given period; on Mars, they will encounter 100 times the terrestrial dose. When NASA sends astronauts on its planned two-year-long Martian trip, they’re probably going to break their own rules about radiation exposure, which already set limits above those for most workers here on Earth. As a report from NASA’s Office of the Inspector General put it, “Based on current knowledge, astronauts on a mission to Mars would exceed NASA’s career radiation dosage limits. Although the Agency plans to continue efforts to develop countermeasures to address the radiation risk, NASA is likely to seek an exception from the current standards for those that cannot be fully mitigated.” 12 Month Study NASA’s understanding of the effects of long-term exposure to radiation in deep space is still in flux. While the government has been concerned with radiation hazards on a potential Mars mission since going to the fourth planet became a goal, it wasn’t until November 2012 that they realized they had the opportunity to perform a controlled experiment on humans, looking at the effects of space radiation.

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NASA was set to announce that astronaut Scott Kelly would go to the Space Station for 12 months, to participate in the agency’s aptly named One Year Mission. The plan was to send an American astronaut—Kelly—and a Russian cosmonaut—Mikhail Kornienko—to orbit for twice as long as most space-farers, and then study the physiological and psychological effects of the trip. The results would help space agencies prepare for longer-term space missions like the planned journey to Mars. Twins Mark and Scott Kelly participated in a NASA study to determine the effects of long-term exposure to space radiation on the human body. The day before the press conference, NASA officials met to help Kelly prep. At the very end of the gathering, as everyone was shuffling papers and standing up to leave, someone asked, “Hey, are we doing anything with the twins?” By this, they meant Kelly’s gene-sharing, same-aged brother, Mark Kelly—who had also spent time in the astronaut corps. “No, that would just be a stunt,” said John Charles, head of the One Year Mission. “We’re not going to do anything.” But as people began to file out of the room, Mike Barrett—Charles’s boss and manager of NASA Human Research Program—stopped Charles and said, “Not so fast.” And soon, they sat down and made a plan for the “Twins Study,” mapping out research that would be good for more than just publicity: a formal project to compare how the bodily and brainy functions of Mark—living, as Charles says, “la vida loca” as a retiree in Tucson—and Kelly—living in space. Scientists would study how the characteristics of a claustrophobic space environment—the lack of gravity, the astronaut ice cream, the serotonin-boosting view out the window, the cortisol of launch, the screwed-up sleep schedule—contributed to any differences between the two men’s biology. “Our experiments are not clean. They are a juxtaposition of all these stressors,” Charles says. “We, being rocket scientists, try to figure out which phenomenon is related to which stressor.” And perhaps the biggest body-stressing difference between Earth and orbit is the amount of bombarding radiation. “Like Cellophane” Radiation is the catch-all term for high-energy particles like protons and nuclei that can tear into human microanatomy. A few different kinds of radiation exist under that umbrella: the radiation that’s trapped by the Earth’s protective electromagnetic shield; the radiation that comes from the Sun; the radiation that comes from deep space, like supernova explosions; and the secondary radiation that is spawned when, say, a supernova particle smashes into some other matter, like a spacecraft hull or an astronaut’s head. The Earth-trapped radiation and the particles that fly from our star don’t pose huge problems, because the former is localized and the latter doesn’t have much energy (comparatively). But those deep space particles, more formally called “galactic cosmic radiation”—watch out, journeyers.

OSHA gave NASA a waiver, allowing the agency to create its own radiation guidelines.

“They rip through you like you’re cellophane,” says biomedical and health informaticist Dan Masys of the University of Washington. Engineers haven’t yet found a way to protect astronauts’ fragile, cellophane selves against such bombardment. NASA sets its own thresholds for how much radiation is too much, but that wasn’t always true. Astronauts used to fall into the Occupational Safety and Health Administration’s “radiation workers” category, like pilots and people who work at nuclear reactors. OSHA places caps on the particles a worker can encounter and, on top of that, demands that organizations keep exposure “as low as reasonably achievable.” They call this the ALARA Principle. But today, ALARA is the only principle by which NASA abides. Terrestrial radiation worker limits proved too low for celestial employees, so OSHA gave NASA a waiver, allowing the agency to create its own guidelines. OSHA’s limits don’t apply anymore. NASA’s Office of the Chief Health and Medical Officer now sets the limits, which say that an astronaut’s exposure to radiation shouldn’t increase their risk of death from cancer by more than 3%. Yet that same office will grant new exceptions if trips beyond low-Earth orbit will put astronauts at radiative risk greater than what’s now allowed, as the agency suspects they will. “It Depends” NASA’s current chief medical officer is J.D. Polk. And Polk tells me that while some other space agencies lay down a blanket radiation limit—saying none of their employees can exceed a set and static dose—NASA doesn’t. Instead, the agency takes an astronaut’s age and sex into account. Women have higher cancer risk because of their breasts, ovaries, and uteri; they also have an unexplained increased risk of radiation-induced lung cancer. Their limits, then, are lower than men’s. The older someone is, the less a doped-up dose means to them. “If I expose a 55-year-old astronaut to radiation and they have 20–30 years in which that radiation exposure might produce a cancer, that’s a different risk than if I expose a 30-year-old to that same radiation,” Polk says. “So if you ask what the NASA career limit is, the answer is, ‘It depends.’ ” And if you ask whether NASA would be willing to break its cancer-focused career limits to go forward with a big-picture space mission, the answer is maybe. But the trouble is that the radiation problem isn’t limited to cancer, something which NASA acknowledges. They have it all laid out in a set of thirty-plus “Evidence Reports on Human Health Risks” that are produced by their Human Research Program and reviewed by the National Academy of Sciences, which selects independent experts to assess the quality and rigor of NASA’s work. Masys is one of those experts. This year, he was the vice-chair of the committee that prepared the fourth of five such assessments, one slated to come out each year from 2014–2018. Each addresses a subset of the tens of evidence reports, which deal with everything from sleep loss to habitat design to the microbiome to nutrition. Much of this year’s analysis dealt with radiation reports. Masys says that, so far, NASA hasn’t been surprised by anything the committee has said—“other than their mild surprise that we have anchored radiation as the deal breaker,” he says. “It is the showstopper for what NASA calls exploration-class missions.” Both NASA’s and the Academy’s documents say that long-term missions will be radiation-risky for the foreseeable future—maybe forever. Masys doesn’t use the words “deal breaker” and “showstopper” lightly. According to NASA’s reports and the Academy’s evaluation, cancer-inducing radiation can also cause cardiovascular and degenerative diseases—like cataracts, premature aging, and endocrine problems—a risk “of much greater concern than previously believed.” It can also rejigger the central nervous system, screwing with everything from cognition to spatial perception to hand-eye coordination. Then there’s the infertility, the cataracts, the slow wound healing, and the problems that astronauts could pass on to future children if they make it back from the long trip to Mars and manage to procreate. For several of these medical matters, scientists don’t understand the underlying mechanisms. And so far, their research into those mechanisms, and their manifestations, has mostly involved the low-energy particles from Earth or near-space—not the high-energy cosmic rays from farther off—and radiation exposure that falls in one fell swoop, like the swoop of a nuclear bomb. Often, too, researchers base their conclusions on animal models that they haven’t translated to humans. Both NASA’s and the Academy’s documents say that long-term missions will be radiation-risky for the foreseeable future—maybe forever. “For as long as there have been catalogs of health effects, radiation has been the most intractable, most severe, hardest problem to solve,” Masys says. “Now, 20 or more years into advances in space technology and propulsion and systems and vehicles, radiation is still the deal breaker. It has never changed.” Engineering Solutions? NASA has been hard at work on the problem. The agency is attempting to determine how radiation might impact crewed Mars missions with research projects like the Twins Study and the One Year Mission, with on-the-ground facilities like the Space Radiation Laboratory, and with biology research in laboratories. But they are also hoping to engineer ways to decrease exposure. “We talk about time, distance, and shielding,” Polk says. If the agency creates faster rockets, astronauts can spend less time in transit. They can time trips for low-emission points in the solar cycle that also put Earth close to Mars. And then they can build better barriers between astronauts and space. Perhaps advances in nano- or materials science will bring a lightweight, launch-friendly material that efficiently traps the offending particles before they slam through skin. Medical types could also develop drugs that undo or protect against bodily harm when particles do slam into skin. But none of those are reality yet. “NASA, as a future-thinking engineering organization, believes they will find a solution,” Masys says. “And so the real issue is, well, how soon? They would be the first to tell you there is not a solution in hand right now.” In the future, when NASA is actually making deep-space trips, engineers and biologists will likely have better tools on hand. But will those tools allow NASA to abide by its astronaut-protecting guidelines? Or will the agency alter the guidelines for the good of human exploration? The Orion crew module will not be enough to protect astronauts from galactic cosmic radiation. It’s a burden that NASA has to bear, but one the private space industry doesn’t have to bother with. If Elon Musk wanted to send someone to Mars tomorrow, radiation guidelines probably wouldn’t stop him.

“Nonemployees are likely to be exempt from dose limitations.”

Private space companies like Musk’s SpaceX fall under the watchful eyes of the Department of Transportation and the Federal Aviation Administration. Crew members—employees of the space tourism company—will be protected by OSHA regulations. But occupational standards don’t apply to the passengers, who are not working for SpaceX or whoever else flies beyond the atmosphere, or for the federal government. As Alyssa Megan Sieffert, now an attorney-advisor at NASA’s Office of the Inspector General, wrote in the journal The SciTech Lawyer , “Nonemployees are likely to be exempt from dose limitations.” They could, potentially, endure as much radiation as they want. If Musk wanted to send a remotely operated, fully-tourist trip to Mars—as with the two tourists he’s sending around the Moon in 2019—he just could, as long as he informed them all the radiation wasn’t good for them. The way the law works, the Secretary of Transportation cannot create preventative regulations that would stop the first rich tourist from dying of cosmos-caused cancer or cardiovascular disease while cataracts cloud their eyes. As the code says, regulations issued by the secretary “shall…be limited to restricting or prohibiting design features or operating practices that…have resulted in a serious or fatal injury…during a licensed or permitted commercial human space flight; or contributed to an unplanned event or series of events during a licensed or permitted commercial human space flight that posed a high risk of causing a serious or fatal injury.” In other words, only once something goes wrong in commercial spaceflight can the Secretary bring into being a new safety regulation to prevent a similar situation from happening in the future. No Easy Task Research like the Twins Study will help medical types determine the effects and ethics of that rule-breaking. NASA released the radiation data from the Kelly Study to researchers on February 28. “They’re just now opening those files up,” Charles says. Figuring out how radiation affected Scott Kelly’s corporeality—and how it didn’t—won’t be easy. “This is not like Bones or CSI ,” Charles says. “You don’t pick up a cigarette butt and put it in your whizmo machine.” Regardless of the findings, though, of these or future studies, astronauts like Kelly would probably always raise their hands to go, whether it was strictly good for them or not. “Astronauts are a risk-taking group. That’s part of their persona,” Masys says. “The agency has to have a more prudent approach to risk than the astronauts themselves.”

Photo credit: NASA, Lockheed Martin