Imagine that it’s 2035 and I’m halfway between Earth and Mars. My spacecraft, a marvel of engineering, is designed to protect me and my fellow astronauts from the thousands of different ways that we could die or that our fragile bodies could be damaged.

High on the list is radiation—invisible particles of energy as small as a quadrillionth of a meter that zip and zap through space at close to the speed of light. They slice right through our bodies to strike our DNA and proteins and other very small and very critical structures in our cells, potentially causing tumors and other molecular mayhem. Zero gravity threatens to turn my muscles and bones to mush. Isolation, anxiety, and the mind-boggling distance from Earth and those I love threaten to drive me mad—and much more.

Yes, I’m a human guinea pig 100 million miles from home. My mission: to find out whether decades of research and countermeasures to protect my tender biology will work, and whether humans should venture out so far in the first place.

That’s what scientists are asking right now, in 2022. NASA has spent billions of dollars in recent years on better understanding and mitigating five “red”-level hazards: radiation, isolation, distance, gravity fields, and hostile environments. More specific perils include damage to an astronaut’s immune system and cardiovascular and nervous systems; changes in a person’s metabolism and the composition of microbes in their gut; and damage to genes, proteins, mitochondria, and more.

This knowledge has come from humans traveling in space for most of the past six decades, mostly near Earth and inside its protective magnetic field that fends off most radiation. Only 24 people have proceeded beyond the magnetosphere, journeying to the moon. Twelve of them have walked on the lunar surface. Among the 600-plus astronauts who have gone into space, only a handful have spent close to or more than a year there—all in orbit around Earth—including, most recently, flight engineer Mark Vande Hei, who spent 355 days on the International Space Station (ISS) before his return this March.

Whether the knowledge gained from such a small pool of test subjects is enough to keep my imaginary doppelgänger safe in 2035 remains an open question. “We’re collecting more and more data, and the knowledge base is rapidly expanding,” says astronaut and physician Michael Barratt, formerly the head of NASA’s Human Research Program at the Johnson Space Center in Houston. His specialty is space medicine, and he once spent 199 days on board the ISS. “But we won’t really know until we send humans out beyond Earth’s orbit for long trips,” like to Mars.

astronaut and physician michael barratt, former head of nasa’s human research program at the johnson space center in houston
Astronaut and physician Michael Barratt, former head of NASA’s Human Research Program at the Johnson Space Center in Houston. He spent 199 days aboard the International Space Station in 2009.
Annie Mulligan

Invisible Dangers

When astronaut Scott Kelly closed his eyes to fall asleep during the 340 days he spent on board the ISS, from 2015 to 2016, he sometimes saw streaks of light like shooting stars behind his eyelids. He wasn’t hallucinating. These were tiny particles of cosmic radiation passing through his eyes and blasting his retinal cells.

Normally, the particles are invisible, but even on Earth they rush through us in a steady drizzle of energy generated by exploding stars and other high-energy, deep-space events as well as by our sun. Too much radiation not only increases the risk of cancer but also can damage the central nervous system, alter cognitive function, reduce motor function, and prompt behavioral changes. It can play havoc with our immune system as well.

This article appears in the Summer 2022 issue of Alta Journal.

Fortunately, on Earth most of these particles are deflected by our planet’s magnetic shield, a protective barrier that becomes thinner the farther you travel out into space. Flying at 35,000 feet on a round-trip flight from New York to Los Angeles, a jetliner passenger is exposed to 0.04 to 0.1 millisieverts of radiation, the equivalent of about one chest X-ray—which isn’t dangerous for most people. Rocketing to Mars and back on a three-year mission could saturate astronauts with something like 1,000 millisieverts, or 100 chest X-rays, an amount that isn’t deadly but can increase the lifetime risk of cancer.

“The biggest limiter to humans in space is really radiation and the excess cancer risk that incurs,” says Barratt. “When I ran the Human Research Program, that was by far the biggest line item in my $160 million annual budget. We’ve learned a lot. But we still don’t understand the actual biological effects of radiation on humans beyond the earth’s magnetic field.”

Another invisible hazard in space is zero gravity, or partial gravity on the moon or Mars. But unlike with space radiation, which usually isn’t present in high enough quantities to cause immediate discomfort, Barratt says that he felt the effects of zero g big-time when he first arrived on the ISS. “Going uphill from one g to zero g kind of sucks,” he says, “because you get a fluid shift from the lower part of your body to your central circulation, the chest, the head, and that is uncomfortable. A large percentage of people get space motion sickness—that’s our version of seasickness. It’s not fun to be nauseated and to barf in space.”

The discomfort goes away in a few days, he says, as your body makes adjustments, including a reset of the natural sensors that detect the body’s location in space and one’s locomotion. “We become three-dimensional,” says Barratt. “We can fly to another module, and we can clock 90 degrees and change our reference frame instantly. You watch people almost evolve over a period of days to weeks into these three-dimensionally navigating extraterrestrials”—the word he uses to describe humans as their bodies adapt to life in space, which in many cases is beneficial to their survival—“and they go from trying to walk from footrail to footrail to flying like Superman.”

Over time, the effects of zero gravity aren’t so super for muscles that lose mass and bones that thin out and become more susceptible to breaking, mimicking the condition of osteoporosis. More recently, doctors have discovered that fluid shifts to the brain and the head can cause an enlargement of the brain’s pituitary gland and a swelling in the ocular nerve that can blur vision.

Returning to Earth is also traumatic. When Kelly touched down in 2016 after his 340 days in space, his body was riddled with anomalies, from ankles swollen to the size of beach balls and an immune system that went berserk to moderate memory loss and patterns of gene expression that had turned on or off owing to the environmental changes of space. He had also grown two inches, apparently from his spine relaxing in zero g.

These findings were included in an elaborate effort by scientists to record, measure, and analyze as much of Kelly’s physiology as possible as part of NASA’s Twins Study, which tracked Kelly and his identical twin, Mark, a retired astronaut and now a United States senator from Arizona, who stayed on Earth as a control subject. “Some of the results were predicted,” says Cornell molecular biologist Chris Mason, who worked with NASA to study Kelly’s molecular data, “but we also had some weird findings.” One of these was that Kelly’s telomeres, structures at the end of chromosomes that get shorter as we age and when we’re tense, actually grew in space rather than shrank from radiation and stress as the scientists had expected.

Mason suspects that Kelly’s healthy diet, daily workouts to reduce bone and muscle loss, and no alcohol might have been contributing factors. “In some ways, his life in space was healthier than it was on Earth,” Mason wrote in his 2021 book, The Next 500 Years: Engineering Life to Reach New Worlds, which starts with Kelly’s results and goes on to map a future in which humans very slowly move out into space, traveling from Mars to the rest of the solar system and beyond to one of the many Earth-like exoplanets that astronomers have detected in nearby star systems. Mason details how scientists in the future will use gene editing and other synthetic-biology techniques to engineer a new phase of human evolution that will make people better able to survive in space as they become true extraterrestrials.

“Back on Earth, most of Scott Kelly’s issues corrected themselves,” says Mason. His height reverted to normal in a few hours; his telomeres, shortly thereafter. Most of his genes returned to their Earth settings, although not all did. “Some genes did carry a ‘molecular echo’ of their time in space,” wrote Mason, “still actively working to continue DNA damage repair and maintain DNA stability.” Kelly says he didn’t feel “normal” until he’d been back on terra firma for seven or eight months.

long distance space travel poses many threats to humans graphic
Graphic by Matt Twombly; Text by David Ewing Duncan

Mental Health

As if radiation, misbehaving fluids, genes flipping on and off, and ocular nerves swelling weren’t enough, astronauts also face constant perils—ranging from the rocket that’s carrying them aloft blowing up to literally thousands of possible mechanical breakdowns. Plus astronauts are sequestered in a small space away from friends and family and can feel overwhelmed by their duties.

“There will be a lot more things to worry about when astronauts go to Mars,” says Stephen Petranek, the author of How We’ll Live on Mars, which was the basis of National Geographic’s recent cable series on the red planet. “If your equipment fails, there’s no place to go if you can’t repair it yourself.” You also have a communication delay of up to 20 minutes each way, meaning that you feel more isolated from your people on Earth.

Not to mention, there will be less to do than on the ISS. “The way to really torture an astronaut is to not have meaningful work for them to do,” says Barratt. “Idle time is not something we deal with very well. On the ISS, which is basically a giant lab, you’re doing science, you’re doing your countermeasures, your exercise, you’re fixing stuff all the time, you’re doing PR events and all that kind of stuff.” NASA is working on ways to fill the time during the 10,000-hour-or-so round trip. “You also can keep people busy training for when they reach Mars,” says Barratt. “But there will be downtime that’s very similar to long sea voyages in the past,” the difference being that those trips usually ended up someplace like Bora-Bora or Virginia, not Mars.

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Researchers studying psychiatric issues in space have seen remarkably few serious mood or neuro disorders among astronauts, like schizophrenia or bipolar disorder, probably because potential astronauts are extensively tested and screened. But some studies have reported cases of anxiety and feelings of isolation, and some former astronauts back on Earth have experienced depression, anxiety, and some difficulty with relationships, as noted by Edwin “Buzz” Aldrin, the second man to walk on the moon, in 1969, in his book Return to Earth. Others have reported being excited and thrilled to be in space, with a few having “transcendental experiences, religious insights, or a better sense of the unity of mankind as a result of viewing the Earth below and the cosmos beyond,” according to a 2016 literature review in Psychiatric Times.

In space-like environments, such as in submarines and in Antarctica, the record isn’t quite as pristine. Researchers have found that about 5 percent of people experience serious psychiatric disorders, like depression and schizophrenia, something to consider as less-well-screened tourists and billionaires travel into space.

Humans in the Machine

Let’s return for a moment to 2035. My imaginary astronaut self is now closer to Mars, which has become a huge red disk outside my spaceship’s windows. Earth is now a tiny blue dot about 170 million miles away. It’s day 175, and I’m sitting on an exercise bike on the first floor of SpaceX’s Starship, a seven-story, 30-foot-wide spacecraft that’s taking me and my fellow crewmates to Mars. I spend two to three hours a day lifting weights and doing cardio, following the latest NASA research on exercise as a countermeasure to keep my muscles and bones as healthy as possible.

This machine is my home for the 200-plus-day trip to and from Mars. But it’s more than a machine. It’s a massive augmentation outfitted with shielding to protect the crew from radiation, along with plenty of technology to maintain the narrow band of temperature, atmosphere, pressure, and lighting. The machine is constantly monitoring the environment inside and outside the ship, as well as each of us humans, via an array of wearable devices that keep track of pulse, blood pressure, oxygenation, brain wave patterns, and much more. Each day, I submit blood, urine, and poop to be tested for hundreds of biomarkers and for changes in my gene expression, proteins, metabolites, and microbiome.

In 2022, this Mars-bound Starship does not yet exist. But SpaceX is testing prototypes, propelling them up into the sky using its Raptor engines; one of the latest headed up to about 10 kilometers, then made a controlled descent to a precision landing on a pad in Texas. Nor have all the safety features been figured out. A big open question remains exactly how to shield astronauts and delicate electronics from radiation. Various materials have been proposed, including some that contain hydrogen, which can effectively block most solar and cosmic particles. Another proposal involves surrounding a spacecraft with a massive sleeve filled with water—which the crew could use during the journey—or even with astronauts’ poop, since organic material works reasonably well to repel solar and cosmic particles.

So far, most ideas for shielding either are too expensive, won’t survive the heat of reentry, or would be too heavy. “It takes about 10 kilograms of shielding to protect 1 kilogram of a person or an instrument just to leave low Earth orbit,” says Robert Braun, a space systems engineer and the director of planetary science for NASA, based at the Jet Propulsion Laboratory in La Cañada Flintridge, California. “If you have to add a bunch more shielding, you will need that much more propellant, which adds weight and slows down the spacecraft.” More time in space, he says, means more radiation exposure for astronauts.

Once on Mars, conditions will be better than in space, although the red planet lacks a strong magnetic field to deflect radiation. The gravity is 1/3 g, but the days are a familiar length, 24 hours and 37 minutes, which human circadian rhythms will like. The atmosphere is 1/160th the density of Earth’s and 95 percent carbon dioxide, and the planet has no traces of life so far and no ready sources of food. But it does have water and the basic chemicals needed to support life.

“It’s going to be tough to live on Mars,” says Petranek, “and the biggest bugaboo may be food. It will be hard to raise enough on Mars for quite a while, meaning supplies will have to be brought from Earth.” But there are raw materials to make most things, everything from some food and medicines to industrial chemicals and building materials. “With advanced 3-D printing, the colonists will be able to make almost anything, even drugs,” says Daniel Kraft, a physician and former flight surgeon for the California Air National Guard and the faculty chair for medicine and neuroscience at Singularity University. Last year, NASA’s Perseverance rover showed that colonists could make oxygen from gases in the atmosphere of Mars.

For astronauts venturing to Mars and beyond in the decades to come, scientists like Chris Mason are developing more radical countermeasures that use advanced technologies like gene editing to fix DNA and stem cells to replace or regenerate cells, including immune cells. “We’re looking at interventions with genetic therapies that are now deployed in thousands of clinical trials to have a more active surveillance of cancer or to cure diseases,” he says. He is working in a field called multi-omics, in which scientists go beyond genomics to incorporate other molecular systems in the body that are critical to understanding and treating disease—involving proteomics, metabolomics, microbiomics, and more.

One intriguing project in Mason’s lab is testing a protein found in a microscopic animal called a tardigrade, which can live in extreme heat and radiation and even survive in the vacuum of space. Called Dsup, the protein protects against—and greatly enhances the repair of—damage from radiation. When Mason inserted Dsup into human cells, it provided up to an 80 percent reduction in DNA damage from radiation. “We’re many years away from editing tardigrade genes into astronauts,” says Mason. “But one day it might be possible.”

However promising Mason’s research, protection from radiation is one of many issues that need to be resolved to overcome skepticism about lengthy space travel. “I’ve noticed a definitive shift over the last couple of years,” says NASA’s Braun. “People used to ask, ‘How can we do this?’ Now, as the reality of interplanetary flights is getting nearer, they’re asking more and more, ‘Why should we do this?’ ”

Even within the space community, some are less than gung ho about the tremendous effort and cost of sending humans to Mars. “Elon Musk and SpaceX take it seriously,” says Braun. “I can’t say that the rest of the aerospace industry does.”

barratt inside an orion crew module used for training and testing
Barratt inside an “Orion” crew module used for training and testing. The “Orion” spacecraft is part of NASA’s Artemis program, which aims to carry astronauts to the moon and beyond.
Annie Mulligan

Space Faith

How much we freak out about the dangers of sending humans to Mars really comes down to a belief—even with incomplete data and numerous unknowns—that humans belong in space. This is not a lot different from the doubts faced by explorers of all ages who believed they could make it despite formidable odds—whether Meriwether Lewis and William Clark in the northwestern United States or Neil Armstrong and Buzz Aldrin on the moon.

Michael Barratt thinks we should keep exploring—and he would love to be one of the humans on that Starship heading to the red planet sometime around 2035, although he’d be 75 years old then. “I believe that learning about our solar system is critical to our survival,” he says. “It’s more than just curiosity. Our ultimate environment is bigger than the earth.”

And if we do belong in space, then we’ll need to find a way to make lengthy journeys possible. “I’d go back, and I’d go fly in space for a year again if I could,” says Scott Kelly, “as long as it was a round trip. Having lived on the space station for a year, I would not want to live for the rest of my life in some habitat on Mars.”•

David Ewing Duncan’s latest book, Talking to Robots, imagines future forays of robots and humans into space.