Upon his return last March from a record-breaking 340-day stay aboard the International Space Station (ISS), Nasa astronaut Scott Kelly was most excited about plunging into the swimming pool in his Houston, Texas backyard.
Kelly, who has spent more cumulative time in space than any other American, spent hours harnessed to a treadmill each day to try to keep his muscles and bones from atrophying. He also endured radiation exposure, nausea and vision problems while living on the ISS for nearly a year.
He has served as a guinea pig of sorts for scientists who are investigating the long term effects of zero-gravity environments on the human body. With Nasa planning a manned mission to Mars in the 2030s – and private outfits like Mars One advertising a colony on the planet in the next two decades – researchers want to know how to best offset the health hazards of a journey that will take two-and-a-half years. These dangers include everything from depression to loss of sight and heart disease.
“The biggest barrier to missions like that are biomedical,” says Leroy Chiao, a retired astronaut who has logged four space flights, including a six-month stint aboard the ISS as commander of Nasa’s Expedition 10. “It’s, how are you going to keep astronauts healthy in that long period of time?”
The biggest barrier to missions like that are biomedical.
Even on a short shuttle mission lasting a few weeks, microgravity causes big physiological changes. “You notice them immediately once you get into space,” Chiao says. While they adapt to the weightless environment, astronauts’ sensorimotor skills and balance are immediately thrown off. The inner ear senses that the body is moving, the eyes see that it isn’t, and the brain is confused by these contradictory signals.
“To me, it feels like you just did a forward roll,” says Chiao of the resulting dizziness and nausea, which can last for days.
Not only that, but the bodily fluids that gravity normally pushes down into the lower extremities will float up to the neck and head, causing headaches and uncomfortable pressure, potentially leading to vision problems due to swelling of the optic nerve.
Upon further study, scientists have discovered that the extended pressure inside the skull has flattened the backs of some astronauts’ eyeballs, making them more farsighted, an effect that is exacerbated by lengthy trips in space. This could have further serious implications for space travelers’ sight.
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“Nobody’s gone two years with exposure to this, and the concern is that we’d have loss of vision,” says Dohit Donoviel, director of the Biomedical Innovation Laboratory at the National Space Biomedical Research Institute (NSBRI), which partners with Nasa and Baylor College of Medicine to study human health in space. “That is catastrophic for an astronaut.”
No astronaut has ever gone blind from space travel, and while about 70% of them do experience vision changes while in flight – more often men than women – astronauts typically bring glasses on their space flights to help them do their jobs.
Still, the current remedy for redistributing fluids – a pair of suction pants made by the Russians called the Chibis suit, which essentially vacuums the fluids back down into the lower body – is “incredibly uncomfortable”, according to Donoviel , and can only be worn for an hour or two.
The NSBRI is testing a number of solutions, including a garment under development with Under Armour that astronauts would wear while they sleep.
Another big concern about prolonged space travel is its effect on the heart. Much like the muscles and bones that are depleted because they no longer need to work to fight gravity, the heart gets used to exerting a far lighter effort to keep blood pumping throughout the body.
Astronauts traveling to Mars, which has about one-third the gravity of Earth, will have to keep up extensive cardiovascular exercise every day in order for their hearts to be able to handle the planet.
No human has been exposed to the level of radiation that it would take to make that trip to Mars.
“It’s kind of like you’re lying still in bed,” says Chiao of the effect of weightlessness on the body and the circulatory system. That’s why Nasa performs bed rest studies in order to see how the body is affected long term.
When paired with radiation exposure, the prognosis doesn’t look good. A recent study of the 24 astronauts who left Earth’s low orbit on Nasa’s Apollo missions in the 60s and 70s showed that they were five times more likely to die of heart disease than the astronauts who didn’t enter deep space – a result scientists think may have been caused by excessive radiation exposure.
Astronauts on missions at the ISS are shielded from too much radiation by Earth’s atmosphere and magnetic field. But on a trip to Mars, humans would be exposed to radiation from the sun and from high-energy particles called galactic cosmic rays, which degrade DNA and drastically increase cancer risk. Nasa studies show that a round trip to Mars would expose astronauts to radiation levels reaching two-thirds of the agency’s lifetime limit.
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“We have no ability to block them,” says Dovotiel of the particles. “In essence, they affect every organ. No human has been exposed to the level of radiation that it would take to make that trip [to Mars].”
Beyond the many physical difficulties astronauts will have to withstand during long journeys, veterans say the psychological aspects of hurtling through deep space shouldn’t be discounted.
Astronauts stay extremely busy during missions, whether they’re conducting research, keeping tabs on equipment or churning out the requisite two hours of daily exercise. Aboard the ISS , that means they can always maintain a visual connection with home. But on a six-month trip to Mars, that comforting view of the Blue Planet will be gone.
“Watching the Earth disappear and turn into a star – that’s going to be different. You are going to feel alone,” says Chiao. “As we go on these longer missions, the psychosocial part is going to become more and more important.”
Heart disease, depression and blindness – the hazards of deep space travel
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