The health risks of space odyssey
Extended stay exacts toll on astronauts — during and after mission
In space, the human body goes a little haywire. No one knows that reality better than Scott Kelly, who spent 520 days in space, more than any other NASA astronaut. In his memoir “Endurance,” Kelly detailed the myriad health issues he endured in that most unforgiving of environments — and those that continued for a time after he returned to Earth.
“I lost bone mass, my muscles atrophied, and my blood redistributed itself in my body, which strained and shrank the walls of my heart,” Kelly wrote.
“I experienced problems with my vision, as many other astronauts had. I’d been exposed to more than 30 times the radiation of a person on Earth, equivalent to about 10 chest X-rays every day.”
In Kelly’s last stay on the International Space Station — a nearly yearlong research project
designed to study what longer durations in space do to the human body — DNA mutated in some of his cells, his immune system went on high alert, and his microbiome gained new species of bacteria, according to research results unveiled in April.
He didn’t feel normal again until eight months after he returned to Earth.
The study was undertaken to get a better sense of how the body will hold up under microgravity conditions for long periods. In the past nearly 60 years, 559 people have flown in space, but few have spent more than a few months at a time there.
That’s not to say that decades of spaceflight haven’t taught NASA how to keep astronauts healthy, a far cry from the 1960s, when the agency was happy just for Mercury, Gemini and Apollo astronauts to complete their missions.
“The big concern was whether humans could even survive in space,” said Dr. Michael Bungo, a professor at McGovern Medical School at UTHealth in Houston and former director of the Johnson Space Center’s Space Biomedical Research Institute. “It took the return of the chimp Ham from space to prove intelligent organisms could survive in microgravity.”
Microgravity, the condition in which people or objects appear to be weightless and floating in space, might seem like an enjoyable aspect of space travel, but it takes a toll on the human biological system. Here are ways it and other forces in space impact health:
Space sickness: Between 60 percent and 80 percent of astronauts develop space sickness in the first few days after a launch because sensors in the inner ear signal to the brain the familiar tug of Earth’s gravity is missing. Symptoms resemble those associated with motion sickness on Earth — headaches, vertigo, nausea and bouts of vomiting. Most symptoms resolve in a few days after astronauts get their “space legs,” but they can return.
Muscle and bone loss: Because muscles don’t have to work as hard against the force of gravity in space, they lose size and function, from 20 percent to 40 percent without countermeasures, according to NASA estimates. The same phenomenon applies to bones — studies of astronauts and cosmonauts who spent many months on the Russian space station Mir found they lost an average 1 percent to 2 percent of bone mass each month.
Cardiovascular problems: One of the muscles affected by the lack of gravity is the heart, which loses mass, becomes more spherical and functions less efficiently. The cardiovascular system generally becomes less efficient as blood flows up toward the head instead of to every part of the body, significantly increasing the risk of developing high blood pressure.
Visual impairment: Twothirds of astronauts on the International Space Station reported newfound problems with their sight. In some cases, the impairment became permanent. Early research into the phenomenon found swelling in the optic nerves and suggested changes in fluids in the eyes and spinal cord in response to microgravity are the cause.
Emotional stress: NASA considers behavioral issues among groups of people crammed in a small space and isolated from other humanity over a long period inevitable, no matter how well trained they are. Crews for a Mars mission will undergo even more preparation, inasmuch as they will travel farther and longer than any previous human beings.
Radiation exposure: The most dangerous aspect of traveling into deep space is the ridiculously high level of radiation. Without the protective cocoon of Earth’s magnetic field and atmosphere, astronauts are exposed to levels more than 100 times greater — enough that travel to Mars could involve a 6 percent increased risk of cancer.
Can NASA resolve all of the issues and ensure the safety of Mars-bound astronauts by the 2030s, the timetable for the mission?
One researcher cites a seemingly overlooked benefit from preparations to go to Mars.
“Learning how to do health care in a tin can on the way to Mars can provide a model for the health care system we need on Earth, one that’s preventive rather than reactive,” says Dorit Donoviel, director of the Translational Research Institute for Space at Baylor College of Medicine.
“Take healthy individuals, monitor them and make sure they remain healthy,” Donoviel says. “If they become sick, use noninvasive, simple technologies to care for them without sending them to the hospital.”
“I lost bone mass, my muscles atrophied, and my blood redistributed itself in my body, which strained and shrank the walls of my heart.” Scott Kelly, who spent 520 days in space, more than any other NASA astronaut