On March 14, what was initially planned as a short mission of just over a week stretched to an extensive nine-month stay in space. NASA astronauts Suni Williams and Butch Wilmore were originally assigned to the first crewed test flight on Boeing’s Starliner and were scheduled to remain at the International Space Station (ISS) for only ten days. However, when NASA detected several helium leaks and propulsion system issues with the spacecraft, it made the decision to send the capsule back without its crew. Consequently, the astronauts had to remain aboard the ISS until another mission could bring them back.
This situation is far from being a mere administrative inconvenience, akin to a low-gravity version of The Terminal. The impact of space on human health can be profound and potentially detrimental. For Williams and Wilmore, their extended stay at the ISS may have led to significant physiological effects.
The process of launching into space involves enduring g-forces more than twice what humans experience on Earth. Former NASA astronaut Dr. Sandy Magnus once likened the sensation to having a “70-pound gorilla sitting on your chest.” However, that is the last sensation of gravity astronauts feel until they reenter Earth’s atmosphere at the end of their mission. Once in orbit, they spend the remainder of their time weightless, floating in their seats.
The absence of gravity, though, is just one of the many ways space alters the human body. Astronauts have reported everything from deteriorating eyesight and genetic changes to skin rashes upon arrival. Some have even noted an unfamiliar sensation with fabric touching their bodies.
“In general, the environment in space causes an accelerated model for disease, and what we kind of say is an accelerated model for aging,” explained Dr. Afshin Beheshti, director of the Center for Space Biomedicine at the University of Pittsburgh. “But you don’t age faster, it’s just that all of the things associated with aging, like cardiovascular risk or cognitive issues… Everything is kind of sped up in space because of that environment.”
This week, four astronauts launched toward the ISS, where they will facilitate the return of Williams and Wilmore. Their extended stay places them among a small group of astronauts—just eight others—who have spent more than 200 days in space. NASA astronaut Frank Rubio holds the record with 371 days. Given the well-documented effects of prolonged space travel on the human body, it will take time for Williams and Wilmore to recover.
“When we get back, even to lift a pencil we will feel the weight,” Wilmore stated in a CNN interview last month. “That’s the transition back.”
One major reason for this difficulty is that gravity on Earth constantly acts upon the skeleton, prompting bone-building cells called osteoblasts to maintain bone density. Without gravity, bones weaken, losing approximately 1% of their density for every month spent in space without countermeasures. Similarly, muscles atrophy from disuse.
Despite daily exercise routines aimed at mitigating these effects, Williams and Wilmore will likely experience significant bone loss. Upon their return, they will be met by medical teams to initiate a 45-day post-mission recovery program, according to NASA’s Lead Flight Surgeon Dr. Stevan Gilmore.
“They work closely with trainers, dedicating two hours each day to return to their pre-flight baseline state of health and fitness,” Gilmore wrote in an email to Salon. “Generally, most crewmembers’ physiological systems recover within this timeframe.”
For comparison, NASA astronaut Scott Kelly, who spent one year in space, had to relearn how to walk after returning, Beheshti noted.
The Cool Down
“Being a year in space like that, it definitely takes a while for them to recoup the damage done,” Beheshti told Salon in a phone interview.
Kelly participated in NASA’s Twin Study, in which biomarkers from his body were compared to those of his twin brother, Sen. Mark Kelly, who remained on Earth. The results showed that Scott Kelly exhibited more signs of heart disease post-flight and developed Spaceflight Associated Neuro-ocular Syndrome (SANS). This condition arises when blood and cerebrospinal fluid shift upwards due to the absence of gravity, affecting both the brain and vision.
“He wasn’t wearing glasses before he went, but he came back and started wearing glasses,” Beheshti remarked.
Disruptions to the body’s internal clock also impact astronauts’ sleep and eating cycles. Some research indicates that spaceflight slows cognitive processing speeds, though performance returns to normal upon returning to Earth. Interestingly, some astronauts show improved cognitive focus while in space.
“Sometimes people actually perform better in space, and they’re even more focused, in a way,” said Dr. Chris Mason, a professor of physiology and biophysics at Weill Cornell Medicine. “But sometimes people get a little slower. It really depends on the crew member.”
Radiation is another significant concern in space. Without Earth’s ozone layer for protection, astronauts are exposed to radiation levels equivalent to a year’s worth of exposure on Earth for each week spent on the ISS. The severity of exposure depends on solar flares and cosmic rays.
This radiation exposure can disrupt cellular mitochondrial function, leading to broader health consequences.
“The mitochondria is your bioenergetics, so your energy in your body is produced by all of the mitochondria in your cells,” Beheshti explained. “When the bioenergetics are damaged, you can imagine that it has detrimental effects… impacting your immune system and circadian rhythm.”
Radiation exposure at these levels is associated with an increased risk of heart disease, cancer, and degenerative eye disorders. Studies tracking astronauts have identified changes in immune system function due to radiation and weightlessness.
A 2024 study in Communications Biology, led by Mason, found that astronauts in space had longer telomeres—DNA-protecting structures at the ends of chromosomes. While longer telomeres are generally associated with youth, they are also linked to cancer risks.
Mason’s study also found that space travel activates several genes involved in immune responses, likely as an adaptive reaction to the body’s stress.
“There are also anti-inflammatory markers called interleukins which get activated, and we’ve seen some of them in almost every mission, so we would expect that they would also have them here,” Mason said. “We see a lot of genes for DNA repair get activated, like the body is detecting some of the damage and then repairing that damage, which is a normal adaptive response.”
While most of these cellular changes revert within weeks of returning to Earth, recovery rates vary. About 90% of the gene changes Scott Kelly experienced returned to normal within six months, and telomere alterations stabilized within days.
However, scientists continue to study ways to reduce astronauts’ health risks. Radiation remains a major challenge, as high-energy particles can break DNA strands. Research efforts are exploring small molecules that might improve radiation resistance, with potential benefits for both astronauts and cancer patients undergoing radiation therapy.
Some researchers are investigating whether induced “artificial hibernation” could mitigate radiation’s harmful effects. Recent studies on animals suggest that entering a hibernation-like state reduces the damage caused by radiation.
“When there’s radiation damage caused to your body, you create reactive oxygen species, and that causes downstream things to impact your immune system… while also suppressing your mitochondria,” Beheshti explained. “But when your body shuts down in that hibernation state, like in these animals, those reactive oxygen species stop getting produced as much, and then there seems to be less damage caused by the radiation.”
With commercial space travel expanding and figures like Elon Musk advocating for missions to Mars, these concerns underscore the challenges of prolonged spaceflight. Human bodies, evolved over millions of years under Earth’s gravity and atmospheric conditions, face immense obstacles in space.
Although Williams and Wilmore trained extensively for this mission, their recovery will take time. Yet, they do not seem troubled by their extended stay.
“I think both of us will be a little bit sad when that feeling of space leaves us after about 24 hours,” Williams reflected in the CNN interview. “That means that physically the spaceflight came to an end.”