NASA astronauts who returned to Earth are expected to feel 'disoriented' and 'dizzy.' What happens to human bodies after being in space, explained.

When NASA astronauts Suni Williams and Butch Wilmore arrived at the International Space Station in June, they thought they would be there for eight days. Instead, 286 days later, they finally started their voyage back to Earth with two other astronauts aboard a SpaceX capsule early Tuesday morning.

The group, which includes NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov, splashed down off the coast of Florida right before 6 p.m. ET Tuesday evening.

Rescue crews came to recover the astronauts around 6:30 p.m. ET and were pulled from the capsule in medical stretchers — not because of anything that might have happened during their mission aboard the International Space Station but because this is the protocol for all astronauts returning to Earth.

Research has found that spending extended time in space can cause significant changes to the human body — however, NASA does not expect the astronauts to experience any serious long-term health repercussions since nine months isn’t a particularly long stay in space.

What happens to an astronaut’s body while in space?

For decades, NASA’s Human Research Program has analyzed what happens to astronauts’ bodies while they’re in space.

The biggest challenge for astronauts is dealing with how the fluids in a human body float upward without gravity, causing faces to swell, sinuses to congest and legs to turn weaker.

Without gravity, astronauts tend to experience symptoms similar to osteoporosis, a disease that weakens bones. Since there isn’t any gravity, astronauts’ bones and muscles aren’t naturally working while they move.

NASA reported that without gravity, bones lose an average of 1% to 1.5% of mineral density per month while in space, which can increase the likelihood of the astronaut suffering from muscle mass loss or fracturing their limbs. This can also cause major headaches and back pain since astronauts are likely to grow 2 to 3 inches taller while in space (although they will revert to their original height months after returning to Earth).

However, astronauts have learned that incorporating a regular workout has helped them protect their bone masses from diminishing. If astronauts do not exercise regularly or follow a specific diet, they will lose muscle mass faster than they would on Earth, which is why astronauts aboard the ISS have strict 2-hour daily fitness routines.

The lack of gravity can also flatten the shape of eyeballs and cause vision problems. Any negative impact on the eyes could cause changes to the retina and affect blood flow, which could change how well astronauts can see.

NASA previously said Williams was in good health

In November, NASA issued a statement on Williams’s health after rumors circulated that she had lost a significant amount of weight after photos of her on the spacecraft were released. NASA’s top medical officer, Dr. James Polk, said that Williams was healthy and not suffering from any medical issues.

In a video interview with the New England Sports Network that same month, Williams claimed she was the same weight as she was before the trip, but noted that the shape of her body — like skinnier legs and a swollen head — could seem to have changed to the public because of the lack of gravity. She said she was doing some weight-lifting exercises to help build up leg muscle.

What happens to an astronaut’s body when they return to Earth?

Immediately upon landing, the vestibular system — which is the organ in the inner ear that maintains balance — will immediately be confused by the force of gravity, which makes it hard for astronauts to walk. Astronauts will also experience “baby feet,” in which the soles of their feet become super soft after spending months not walking around, so it can be painful for them to walk again on Earth.

Matthew Dominick, commander of the SpaceX Crew-8 mission in March 2024, said that recovery could take weeks or months.

Dominick told reporters in November that there are big recoveries astronauts expect, like “being disoriented, being dizzy,” but then some surprising ones like “little things like just sitting in a hard chair” were difficult enough that he preferred to lie down on a towel during family meals instead.

The most in-depth study on lasting changes was done on NASA astronaut Scott Kelly, who spent 340 days at a space station starting in 2015, and who agreed to a yearlong study of his health after he returned to Earth. His health analysis was then compared to his identical twin brother, Mark Kelly, an Arizona senator and fellow astronaut who had stayed on Earth. NASA researchers found that Scott’s DNA had mutated in some of his cells, his immune system responded in new ways and his microbiome gained a new bacteria species.

It’s not just physical ailments

Frank Rubio, an American astronaut who holds the U.S. record for the longest stay in space, at 371 days, told reporters when he returned to Earth in September 2023 that a difficult health-related side effect of being in space for that long was the psychological aspect.

The Baylor College of Medicine found that early on in space missions, astronauts are likely to experience disorientation and a loss of a sense of direction, which can negatively affect completing the most basic tasks. Factors like being confined in a small space with other people, the high demands of work and the loss of a regular 24-hour day-to-night lighting cycle can cause a lot of stress for astronauts while up in space.

Sleep is also an important issue. Astronauts have to strap themselves to a wall to rest in a bed without gravity and the environment is never fully silent or dark, a fact that has been blamed for the disappearance of astronauts’ circadian rhythms.

How are Williams and Wilmore feeling?

NASA expects the pair will be physically fine when they land on Earth. And even though they were removed from the SpaceX capsule by stretchers and will undergo immediate health evaluations, it’s all done as a precautionary measure.

The astronauts themselves seem confident that once they land, they will feel OK.

"Been working out for the past nine months," Williams wrote in an email to Live Science. "We feel strong and ready to tackle Earth's gravity."