The pair performed the first astronaut-crewed Boeing's Starliner capsule flight to the International Space Station (ISS) in June 2024.
Wilmore and Williams were only supposed to spend about one week in space. However, issues with Starliner extended their mission by several months and delayed their return until early 2025.
Experts have said that spending a prolonged period in space -- especially many months -- can come with many changes to human physiology and psychology.
One of the biggest changes comes from spending time in microgravity, which allows astronauts to float inside a spacecraft or outside during spacewalks.
During this period, there is a decrease of muscle mass -- due to decreased use and lack of stimulus through exercise equipment -- and bone loss, according to NASA.
Without Earth's gravity, bones that support the body's weight can lose 1% to 1.5% of mineral density on average per month in space, the federal health agency says.
Additionally, without eating a proper diet and getting proper exercise, astronauts lose muscle mass faster in microgravity than they would on Earth.
NASA also says that in microgravity, blood and cerebrospinal fluid often shift upward from the lower extremities to the head and eyes, which is believed to cause eye and brain structural changes.
Crews are at risk of developing kidney stones due to dehydration or excreting calcium from their bones without preventive or countermeasures.
Upon returning to Earth, astronauts are often examined by a medical team as they work to readapt to Earth's gravity and rebalance their equilibriums for everyday tasks such as walking and standing upright.
Space radiation is different from radiation experienced on Earth. It's made up of three kinds of radiation: particles trapped in Earth's magnetic field, particles from solar flares and galactic cosmic rays NASA said.
Earth is surrounded by a system of magnetic fields, called the magnetosphere, that protects people from harmful space radiation. However, the higher a person is in altitude, the higher the dose of radiation they are exposed to.
Due to prolonged exposure, astronauts can be at significant risk for radiation sickness and have a higher lifetime risk of cancer, central nervous system effects and degenerative diseases, according to NASA.
Crews aboard the ISS receive an average of 80 mSv to 160 mSv during a six-month stay, according to a 2017 NASA report. Millisieverts (mSv) are units of measurement for how much radiation has been absorbed by the body.
Although the type of radiation is different, 1 mSv of space radiation is roughly the same as receiving three chest X-rays, the federal space agency said.
By comparison, a person on Earth receives an average of 2 mSv every year from just background radiation, NASA said.
There are also physical and psychological effects that come from being isolated and in a closed environment for a long duration.
NASA says that crews selected for ISS missions are carefully chosen and trained to make sure they can handle a mission that may last for six months or longer.
Source: https://abcnews.go.com
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