Sunita Williams gives a thumbs up after returning from a four-month mission aboard the International Space Station in 2012. She and her fellow astronauts were strapped into their seats while they recovered from “space sickness” and adapted to Earth's gravity. (Photo by NASA/GCTC/Andrey Shelepin)
NASA astronauts Sunita Williams and Butch Wilmore are expected to land safely in Earth's oceans inside a SpaceX capsule on Tuesday (March 18), ending a more than nine-month mission to space that was originally only planned for a few weeks. When their capsule opens, the astronauts will likely be carried out and placed on stretchers.
As experts told Live Science, this requirement is not specific to Williams and Wilmore's mission to the International Space Station (ISS), but is a standard procedure that all astronauts must follow.
After returning from orbit, astronauts cannot immediately stand up on their feet after landing. This is due to temporary changes in the body that occur in space, which NASA takes into account in its strict safety protocols.
“A lot of them don’t want to be carried out on a stretcher, but they’re told it’s necessary,” John DeWitt, director of applied sports science at Rice University in Texas and a former senior scientist at NASA’s Johnson Space Center, where he developed methods to improve astronaut health during missions, told Live Science.
“Space motion sickness”
Just as someone might feel motion sickness on a roller coaster or while riding a boat through rough waters, astronauts can feel dizzy and nauseous after returning to Earth. That's why astronauts are usually carried out on stretchers after landing as a precaution, DeWitt explained.
This temporary sensation occurs because our bodies are adapted to the constant force pulling us down on Earth: gravity. However, inhabited space stations like the ISS are in constant free fall toward our planet, creating a zero-gravity effect for the astronauts inside and forcing their bodies to adapt to the changed conditions.
One significant change occurs in the vestibular sensory system of the inner ear, which plays an important role in maintaining balance, DeWitt said. In space, this system begins to ignore certain sensory signals as the brain learns to adapt to weightlessness. So when astronauts return to Earth and encounter gravity again, their bodies begin to readjust, which can temporarily lead to “space motion sickness,” DeWitt said.
Another change that astronauts experience, especially those who spend long periods of time in space, is the gradual loss of muscle and bone mass. On Earth, walking provides enough exercise to maintain muscle strength thanks to gravity, but in space, astronauts don’t use their muscles as much. Due to lack of physical activity, muscles weaken and shrink over time, leading to a condition known as muscle atrophy.
Sourse: www.livescience.com
