New Delhi: It may be fun to watch astronauts float around inside the International Space Station, but the absence of gravity has its effects on long-duration space travellers, who experience dizziness, nausea and an unstable gait when they return to earth.NASA astronauts Sunita Willams and Butch Wilmore, and Russian cosmonaut Aleksandr Gorbunov are scheduled to return to Earth on Wednesday onboard SpaceX’s Dragon spacecraft.For Williams and Wilmore, test pilots for Boeing’s new Starliner capsule, the eight-day mission stretched to more than nine months as a series of helium leaks and thruster failures deemed their spacecraft unsafe and had to return empty in September.Astronauts who have travelled on space missions earlier have reported facing difficulty in walking, having bad eyesight, dizziness, and a condition called baby feet where space travellers lose the thick part of the skin on the soles that become soft like a baby’s.”Once the astronaut returns to Earth, they are immediately forced to readjust again, back to Earth’s gravity, and can experience issues standing, stabilising their gaze, walking, and turning. For their safety, returning astronauts are often placed in a chair immediately upon return to Earth,” the Houston-based Baylor College of Medicine said in a note on body changes in space.It takes astronauts several weeks to re-calibrate themselves to life on Earth.The vestibular organ deep inside the ear helps humans keep their bodies balanced while walking on Earth by sending information about gravity to the brain.”In the low gravity of space, the information received from the vestibular organs changes. This is thought to confuse the brain, leading to space sickness. When you return to earth, you experience the effects of earth’s gravity again, and thus ‘gravity sickness’ sometimes occurs, with similar symptoms as space sickness,” the Japanese space agency JAXA said.On Earth, gravity pulls blood and other body fluids into the lower part of the body, but for astronauts experiencing weightlessness in space, these fluids accumulate in the upper parts of the body, making them look bloated.”Astronauts returning to earth often experience dizziness when standing up, known as orthostatic hypotension. This occurs because gravity on the earth is stronger than in space, and it is more difficult to deliver blood from the heart to the head,” the JAXA said.The lack of gravity causes significant and often irreparable bone density loss. According to NASA, for every month in space, astronauts’ weight-bearing bones become roughly one per cent less dense if they don’t take precautions to counter this loss.To help combat this, astronauts aboard the International Space Station (ISS) have a strict exercise regimen.”Astronauts are required to exercise two hours per day, using the treadmill or stationary bicycle, to avoid the bone and muscle deterioration that occurs in zero gravity. Without this exercise, astronauts would be unable to walk or stand up when they return to Earth after months of floating in space,” NASA said.Canadian astronaut Chris Hadfield reported to have experienced a weightless tongue on his return from a stint at the International Space Station in 2013.”Right after I landed, I could feel the weight of my lips and tongue and I had to change how I was talking. I hadn’t realised that I learned to talk with a weightless tongue,” Hadfield had said.Astronauts may also be more susceptible to infection and illness due to a suppressed immune system.”While we see that immune cells do not behave in the way they should in space, so far we haven’t had any severe infection on board the Space Station, so cell altered behaviour is not directly transferable to immune protection,” European Space Agency’s flight surgeon Sergi Vaquer said in a blog post on the agency’s website.
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