Astronauts can survive on the International Space Station (ISS) for quite a while. On average, they stay up there for about six months. The ISS is like a high-tech home, complete with exercise equipment and scientific experiments. But living in microgravity can weaken muscles and bones, so astronauts have to work out every day to stay in shape. Eventually, they would need to return to Earth. If they stayed up there too long, their muscles and bones could weaken to the point where they'd struggle to walk when they got back. Plus, they'd run out of supplies sent from our planet.

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