Last December, U.S. astronaut Don Pettit launched from Kazakhstan in a Russian Soyuz space capsule and arrived at the International Space Station, where he spent the next 191 days. While there, Pettit orbited the Earth 3,088 times and witnessed the arrival of the SpaceX Dragon, the first commercial craft to dock at the ISS. He also experienced significant physiological changes. Extended periods in low gravity lead to bone density loss and heart shrinkage. When Pettit returned to Earth in July, his body could not endure even minor physical exertion in normal gravity, so the ground crew carried him to a nearby medical tent for routine post-spaceflight examinations. Research has shown that astronauts’ muscle tone improves after a few weeks, but their bone density may never return to pre-spaceflight levels.