NEWS: Scott Kelly, NASA's 1-Year Space Twin, Returns Today
Kelly was also part of an experiment comparing his development and changes in space with his identical twin brother -- Mark -- back on Earth.
"Spaceflight is the biggest team sport there is, and it's incredibly important that we all work together to make what is seemingly impossible possible," Kelly said when handing over command of the ISS to fellow NASA astronaut Tim Kopra on Monday.
In his year aboard the space station Kelly has been an avid Internet poster, capturing stunning views on his Instagram page and tweeting regularly to nearly a million followers while traveling some 143 million miles (230 million kilometers).
In one particularly eye-catching stunt the bald-headed astronaut posted a short video of himself dressed up in a gorilla suit and floating through the ISS in pursuit of a colleague.
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"Needed a little humour to lighten up a year in space," he wrote on Twitter on Feb. 23, when he posted the video.