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NASA's Scott Kelly goes head over heels in space

International Space Station commander Scott Kelly says he's "feeling great," a little more than halfway through his year-long mission in orbit.

"I'm looking forward to the second half of this year in space," Kelly told CBS News' Vlad Duthiers in a video interview from the ISS on Friday.

But he said the extended mission does pose some physical challenges. "There are some negative effects to living in this microgravity environment. Effects due to radiation, effects on our immune system. Bone loss, muscle loss, things like that," he said.

Kelly is a veteran of previous space station missions, so he was prepared for conditions others might find daunting, like the tight quarters and lack of time outdoors.

Kelly said he and his crew-mates have been keeping busy with scientific experiments. But he took some time out for fun, too, showing off his "Olympic-caliber flip technique" with a series of somersaults for the camera. Watch the video above for more.