Calling it "bittersweet," Nasa astronaut Scott Kelly handed over command of the International Space Station to Tim Kopra on 29 February, as he prepared to return home after enduring the longest spaceflight by an American ever.

"A really smart person said to me one time, 'team work makes the dream work in space flight'," said the 52 year-old astronaut, who has participated in three previous flights. "Space flight is the biggest team sport there is, and it's incredibly important that we all work together to make what is seemingly impossible, possible," said Kelly.

Kelly is set to return to Earth on 1 March, after spending 340 days in space, making the New Jersey native the first American to live in space for such a long period. During his time on the space station, Kelly celebrated a birthday, conducted space walks and nibbled on space veggies.

Kelly told reporters he hoped his marathon mission would provide critical details that would help mankind reach Mars. The extended stay is among other things that should help Nasa better understand the effects that prolonged weightlessness has on the human body.

Kelly and Russian cosmonauts Mikhail Kornienko and Sergey Volkov are scheduled to touch down in Kazakhstan, at about 11.45pm EST after spending 340 days on in space. Since arriving at the space station on 27 March 2015, Kelly and Korneinko have served with eight different crewmates, unpacked six cargo ships, weathered two botched supply runs and participated in dozens of science experiments.