Chris Hadfield hands over command of ISS

Chris Hadfield handed over command of the International Space Station to a new leader on Sunday, one day before he is scheduled to return to Earth.

The Canadian astronaut handed over the job to Russian cosmonaut Pavel Vinogradov at 3:40 p.m. ET

Hadfield had high praise for the station’s six-person crew and his successor in particular. Vinogradov was the first to notice the station’s recent ammonia leak, which led to a hastily organized spacewalk and repairs on Saturday.

"For me, it really all came together in the last three days," said Hadfield, citing the crew’s performance during the dangerous and "extremely complex" job.

Hadfield went on to praise the station's overall pursuit of scientific research and its spirit of international co-operation.

"This is a human research vessel. We’ve shared it with millions of people around the world, and we’ve done our absolute best to accomplish the work on board," he said.

Hadfield has spent the past five months aboard the orbiting outpost, but on Monday, he and two crew members are scheduled to leave the space station, just after 7 p.m. ET.

American Tom Marshburn and Russian Roman Romanenko will join Hadfield as they undock their Russian Soyuz spacecraft from the station and head back to Earth for a planned 10:31 p.m. ET landing in Kazakhstan.

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A helicopter will take them to a local airport, where a waiting NASA plane will fly them to Houston, Tex.

"Time to rev up the Soyuz, home tomorrow," Hadfield wrote earlier on Twitter.

Vinogradov and fellow cosmonaut Alexander Misurkin will stay behind on the ISS, along with American Chris Cassidy. Cassidy and Marshburn installed a new ammonia pump on Saturday after removing the old one, which was suspected of spewing flakes of frozen coolant into space.

They uncovered "no smoking guns," said NASA, responsible for the leak and kept a sharp lookout for any icy flecks that might appear from the massive frame that holds the solar panels on the left side.

NASA officials remain mystified as to why the leak erupted. Managers wanted to deal with the leak while it was fresh and before Marshburn returns to Earth on Monday.

NASA says it could be weeks before it knows whether the 5½-hour spacewalk was a success.