Astronauts Replace Pump on Emergency Spacewalk
Chris Cassidy and Tom Marshburn completed the work an hour ahead of schedule, reporting no further escape.
The crew had spotted particles of ammonia drifting away from the laboratory on Thursday.
Nasa said the crew were not at risk but managers wanted to solve the problem before Mr Marshburn left the station.
He is due to return to Earth early next week along with the space station’s Canadian commander Chris Hadfield and Russian cosmonaut Roman Romanenko, after six months in space.
Liquid ammonia is used to extract the heat that builds up in electronic systems, dumping that excess energy to space through an array of radiators.
Ammonia flows through radiators (white panels) to dump heat into space
“No leaks! We’re bringing Tom & Chris back inside,” Mr Hadfield wrote on his Twitter account, some four and a half hours into the spacewalk.