Astronauts have made an emergency spacewalk to fix a coolant pump needed to keep the International Space Station at full power.
NASA astronauts Chris Cassidy and Tom Marshburn left the space station's airlock on Saturday to attempt to stem an ammonia coolant leak that cropped up on Thursday.
Over the next four hours, they installed a spare pump, then positioned themselves to check for signs of escaping ammonia ice crystals when the system was turned back on. The entire spacewalk lasted five-and-a-half hours
Engineers will monitor the system over the next several days and beyond to make sure the pump replacement fixed the problem.
The station crew discovered a steady stream of ammonia flakes flowing away from the far left side of the station's exterior frame on Thursday. Flight controllers spent the next 48 hours diagnosing the problem and coming up with potential solutions.
Engineers believed the leak was most likely coming from in or around a 118 kg pump that pushes ammonia throughout the system. The coolant dissipates heat from electronics in space station's solar-powered electrical system.
The station can be reconfigured to compensate for a system shutdown, but if a second problem should occur, that likely would mean a cutback in power available for the experiments.
The $US100 billion station which flies about 400 kilometres above Earth is a research laboratory for biomedical, physics, astronomical and other experiments, as well as for technology development and demonstrations.
On Sunday, station commander Chris Hadfield, the first Canadian to lead the international outpost, turns over the helm to Russian cosmonaut Pavel Vinogradov. The Canadian, Tom Marshburn and cosmonaut Roman Romanenko, who have been aboard the station since December, are scheduled to depart on Monday.
Their replacements are NASA's Karen Nyberg, Italy's Luca Parmitano and Russian Fyodor Yurchikhin who are due to launch on 28 May.