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Astronauts replace pump on spacewalk

Two US astronauts have replaced a pump on a spacewalk in the hope of fixing a leak of ammonia from the International Space Station's cooling system.

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.

Jane O'Brien reports.

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