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PERIL in ORBIT: ISS leak plugged in FIVE-HOUR spacewalk

Nauts lash new ammonia pump on leaky truss

International Space Station engineers Chris Cassidy and Tom Marshburn have plugged the ammonia coolant leak on the orbiting science lab.

The pair's successful spacewalk and repair job over the weekend has cleared the way for their crewmates to set off home for Earth tonight.

Flight Engineers Cassidy and Marshburn completed their five-and-a-half-hour task at 7pm BST on Saturday during which they replaced a pump controller box on the far port truss - which was streaming the ammonia needed to keep the station's power supply electronics cool.

The 'nauts installed the new 260-pound spare controller box on the truss and stayed out in the obsidian void while planet-side Mission Control tested the pump. The pair didn't see any white ammonia flakes, meaning the chemical was no longer leaking from the platform. NASA said long-term monitoring will be necessary to make sure the problem is definitely fixed.

The P6 truss is the oldest component of the station's backbone, and was launched into space aboard the shuttle Endeavour in November 2000. It was moved to the far left side of the station during the Discovery mission seven years later.

The weekend spacewalk was approved late on Friday after Commander Chris Hadfield noticed the coolant system breach on Thursday evening. Although the crew was never in any danger, Hadfield, Marshburn and Russian cosmonaut Roman Ramanenko could have missed their window to return home tonight.

The three 'nauts are due to set off from the station at a few minutes past midnight, British time, aboard a Soyuz TMA-07M transport craft, and arrive at 3.30am BST on Tuesday in Kazakhstan, after 146 days in space.

Cmdr Hadfield has already ceremonially handed over control of the station to Expedition 36 Commander Pavel Vinogradov, the first half of the crew along with Flight Engineers Cassidy and Alexander Misurkin. ®

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