- Astronaut Rick Mastracchio, on the first of two successful spacewalks (Image: NASA)
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The system circulates ammonia to keep internal and external instruments at the correct temperature. NASA had to power down parts of three ISS modules when the system malfunctioned on 11 December.
On 24 December, astronauts Rick Mastracchio and Mike Hopkins completed the second of three planned spacewalks to replace a failed pump module on the station's exterior. Although they were hit by a "mini blizzard" of toxic ammonia flakes that burst from a supply line, they finished the job ahead of schedule, eliminating the need for a third outing.
Snorkels on standby
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Hopkins was wearing the same spacesuit used last July by Italian astronaut Luca Parmitano, who nearly drowned when his helmet started filling with water. NASA investigators concluded that the most likely cause of the leak was contamination in the suit's cooling system, which blocked a filter.
Although the filter was cleared NASA didn't want to take any chances so instructed the astronauts to fashion snorkels from plastic tubes and Velcro. That would allow them to breathe air from lower in the suit in the event of a leak. As it was, their helmets remained bone dry.
While things went smoothly, the repairs meant delaying the first resupply mission for private company Orbital Sciences Corporation of Dulles, Virginia. Its Cygnus cargo craft is now scheduled to begin official deliveries to the ISS in January.
On return to the ISS, Hopkins thanked ground crew: "Merry Christmas to everybody. It took a couple of licks to get her done, but we got it."