NASA astronauts took a spacewalk Wednesday to shuffle around a couple of space station pumps.

Popping out early, Drew Feustel and Ricky Arnold quickly began rearranging the International Space Station’s external cooling system by swapping the positions of two spare ammonia pumps.

NASA wants the best spare in the best spot to call into action if needed down the road. One pump got too cold because of a power shutdown 17 years ago and is called Frosty. The other spewed out ammonia five years ago and is dubbed Leaky.

Mission Control warned the spacewalkers to be careful of possible leaks of the toxic ammonia coolant.

Meanwhile, the station’s six-man crew is expecting a delivery. Orbital ATK plans to launch a supply ship Sunday from Wallops Island, Virginia. Weather permitting, the pre-dawn flight of the Antares rocket should be visible along the East Coast from New England to South Carolina.

Feustel and Arnold went spacewalking at the end of March, shortly after arriving at the 250-mile-high lab. They have another spacewalk lined up for next month.
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