Science

Two astronauts went on a last-minute spacewalk Saturday to replace a pump suspected of being the source of a serious ammonia leak.

It was unclear what caused the ammonia leak, NASA spokesman Rob Navias said, "but the installation of this spare pump package — at least at the moment — seems to have done the trick."

NASA officials called the spacewalk a success, but said it would take time to see if the leak was indeed stopped. Engineers will review photos the astronauts took at the site.

Astronauts aboard the International Space Station will undertake a spacewalk Saturday morning to try to repair a leak in their cooling system.

The leak appears to be ammonia used in a power supply. It was spotted midmorning on Thursday. Commander Chris Hadfield reported seeing "a very steady stream of flakes or bits" floating away from the station. On the ground, mission control noticed a steady drop in ammonia levels on one of the station's eight power channels. The same channel had problems back in November of 2012.

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