Astronauts successfully spacewalk, replace pump outside International Space Station

CAPE CANAVERAL, Fla. – Astronauts making a rare, hastily planned spacewalk replaced a pump outside the International Space Station on Saturday in hopes of plugging a serious ammonia leak.

The prospects of success grew as the minutes passed and no frozen flecks of ammonia appeared. Mission Control said it appeared as though the leak may have been plugged, although more monitoring was needed before declaring a victory.

“No evidence of any ammonia leakage whatsoever. We have an airtight system – at the moment,” Mission Control reported.

WATCH: NASA officials hold a news conference following a spacewalk outside the International Space Station to replace a broken coolant pump.

Christopher Cassidy and Thomas Marshburn installed the new pump after removing the old one suspected of spewing flakes of frozen ammonia coolant two days earlier.

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The leak was reported by ISS Commander Chris Hadfield of the Canadian Space Agency on Thursday.

“[I saw] a very steady stream of flakes or bits coming out…” Hadfield reported.

Listen: Hadfield tells Mission Control that the ISS crew is ready for a space walk.

Commander Hadfield did not make the EVA. Instead, astronauts Chris Cassidy and Tom Marshburn conducted an investigation.

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