Two astronauts working speedily outside the International Space Station removed a faulty pump module ahead of schedule, potentially negating the need for a planned Christmas Day spacewalk as they work to repair the outposts critical cooling system.

NASA astronauts Rick Mastracchio and Mike Hopkins ventured outside the space station at 7:01 a.m. EST (1101 GMT) today (Dec. 21), just 10 days after a flow control valve malfunctioned inside the pump module that they were set to remove and replace during another 6.5-hour spacewalk on Monday. Saturdays spacewalk ended at 12:29 p.m. EST (1729 GMT), five hours and 28 minutes after it began.

Originally, the astronauts were just going to prepare the faulty pump for removal today, but the spacewalkers completed the majority of the planned tasks for Saturdays spacewalk in just three hours. The astronauts were then given a go by Mission Control in Houston to press ahead with removing the faulty refrigerator-size pump module and stow it on a nearby platform. [See photos from the speedy spacewalk]

Were about an hour and a half ahead of the timeline, so, choosing your own adventure, were going to go ahead and look forward to doing the pump module exit, Mission Control advised the astronauts.

Ahead of the spacewalk schedule

The early removal could mean that a third spacewalk planned for Dec. 25, Christmas Day, may not be needed.

The faulty valve, which regulates the temperature of ammonia flowing through the pump, ceased working properly on Dec. 11. Non-critical systems and science experiments in two of the stations laboratories have been powered down since.

Saturdays spacewalk was originally focused on only disconnecting the fluid lines from the failed pump module and installing a jumper box to keep the ammonia from over pressurizing during the pumps replacement.

Working along the starboard, or right, side of the stations backbone truss, Mastracchio (riding on the end of the Canadarm2 robotic arm) and Hopkins first set about demating quick disconnect fluid lines from the faulty pump.

As their name implies, the quick disconnects were designed to be plugged in and out, but past spacewalks, including an August 2010 outing to replace the same pump module, ran into problems getting the pressurized lines loose. Learning from previous experiences, the pressure in the lines was reduced in preparation for Saturdays spacewalk.

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Spacewalking Astronauts Remove Faulty Space Station Pump