Astronauts  Rick Mastracchio and  Mike Hopkins are now outside the ISS installing the spare pump in the cooling system. It is the second of perhaps three spacewalks needed to fix the system. (See earlier post on the first EVA last Saturday.) So far they have mechanically installed the pump and are now reconnecting the ammonia lines to the pump.

They had difficulty disconnected one line from a temporary jumper box. After they finally disconnected it, there was venting of ammonia as small snowflakes, some of which got on their suits. They will have to go through a decontamination procedure before they reenter the airlock. This could mean shortening the spacewalk.

See updates and pictures at ISS Updates (ISS101) on Twitter.

[ Update: The astronauts finished their EVA and they also completed the repairs to the cooling system. So a third EVA will not be needed:

• Spacewalkers finish crucial space station repairs in time for Christmas – NBC News.com
• Holiday calendar: Santa never had a view like this! – MSNBC PhotoBlog
• Astronauts complete installation of new ISS Pump Module  – NASASpaceFlight.com

]

Other updates and info at:

• Space Station Mission Report | Mission Status Center – Spaceflight Now
• Spacewalkers aim to finish coolant system repairs – CBS News/Spaceflight Now

Some images of the astronauts moving the spare pump into place:

Astronauts  Rick Mastracchio and  Mike Hopkins have just concluded what appears to have been a very successful EVA this morning. It is the first of two or perhaps three spacewalks needed to fix the balky pump in the cooling system for the station. Today they removed the failed pump and prepared for inserting a spare pump on Monday.

• Space Station Mission Report | Mission Status Center – Spaceflight Now
• Spacewalkers conducting first of three Pump Module replacement EVAs – NASASpaceFlight.com
• Spacewalk begins complex job of replacing coolant pump – Spaceflight Now

Lots of pictures from the EVA were posted at ISS Updates (ISS101) on Twitter.

NASA astronauts will make up to three spacewalks starting on Dec. 21st to fix a pump valve in the cooling system. The EVAs are complicated by the spacesuit leak that occurred during a spacewalk last July by Italian astronaut Luca Parmitano, who came close to drowning in space.

Here are some details about the cooling system and the spacesuit issue:

• Leaky Spacesuit Fixed For Christmas Spacewalk Blitz On Station, NASA Says – Universe Today
• NASA equips astronauts with snorkels, absorbent pads – CBS News/Spaceflight Now
• NASA orders spacewalks to fix station coolant loop – CBS News/Spaceflight Now

NASA gave a briefing on Wednesday on plan:

Caption:

During NASA Television press briefing from Johnson Space Center, agency managers discussed a series of planned spacewalks, Dec. 21, 23 and 25 by NASA astronauts Rick Mastracchio and Mike Hopkins to replace a faulty coolant pump on the International Space Station.

The pump is associated with one of the station’s two external cooling loops, which circulate ammonia outside the station to keep both internal and external equipment cool.

The previously planned Orbital Sciences commercial cargo resupply mission to the International Space Station has been postponed until no earlier than mid-January. The postponement will allow ample time for the station crew to focus on repairing the pump module, which stopped working properly on Dec. 11.