Mission Control said Monday that unless something goes awry, two astronauts ought to finish installing a new ammonia pump Tuesday, during this second spacewalk. NASA originally thought three spacewalks might be needed.
Astronauts Rick Mastracchio and Michael Hopkins removed the faulty pump Saturday. Everything went so well, they jumped ahead in their effort to fix the external cooling line that shut down Dec. 11.
A bad valve in the pump caused the breakdown, prompting the urgent series of spacewalk repairs.
The second spacewalk should have been Monday, but was bumped a day so Mastracchio could swap suits. He inadvertently hit the water switch in the air lock following Saturday's spacewalk, and engineers suspect water entered his suit. The suit needs to dry out for at least a week before being used again, said flight director Judd Frieling.
Saturday's water intrusion is unrelated to helmet leakage that almost drowned an Italian spacewalker in July.
Two of the three Russians crew members, meanwhile, will conduct a Moscow-directed spacewalk on Friday to install cameras and fresh experiments. It was planned long before the U.S. cooling system ran into trouble.
The sixth space station resident is Japanese and will assist from inside during Tuesday's U.S. spacewalk.
NASA has conducted a Christmas Eve spacewalk only once before, during a Hubble Space Telescope repair mission in 1999.
Mission Control said it expects no conflicts between the path of the space station and Santa's flight: "The skies are all clear," commentator Rob Navias observed from Houston.
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