"We are going to slip EVA-25 one day and so that's going to move to Tuesday, Dec. 24. Merry Christmas Eve," radioed astronaut Kate Rubins from mission control. "We are going to cancel the morning DPC (daily planning conference) tomorrow so you guys can sleep in a few extra hours."
A NASA statement released late Saturday said the decision to delay the spacewalk from Monday to Tuesday would give the crew time to assemble a backup spacesuit for Mastracchio after a "configuration issue" raised questions about whether the original suit could be used.
"The extra day will allow time for the crew to resize a spare spacesuit on the space station for use by Mastracchio," the agency said in a brief statement. "During repressurization of the space station's airlock following Saturday's spacewalk, a suit configuration issue put the suit Mastracchio was wearing in question for the next excursion. The flight control team at the agency's Johnson Space Center in Houston decided to switch to the backup suit for the next spacewalk.
"This issue is not related to the water leak that was seen during a July spacewalk by European Space Agency astronaut Luca Parmitano and NASA's Chris Cassidy. Both Mastracchio and Hopkins reported dry conditions repeatedly throughout today's activities."
No other details were provided.
Earlier, the crew was told Mastracchio's suit needed to be dried out because of water in its sublimator, a device that helps dissipate excess heat. What caused the excess dampness was not explained.
Assuming no other problems crop up, the second spacewalk will begin at 7:10 a.m. EST Tuesday.
Despite the delay, Mastracchio and Hopkins were able to complete the primary objectives of Saturday's spacewalk, along with a major item on the list of tasks planned for their second excursion. Barring major problems, it appears likely the astronauts will be able to complete the coolant system repair work in two spacewalks without the need for a third excursion.
In any case, the delay from Monday to Tuesday takes a Christmas spacewalk off the table. If a third EVA is required for some reason, it is unlikely to take place before Thursday.
In the meantime, Rubins said, "we're working the plan to let you guys sleep in tomorrow."
"Sounds good. Thank you very much," Wakata replied.
Mastracchio and Hopkins switched their spacesuits to battery power at 7:01 a.m. to officially kick off the first of at least two spacewalks to remove a suspect ammonia pump module and install a replacement. Trouble with a valve inside the pump assembly partially disabled one of the station's two cooling loops, which are needed to dissipate the heat generated by the lab's electrical systems.
While the failure did not put the crew in any danger, the partial loss of cooling forced flight controllers to power down non-essential equipment in the forward modules of the outpost, including equipment used for scientific research. Repairing coolant loop A is a high-priority for the crew, both to resume normal operations and to restore lost redundancy in a critical system.
The pump module in question was installed during a series of spacewalks in August 2010. Major problems getting large ammonia lines disconnected and re-attached delayed the repair work and forced the crew to carry out a third, unplanned EVA to finish the work.
This time around, flight planners built a third spacewalk into the timeline right off the bat in case similar problems developed. But Mastracchio and Hopkins had no problems disconnecting the pump module Saturday and, running well ahead of schedule, they were able to remove it from the station's solar power truss and mount it on a storage fixture.
The original plan called for the spacewalkers to simply disconnect the pump module and to remove it during a second spacewalk Monday. But Mastracchio and Hopkins got the pump out well ahead of schedule, prompting flight planners to ask the astronauts to extend the spacewalk in order to complete a few other get-ahead tasks on Monday's timeline.
Astronauts seldom object to such extensions, but Mastracchio told Douglas Wheelock in mission control that he preferred ending the spacewalk at that point.
"My vote would be to call it (off) for today, but it's up to you guys if you really want to go out there," Mastracchio radioed shortly after mounting the old pump on a storage fixture.
"And Rick, could you give us some ideas if it's temperature, your (suit) temperature?" Wheelock asked. He was referring to an earlier conversation when Mastracchio reported his feet were unusually cold.
"It's just, more a couple of things," Mastracchio replied, declining to provide details on the open space-to-ground audio loop.