Spacewalkers Rick Mastracchio and Mike Hopkinscompleted phase one of a complex coolant system repair jobaboard the International Space Station Saturday, but a problem with Mastracchio's suit prompted flight controllers to delay a second spacewalk for 24 hours, from Monday to Christmas Eve.

"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 second 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. "During repressurization of the station's airlock following the spacewalk, a spacesuit configuration issue put the suit Mastracchio was wearing in question for the next excursion -- specifically whether water entered into the suit's sublimator inside the airlock."

The sublimator is a device in the spacesuit's backpack that helps dissipate excess heat.

In any case, NASA said, "the flight control team at NASA's Johnson Space Center in Houston decided to switch to a backup suit for the next spacewalk."

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During an earlier post-spacewalk exchange between Japanese astronaut Koichi Wakata and mission control, it appeared an inadvertent switch throw might have played a role.

"And Houston, (this is the) airlock, on one," Wakata called down. "EV-1, he inadvertently moved the water switch to on and it was quickly returned to off, o-f-f."

"Copy, standby," astronaut Akihiko Hoshide replied from Houston. "And Koichi, just to confirm, that was a very brief moment?"

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International Space Station Spacewalk Delayed