A NASA space walker overcame a literal case of cold feet Saturday to breeze through the start of repairs to a critical International Space Station cooling system.
Rick Mastracchio removed a faulty coolant pump far ahead of schedule, potentially enabling him and partner Mike Hopkins to install a spare on a second spacewalk, now planned Tuesday, and not have to go outside a third time.
But given the opportunity to get further ahead Saturday, Mastracchio said he'd prefer to "call it a day" on his seventh career spacewalk.
He had earlier reported feeling "very, very cold," first in his fingers and then his toes, which he could barely move with his feet fastened to the end of the station's 58-foot robotic arm.
"Because I'm just floating here on the arm, I've got very, very good air flow in my boots, but my toes are quite cold," he said.
Mastracchio turned on spacesuit heaters, but apparently needed to return inside the station to thaw out.
He plans to switch to a different spacesuit for the next excursion, which had been planned Monday but will take an extra day to get ready.
Despite ending an hour earlier than planned, Saturday's five-hour, 28-minute spacewalk accomplished more than expected.
Masstracchio and Hopkins, who was on his first spacewalk, successfully slid a refrigerator-sized pump module from a station girder and stowed it away.
Timelines had called for preparing the 780-pound box for removal but completing that work on a second spacewwalk.
"Early Christmas," astronaut Doug Wheelock radioed from Houston after Mastracchio released a last bolt.
A valve inside the pump module failed on Dec. 11, limiting its ability to regulate temperatures in one of the two external coolant loops that dissipate heat generated by station systems.
Non-essential systems were shut down in the U.S. portion of the complex, putting science research on hold and leaving the station more vulnerable to a failure of the second loop.
NASA delayed the launch of a resupply mission and scheduled up to three spacewalks to replace the pump module with the bad valve.
Mastracchio got things off to a fast start, accomplishing with surprising ease what was expected to be the day's toughest task.
He benefited from lessons learned in 2010 when Wheelock and Tracy Caldwell Dyson struggled to disconnect the pump module's four coolant hoses and dealt with leaks of ammonia.
This time, only a few ammonia snowflakes squirted out, causing no concern that contaminated spacesuits could track the highly toxic substance back inside the station and endanger the six-person crew, which also includes three Russian cosmonauts and a Japanese astronaut.
Other than Mastracchio's frosty feet, Saturday's spacewalk fared much better than the previous one in U.S. spacesuits from a safety standpoint.
Neither astronaut reported any water leaking into their helmets, a problem that threatened to drown Italian astronaut Luca Parmitano in July.
Mastracchio and Hopkins set out with new absorbent pads in their helmets and "snorkels" they could breathe through as a last resort, and they periodically paused to check for signs of "squishiness."
The day included moments of holiday-inspired humor, like when Mastracchio caught a small O-ring before it floated away.
"Don't let that go," said Wheelock. "It's a stocking stuffer."
"Don't tell my wife," replied Mastracchio, who stuffed the part into a trash bag to prevent it from becoming orbital debris.
It remains to be seen if the spacewalkers need a third spacewalk to complete their repairs. They might not, if the new pump goes in as easily on Tuesday as the old one came out Saturday.
That would be ideal, because two cosmonauts are already preparing to conduct another, unrelated spacewalk late this week.
Saturday's spacewalk was the 175th supporting assembly and maintenance of the 15-year-old station, which has been inhabited continuously since 2000.