WASHINGTON -- Two NASA astronauts successfully upgraded the International Space Station's (ISS) cooling system Sunday during the second in a series of landmark spacewalks outside the orbital laboratory.

ISS Expedition 14 commander Michael Lopez-Alegria and flight engineer Sunita Williams pushed through more than seven hours orbital work despite a minor leak of toxic ammonia coolant that prompted brief pause for spacesuit inspections [image].

"I don't see anything that looks like any type of build-up," Williams said.

Derek Hassmann, NASA's lead flight director for Expedition 14's U.S. spacewalks, said the leak was so slight it could be seen in video views from the crew's helmet cameras. A planned Feb. 8 spacewalk does not in include any ammonia line work, he added.

"I would say that we've got the most challenging pieces of this EVA triplet behind us, Hassmann said after the spacewalk. "I couldn't be any more happier with the crew."

Sunday's extravehicular activity (EVA) marked the second in nine days for the Expedition 14 crew in what is densest period of ISS spacewalks to date without a visiting space shuttle.

Cooling system upgrades

Sunday's spacewalk began at 8:38 a.m. EST (1338 GMT).

"Good luck and be careful," ISS Expedition 14 flight engineer Mikhail Tyurin, who helped the two spacewalkers don their U.S. spacesuits, told his crewmates as they began today's excursion. "I'll see you out the window."

Lopez-Alegria and Williams sped through their ISS cooling system work, reconfiguring four "Loop B" fluid lines that allow liquid ammonia to cool avionics and payload systems inside the station's U.S. Destiny laboratory.

The astronauts switched the cooling system from a temporary set up, on the station's mast-like Port 6 truss, to its permanent configuration running through Destiny. They then helped retract an unneeded radiator extending aft from the Port 6 truss [image].

The spacewalkers reconfigured the system's other half -- Loop A -- during a Jan. 31 spacewalk. The two spacewalks primed the station's cooling system to handle future ISS construction and prepare the Port 6 element for its eventual relocation to the port-most edge of the ISS in September.

In both EVAs, the spacewalkers took great care handling the ammonia lines, since the toxic coolant can be an irritant in small quantities and cause respiratory problems in larger amounts.

"They're tiny, little, tiny flakes," Lopez-Alegria said of Sunday's ammonia sighting, adding that the bits of toxic frozen flakes were not like those seen during a Jan. 31 spacewalk that prompted more lengthy decontamination efforts. "They look like pinpoints."

The spacewalkers did have to perform some final minor ammonia decontamination tests, though Lopez-Alegria held out hope to end that Mission Controllers would change their mind.

"I was wondering if you guys want to give that a second thought since we have a football game to watch," said Lopez-Alegria, referring to today's Super Bowl contest between the Chicago Bears and the Indianapolis Colts [image].

Despite his pleas, flight controllers opted for the decontamination tests.

"Gosh, it was worth a try," Lopez-Alegria joked.

Setting records, other tasks

Williams [image] set an all-time record for female spacewalkers, taking the No. 1 spot after today's EVA -- her third -- and racking up a total of 22 hours and 37 minutes. She surpassed the more than 21 hours of the previous record-holder: former NASA astronaut Kathryn Thornton.

Lopez-Alegria, too, climbed up the ranks of all-time spacewalkers.

He began the EVA in fourth place but ended in third, with a total of 54 hours and 42 minutes. NASA astronaut Jerry Ross -- the U.S. spacewalking champion with 58 hours and 32 minutes -- and Russian cosmonaut Anatoly Solovyev, who staged 16 career spacewalks for a total of 72 hours and 28 minutes, still lie ahead of Lopez-Alegria.

In addition to completing the ISS cooling system overhaul, Lopez-Alegria and Williams retrieved the second of two fluid lines from a disposable ammonia coolant container.

Lopez-Alegria also removed an unneeded thermal cover from a computer relay box outside the ISS and conducted a photographic survey of the station's starboard-reaching solar array extending from the Port 6 truss [image]. The survey images will allow engineers on Earth to study the best way to retract the solar array -- its port-reaching counterpart was stowed in NASA's December shuttle flight -- during next month's STS-117 construction mission to the ISS.

But the two spacewalkers were unable to completely install a series of electrical cables that, when activated this summer, will allow visiting NASA shuttles to draw on the station's power supply and stay docked at the outpost for longer periods [image].

Sunday's spacewalk marked the 79^th EVA aimed at ISS assembly or maintenance and the 51^st staged from the orbital laboratory itself. It was also the 31^st spacewalk to begin at NASA's Quest airlock, but won't be the last.

Lopez-Alegria and Williams are scheduled to make one last NASA spacewalk together on Thursday, Feb. 8 to perform a series of ISS maintenance and construction jobs. That spacewalk, like Sunday's, will also be staged from the Quest airlock.

"We look forward to one more," Lopez-Alegria said.

The fourth spacewalk in Expedition 14's EVA quartet, a Russian excursion to help free a cargo ship's jammed antenna, will begin from the station's Russian-built Pirs docking compartment on Feb. 22.  

The third of four Expedition 14 spacewalks is scheduled begin at 9:00 am. EST (1400 GMT) on Thursday, Feb. 8, and will be broadcast live on NASA TV.

• VIDEO: Expedition 14 Feb. 4 Spacewalk Overview
• VIDEO: Expedition 14 Jan. 31 Spacewalk Overview
• ISS Crew Prepares for Record Setting Spacewalks
• Complete Coverage: ISS Expedition 14
• All About the International Space Station