NASA astronauts Tuesday successfully replaced a faulty fluid pump in the International Space Station, following two days of work in the open vacuum of space 260 miles above the Earth's surface.
The 7 1/2-hour spacewalk was only the second in NASA history to occur on Christmas Eve. The first was in 1999, when astronauts made repairs to the Hubble Space Telescope.
Like any DIY home-improvement project, the work involved a glitch or two. The first occurred when a fluid line refused to budge and Astronauts Rick Mastracchio and Michael Hopkins struggled to remove it.
When they finally did get it off, tiny flakes of frozen ammonia drifted from the connection, raising concerns that the flakes had landed on the astronauts' spacesuits and might be brought back into the ISS, where they would instantly turn to a corrosive gas.
Though the crewmen initially planned to undergo a decontamination procedure known as a "bake-off," that requirement was waived in the final minutes of the mission. Lengthy exposure to the sun during the work probably eliminated the threat, Mission Control in Houston determined.
"Head to the barn," Mission Control told the astronauts as they entered the space station's airlock just before 11 a.m. PST, after completing the work.
On Saturday, the astronauts worked 5 1/2 hours to disconnect the faulty pump from four ammonia fluid lines and move it to a storage site.
Early Tuesday morning, the astronauts maneuvered a new, refrigerator-sized pump into place with the help of a massive robotic arm controlled by Japanese astronaut Koichi Wakata inside the station.
"Mike Hopkins taking a special sleigh ride on this Christmas Eve," Mission Control commentator Rob Navias said as Hopkins stood on the end of the robotic arm gripping the new pump.
The 3-year-old ammonia pump stopped working on Dec. 11 due to a faulty valve, requiring astronauts to halt numerous science experiments until the problem was resolved. The replacement pump is one of three spares on the ISS.
The second day of repair work was initially planned for Monday, but the spacewalk was postponed a day due to a potential problem with Mastracchio's spacesuit. Crew members reported that water entered the suit when the astronaut accidentally hit a switch in the space station airlock.
The postponement allowed crew members to assemble a second replacement suit for Mastracchio.
The recent spacewalks were absent the problems that plagued Italian astronaut Luca Parmitano of the European Space Agency in July. During that walk, Parmitano's helmet began to fill with water when the suit's cooling system backed up and began to leak. The astronaut nearly drowned as blobs of weightless water clung to his head.
NASA officials said the problems with the two spacesuits were unrelated, and that the suits had been modified to prevent such episodes in the future. Those modifications included the installation of absorbent pads and breathing snorkels.