Astronauts aboard the International Space Station removed an old pump Saturday, sailing through the first of a series of urgent spacewalks needed to repair a crippled cooling line.
The two Americans on the crew, Rick Mastracchio and Michael Hopkins, successfully pulled out the ammonia pump with a bad valve well ahead of schedule. That task had been planned for the next spacewalk on Monday.
"An early Christmas," observed Mission Control as Mastracchio tugged the refrigerator-size pump away from its nesting spot.
If Mastracchio and Hopkins keep up the quick work, two spacewalks may be enough to complete the installation of a spare pump and a third spacewalk will not be needed on Christmas Day as originally anticipated.
The breakdown 10 days earlier left one of two identical cooling loops too cold and forced the astronauts to turn off all nonessential equipment inside the orbiting lab, bringing scientific research to a near-halt and leaving the station in a vulnerable state.
Mastracchio, a seven-time spacewalker, and Hopkins, making his first, wore extra safety gear as they worked outside.
The pump replacement is a huge undertaking attempted only once before, back in 2010 on this very unit. The two astronauts who tackled the job three years ago were in Mission Control, offering guidance.
The 780-pound pump is about the size of a double-door refrigerator and extremely cumbersome to handle, with plumbing full of toxic ammonia. Any traces of ammonia on the spacesuits were dissipated before the astronauts went back inside, to avoid further contamination.
In the days following the Dec. 11 breakdown, flight controllers attempted in vain to fix the bad valve through remote commanding. Then they tried using a different valve to regulate the temperature of the overly cold loop, with some success. But last Tuesday, NASA decided the situation was severe enough to press ahead with the spacewalks. Although the astronauts were safe and comfortable, NASA did not want to risk another failure and a potential loss of the entire cooling system, needed to radiate the heat generated by on-board equipment.
Until Saturday, U.S. spacewalks had been on hold since July, when an Italian astronaut's helmet was flooded with water from the cooling system of his suit. Luca Parmitano barely got back inside alive.
For Saturday's spacewalk, Hopkins wore Parmitano's suit, albeit with newly installed and thoroughly tested components.
Just in case, NASA had Mastracchio and Hopkins build snorkels out of plastic tubing from their suits, before going out. The snorkels will be used in case water starts building up in their helmets. They also put absorbent pads in their helmets; the pads were launched from Earth following the July scare.
Besides the two Americans, three Russian and one Japanese astronaut are living on the space station, all men.
The Associated Press