A pair of NASA astronauts are gearing up for a trio of spacewalks to fix a cooling loop aboard the International Space Station. The three-part show will take place Saturday, Monday and Wednesday – Christmas Day.
Astronauts Rick Mastracchio and Michael Hopkins are assigned to replace a faulty pump for one of the station's two ammonia cooling loops. The loop has been out of commission since the pump automatically shut down last week after it got too cold for comfort, NASA officials said.
The space station uses ammonia in its external cooling loops, but it’s far too toxic to use in the loops inside the station; the internal ones use water instead. But if the ammonia gets too cold, it can freeze the water from the internal system in its pipes. As the water turns into ice, it expands and could crack the pipe, allowing ammonia to enter and poison the system.
Engineers at NASA’s Johnson Space Center in Houston identified a problematic valve inside the pump and tried fiddling with the mechanism to see if they could figure out what was wrong and find a way to fix it. Failing that, the NASA team decided to send out Mastracchio, a six-time spacewalk veteran, and Hopkins, a rookie spacewalker who is “very excited to go out the door,” said Allison Bolinger, lead U.S. spacewalk officer.
Mastracchio will take the lead for the first two spacewalks, hooking up to the space station’s giant robotic arm. The arm will be operated from inside the station by Japanese astronaut Koichi Wakata.
Even though spacewalks are long – often exceeding six hours – the work will require three of them. It involves a complex set of steps to remove the broken giant pump module – which appears to be roughly the size of a refrigerator — and put in the new one.
For the first spacewalk, the astronauts will focus on pulling out the failed pump module and safely severing the ties between the pump and the larger system, removing four connections called "quick disconnects." They’ll also spend a little time working on the spare pump module that will replace the faulty one, removing layers of insulation.
During the second spacewalk, the astronauts will fully remove the failed pump module and temporarily stow it out of the way. Then they’ll return to the spare pump, pull it out and fly it back over to the hole where the faulty pump was. On this spacewalk, they plan to hook up only the bolts and the electrical connectors on the spare pump, Bolinger said.
On the Christmas Day spacewalk, Hopkins is expected to take the lead and step into the robotic arm. They’ll finish installing the spare pump module, stow the failed pump module in the spot it originally came from, and pack up their tool bag.
It’s possible the astronauts may get Christmas off, said Michael Suffredini, International Space Station program manager.
“It could take a little less if we get lucky with the QDs,” Suffredini said, referring to the quick disconnects. “And it could take a little more if we’re not lucky with the QDs — or we have any other challenges that come up.”
The spacewalks would be the first for the United States since Italian astronaut Luca Parmitano nearly drowned in space during the summer. The European Space Agency astronaut’s helmet started to fill with water as he floated outside the space station.