Doug Wheelock installs new cooling system pump module while perched on the space station's robot arm Photo Credit/NASA TV
Spacewalking astronauts Doug Wheelock and Tracy Caldwell Dyson completed repairs to the crippled cooling system aboard the International Space Station on Monday, with their third spacewalk in 10 days.
Mission managers believe the station’s vital thermal control system can return to normal operations by Thursday.
Loop A of the station’s dual loop cooling system faltered on July 31, when the pump motor assembly responsible for circulating an ammonia coolant through outstretched external radiator panels experienced an internal electrical short. The unprecedented malfunction forced the station’s six U. S. and Russian astronauts to shut off nonessential electrical systems and curtail science experiments in the U. S., European and Japanese laboratory modules.
If the recovery goes as planned, science activities in those lab compartments will be re-doubled by next week, said Kirk Shireman, NASA’s space station deputy program manager.
“Things are certainly looking positive,” Shireman said after Monday’s more than seven hour spacewalk. During the outing, Wheelock and Caldwell Dyson shifted a replacement pump from a storage platform on the Quest airlock to the cooling system work site on the right inboard side of the 357-foot long solar power system truss.
The old 780 pound pump was successfully removed during an Aug 11 excursion by the two Americans.
The first spacewalk to address the problem, on Aug 7, did not go nearly so well. Wheelock and Caldwell Dyson were prevented from removing the old pump module as toxic ammonia leaked from one of four coolant lines they were attempting to de-mate at a quick disconnect valve.
Monday, the two spacewalkers got an early start and gained ground as they worked to retrieve and install the new pump, secure it with four bolts as well as re-mate five electrical cables and four coolant lines.
The new pump was activated in a brief but successful test while the excursion was still under way.
“The pump is looking good,” Mission Control informed the anxious spacewalkers.
“Oh, sweet,” said Wheelock, who spent much of the excursion perched on the tip of the station’s robot arm while lugging the new pump module. “I hope the day continues like this as we start everything back up and we’ve got our station back.”
Back on Earth, NASA experts who have been working around the clock since July 31 to devise a recovery strategy breathed a sigh of relief.
“That was a big step in the right direction,” said Courtenay McMillan, who supervised the spacewalks from Mission Control as the lead flight director.
”We really need to make sure we can get the loop back up and running,” said McMillan “Then, we will know for sure that what we saw on the spacewalk and from the pump during the check out is really good. But that was a huge relief for a whole lot of people.”
After the spacewalk, flight controllers began thermally re-conditioning fluid lines and raising the internal pressures in the once crippled cooling system. They planned to deactivate and then re-start the system on Tuesday, gradually re-powering systems that were turned off after the malfunction to lower the cooling requirements..
The two cooling loops dissipate heat generated by avionics, life support systems and scientific research gear.