December 24, 2013
– Astronauts aboard the International Space Station received a gift just in time for Christmas: a new pump module to repair their ailing cooling system and to restore the outpost to full power.
Expedition 38 flight engineers Rick Mastracchio and Mike Hopkins embarked on their second spacewalk together
at 5:53 a.m. CST (1153 GMT) on Tuesday morning (Dec. 24) to complete the work they began on Saturday to replace a pump module with a faulty flow control valve.
"Houston from the airlock, we'd just like to say thanks to all the great folks doing all this hard work to get this space station back up and running," Mastracchio radioed at the end of the spacewalk, which concluded at 1:23 p.m. CST, seven hours and 30 minutes after it began.
"No, thank you guys," astronaut capcom Doug Wheelock replied from NASA's Mission Control in Houston. "It is the best Christmas ever. Thanks, guys."
"I'd just like to add to that," Hopkins said. "Fantastic work, merry Christmas to everybody. It took a couple of licks to get her done, but we got it."
Mike Hopkins, riding the space station's Canadarm2 robotic arm, carries a spare pump module for its installation. (NASA TV)
The Christmas Eve
EVA – extravehicular activity, NASA's term for a spacewalk – had the two astronauts retrieve a spare of the refrigerator-size cooling system device and install it on the station's starboard, or right, side backbone truss. The 780-pound (355 kg) pump module replaced a malfunctioning unit Mastracchio and Hopkins successfully and speedily removed three days ago.
The removal, which came just 10 days after a valve inside the module ceased working properly, was originally slated to be part of this second excursion, but Mastracchio and Hopkins made quick work of disconnecting the degraded unit, providing them the time to also remove and stow the module during the spacewalk Saturday.
Their get-ahead work negated the need for a planned third spacewalk
Pump module in place
The failure of the flow control valve, which regulates the temperature of the ammonia coolant passing through the pump, resulted in restricting the space station to the use of just half of its cooling loop system needed to maintain equipment temperatures inside and outside of the outpost. Non-critical systems and science experiment hardware in two of the station's laboratories have been without power since the valve malfunctioned on Dec. 11
The new pump, installed by Mastracchio and Hopkins on Tuesday, was to return the space station to its full cooling and power capacity.
Mike Hopkins, hidden behind the refrigerator-size pump module, rides on the end of the space station's robotic arm. (NASA TV)
Trading spaces since their Saturday spacewalk, Hopkins, riding the end of the robotic arm, and Mastracchio working alongside him, retrieved the spare pump module from the space station's External Stowage Platform 3 (ESP-3) and installed it in the slot on the truss they earlier emptied of the faulty unit.
"Mike, I think you're in charge now of the pump module," Japanese astronaut Koichi Wakata radioed Hopkins as he controlled the arm to pull Hopkins and the pump module away from ESP-3. "It looks good, you're doing a great job, it looks beautiful."
The pump module was bolted into place at 9:08 a.m. CST (1508 GMT), three hours and 15 minutes into the EVA.
'Snow' on Christmas Eve
The astronauts then worked on connecting five electrical and four fluid lines linking the new module to the station's systems. In the process, the pair had difficulty freeing one of the quick disconnect lines from a temporary jumper box that the two had installed during Saturday's spacewalk.
"One thing we never expected," Mastracchio observed.
"Getting it off the jumper box?" Hopkins replied.
"Yeah," Mastracchio said.
The spacewalkers eventually freed the stubborn line using some additional tools. In the process, they released some frozen ammonia flakes, or "snow."
"About one little snowflake a second," Mastracchio stated to Mission Control, adding that the flakes were contacting both his and Hopkins' suits, a concern for contamination
"Big chunks, big chunks," Mastracchio noted as Mission Control sent a command to vent the fluid line. "Some little ones, some big ones."
As the line was vented, the spacewalkers confirmed it had "stopped snowing" and they proceeded with connecting it and the remaining lines to the new pump module. All nine lines were connected at 11:45 a.m. CST (1645 GMT), five hours and 52 minutes into the spacewalk.
"Houston, you have a new pump module, congratulations," Mastracchio radioed Mission Control.
Second eve EVA
Spacewalkers Mike Hopkins (left) and Rick Mastracchio work to connect fluid and electrical lines to the pump module. (NASA TV)
With the pump module in place and its lines connected, flight controllers will work Tuesday evening to test the unit and then, should everything check out, begin reintegrating it into the station's cooling system over the next day.
Tuesday's spacewalk marked Mastracchio's eighth career EVA and Hopkins' second. It was the 176th devoted to the assembly and maintenance of the space station
, and the tenth such outing in 2013.
One more spacewalk is scheduled for this year on Friday (Dec. 27) by Russian cosmonauts Oleg Kotov and Sergey Ryazanskiy
to install a pair of high-definition cameras and refresh several experiment packages on the exterior of the Russian segment of the station.
Tuesday's spacewalk was only the second Christmas Eve EVA in history. Space shuttle Discovery astronauts Steve Smith and John Grunsfeld conducted an 8-hour, 8-minute excursion on Dec. 24, 1999 to upgrade the Hubble Space Telescope.