Realtime Coverage of U.S. EVA-16
4:00 p.m. EDT Update: Spacewalk ends
Astronauts Tracy Caldwell Dyson and Douglas Wheelock began repressurizing the International Space Station's Quest airlock at 3:53 p.m. to officially close out a seven-hour 26-minute spacewalk.
This was the 149th EVA devoted to station assembly and maintenance since construction began in 1998, the 13th so far this year, the fifth for Wheelock and the second for Caldwell Dyson.
Total space station EVA time now stands at 937 hours and four minutes. Wheelock's total through five spacewalks is 36 hours and 10 minutes, moving him up to 27th on the list of most experienced spacewalkers. Caldwell Dyson's total through two excursions stands at 15 hours and 29 minutes.
A news briefing with space station Program Manager Mike Suffredini, Flight Director Courtenay McMillan and spacewalk officer David Beaver is expected around 5 p.m.
3:05 p.m. EDT Update: Astronauts wrap up initial work on spare pump module
Astronauts Douglas Wheelock and Tracy Caldwell Dyson have completed initial preparation of a replacement coolant pump, disconnecting three of five electrical cables and reconfiguring insulation. They had planned to loosen bolts holding the module to its storage platform, but that work was deferred.
If all goes well, the spare pump will be installed on the S1 truss during a spacewalk Sunday to complete the loop A coolant system repair.
Wheelock and Caldwell Dyson now will stow their tools and head back to the Quest airlock module to wrap up today's spacewalk.
2:00 p.m. EDT Update: Pump module mounted on attachment fixture
Douglas Wheelock mounted a failed ammonia pump module on an attachment fixture at the base of the space station's robot arm transporter at 1:55 p.m., completing a complex removal procedure.
Wheelock and Tracy Caldwell Dyson plan to close out today's spacewalk by preparing a spare pump module for installation during a third spacewalk Sunday.
The astronauts plan to loosen three of four bolts holding the spare pump in place on external stowage platform No. 2. They also plan to disconnect electrical lines before cleaning up and heading back to the Quest airlock.
1:45 p.m. EDT Update: Faulty coolant pump removed, moved to temporary storage fixture
Successfully completing a major objective, astronauts Douglas Wheelock and Tracy Caldwell Dyson unbolted and removed a faulty 780-pound ammonia coolant pump from the space station's starboard one, or S1, truss segment today after disconnecting a final ammonia line and five electrical cables.
The astronauts had problems lining up and attaching a handling fixture called an adjustable grapple bar to the pump, but they finally got it lined up and attached.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pmeva2/eva10.jpg)
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pmeva2/eva11.jpg)
pump module from the S1 truss. (Photo: NASA TV)
That cleared the way for robot arm operator Shannon Walker, working inside the Destiny lab module, to pull Wheelock, holding the pump by the grapple bar, away from the S1 truss at 1:30 p.m.
"How you doing, Wheels?" Caldwell Dyson called as Wheelock pulled the pump module from the truss.
"Doing good," he replied. "Trying to be still with this thing."
Walker then carefully repositioned the arm so Wheelock could mount the pump module on a powered payload attachment fixture at the base of the station's robot arm transporter.
Caldwell Dyson, meanwhile, was cleared to make her way to external storage platform No. 2 where she planned to loosen three of four bolts holding a spare pump module in place.
The spare pump will be installed on the S1 truss during a spacewalk Sunday.
Assuming the astronauts don't run into problems re-attaching five electrical cables and four ammonia lines, flight controllers will be able to re-activate the loop A coolant system, completing a complex repair job.
12:25 p.m. EDT Update: Astronauts, ahead of schedule, prep pump for removal
Astronaut Douglas Wheelock, anchored on the end of the space station's robot arm, has retrieved an adjustable grapple bar from external storage platform No. 2. Tracy Caldwell Dyson, meanwhile, has removed three of four bolts holding a faulty coolant pump in place on the starboard one, or S1, truss segment.
After the final bolt is removed and the grapple bar is attached to the pump module, the astronauts will move the pump to a nearby attachment fitting at the base of the space station's robot arm transporter.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pmeva2/eva6.jpg)
220 miles below. (Photo: NASA TV)
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pmeva2/eva5.jpg)
(Photo: NASA TV)