Station's bad pump removed; more spacewalking ahead
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 11, 2010
Spacewalker Douglas Wheelock, given permission to "shake violently" a stuck ammonia connector, used a healthy dose of elbow grease to finally get a troublesome coolant system quick-disconnect fitting to release Wednesday. With the fourth and final ammonia line finally free, Wheelock and crewmate Tracy Caldwell Dyson removed a faulty coolant pump, clearing the way for installation of a replacement during a third spacewalk Monday.
A fourth spacewalk likely will be required later to wrap up loose ends and move the old pump to a permanent stowage location.
Wheelock and Caldwell Dyson spent seven hours and 26 minutes during their second coolant system repair spacewalk, removing the fourth and final ammonia line, disconnecting five electrical cables, loosening four bolts and moving the 780-pound pump module to a nearby attachment fitting. They also prepared the replacement pump for installation by disconnected three of its five electrical lines.
The third spacewalk originally was targeted for Sunday, but Suffredini said he decided to delay the excursion one day to give the team a chance to catch its collective breath and complete additional planning.
"Based on the amount of work that has been required over the last several days to prepare and implement these last two EVAs, we've decided one additional day between EVAs is necessary," he said. "Therefore, we're going to do EVA-3 ... on Monday.
"Our goal on that EVA is to try to get the (replacement) pump installed and hooked up so the team can activate the pump subsequent to that EVA. That'll be a stretch goal. I think the team's up to it, we'll have to have a little more cooperation from the hardware. But I think we can get there."
But, he added, "that won't be the end of it. It'll still probably take us another (spacewalk) to get everything cleaned up and the old pump back in place. But with any luck, we'll be in position after that EVA to wait a little while before we have to go back out the door."
The ammonia pump in coolant loop A failed July 31, leaving the space station with just one coolant system to dissipate the heat generated by the lab's electronics. The loop A failure forced the astronauts and flight controllers to implement a widespread powerdown to prevent critical equipment from overheating.
With four spare pump modules already on board, NASA planners quickly developed plans for two spacewalks to remove the old pump and install a replacement. But those plans ran into problems during the first excursion Saturday when a leak prevented the spacewalkers from disengaging one of four ammonia quick-disconnect fittings.
Engineers suspected a problem with one of two internal valves on the outboard side of the pump module. Prior to the second spacewalk, nitrogen gas was vented, lowering pressure in the line from 350 pounds per square inch to about 143 psi to make it easier for the astronauts to manipulate the quick-disconnect fitting.
For the second spacewalk, Wheelock and Caldwell Dyson planned to first close a quick-disconnect fitting on the outboard end of the S1 truss to isolate the line leading to the M3 connector. But Caldwell Dyson was unable to depress a release button, preventing her from closing the outboard quick-disconnect.
Flight controllers then told Wheelock, anchored to the end of the space station's robot arm, to press ahead with an attempt to simply close the leaking M3 connector in hopes that lower pressure in the line would reduce the leakage enough to disconnect the line from the pump.
To the relief of anxious flight controllers, the connector closed easily and no major leakage was observed.
"I don't see anything leaking," Wheelock reported.
"Excellent," replied Oscar Koehler from mission control in Houston. "And Wheels, if you see any leak, we're comparing this leak to what you saw when you first did the SPD on EVA-1."
"OK, I see a couple of little snowflakes," Wheelock reported a moment later. "But I don't see anything leaking around the white band like last time. ... OK, here they start to come out now by the white band, just little snowflakes."
The leakage quickly diminished and flight controllers told Caldwell Dyson there was no need to continue work to close the outboard quick-disconnect.
"That's great news," Wheelock said.
"It's awesome," Koehler agreed.
A few moments later, with no observable leakage, engineers decided there was no need to install a vent tool to release any residual ammonia that might be trapped in the line. Wheelock was then cleared to remove M3 from the pump module.
But in keeping with M3's now-familiar behavior, Wheelock was initially unable to pry the fitting apart using a lever tool.
"We believe there may be ice in there that's keeping it from releasing," Koehler advised. "So you've got a go to ... move the QD left to right to try to shake some of that ammonia ice out of there."
After working the fitting from side to side with no success, mission control told Wheelock "you've got a go to shake violently, that's the words I was given, in all directions."
Television views from Wheelock's helmet camera showed him energetically shaking the fitting from side to side. After multiple attempts, the connector finally released and Wheelock pulled the M3 line away from the pump at 10:23 a.m.
There were no obvious signs of problems with the connector and the astronauts were cleared to press ahead with their pump removal work. Five electrical cables were demated by Caldwell Dyson before the astronauts loosened four bolts to free the pump from the S1 truss.
Using a grapple bar, Wheelock maneuvered the faulty pump to a payload attachment fitting at the base of the station's robot arm transporter.
The astronauts then moved to external stowage platform No. 2 and prepared the spare pump for installation, disconnecting three of five electrical cables and reconfiguring insulation. The remaining lines, and the four bolts holding the pump to ESP-2, will be disconnected during the third spacewalk Monday, clearing the way for installation on the S1 truss.
Asked what might have gone wrong with the original pump, Suffredini said engineers reviewing data from the system discovered unusual currents in the pump motor starting about two months before it shorted out on July 31. Troubleshooters quickly checked the performance of the pump in coolant loop B, but no similar signature was found.
As for problems with the M3 quick-disconnect, Suffredini said it was possible a small piece of debris lodged in one of the internal valves, resulting in the leak seen Saturday.
The procedure to lower pressure in the system prior to the second spacewalk forced ammonia coolant back through the quick-disconnect, possibly freeing any debris that might have been trapped there.
Reactivating coolant loop A will take a few days after the replacement pump is installed. Along with activating the pump and re-pressurizing the ammonia system, flight controllers will need to reconfigure a variety of systems to properly share the thermal load between loops A and B.
"It's not going to be an immediate process, there's not one switch we can flip, obviously," said Flight Director Courtenay McMillan. "Folks are looking hard at what's the right sequence of steps to take and what do we need to go back and do."
But activating the new pump "will happen fairly quickly," Suffredini said. "There's a lot of work to do to reconfigure the ISS back to the normal configuration where we share loads across the two systems. That's the part that will probably take us several days. We'll know that the pump is healthy pretty early on after the EVA, assuming it's all hooked up correctly."