Troubles stall replacement of space station coolant pump
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 7, 2010
An unexpected ammonia leak and a jammed quick-disconnect fitting disrupted an eight-hour three-minute spacewalk Saturday to replace a faulty coolant system pump on the International Space Station. Assuming engineers can come up with a quick fix for the leak, the astronauts may attempt to replace the pump during a second spacewalk Wednesday.
"It would take a lot of good luck and somebody coming up with a really short tweak to the EVA for us to get to the point where we could start that ammonia pump after the next EVA," he said. "I really think we're going to end up at three EVAs.
"So I think we're going to end up being in this condition, this risk posture, a few more days than we had originally planned. That, to me, is the risk. I fully expect us to get through this particular problem and move on. I just am not optimistic we'll get all the way to the point where we can hook up the ammonia (lines) to the new pump and start it after the second EVA."
Douglas Wheelock and Tracy Caldwell Dyson began the spacewalk at 7:19 a.m. when they switched their spacesuits to battery power before floating out of the station's Quest airlock module.
The astronauts already knew it would take two EVAs to replace the shorted ammonia pump module, which failed last Saturday and knocked out one of the station's two coolant loops.
During Saturday's excursion, Wheelock and Dyson hoped to disconnect three 1.5-inch-wide ammonia coolant lines, one .5-inch cooling line and five electrical cables before unbolting the pump and removing it from the starboard one, or S1, truss segment
They planned to install a replacement pump and, if time was available, reconnect the electrical cables. The ammonia lines were to be reconnected during the second spacewalk Wednesday.
The astronauts had no problem disconnecting the smaller M4 cooling line. But Wheelock ran into major problems with the quick disconnect fitting on the second line he attempted. The fitting on the larger M3 line refused to unlatch initially, forcing Wheelock to use a lever to pry it open. That finally worked, but he reported seeing ammonia leaking out of the fitting.
"I see little sparklets of ammonia coming from the line," Wheelock reported.
"I copy. Are they continuous, or did you just see a few at first?" asked Oscar Koehler in mission control at the Johnson Space Center in Houston.
"It's just sort of random, like little tiny snowflakes," Wheelock said.
He was then asked to cycle the quick-disconnect latch, fully re-mating the connector. When he tried to reopen the QD fitting, the latch refused to budge.
After multiple attempts with the lever tool, he muttered "wow, that thing is not budging, Oscar." Astronaut Shannon Walker, operating the station's robot arm, moved Wheelock into a more favorable position and he tried again. But again, he was unable to re-open the latch.
Koehler told him to take a break at that point and to wait for orbital darkness in hopes that the temperature change would reduce internal pressure in the line and make the latch easier to throw. But again, the latch refused to budge.
While flight controllers considered various options, Wheelock and Caldwell Dyson pressed ahead with work to disconnect the other two 1.5-inch ammonia lines. Both unlatched without any trouble and there were no signs of additional ammonia leakage.
The M2 ammonia line was plugged into a so-called "jumper box," as was the .5-inch M4 cooling line. The jumper box will allow ammonia in the loop A cooling system to respond to temperature-induced pressure changes while the pump repair work continues.
With three of the lines successfully demated, Koehler asked Wheelock to give the M3 connector one more try. After applying more elbow grease - and lightly whacking the fitting with a tool - the latch released and engineers were hopeful the line could be disconnected as planned.
But once again, ammonia ice crystals spewed out of the connector and flight controllers, worried an internal valve might not be fully closed, told Wheelock to re-latch the M3 quick-disconnect fitting and leave it in place. Otherwise, the crew might run the risk of inadvertently draining a significant amount of coolant.
By that point, Wheelock and Caldwell Dyson were several hours behind schedule. And because of the ammonia leak, flight controllers had to protect a block of time at the end of the spacewalk for spacesuit decontamination. Anytime spacewalkers are exposed to ammonia, extra time is needed to make sure any ice crystals attached to the suits can evaporate before the astronauts re-enter the station.
With time running out, Wheelock and Dyson attached insulation to the ammonia line fittings and headed back to the Quest airlock. The spacewalk ended at 3:22 p.m. when airlock repressurization resumed after decontamination.
Suffredini said it appears one of two internal QD valves may be to blame for the leak, one that is on the outboard side of the coolant line. There are no nearby isolation valves upstream of that side of the connector and flight controllers cannot easily reduce the pressure in the system.
"There are a few options," Suffredini said. "One is try it again, does it work? Two is to see can we handle a leaky QD? If it's the female QD, can we just handle it and deal with the leak and put it somewhere else, perhaps on the jumper box, until we're ready to install it later?
"Another possibility we're kicking around is the idea of just depressing that side of the system - and that's a much more drawn-out process where we'd have to disconnect jumpers between trusses and things of this nature. They'll go through all those cases. But I'm afraid there's nothing really we can do on the ground, command wise, that necessarily will clear these leaks."
And until the leak is cleared and the M3 coolant line demated, the failed pump module cannot be removed and replaced.
This was the longest station-based spacewalk by an expedition crew, although still shy of the U.S. EVA record of eight hours and 56 minutes.
Space station EVA time now stands at 929 hours and 38 minutes, or 38.7 days, over 148 spacewalks since assembly began in 1998. This was the first spacewalk for Caldwell Dyson and the fourth for Wheelock, who has now logged 28 hours and 44 minutes of EVA time.