Plugging potential leaks
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: September 26, 2002
The primary goals of the second spacewalk are to:
"So the work around is to basically take one of those seals out of the loop so if you have a leak - and we're talking very small leaks - you just leak past the other seal, you won't build up that pressure so when we come back to do maintenance, you can get the QD off."
The SPDs Wolf and Sellers will attach to each quick-disconnect fitting lock the handle, or bale, used to draw the two sides of a connector together so that only one of the internal seals can engage.
"They position the bale, the handle, so the valve is partly open and it's only open enough to take one of those seals out," Koehler said.
Additional SPDs will be installed on the next two shuttle missions to protect all of the station's planned coolant line quick-disconnect fittings. For this flight, 24 one-inch-wide SPDs will be installed, six 1.5-inch SPDs and one 0.5-inch SPD. All but two will be installed during the second spacewalk with the final pair installed during the crew's third excursion.
"If at some point we have a radiator leak or we have a radiator get damaged, we can actually remove that radiator and replace it with a new one," Koehler said. "And the QD is what allows you to disconnect your fluid lines from that ORU. Almost all the ORUs that have ammonia going to them outside have the same type of QDs."
Ammonia will not flow through S1's thermal control system until a later mission. But six QDs connecting coolant lines running between the Destiny lab module and the station's current radiators on the P6 solar array atop the Z1 truss are pressurized with ammonia.
If Wolf and Sellers have any problems installing SPDs on these connectors, they will simply press on with other tasks and astronauts on a future assembly mission will use a special tool to pry any stuck QDs apart as required.
Because of the possibility of a leak, both spacewalkers have practiced procedures to remove any residue of the chemical before re-entering the space station.
"Ammonia is the primary external coolant in the coolant loops of the space station and there is the potential for it to escape in the various operations we do," Wolf said. "First of all, it is not dangerous immediately to the space suit. The spacesuit can tolerate large amounts of ammonia. We don't want to contaminate the internal atmosphere, of course, when we come in. So it will sublimate or bake off.
"We try to get out in the sun first of all. We try to do those tasks early in the EVA so if we get contaminated there will be more time for it to bake off into the vacuum. We have some special brushes to brush it off. We even have detection techniques in the airlock."
If any residue is suspected, the astronauts will partially repressurize the airlock, take an air sample, and if necessary, depressurize the airlock again to allow additional time to bake out the chemical.
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Mission overview - Atlantis to launch outward extension of station truss.
A trying summer for NASA - Small cracks in fuel flow liners grounded shuttle fleet.
Rendezvous and docking - Description of Atlantis' trek to catch the station.
Installing the S1 truss - The day after docking the Starboard 1 truss will be attached to the station with help of spacewalkers.
Plugging potential leaks - The second spacewalk will ready the S1 ammonia cooling system.
Odds and ends - The remaining highlights of the mission include a radiator deploy, treadmill repair and a final spacewalk.
Undocking, re-entry and landing - A look at the conclusion of Atlantis' 11-day voyage.
STS-112 index - A full directory of our mission coverage.
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