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Thu, March 20, 2008 10:15:45 PMFrom:
CBS Space News
Subject:
10p 3/20 Update: Tile repair tests go smoothly
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CBS NEWS STS-123 STATUS REPORT: 51
Posted: 10:00 PM, 3/20/08
By William Harwood
CBS News Space Analyst
Changes and additions:
SR-48 (03/20/08): Heat shield repair demonstration on tap
SR-49 (03/20/08): Spacewalk No. 4 begins
SR-50 (03/20/08): Circuit breaker replaced; stuck electrical connector prevents cable change
SR-51 (03/20/08): Heat shield repair tests go smoothly
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10:00 PM, 3/20/08, Update: Heat shield repair tests go smoothly
Astronaut Michael Foreman earned some of the more unusual kudos in spacewalking history this evening during tests of a new heat shield repair technique. Filling deliberately damaged tiles with a thick pink toothpaste-like material, "Mr. Goo" was praised his skill as a "tile and grout specialist," a "brain surgeon" and a "Rembrandt" for his deft work.
After testing a pressure-driven caulk gun-like applicator, Foreman, assisted by Robert Behnken, began filling various cavities in a tile sample board mounted on the bottom of the Destiny laboratory module.
"Looking for a success here," Foreman said as the work began.
"You are Capt. T-RAD, Mr. Goo," Richard Linnehan replied from inside the shuttle Endeavour. "You're in control today."
The repair material, known as STA-54, looks like pink silly putty. It is made up of two compounds that are mixed together in a pressure-driven applicator gun just before they exit the nozzle. The gun, called a tile repair ablator dispenser, or T-RAD, was operated by Foreman, wearing an STA-54 reservoir attached to the bottom of his spacesuit's emergency jetpack.
One of the compounds making up STA-54 causes bubbles to form. On Earth, those bubbles typically rise to the top. During this evening's test in the absence of air or gravity, the bubbles tended to spread throughout the material causing it to bulge slightly in a phenomenon known as "bread loafing."
Too much bulging could cause the material to swell up over the surface layer of surrounding tiles, disrupting air flow during re-entry and causing excessive downstream heating. Based on this evening's tests, though, the STS-54 appeared to behave more benignly. While bubbles formed, the astronauts were able to use pads to tamp the material down and as the STA-54 "set up," the swelling seemed to diminish.
"You're going to be our tile and grout specialist," Linnehan said at one point as Foreman worked the material in a cavity.
"I hope we don't need one," Foreman said.
Later, he said "I can see the bubbles under the surface, those little nodule-type bubbles, they're still forming in the material but it's not building as much as it was. ... It's still bread loafing, but it seems like when I hit it with the tamping it doesn't bounce back quite as quickly or as much."
"And for Houston, we're pretty happy with how things are going," Linnehan called to flight controllers in Houston. "These guys are doing a great job and the material is reacting in a very, I guess, tame way."
"Endeavour, Houston, EVA," Steve Robinson replied from mission control. "We are absolutely captivated by what you guys are doing here. It's like brain surgeons up there."
"You hear that Mike? You're a brain surgeon," Linnehan said.
"I've never been called that before."
"Probably never will be again," Linnehan agreed.
Wrapping up the work, Behnken added: "Mike, you're a regular Rembrandt. I think he was a brain surgeon."
"I'm sure not every work was a masterpiece," Foreman said.
"This is."
Foreman and Behnken finished the tile repair demonstration well ahead of schedule.
After cleanup, the astronauts were expected to make another attempt to free a stuck electrical cable on a patch panel on the space station's Z1 truss. Foreman attempted to move the cable to a different connector after a circuit breaker was replaced earlier in the spacewalk. The goal was to reconnect one of the station's four gyroscopes, CMG-2, to its own power supply. Without the cable swap, CMGs 2 and 3 remained connected to the same circuit. A failure in that circuit could take out both CMGs, a condition NASA wants to rectify with the cable swap.
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