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Shuttle Astronauts Test Heat-Tile Putty, Lose Spatula

Two astronauts lost a bit of time and a spatula during their spacewalk Wednesday, but otherwise their experiments went well as they tested new repair techniques that might some day be necessary to save a damaged space shuttle.

The main job of Discovery astronauts Michael Fossum and Piers Sellers, squeezing out putty-like sealant and patting it down, went slowly as bubbles kept appearing in the peanut butter-like material designed to fix cracks in the shuttle's delicate heat shield.

The bubbles were expected, but it meant that the two spacewalkers could only complete five of their eight repair tasks in the scheduled six-and-a-half hour spacewalk.

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"It's behaving very differently now," Sellers said. "It's bubbling. It's growing. It's scary looking."

At times, Fossum worried that they did not have a good repair, but Mission Control was happy with much of the work.

The real test will come when the patch jobs are put to test in ground labs after Discovery lands July 17.

Sellers provided a bit of excitement when the spatula — about the size of a normal kitchen tool — he used to spread the sealant disappeared when he wasn't looking.

"No sign of the spatula; I think it's gone, gone, gone," Sellers said.

NASA officials said it is not common to lose instruments in a spacewalk, but it's happened before and bigger items have been lost with no ill effects.

But most of the time the astronauts worked smoothly, with wisecracks.

At Sellers began squeezing out the sealant, he asked Fossum how it looked.

"Good goo?" Sellers asked.

"Good goo!" Fossum responded.

Wednesday's was the third and final spacewalk planned while Discovery is docked at the space station.

The sealant was squirted onto 12 deliberately damaged reinforced carbon-carbon samples mounted on a pallet in Discovery's open payload bay.

Wearing bulky spacesuit gloves, Sellers and Fossum massaged the sealant with a putty knife to keep it from bubbling in zero gravity.

"Those bubbles behave differently in zero-g — they don't rise to the surface," Fossum told The Associated Press on Tuesday. "If you have too many bubbles trapped beneath the surface, then you're not going to get the repair you want."

Because of temperature concerns, the testing needed to be done when it was between 35 degrees and 100 degrees Fahrenheit, so the experiment was conducted during the night portions of their orbit. The international space station circles the Earth every 1½ hours.

Reinforced carbon-carbon is used to protect the shuttle's wing leading edges and nose from searing heat that can reach 2,300 degrees Fahrenheit during re-entry into Earth's atmosphere.

A crack in Columbia's wing in 2003 allowed fiery gases to penetrate the shuttle, destroying that shuttle over Texas and killing its seven astronauts.

The repair technique was devised by NASA to make sure such a disaster never happens again.

More than an hour into Wednesday's 6½-hour spacewalk, the astronauts ran into a brief delay when one of Fossum's safety tethers became unlocked. There was no danger of the astronaut floating away since he is attached to the complex by more than one tether, and he was able to relock it.

NASA spokesman Rob Navias said problems like that happen on occasion. During Monday's spacewalk, Seller's safety jet backpack almost came loose while he worked on repairs.

"They are double and in some cases, triple tethered at all times depending on where they are," Navias said. "Their chances of ever floating away are zero."

Wednesday's was the third and final spacewalk planned while Discovery is docked at the space station.

During interviews with The Associated Press and USA Today on Tuesday, Sellers described the third spacewalk as "a careful, meticulous lab experiment."

"The first two were kind of heavy lifting," Sellers said. "We were moving heavy pieces of equipment around and doing a lot of hard work."

During the first spacewalk last Saturday, Sellers and Fossum demonstrated that emergency shuttle repair work could be made from the end of a boom connected to a robotic arm.

For the second spacewalk on Monday, they got the space station's crucial rail car working again and installed a pump compartment for the complex's cooling system.

Although the astronauts had trained for it, the third spacewalk was a last-minute addition, approved after Discovery was in space. It added an extra day to what is now a 13-day mission.

The spacewalks can be tiring, but Sellers said he and Fossum had a surefire way of regaining their energy after each trip outside the space station.

"Four cups of coffee later, we feel much better," Sellers cracked.