Spatula in Hand, Astronauts Test Repair Kit for Space Shuttle

Photos
Discovery's Mission in Space
Astronauts aboard space shuttle Discovery spend their time in space replenishing the international space station, repairing machinery and testing shuttle equipment.

HOUSTON, July 12 -- Like a short-order cook flipping pancakes, Discovery spacewalker Piers J. Sellers successfully cooked flat disks of "black goo" in the sunshine Wednesday to test an experimental caulking material for space shuttle repairs, but he inadvertently let one of his spatulas drift into space.

"It's gone, gone, gone," Sellers lamented as the 14-inch putty knife slipped over the starboard side of the shuttle about halfway into the 7-hour, 11-minute spacewalk.

Flight Director Tony Ceccacci said later that Discovery Mission Commander Steven W. Lindsey tracked the "escaped spatula" as it meandered into the void and that it posed "no hazard to us."

Sellers and fellow spacewalker Michael E. Fossum smeared the black polymer goo, called NOAX, on plates of brittle "reinforced carbon-carbon" heat shielding that had been deliberately cracked and gouged to simulate flight damage.

In 2003, a suitcase-size piece of foam insulation from the external fuel tank of space shuttle Columbia breached the carbon-carbon shielding on the left wing during launch, causing the orbiter to disintegrate two weeks later during reentry. Shuttle engineers have been working on repair techniques ever since.

While the NOAX, short for "non-oxide adhesive experimental," is not designed to plug anything remotely approaching a hole the size of the one in Columbia, NASA engineers have had success in experiments using it on dings and chips. Wednesday's excursion put these lessons to work in space.

Lead spacewalk officer Tomas Gonzalez Torres termed the outing "very successful" in a news conference at Houston's Johnson Space Center. He said engineers on the ground will test the heat resistance of the carbon-carbon plates to see if the repairs could withstand the temperature of 2,900 degrees Fahrenheit that the shielding encounters during reentry.

Wednesday's spacewalk was the last of three during Discovery's 13-day mission to the international space station. Ceccacci said the shuttle's six astronauts and the station's three-member crew had virtually finished unloading station supplies and storing the station's trash for Discovery's trip home Monday.

The NOAX experiment followed a much more modest demonstration last year, in which spacewalkers smeared the goo on plates simply to see if it could be done relatively comfortably in space and whether the substance would adhere to cracks.

Gonzalez Torres said the key to successful NOAX application is to manage the bubbles of gas it emits as it cures. If not eliminated, bubbles could create dangerous "voids" that weaken the repairs.

On Earth, the problem is easily solved, Gonzalez Torres said, because gravity causes the gas to boil off. "In space, though, it's just a blob," he said.

This meant that Sellers, handling the spatula in the shuttle's cargo bay with Fossum assisting, had to prepare the NOAX for application by flattening it on a palette to force out gas and let it cook in the sunshine, flipping it and squashing it again. He didn't immediately notice when he lost his spatula because his tool kit had five spares.

Gonzalez Torres said the optimum temperature to produce the bubbles and knead them out of the NOAX is 140 degrees, easily achieved in the sunshine in space. At that temperature NOAX is supposed to be the consistency of peanut butter.

Unfortunately for Sellers and Fossum, the orbiting shuttle sees a sunrise and a sunset every 90 minutes, so conditions were often less than ideal. Sellers remarked at one point that "this is quite hard work," noting that cold NOAX was more like putty without enough oil in it.

Sellers compared the chore to working on "an old house in Houston."

"Done that," Fossum quipped.