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Thursday, August 04, 2005

CNN.com - NASA fixes one glitch, ponders another - Aug 3, 2005

CNN.com - NASA fixes one glitch, ponders another - Aug 3, 2005NASA fixes one glitch, ponders another
Engineers review possible problem with thermal blanket

JOHNSON SPACE CENTER, Texas (CNN) -- After Discovery astronaut Steve Robinson completed an unprecedented repair of a space shuttle in orbit Wednesday, NASA pondered the possibility of another threat.

Engineers now have to decide whether another spacewalk is needed to repair a damaged thermal blanket under one of the cockpit windows.

Of concern is whether the material would tear away during re-entry to Earth's atmosphere and strike the orbiter, especially when the shuttle slows from Mach 20 to less than Mach 6, said deputy shuttle program manager Wayne Hale.

Engineers estimate that any chunk of the blanket would weigh less than an ounce, Hale said. But NASA officials have to be concerned about "where might it go and what might it do."

The space agency has flown three samples of the material to its Ames Research Center in California to test them in a wind tunnel overnight.

Photos of the 20-inch-by-4-inch blanket show that it was punctured at one end -- possibly by debris -- and "poufed out" at the other, Hale said.
'A ride of a century'

During his six-hour spacewalk, Robinson removed fabric gap fillers sticking out from heat-resistant tiles on the shuttle's belly.

NASA had worried that protrusions of the fabric would cause excessive heating during re-entry.

"I'm grasping and pulling. ... It's coming out very easily. ... Beautiful," he said.

The challenge he faced was to remove the gap fillers without damaging the tiles, which protect Discovery from the 2,300-degree heat of re-entry. If that happened, the repair could pose more of a threat than the original problem.

Robinson called the spacewalk "a ride of a century," as Discovery's robotic arm maneuvered him to two areas along the spacecraft's underside near the nose.

His wireless mounted camera provided a spectacular view of the shuttle's hull as the craft orbited more than 220 miles above Earth.

"My eyes have never seen such a sight," Robinson said. (Full story)

"Stand tall and lean forward," NASA's mission control said as it moved him closer for the repair.

He carried forceps and a makeshift hack saw -- fashioned on the fly Tuesday by Discovery's crew -- in case he could not remove the fillers by hand.

The fillers are made from thin fabric stiffened with a ceramic material and plug gaps between the tiles.

Damage to the tiles was blamed for the loss of the shuttle Columbia, which broke up up during re-entry over Texas in February 2003, killing all seven astronauts on board.

Discovery's mission, which began July 26, is NASA's first manned flight since that disaster.

"We proved we can get access to the bottom of the vehicle," said Cindy Begley, the Houston-based flight controller in charge of the spacewalk. "We just never needed to do that before."

She said the most important accomplishment of the flight has been the use of the robotic arm to view the entire underside of the shuttle.

That inspection -- mandated after the Columbia disaster -- turned up the protruding gap fillers.

Discovery flight director Paul Hill said he was "absolutely relieved" by the ease of the repair.

"You could hear sigh of relief through the building over there," he told reporters. "When he pulled the second one out, it was a huge relief. It's all downhill from here."

The spacewalk began at 4:48 a.m. ET, about a half-hour later than scheduled, and ended at 10:49 a.m.

Robinson and Japanese astronaut Soichi Noguchi first had to install a new storage platform to the exterior of the international space station, with which Discovery has been docked since last week.

On Thursday, the crew will continue to transfer cargo from the space station to the shuttle's Raffaello multipurpose logistics module and then get some well-deserved downtime.

Discovery is scheduled to return to Earth on August 8.

Protruding gap fillers have been found after previous shuttle flights, but only after landing, leaving NASA experts with no way to know whether the material shifted before or after re-entry.

Because of the uncertainty about just how dangerous the protrusions might be, the space agency decided to err on the side of caution and try to remove them.

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