Filler material dangles from shuttle

Experts debate whether loose cloth between tiles is dangerous, what to do

August 01, 2005|By Michael Cabbage | Michael Cabbage,ORLANDO SENTINEL

HOUSTON - NASA managers are expected to decide today whether to have spacewalkers do precautionary maintenance on shuttle Discovery's heat shielding.

Engineers have spent the six days since the launch analyzing images and inspection data to make sure there are no issues that could threaten the shuttle's planned Aug. 8 homecoming. Mission managers were close to concluding yesterday that Discovery's heat-resistant tiles and thermal panels had not sustained any significant damage.

One final concern, however, has yet to be resolved.

Photographs of Discovery taken by astronauts aboard the International Space Station before the ships docked Thursday showed two "gap fillers" protruding from tiles on the shuttle's belly. The thin cloths with ceramic fibers are wedged in gaps between the tiles and glued to the orbiter's airframe.

Both of the fillers are near the landing gear door under Discovery's nose and were likely shaken out during launch. One sticks out about 1.1 inches, the other about 0.6 inches.

"This is the first time we've ever seen it in flight before entry," deputy shuttle program manager Wayne Hale said, "and the first time we've had an opportunity to even consider doing something about it."

The two gap fillers are a concern because they could disturb the "boundary layer" that envelops Discovery during landing.

When the shuttle re-enters Earth's atmosphere, the fast-moving spacecraft compresses the thin air in front of it. That creates a boundary layer around the ship that is several inches thick and acts as a natural heat buffer. The boundary layer keeps temperatures on the shuttle's surfaces to 3,000 degrees or less while, inches away, the heat can exceed 10,000 degrees.

Smooth surfaces are critical to forming and maintaining the boundary layer. If it is seriously disrupted, the insulating effect could be impeded and the shuttle subjected to much higher temperatures than it is designed to withstand.

Protruding gap fillers are neither new nor rare. A 1995 mission aboard Columbia landed safely with a gap filler that stuck out about 1.4 inches and disturbed the boundary layer.

"There was some noticeable heating in a couple of areas where we had some damaged tile, but nothing that ultimately became a concern," said Steve Poulos, NASA's orbiter project manager.

Engineers are doing a heating analysis and continue to debate what, if anything, needs to be done. If shuttle managers decide to take action, astronaut Steve Robinson or Soichi Noguchi would likely make the fix during a third spacewalk scheduled Wednesday.

Mission planners are looking at having the space station's robot arm maneuver one of the astronauts to the gap fillers' locations. Among the options are having the spacewalker pull out the gap fillers or trim them down.

"My immediate knee-jerk reaction was that we can live with this," Hale said. "The ... [spacewalk] guys have gone out and are putting together a plan that we'll hear about tomorrow. And if it's relatively simple, why worry? Why would you not just go take care of it if you had a simple plan to deal with it?"

Yesterday was a relatively quiet day in orbit as Discovery's crew and the space station's two residents spent much of their time unloading some of the 12,000 pounds of cargo and supplies delivered to the outpost.

Astronauts also prepared for the mission's second spacewalk this morning. Robinson and Noguchi planned to replace a failed gyroscope outside the station. The device, the size of a washing machine, is one of four gyroscopes that help the station maintain the proper orientation to Earth.

The Orlando Sentinel is a Tribune Publishing newspaper.

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