NASA Studies Potential Fix for Discovery's Heat Shield

This story was updatedat 8:40 p.m. EDT.

HOUSTON - NASA engineers are drawingup plans to remove two strips of filler material jutting out from theheat-resistant tiles the space shuttle Discovery belly should mission managersdecide the action is needed to safeguard the orbiter's heat shield, shuttleofficials said Sunday.

The potential repair, a first ifimplemented, could be folded into the last of three planned spacewalks forDiscovery's crew on Aug. 3, or even warrant a fourth extravehicular activity(EVA), though it is still undecided whether any action is required, they added.

"The jury is out, at this point, onwhether any we'll do anything," said Wayne Hale, NASA's deputy shuttle programmanager, during an afternoon briefing at here at Johnson Space Center (JSC)."Just the fact that we know about this situation is something new andcompletely different."

Hale said the imaging provided byastronauts aboard the International Space Station (ISS) - where Discovery iscurrently docked- and the shuttle's orbital inspection boom have given flight controllersthey're first glimpse of the heat shield protrusions, gap-fillers made of aceramic fiber cloth. In past shuttle flights, they have only been found afterlanding, shuttle officials said.

While space shuttles have landedsafely numerous times with such protrusions, aerodynamics experts are workingto determine how the protruding gap-fillers would affect Discovery's reentrythrough Earth's atmosphere during its planned Aug. 8 landing.

"We have a team of folks workingaggressively on options to make that gap filler safe if we decide it's anissue," said Paul Hill, lead flight director for Discovery's STS-114 mission,adding that a separate team is studying the reentry heating effects involvedwith leaving the protrusions in place. "We expect to have final results on aeroheating and a decision on whether we need to doanything about the gap fillers on Monday."

The aeroheatingresults should be among of the last pieces of data NASA needs to give Discoverya clean bill of health. NASA engineers are currently working to complete theiranalysis of Discovery's wing leading edges to ensure the heat-resistantreinforced carbon carbon panels (RCC) are safe for reentry.Initially projected for completion today, image analysts have asked for anadditional day to finish studying data collected by Discovery astronauts duringa follow-up inspection, Hale said.

The shuttle's ceramic tiles andthermal blankets were clearedfor reentry Saturday, NASA officials said.

"We think Discovery is safe to bringhome," NASA's top administrator Michael Griffin said on NBC's "Meet the Press"Sunday. "We have approximately one-sixth the number ofscars on this orbiter, by actual count, as compared to the average of the last113 flights."

During in-flight inspections ofDiscovery's heat shield, astronauts aboard the International Space Station(ISS) photographed the two gap-fillers sticking out; one about 1.1 inches (2.7centimeters) out from just behind the nose landing gear and another fartherback jutting between six-tenths (1.5 centimeters) to nine-tenths (2.3centimeters) of an inch into space. The protrusions were not caused by impacts orother damage and have been seen in past shuttle flights, but can causeincreased drag during reentry and hotter temperatures just aft of the fillermaterials, NASA officials said.

A typical shuttle reentry generatestemperatures of about 2,300 degrees Fahrenheit along the orbiter's tile-coveredunderside.

During NASA's STS-73 shuttle flightaboard Columbia in 1995, an errant gap-filler was found jutting from its heatshield after landing, said Steve Poulos, NASA'sorbiter projects manager. Measuring about 1.4 inches (3.5 centimeters)unrolled, the gap-filler actually stuck out about 0.6 inches (1.5 centimeters)during the descent, with reentry temperatures for the tile section in that flightwere estimated at about 2,700 to 2,800 degrees Fahrenheit, he added.

Hill said that gap fillerprotrusions from the shuttle's forward tile sections are understood out toabout a quarter-inch (0.6 centimeters). Since the largest protrusion seen onDiscovery is about an inch long, it warrants the added study, he said.

A spacewalk activity

If a fix is needed, it appearsrelatively straightforward.

One of Discovery's two spacewalkers,mission specialists Soichi Noguchi and StephenRobinsons, could snip away the excess gap filler or pull it out entirely whilestanding at the end of a robotic arm, but whether that arm is attached to theshuttle or ISS is still under discussion.

Both astronauts have rehearsed somegap-filler removal techniques as part of the thermal protection repair methodtraining they received for their mission's first spacewalk,Poulos said. Removing both gap-fillers entirely, ifneeded, would not compromise the shuttle's heat shield, he added.

The station's arm could berepositioned from its current location outside the Destiny laboratory to itsMobile Base Platform, which would allow more clearance between the arm andDiscovery during any fix operation, Hill added.

"If it's relatively simple...why wouldn't you not go out and take care of it," Hale saidof the potential spacewalk repair.

Discovery's arm could reach the twogap fillers - which are located behind the shuttles nose landing gear doors -but is currently carrying the 50-foot (15-meter) orbital boom sensor system(OBSS) used for heat shield inspections.Shuttle arm operators would have to hand off the boom to station armcontrollers for stowage in Discovery's payload bay, where it could block accessto other equipment.

"So the options get complicated,"Hill said.

One option not on the table callsfor placing a spacewalker at the end of Discovery's orbital boom, an operationplanned to be tested in a future shuttle flight, Poulossaid.

If mission managers decide any fixis needed, it will likely be tacked onto Discovery's third spacewalk - whichcurrently has about 30 minutes spare time thanks to get ahead activitiesperformed but Noguchi and Robinson in a July 30 spacewalk- instead of a fourth EVA since flight controllers hope to dedicate an extramission day announced Saturday to additional cargo transfer, Hill added.

Meanwhile, Discovery astronautscontinue to haul cargointo the ISS from their orbiter's mid-deck and a cargo pod they delivered tothe station.

"I can't be happier with theprogress of this mission and I couldn't be happier with the performance of thiscrew and the flight control team," Hill said.

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