NASA Performs Tests on Shuttle Tile Damage

HOUSTON -- NASA engineers are running a battery of tests to determine whether Endeavour shuttle astronauts will have to repair a deep gouge on their orbiter's underbelly, while a separate team weighs the best of three options for any fix required, mission managers said Monday.

John Shannon, chairman of Endeavour's mission management team, said a decision on whether any repair is required is expected by Wednesday.

A piece of fuel tank debris struck Endeavour's belly-mounted tiles 58 seconds after launch on Aug. 8, carving the 3 1/2-inch by 2-inch (9-centimeter by 5-centimeter) gouge. The debris did penetrate through the tile to expose a small strip of felt about one inch (2.5 centimeters) wide and 0.2 inches (0.5 centimeters) long.

The damaged tile, however, does not represent to risk for Endeavour's STS-118 astronaut crew, but rather the orbiter itself, Shannon said. The shuttle's heat shield is sound enough to return its crew to Earth safely in an emergency, but mission managers hope to avoid causing any additional damage to the spacecraft that would require lengthy repairs before its next construction flight to the International Space Station (ISS), he added.

"This is not a catastrophic loss of orbiter case at all," Shannon told reporters during a briefing here at NASA's Johnson Space Center. "This is a case where you want to do the prudent thing for the vehicle."

Engineers are subjecting mockups of the damaged tile to the same searing temperatures Endeavour will experience during its planned reentry and landing on Aug. 22, as well as running computer model analysis. The results of those tests should determine whether a repair is required, Shannon said.

NASA has kept a watchful eye on fuel tank debris and the health of its shuttle heat shields since the 2003 Columbia accident, when a piece of foam insulation breached that orbiter's left wing and led to the loss of the spacecraft during reentry.

Weighing options

Meanwhile, a second team is evaluating whether a heat-resistant paint, a carbon-composite overlay or an ablative goo-like material would be the best method of repairing Endeavour's dinged tile.

Joel Montalbano, NASA's lead ISS flight director for STS-118, told reporters that any repair, if required, would not occur before a planned Friday spacewalk.

Montalbano added that mission managers are also eyeing options of extending Endeavour's construction flight up to three extra days should any fix be required. Another option includes the possibility of adding a fifth spacewalk to the already extended mission, he added.

Endeavour's STS-118 mission to the ISS is delivering cargo, spare parts and a new piece to the station's starboard truss. The success of a new power transfer system, which allows Endeavour to siphon electricity from the station's solar power grid and conserve its own resources, led mission managers to stretch the orbiter's flight from an initial 11 days to 14 days and add a fourth spacewalk to the STS-118 crew's docket.

Mystery debris

The debris that struck Endeavour fell from a fuel tank bracket at a rate of about 204 miles an hour (328 kph) 58 seconds after the shuttle's Aug. 8 launch, bounced of a metal strut and hit the orbiter's tiles at about 141 miles per hour (226 kph), NASA said.

About the size of a baseball, the debris was initially thought to be ice before engineers shifted on foam insulation. But it may actually have been foam, ice or a piece of ablative material a bit denser than foam, Shannon said.

"We wouldn't expect just foam to look like that," Shannon said. "So it's a little bit of a mystery."

That the debris managed to damage Endeavour in the first place also surprised engineers, since previous studies showed that foam debris from the bracket region would either miss an orbiter entirely or be destroyed if it hit a tank strut.

Engineers will study the debris event to determine if the foam-covered shuttle fuel tank brackets, which secure a liquid oxygen fuel line in place, will have to be modified in any way before NASA's next shuttle flight in October. Any lengthy fix, if required, could temporarily stall shuttle flights and delay NASA's already tight schedule to launch at least 11 more missions to complete assembly of the ISS.

"The tank is going to shed some foam," Shannon said, adding that while NASA continues work to minimize such debris but there will also be some shedding. "It's our challenge to understand why, and then go and fix that if possible."

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