Testing Now Underway; Gouge Penetrated Tiles

Spacewalkers Dave Williams and Rick Mastracchio removed a faulty attitude control device on the International Space Station Monday, during their second spacewalk in three days... but most of the world's attention is focused on launch damage to the shuttle Endeavour, which may be worse than first believed.

Scans taken of the orbiter's underside Sunday show a 3.5-inch-long gouge in two adjoining thermal tiles near Endeavour's right maingear door. Some of the damage penetrates the tiles' one-inch thickness, down to the orbiter's aluminum skin -- meaning a spacewalk to attempt to repair the damage might be necessary.

Fortunately, NASA says, astronauts have trained extensively for such a repair, in the wake of the 2003 reentry loss of Columbia.

"This is something we would rather not deal with, but we have really prepared for exactly this case," John Shannon, the chair of NASA's mission management team, told The Associated Press. "I feel very comfortable that whatever is required, we can go do and do successfully."

Shannon added the shuttle Discovery suffered even more damage in the same location as Endeavour during a l998 mission -- and landed safely.

Engineers are now conducting computer-based thermal analyses, to determine if Endeavour can withstand reentry will the damage. They are also testing samples of tiles with identical damage under simulated reentry conditions. Those results should be available by Tuesday at the latest, Shannon said.

Should a spacewalk be necessary, two astronauts would secure themselves to Endeavour's robotic arm using a special 100-foot-long extension. Crewmembers onboard the shuttle would then maneuver their fellow STS-118 astronauts under the wing to effect repairs.

The nature of those repairs will depend on the results of NASA's testing. Possible repair methods include covering the gouge with a screw-on panel, dabbing a dark silica-based undercoating over the damage, or pumping a thicker caulk-like substance, also composed of silica and carbon, into the opening and smoothing it down.

Will This Mean More Delays For Shuttle Program?

Meanwhile, NASA has narrowed the likely cause of the damage to a baseball-sized chunk of insulating foam, that sheared off a bracket connecting a propellant line to the shuttle's external fuel tank 58 seconds into the flight.

Images taken during launch show the foam striking a strut connecting Endeavour to the tank at a velocity of 200 mph. The impact deflected the foam onto the underside of the orbiter's right wing.

A similar incident -- in which a chunk of foam hit the leading edge of Columbia's left wing during its January 2003 launch -- led to the reentry loss of that orbiter, as hot gasses caused by reentry were able to breach the shuttle's heat shield through the resulting damage.

Program managers were already planning to phase in titanium fittings, to replace the foam-covered brackets, on future missions. The new design would fix a flaw in the current bracket system, which allows the propellant line to move during launch -- causing the ice-coated line to grind against the tank's foam insulation.

However, three more missions are scheduled to fly with the current tank design -- but after this latest incident, NASA may opt to hold future missions until the new design is ready to fly, adding at least six months to the current schedule of shuttle flights ahead of the planned 2010 retirement of the fleet.

"We have a lot of discussion to have before we decide to fly the next tank," Shannon said. The next mission is scheduled to fly in October.

FMI: www.nasa.gov