HOUSTON – A close-up laser inspection by Endeavour's astronauts Sunday revealed that a 3 1/2-inch-long gouge penetrates all the way through thermal tiles on the shuttle's belly, and had NASA urgently calculating whether risky spacewalk repairs are needed.
A chunk of insulating foam smacked the shuttle at liftoff last week in an unbelievably unlucky ricochet off the fuel tank and carved out the gouge.
The unevenly shaped gouge — which straddles two side-by-side tiles and the corner of a third — is 3 1/2 inches long and just over 2 inches wide. Sunday's inspection showed that the damage went all the way through the 1-inch-thick tiles, exposing the felt material sandwiched between the tiles and the shuttle's aluminum frame.
Mission managers expect to decide Monday, or Tuesday at the latest, whether to send astronauts out to patch the gouge. Engineers are trying to determine whether the marred area can withstand the searing heat of atmospheric re-entry at flight's end, and actual heating tests will be conducted on similarly damaged samples.
"We have really prepared for exactly this case, since Columbia," said John Shannon, chairman of the mission management team. "We have spent a lot of money in the program and a lot of time and a lot of people's efforts to be ready to handle exactly this case."
The damaged thermal tiles are located near the right main landing gear door. In a stroke of luck, they're right beneath the aluminum framework for the right wing, which would offer extra protection during the ride back to Earth.
This area is subjected to as much as 2,300 degrees Fahrenheit during re-entry. A hole, if large and deep enough, could lead to another Columbia-type disaster.
Teacher-astronaut Barbara Morgan — who was the backup for Challenger's Christa McAuliffe in 1986 — conducted the slow and painstaking survey, along with crewmate Tracy Caldwell. They used the 100-foot robotic arm and extension boom that flew up on Endeavour, steering the instrument to a spot just above the gouge and keeping it hovered there.
Laser sensors and cameras zoomed in on the damage, white and easily visible against the black tiles, from a variety of views.
Four other damaged areas also were scanned. Engineers believe the piece of foam struck the shuttle's underside, creating the big gouge, then skimmed along the bottom and nicked it in at least three spots. Those smaller gouges pose no threat, Shannon said.
The foam came off a bracket on the external fuel tank 58 seconds after Wednesday's launch, fell down onto a strut on the tank, then bounced up, right into Endeavour's belly. Ice apparently formed before liftoff near the bracket, which helps hold the long fuel feed line to the tank, and caused the foam to pop off when subjected to the vibrations of launch.
It's possible some ice was attached to the foam, which would have made the impact even harder. The debris that came off is believed to have been grapefruit-sized.
These brackets have lost foam in previous launches, a concern for NASA, Shannon said. A switch to titanium brackets, eliminating foam, will not occur before next year.
Shannon said he did not know whether the recurring foam problem would delay the next shuttle flight, currently scheduled for October.
"We have a lot of discussion to have before we decide to fly the next tank," he said.
The inspection consumed much of the astronauts' day. On Monday, two of them will go back out for the second spacewalk of the mission to replace a broken gyroscope at the international space station.
Endeavour has been docked at the space station since Friday. It will remain there until Aug. 20 for a record 10-day stay. Mission managers on Sunday approved the prolonged visit based on the successful testing of a new power transfer system flying on Endeavour. The system is drawing power from the station and converting it for use aboard the shuttle.
On the space station, meanwhile, two cosmonauts continued repairs to a Russian computer system that failed during shuttle Atlantis' visit in June. Condensation from an air conditioning unit apparently is collecting behind the panels where the computer equipment is located.
And a U.S. command-and-control computer that shut down during Saturday's spacewalk was working again Sunday.