HOUSTON -- Investigators are looking at new scenarios for how hot gases entered shuttle Columbia's left wing, causing it to disintegrate over Texas on Feb. 1.
Contrary to previous analyses, investigators said yesterday that they now suspect that an object seen floating near Columbia on its second day in space was a fragment of a carbon panel that wraps around the wing's edge or a seal from that region.
Investigators think the piece came loose after being damaged by a chunk of foam insulation that flew off the external tank and slammed into the wing during launch.
The mystery object was tracked by radar, and early tests suggested it was a so-called "carrier panel" that connects to the leading edge of the wing. But investigators now think it's more likely that a piece of reinforced carbon-carbon panel broke off or that one of the "T-seals" between the panels was knocked out of place.
If it was a seal, the searing hot gases that surround the ship during re-entry would have had a clear path into the shuttle's aluminum skin, said Harold Gehman Jr., chairman of the Columbia Accident Investigation Board.
During the board's weekly update yesterday, Gehman said that even if one side of the T-shaped seal had been broken off, the heat would have had ample room to burrow into the wing.
The gases could get "directly into the wing, with nothing to stop it," Gehman said.
Beyond the mystery object, investigators said they also are revising their views on what specific area of the left wing was struck with the piece of foam, estimated to be about 2 pounds.
Board member Scott Hubbard said video analysis indicates the foam hit the wing farther out than expected.
The wing's edge is covered by 22 of the reinforced panels, and investigators thought initially that the foam struck at about panel 6.
Now they think it was about panel 7 or 8, Hubbard said. At the same time, however, there is increasing evidence that the breach in the wing occurred even farther out.
Data from a flight recorder that was recovered in Columbia wreckage indicates that temperature sensors -- located in the vicinity of panels 9 and 10 -- showed substantial heating, then dropped quickly, as if the wires had been cut or burned through, Hubbard said.
In addition, recovered debris from that part of the wing shows massive deposits of metal, as if aluminum was being melted and sprayed onto it.
Also, a nearby carbon-carbon panel had been whittled down from a quarter-inch in thickness to about the thickness of a dime.
"This kind of heating event indicates long duration, very extreme heating," Hubbard said.
Investigators said the pieces of the puzzle aren't fitting together perfectly -- with foam affecting one area and a breach in the wing believed to be located in another region.
But Hubbard said it was possible that the force of the impact moved down the wing and caused a breach.
Gwyneth K. Shaw and Robyn Suriano write for the Orlando Sentinel, a Tribune Publishing newspaper.