"We are primarily interested in any debris, structure, tiles upstream [west of] Fort Worth," even as far away as New Mexico and Arizona, he said. "If that exists, it is extremely important to us. It's going to be a key to the puzzle."
That's because any debris shed by the shuttle early in its descent might reveal where in its structure the fatal malfunctions began. Heat shield tiles bear codes that would reveal exactly where on the shuttle's skin they were lost.
"Where are they?" Dittemore asked.
NASA's continuing examination of data from the shuttle during its last minutes shows that the first sign of trouble was unusual heating in brake lines in the spacecraft's left landing gear that began at 8:52 a.m., eight minutes before contact with Columbia was lost.
The 50 degrees of extra heat in the wheel well is "interesting," Dittemore said, but does not look like what would occur if the heat shield had failed.
"There's some other missing link that we don't have yet," he said, "and we've got to go find it."
He expressed confidence in the validity of the original finding that there was little risk to the astronauts from damage to the shuttle's heat shield caused by flying insulation. But investigators will review the assumptions, anyway.
Such damage has occurred at least twice before during shuttle launches, without serious incident.
In their analysis this time, Dittemore said, engineers estimated that the piece of hardened foam insulation that broke from the external fuel tank's nose was 20 inches long and 6 to 16 inches wide, weighing about 2.7 pounds.
They calculated that it would have struck a glancing blow to the wing near the landing gear door. That could have resulted in a complete loss of one tile or shallower damage to an area 32 inches long and 2 to 7 inches wide, extending to the wing's trailing edge.
In the end, Dittemore said, his engineers concluded that "you would not have had damage sufficient to cause a catastrophic event, and no impact on the flying qualities of the vehicle."
Michael Kostelnik, deputy associate administrator for NASA's office of space flight, said the engineers' conclusions were reported to NASA headquarters. "We were in complete concurrence with their assessment, and their plan ahead," he said.
Even if engineers had concluded that the damage was a risk to the crew, Dittemore said, there would have been no good options for saving the astronauts.
Steering the shuttle to favor the left wing and protect it from fatal heat damage would have risked overheating the right wing, he said.
Even if such a maneuver had been possible, he said, the shuttle, because it returns to earth as an unpowered glider, could not have reached the spaceport in Florida.
The crew would have had to ride the spacecraft to a safe speed and altitude and bail out, allowing the shuttle to crash.
"I just don't believe we ever would have had the type of information to make that type of risk trade," he said.