Robert H. Daugherty, responding to an inquiry from Johnson Space Center, cautioned in an e-mail to NASA colleagues that damage to delicate insulating tiles near Columbia's landing gear door could cause one or more tires inside to burst, perhaps ending with catastrophic failures that would place the seven astronauts "in a world of hurt."
Such an explosion inside Columbia's belly, Daugherty predicted, could blow out the gear door and expose the shuttle's unprotected innards to searing temperatures as it raced through earth's atmosphere.
NASA spokesman William Jeffs confirmed Thursday that at least one sensor indicated Columbia's left gear was lowered moments before the shuttle broke apart over Texas at 209,000 feet and flying at 18 times the speed of sound — far too high and too fast for that to happen. But Jeffs cautioned that two other sensors at the time indicated the gear was still properly raised.
"We're not certain if the readings showed the landing gear deployed or were the result of a faulty sensor that sent bad data," Jeffs said. "One indicated (the wheel) was down and locked, and that was shortly before radio contact with the orbiter was lost."
Meanwhile, NASA said Thursday that the remains of all seven members of Columbia's crew have been positively identified.
The identifications were made at the military mortuary at Dover Air Force Base, where the remains were taken after the space shuttle disintegrated Feb. 1.
"We are comforted by the knowledge we have brought our seven friends home," said Bob Cabana, Director of Flight Crew Operations at the Johnson Space Center, in a statement. "We are deeply indebted to the communities and volunteers who made this homecoming possible, and brought peace of mind to the crew's families, and the entire NASA family,"
"We are working toward releasing the crew remains to the families for their own private memorial services," said Eileen Hawley, a spokeswoman for the Johnson Space Center in Houston.
On the same day NASA disclosed the contents of Daugherty's e-mail, searchers near Hemphill, Texas, about 140 miles northeast of Houston, recovered what they believed to be one of Columbia's tires. The tire was blackened and sustained a massive split across its tread, but it was impossible from photographs to know whether the tire was damaged aboard Columbia or when it struck the ground.
NASA officials in Washington and Houston on Thursday said they could not confirm the tire was the shuttle's, but one person familiar with tires on the orbiter looked at a photograph of the tire found in Texas and said it appeared to be from a shuttle.
In his e-mail, which included remarkably strident language, Daugherty wrote that even if astronauts survived the heat, the blast could damage critical systems inside the wheel compartment, prevent the landing gear on one side from lowering, necessitate a risky belly landing or force the crew to bail out.
Bailing out would be "not a good day," he wrote. But attempting to fly the shuttle with only one side's landing gear lowered would be worse: "You're finished."
Flight Director Leroy Cain said Wednesday that investigators were confident the gear door did not fall off in flight because such a failure would have been indicated on sensor readings.
Other NASA officials have cited mysterious sensor readings in the wheel well moments before Columbia's breakup but have said they were confident the tire didn't burst inside the shuttle.
Daugherty acknowledged these were "absolute worst-case scenarios," adding, "I don't really believe things are as bad as I'm getting ready to make them out." But he defended raising the issues in e-mail to avoid a "gut-wrenching decision" days later during Columbia's descent.
Daugherty on Wednesday referred questions about his concerns to a NASA spokesman. Agency officials indicated they did not want reporters to speak with Daugherty because accident investigators had not yet questioned him. NASA disclosed the contents of his e-mail Wednesday.
The e-mail from Daugherty, an engineer at NASA's Langley research facility in Hampton, Va., was prompted by a telephone call Jan. 27 from experts at the Johnson Space Center in Houston who asked what might happen if Columbia's tires were not inflated when it attempted to land.
The inquiry from Johnson has attracted interest because it came four days after engineers at The Boeing Co., a contractor, assured NASA that Columbia could return safely despite damage to left wing tiles that might have occurred on liftoff.
Senior NASA officials said Daugherty's concerns were part of a "what-if" analysis by a small group of engineers who already had been assured that Columbia would land safely. They acknowledged that concerns about threats to the shuttle's tires were not passed along to NASA flight directors.
Milt Heflin, chief of the flight director's office, said Daugherty and others involved in the tire questions "were happy with the analysis and the work that was done" by Boeing. "They were continuing to do more what-if'ing."
Heflin added that that is a common practice.
However, reports CBS News Correspondent Peter King, Heflin couldn't say whether anyone at NASA knew of both the e-mail messages and a Boeing study on the protective tiles that said losing some tiles in that area of the shuttle wouldn't be a flight safety issue.
An e-mail back to Daugherty the next day from a Johnson Space Center engineer, David F. Lechner of the United Space Alliance LLC, another NASA contractor, thanked Daugherty for his "candid remarks." He said they "generated extremely valuable discussion in our group."
"We hope the debris impact analysis is correct and all this discussion is mute," Lechner wrote.
Another Langley employee, Mark J. Shuart, responded by e-mail later that day, "Looks like they believe all this has been addressed." His message was time-stamped about 20 hours before the shuttle disintegrated.
Senior NASA officials have repeatedly expressed confidence in Boeing's conclusions, which predicted "safe return indicated" even if foam insulation that fell from Columbia's external fuel tank had caused "significant tile damage." That study assumed foam debris struck part of Columbia's left wing, including its toughened leading edge and the thermal tiles covering the landing gear.
Testifying at a joint congressional hearing Wednesday, NASA Administrator Sean O'Keefe told lawmakers that during Columbia's 16-day mission, "there were no abnormalities that would suggest a problem. If there was any indication, they would have showed up."
Among the earliest warning signs aboard Columbia in the minutes before its demise was an unusual heat buildup of about 30 degrees inside the left wheel well. Investigators have said they are confident the tire inside didn't deflate, but they have been unable to explain the readings.