Break in shuttle's heat shield more than a missing tile
February 14, 2003
WASHINGTON -- The space shuttle Columbia almost certainly suffered a devastating breach of its skin, allowing superheated air inside the left wing and possibly the wheel compartment during its fiery descent, investigators said Thursday.
In its first significant determination, the accident investigation board announced that heat damage from a missing tile would not be sufficient to cause the unusual temperature increases detected inside Columbia minutes before it disintegrated. Sensors noticed an unusual heat buildup of about 30 degrees inside the wheel well before the accident.
Instead, the board determined those increases were caused by the presence inside Columbia of plasma, or superheated air with temperatures of roughly 2,000 degrees. It said investigators were studying where a breach might have occurred to allow plasma to seep inside the wheel compartment or elsewhere in Columbia's left wing.
The board did not specify whether such a breach could be the result of a structural tear in Columbia's aluminum frame or a hole from debris striking the spacecraft. The board also did not indicate when the breach occurred during the shuttle's 16-day mission.
Officials have previously focused on an unusually large chunk of foam that broke off Columbia's external fuel tank on liftoff. Video footage showed it struck part of the shuttle's left wing, including its toughened leading edge and the thermal tiles covering the landing gear.
The announcement focused renewed attention on possible catastrophic failures inside the wheel compartment that may have contributed to the Feb. 1 breakup that killed seven astronauts.
Officials are not sure where a breach might have opened in Columbia's skin, NASA spokesman James Hartsfield said. But he said the leading edge or elsewhere on the left wing, the fuselage or the left landing gear door were prime candidates.
"Any of those could be potential causes for the temperature change we saw," Hartsfield said. "They do not and have not pinpointed any general location as to where that plasma flow would have to originate."
In an unusual plea for assistance, NASA urged Americans on Thursday to share with them any photographs or videotapes of Columbia's descent from California to eastern Texas. Some members of the public have already handed over images, "but more material will help the investigation of the Columbia accident," the agency said.
The board's announcement didn't surprise those experts who have believed that a mysterious failure of sensors within Columbia's left wing indicated that super-hot plasma had penetrated the shuttle.
"I think there was a substantial hole in the wing," said Steven P. Schneider, an associate professor at Purdue University's Aerospace Sciences Laboratory. "That would not be at all surprising. All the sensors in the wing failed or gave bad readings" by the time ground controllers lost contact with Columbia, he said.
The board dismissed suggestions Columbia's left landing gear was improperly lowered as it raced through Earth's atmosphere at more than 12,000 mph. NASA disclosed earlier Thursday that a sensor indicated the gear was down just 26 seconds before Columbia's destruction.
If Columbia's gear was lowered at that speed -- and in those searing temperatures as the shuttle descended over Texas from about 40 miles up -- the heat and rushing air would have sheared off Columbia's tires and led quickly to the spacecraft's tumbling destruction, experts said.
Officials said they were confident that unusual sensor reading was wrong. Tires are supposed to remain raised until the shuttle is about 200 feet over the runway and flying 345 mph.
Two other sensors in the same wheel compartment indicated the gear was still properly raised, they said.
While Columbia's piloting computers began almost simultaneously firing thrusters, struggling to keep wings level, officials said, a mysterious disruption in the air flowing near the left wing was not serious enough to suggest the shuttle's gear might be down.
The investigating board concluded that its research "does not support the scenario of an early deployment of the left gear."
NASA also confirmed that searchers near Hemphill, Texas, about 140 miles northeast of Houston, recovered what is believed to be one of Columbia's radial tires. A spokesman was not immediately sure which of the shuttle's tires was found.
The tire was blackened and sustained a massive split across its tread, but it was impossible to know whether the tire was damaged aboard Columbia or when it struck the ground.
The board's announcement came one day after NASA released e-mails showing mid level safety engineers in Virginia and Houston considered the risks of tires bursting inside Columbia's belly from heat damage.
Robert H. Daugherty, responding to an inquiry from Johnson Space Center, cautioned in one of those e-mails that damage to insulating tiles near the landing gear door could cause one or more tires inside to rupture, perhaps ending with "catastrophic" failures that would place the seven astronauts "in a world of hurt."
Ret. Adm. Harold Gehman, who heads the panel investigating the Columbia accident, called Daugherty's concerns "one of the many, many interesting leads that we have."
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