February 13, 2003
Investigators: Shuttle exterior was penetrated during descent
WASHINGTON - The space shuttle's skin almost was certainly pierced, allowing superheated air inside the left wing and possibly the wheel compartment during Columbia's fiery descent through Earth's atmosphere, 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 unusual temperature increases inside Columbia minutes before it disintegrated. Sensors detected an unusual heat buildup of about 30 degrees inside the wheel well before the accident.
The board determined those increases were caused by the presence inside Columbia of plasma, or superheated air, with a temperature 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 announcement focused renewed attention on possible catastrophic failures inside the wheel compartment that may have attributed to the Feb. 1 breakup that killed seven astronauts.
Officials are not sure where a hole 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."
The board dismissed suggestions Columbia's left landing gear was improperly lowered as it raced through Earth's atmosphere at more than 12,000 miles per hour. 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 miles per hour.
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 six 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 midlevel 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."
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