Upon re-entry, hot gases entered the breach, causing the breakup of the spacecraft.
The debris struck the left wing, possibly breaching the shuttle skin to let superheated gases enter on re-entry, setting off the fatal chain of events upon re-entry on Feb. 1, some experts said.
When the coating comes off, tiles might partly melt upon re-entry, but even partial tiles have dissipated heat, she said.
The undetected damage allowed hot gases to penetrate the wing upon re-entry, dooming the shuttle and its seven-member crew.
Also in their elite group were David M. Brown, Laurel B. Clark and William C. McCool, who perished -- along with four astronauts from other groups -- aboard the Columbia in February upon re-entry.
The remaining three space shuttles have been grounded since the Columbia and its crew of seven was destroyed upon re-entry from space on Feb. 1, 2003.
The shuttle program has been grounded since the Columbia broke up upon re-entry on Feb. 1, 2003, killing its crew of seven.
Experts believe much of Mir would not burn up upon re-entry and could pose a major hazard to people and property if it fell on land.
A14 More Data on Shuttle Damage The chairman of the panel investigating the shuttle Columbia accident said that newly recovered data from a recorder indicate that the shuttle already had severe damage upon re-entry.
In its investigation, the Gehman board has interviewed more than 250 people about the Feb. 1 accident, which killed all seven crew members when the Columbia disintegrated upon re-entry.
