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Latest Clues Point to Early Damage on Space Shuttle - 2003-04-01

The latest clues from the U.S. space shuttle Columbia disaster probe strengthen the theory that the orbiter was damaged almost from the start of the mission perhaps by external fuel tank foam hitting the left wing. A recently recovered data recorder confirms that extremely hot atmospheric gases leaked through a break in the wing, causing it to disintegrate as it headed for a landing.

The data recorder's magnetic tape stored information from hundreds of sensors around the shuttle about temperature, vibrations, pressure and aerodynamic conditions during launch and re-entry.

According to investigators, the tape reveals that two temperature sensors on the left wing's leading edge got much hotter than sensors elsewhere on the left side had originally indicated at the time of re-entry. The wing sensors reached 230 degrees Celsius before they failed. Furthermore, the temperature in the wing sensors rose earlier than it did in other parts of the shuttle.

The head of the investigating panel, retired U.S. Navy Admiral Harold Gehman, says this means the left wing's front edge is almost certainly where superheated atmospheric gases first penetrated the shuttle before winding their way through other parts of the structure. "It kind of points us toward the leading edge," he says. "Nothing that has been reported to me contradicts the scenario that somehow heat got into that left wing."

But the data do not yet pinpoint the precise location of the wing opening that allowed the hot gases in.

The left wing has been suspect since Columbia broke up over the southwestern United States on February 1. Film of the shuttle's launch 16 days earlier showed that several pieces of hard insulating foam broke away from the orbiter's external fuel tank and smashed into the wing in the strong downdraft. This has caused speculation that it might have damaged the reinforced carbon panels protecting the wing's leading edge, especially if it had been laden with ice.

Despite the focus on the foam strike, investigators have said they are considering all possible causes of damage, including a hit by space debris during re-entry into the atmosphere or some other re-entry stress.

But Admiral Gehman now says such events are unlikely because the heat began affecting the shuttle at an altitude where there is not enough air pressure to harm a spacecraft. "There is so little dynamic air pressure up there that probably whatever was misformed about the orbiter, it came in that way," he says. "It wasn't something that happened like re-entry debris or something like that. The orbiter probably had this problem before she ever started her entry."

Investigators soon will test the notion that falling fuel tank foam could damage the shuttle. They will propel foam pieces at high speeds at the kind of reinforced panels that cover shuttle wings' front edges.

They are also continuing to analyze the data recorder tape to see if it shows any other launch stresses on the shuttle that could combine with the foam strike to put a hole in the wing.