The technical flaw, as stated in the Columbia Accident Investigation Board's (CAIB) final report last August, was a critical breach in the ceramic tiles that made up the shuttle's protective heat shield and should have protected it from the excruciating heat of re-entry.

The breach was caused during takeoff when a large chunk of insulating foam broke free from one of the shuttle's external fuel tanks and crashed into the leading edge of the left wing. The spent fuel tanks themselves were jettisoned 81.7 seconds after takeoff.

"During re-entry, this breach in the thermal protection system allowed superheated air to penetrate though the leading edge insulation and progressively melt the aluminum structure of the left wing," said the CAIB's report last August.

The result was "a weakening of the structure until increasing aerodynamic forces caused loss of control, failure of the wing, and breakup of the orbiter.

"There was no possibility for the crew to survive."

But beyond the technical reasons for the accident, the investigators cited "organizational causes ... rooted in the history and culture" of NASA's space shuttle program.

Those, they said, go back to "original compromises ... required to gain approval for the shuttle ... years of resource constraint, fluctuating priorities, schedule pressures (and) reliance on past success as a substitute for sound engineering practices."

There were, said the CAIB report, "organizational barriers that prevented effective communication of critical safety information and stifled professional differences of opinion (and) an informal chain of command and decision-making processes that operated outside the organization's rules."

SPACE.WIRE