HOUSTON -- Up to three pieces of insulation foam fell from the external tank and struck the left wing of shuttle Columbia during its Jan. 16 launch, something NASA knew all along but apparently had never made clear, agency officials said Friday.
That fact surfaced when NASA released the presentation charts Boeing created for a trio of meetings held during Columbia's mission to discuss the potential damage to the shuttle's heat shield from the falling debris.
"If we did not say three pieces at first, it was completely inadvertent on our part and it was a mistake. We certainly should have made that clear," said NASA spokesman James Hartsfield.
Video analysis of the debris strike seems to show one piece coming off the tank about 82 seconds after liftoff. Before striking the wing, the debris either broke up into three pieces, or three pieces came off the tank together and appeared as one piece.
Hartsfield said officials are sure two of three pieces struck the left wing, but are not sure if the third piece did.
Nothing in the charts contradict what NASA managers have said all along was the final conclusion of the analysis, which was that although some localized damage to Columbia's wing might happen, there was no risk to the safety of the seven astronauts.
History and the Columbia Accident Investigation Board have yet to judge whether the mission managers were right or wrong, something that NASA officials also have said since the very first post-accident technical briefing to news media on Feb. 1.
"When the flight took place, everyone agreed with the analysis and agreed with the conclusion it was not a safety of flight issue, but this is not something that has been discounted as a possible cause of the accident in any way," Hartsfield said.
According to investigators, super hot air somehow breached the shuttle's heat shield and got inside the left wing during re-entry, triggering the ultimate loss of the vehicle and crew over Texas.
The exact reason why the thermal protection system failed in some place on the wing isn't known yet, which is why there is so much attention on the possibility that the foam debris striking the wing did more damage than initially believed.
The charts are filled with engineering analysis that takes into account a number of variables and predicts the amount of damage to the wing.
The variables include the exact size and density of the foam debris, the speed at which it strikes the wing, the angle at which it strikes the wing and exactly where on the wing's surface or leading edge the piece hits.
Using conservative predictions when actual data wasn't available, and predicting for the worst case, engineers concluded there would not be any serious problems during landing.
The final line of Boeing's final report dated Jan. 24 -- a week before the disaster -- states that taking into account some additional analysis still needs to be done, a "safe return (is) indicated even with significant tile damage."
The briefing charts also make it clear there were many unknowns about the analysis and that some numbers were based on previous experience that might or might not apply to Columbia's case.
Some of the potential faults in the analysis and the possible problems Columbia might experience after re-entering the atmosphere was the subject of a series of e-mails between engineers at the Johnson Space Center here and NASA's Langley Research Center in Hampton, Va.
One e-mail from Langley's Robert Daugherty was previously released by NASA and discusses possible last-minute decisions the flight control teams might have to make if they saw certain sensors fail or deflated main landing gear tires as the shuttle neared Florida.
The options discussed in detail by Daugherty included trying to land with one landing gear deployed, landing on the shuttle's belly or ditching in the ocean after the crew bailed out.
Additional e-mail traffic between Daugherty and other colleagues was released Friday by NASA and offered insight into more of the same kind of "what if" discussion that took place as Columbia's mission drew to a close.
In an e-mail dated Jan. 29, Daugherty writes to a Langley colleague about the tile damage analysis, having seen the charts that NASA released to the public today:
"We can't imagine why getting information is being treated like the Plague. Apparently the thermal folks have used words like they think things are 'survivable,' but 'marginal.' I imagine this is the last we will hear of this."
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