SPACE CENTER, Houston -- Columbia began exhibiting problems earlier than suspected and experienced the bulk of its breakup later than previously thought, according to the latest flight timeline released by the shuttle accident investigation board Monday.
No one at NASA is speculating, at least openly, how long the seven astronauts may have survived under this new scenario.
What is apparent, however, is that alarms were going off in the final two seconds of transmitted data, the left orbital maneuvering system and the left wing were either heavily damaged or gone, and the spaceship was swinging out of control. Sensors registered the maximum so-called yaw rate of 20 degrees per second, and it could have been more.
"Data suggest vehicle was in an uncommanded attitude and was exhibiting uncontrolled rates," states the master timeline, which was prepared by NASA and presented to the investigation board.
Thirteen seconds after all communication ceased, a large, major piece of debris was observed falling away from the shuttle, according to the timeline. A second piece came off a second later. And the onset of the breakup of the ship's main body occurred three seconds after that -- and a full 17 seconds from the time the last bit of data was conveyed.
Columbia disintegrated above Texas on Feb. 1, just 16 minutes shy of a touchdown in Florida.
The timeline -- labeled Revision 14 and expected to be replaced by No. 15 in just a few days -- stresses that the last two seconds of data are suspect because of multiple errors. "Some of the conclusions drawn below may be in error or misinterpreted," the timeline cautions.
On Sunday, officials acknowledged that based on this reconstructed data, one of the shuttle pilots may have tried to override the autopilot or may have bumped the manual control stick. In any event, the autopilot remained on, according to the data.
Not using data
When asked if anything else could be gleaned about the crew's actions from the final two seconds of data -- or how long the astronauts may have survived -- NASA spokesman James Hartsfield said: "We're not using this data to further interpret crew actions."
Neither NASA nor the investigation board provided a map to pinpoint the location of the various events. Officials said that would accompany the next timeline, Rev 15.
The 14th timeline also has the trouble starting a full minute earlier than before, as Columbia was flying over the Pacific toward the California coast. Remote sensors indicate "off-nominal" readings as early as 8:51 a.m. Eastern, somehow involving jet firings.
NASA and other experts have been trying for weeks to reconstruct the last two seconds of data. It has been a difficult job because of the poor quality of the information.
A large piece of debris -- called Debris A -- was seen falling away from the shuttle almost right at 9 a.m. Eastern, milliseconds before the final two seconds of data.
NASA also reported that 15 pieces of smaller debris were observed to have "shed" from Columbia, two of them very bright, before the ship crossed the Arizona-New Mexico state line. The first report of debris occurred over California.
The investigation board received the latest timeline from NASA over the weekend. Its members are still trying to ascertain whether launch debris caused a breach in the left wing, quite possibly along the leading edge.
Insulating foam or other debris broke off Columbia's external fuel tank shortly after liftoff on Jan. 16 and struck the left wing.
On the Net:
Columbia accident investigation board: www.caib.us