That initial bank had been as steep as about 80 deg. between Hawaii and the California coast, a normal flight path angle for the early part of the reentry. The abnormal events seen on orbiter telemetry in Houston indicate a slow penetration of reentry heat into the orbiter and damage on the wing, overpowering the flight control system. Key events were:
* 7:52 a.m. CST: Three left main landing gear brakeline temperatures show an unusual rise. "This was the first occurrence of a significant thermal event in the left wheel well," Dittemore said. Engineers do not believe the left wheel well was breached, but rather that hot gasses were somehow finding a flow path within the wing to reach the wheel well.
* 7:53 a.m. CST: A fourth left brakeline strut temperature measurement rose significantly -- about 30-40 deg. in 5 min.
* 7:54 a.m. CST: With the orbiter over eastern California and western Nevada, the mid-fuselage mold line where the left wing meets the fuselage showed an unusual temperature rise. The 60F rise over 5 min. was not dramatic, but showed that something was heating the wing fuselage interface area at this time. Wing leading edge and belly temperatures were over 2,000F. While the outside fuselage wall was heating, the inside wall remained cool as normal.
* 7:55 a.m. CST: A fifth left main gear temperature sensor showed an unusual rise.
* 7:57 a.m. CST: As Columbia was passing over Arizona and New Mexico, the orbiter's upper and lower left wing temperature sensors failed, probably indicating their lines had been cut. The orbiter was also rolling back to the left into about a 75-deg. left bank angle, again to dissipate energy and for navigation and guidance toward Runway 33 at Kennedy, then about 1,800 mi. away.
* 7:58 a.m. CST: Still over New Mexico, the elevons began to move to adjust orbiter roll axis trim, indicating an increase in drag on the left side of the vehicle. That could be indicative of "rough tile or missing tile but we are not sure," Dittemore said. At the same time, the elevons were reacting to increased drag on the left side of the vehicle, the left main landing gear tire pressures and wheel temperature measurements failed. This was indicative of a loss of the sensor, not the explosion or failure of the left main gear tires, Dittemore believes. The sensors were lost in a staggered fashion.
* 7:59 a.m. CST: Additional elevon motion is commanded by the flight control system to counteract right side drag. The drag was trying to roll the vehicle to the left, while the flight control system was commanding the elevons to roll it back to the right.
But the rate of left roll was beginning to overpower the elevons, so the control system fired two 870-lb. thrust right yaw thrusters to help maintain the proper flight path angle. The firing lasted 1.5 sec. and, along with the tire pressure data and elevon data, would have been noted by the pilots.
At about this time, the pilots made a short transmission that was clipped and essentially unintelligible
In Mission Control, astronaut Marine Lt. Col. Charles Hobaugh, the spacecraft communicator on reentry flight director Leroy Cain's team, radioed "Columbia we see your tire pressure [telemetry[ messages and we did not copy your last transmission."
One of the pilots then radioed "Roger," but appeared to be cut off in mid transmission by static. For a moment there was additional static and sounds similar to an open microphone on Columbia but no transmissions from the crew.
All data from the orbiter then stopped and the position plot display in Mission Control froze over Texas, although an additional 30 sec. of poor data may have been captured.
Controllers in Mission Control thought they were experiencing an unusual but non-critical data drop out. But they had also taken notice of the unusual buildup of sensor telemetry in the preceding few minutes.
About 3 min. after all data flow stopped, Hobaugh in mission control began transmitting in the blind to Columbia on the UHF backup radio system. "Columbia, Houston, UHF comm. check" he repeated every 15-30 sec., but to no avail. In central Texas, thousands of people at that moment were observing the orbiter break up at Mach 18.3 and 207,000 ft.
Actually, the drag would tend to YAW the vehicle to the left. The loss of lift on that side would tend to ROLL the vehicle to the left.
I don't know enough about the orbiter flight control system to predict how it would react to something like this. I know there are IMUs [Inertial Measurement Units] which are the main "attitude gyroscopes". There are also accelerometers, but I don't recall their function.
On a light aircraft, the turn coordinator gyro responds to both roll and yaw. Certainly the shuttle FCS responds independently to yaw and roll inputs.
Any FCS experts out there?
Maybe someone has already addressed this but the MSNBC expert (Barberi? )said this morning that NASA's computers are designed to screen out "nonsense" data. According to him there maybe relevant and possibly recoverable data that the computers screened out because they thought the data was nonsense.