Posted on 02/06/2003 9:45:33 AM PST by Zavien Doombringer
NASA investigators want to know if adjustments made to the position of the space shuttle Columbia during its last minutes by the vehicle's onboard control computers could have played a role in its breakup during re-entry Feb. 1. In a revised timeline of events released Feb. 3, Ron Dittemore, NASA's space shuttle program manager, said that at 8:59 a.m. EST, Columbia's five onboard computer systems began to detect a significant increase in drag on the vehicle's left wing and ordered two of the shuttle's four yaw jets to fire for 1.5 seconds to compensate for the change.
Investigators aren't sure yet whether the adjustments ordered by the computer played a role in the shuttle's breakup. "It was well within the flight control system's capability to handle the [maneuver]," said Dittemore. "But what is becoming interesting to us now is the rate of change."
While Dittemore acknowledged that NASA may never be able to determine the exact root cause of the crash, he said investigators are now studying all of the data from the launch process as well as the shuttle's flight control systems.
The focus on Columbia's flight control systems could be significant. On Feb. 3, Computerworld reported that Columbia and other space shuttles have a history of computer glitches that have been linked to control systems, including left-wing steering controls (see story).
Although officials said it's too early in the investigation to pin the blame for the crash on the control computers, William Readdy, deputy administrator of NASA, said officials are actively searching for any of the shuttle's five onboard computer systems. Although it's unlikely they survived the crash, he said, the computers have "memory resident in them" that could shed light on the status of the shuttle after communications were lost with ground control.
Each computer's memory stores "telemetry of thousands of parameters that affect the flight of the shuttle," Readdy said.
Columbia and other space shuttles have experienced a series of control computer failures during the past two decades, including one that had a direct link to the spacecraft's left-wing control systems. During a March 1996 return flight, NASA officials discovered a computer circuit problem that controlled steering hardware on Columbia's left wing. The computer circuit was responsible for controlling the spacecraft's left rudder, flaps and other critical landing functions.
Speaking at a news conference prior to Columbia's landing in March 1996, NASA spokesman Rob Navius downplayed the seriousness of the computer problem.
"There are three additional paths of data that are up and running in perfect shape, and there's multiple redundancy that would permit a safe landing," he said. Although Columbia landed without incident that time, NASA officials said the failure was significant enough that had it happened earlier in the flight, the agency would likely have ordered the shuttle home early.
The General Accounting Office, the investigative arm of Congress, has also criticized NASA in the past for relying on the same commercial contractors to develop, test and validate the space shuttle software (see story).
However, Donna Shirley, the former manager of NASA's Mars Exploration Program and the team that built the Sojourner Microrover, said there is no evidence yet that flaws in NASA's software-validation program had anything to do with the disaster.
When I read this headline, I couldn't help but think of the film "2001, A Space Odyssey" and HAL.
I assume they use a subroutine that used to be called fuzzy logic, which allows them to learn from their situation and make appropriate adjustments as conditions change.
Sounds to me like the shuttle was not responding to input to the flight control surfaces and the computer sensed this and took actions.
The word is that Dittemore is on his way out. That's what I hear from people at JSC.
If the control surfaces were not working on the left wing at that time, it would have had a hell of a time keeping trimmed out and would be fighting to make the turns that it was being asked to do. The computers would likely begin to over correct and gradually loose control. (which it did)
Can't find the cause? Really?
I don't know of 80 degree turns make sense. Where did you read that? Here is what I dound on the standard de-orbit procedures:
The commander begins the de-orbit burn by firing the orbiter's engines to slow its speed and take it out of orbit. Using the RCS engines, the orbiter is turned around so that it is moving backwards at a slower speed. To maneuver the orbiter while it is in this position, the commander uses the RCS engines to control roll, pitch and yaw motions. The OMS engines (space engines) are then fired, taking the orbiter out of orbit and thrusting it into the earth's upper atmosphere. The RCS engines are used one last time to turn the orbiter around so that it is moving nose forward and pitched up slightly. In the upper reaches of the atmosphere the vehicle's motions of yaw, pitch and roll are controlled by the RCS engines. As the atmosphere thickens, the airplane control surfaces become usable. The orbiter re-enters the atmosphere at a high angle of attack (about 30 degrees). This high angle of attack is used to direct most of the aerodynamic heating to the underside of the vehicle where the heat resistant tiles give the greatest amount of protection.
At an altitude of approximately 30 miles, the orbiter makes a series of maneuvers and S-turns to slow its speed. At 9.5 miles in altitude and at a speed of Mach 1, the orbiter can be steered using its rudder. The on-board computers fly the orbiter until it goes subsonic (slower than the speed of sound: Mach 1). This happens about 4 minutes before landing. At this time the commander takes manual control of the orbiter and flies a wide arc approach. At 7.5 miles from the runway, the orbiter is flying about 424 miles per hour at an altitude of 13,365 feet. About 2 miles from the runway, the orbiter is flying at nearly 360 miles per hour on a glide slope of 22 degrees.
Once lined up with the runway on approach, the orbiter continues its steep glide slope of 18 - 20 degrees. The commander levels the descent angle at a final glide slope of 1.5 degrees by performing a ``flare maneuver''. The nose of the orbiter increases its pitch (noses up) which slows its speed. The orbiter touches down at a speed of about 215 miles per hour. It is slowed and eventually brought to a stop by the speed brake, wheel brakes and a drag chute.
It is this unique aerospace vehicle, a lifting body, that launches like a rocket, orbits like a spacecraft and lands like a glider that continues to link earth and space.
Hey, you'd think NASA would be eager to blame this on the insulation impact at launch. The film of that is as damning as the plume of flame escaping past Challenger's SRB o-ring.
However, the chunk of insulation was not hovering there in the sky for Columbia to hit, it was moving at the same speed and only began to lose velocity (relative to the orbiter) for a second or so before impact. The tiles are fragile, but for NASA to be veering away from the "easy explanation" is at least interesting - and unexpected.
When this happened my initial thought was a control system problem. It doesn't take much at those speeds to lose control. Loss of yaw control would put it into a spin. From that one video there seemed to be a violent yaw 90 deg. to the flight path. Whether that was a sympton or cause, we don't know.
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