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Re: OT:I think the rudder stuck



A Thomas wrote:

 > The autopilot would have sensed the temperature difference and,
 > assuming it to be the result of drag, would have tried to roll.

I don't think the STS autopilot uses temperature inputs for attitude 
control, does it?

The inference I'm seeing drawn is that roll trim was being added to 
maintain commanded attitude, and the demand for increased trim is 
interpreted as evidence of asymmetric aerodynamic drag. I didn't think 
temperatures were really part of this system.

"At 7:58 a.m. over New Mexico, the roll trim in the elevon started to 
increase, indicating that we had an increase in drag on the left side of 
the vehicle...At 7:59 a.m. we were over West Texas. Again we see an 
increase in the roll trim as indicated by elevon motion, indicating that 
the vehicle was reacting to an increased drag on the left-hand side. The 
flight control system was countering that drag by trying to command the 
vehicle to roll to the right-hand side. So we were seeing a drag causing 
the vehicle to roll to the left. The flight control system was 
commanding surfaces to get the vehicle back to where it believed it 
should be, more to the roll to the right. Soon after, we had loss of 
signal." --Ron Dittemore in Sunday's press conference.

Also note that Flight Problem STS-78-V-07 that you cite apparently only 
describes a failure in a single channel of four redundant channels of 
rudder position feedback data. I don't see an indication in this 
narrative that the rudder was actually "stuck" duing STS-78.

There's an awful lot of data and other evidence yet to be collected an 
analyzed about this accident. Premature speculation about particular 
failure modes probably isn't very helpful at this point, no matter how 
strong the temptation is to play fortune-teller.

The possibiity that disturbs me most is that there might have been 
unobserved and undetected damage to the thermal protection system while 
on-orbit, perhaps caused by a collision with a small meteor or man-made 
orbiting debris. In this case, it's possible that no direct evidence of 
the original damage will ever be found, leading to a prolonged, 
inconclusive post-accident investigation.

  73 de Maggie K3XS

-- 
-----/___.   _)   Margaret Stephanie Leber    / "The art of progress  /
----/(, /|  /| http://voicenet.com/~maggie   / consists of preserving/
---/   / | / |  _   _   _    `  _AOPA 925383/ order amid change and /
--/ ) /  |/  |_(_(_(_/_(_/__(__(/_  FN20hd / change amid order."   /
-/ (_/   '  K3XS  .-/ .-/    ARRL 39280   /___ --A.N.Whitehead ___/
/____ICQ 7161096_(_/_(_/__AMSAT 32844____/ <maggie@voicenet.com>


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