General Discussion > Q&A Section
Shuttle Questions Q and A
Rocket Ronnie:
Cool, another NASA person on here! What's the last point in which a countdown can be cutoff? I've seen at least one where the SSMEs are on the way to 100 (or 104) percent and an abort has been called, engines shut down, stack is rolling about because of the SSMEs and the safing even had jets of water spraying on the aft of the orbiter. That was about T-3seconds I think.
psloss:
--- Quote ---Rocket Ronnie - 12/1/2006 8:03 AM
Cool, another NASA person on here! What's the last point in which a countdown can be cutoff? I've seen at least one where the SSMEs are on the way to 100 (or 104) percent and an abort has been called, engines shut down, stack is rolling about because of the SSMEs and the safing even had jets of water spraying on the aft of the orbiter. That was about T-3seconds I think.
--- End quote ---
Hopefully Mr. Mathews or one of the other NASA or contractor folks here can answer that; from past experiences, I believe that the cutoff logic/philosophy changes from before liftoff to after liftoff. I would presume that the launch can be aborted anytime up to the commands that start the SRBs and fire the pyros for the hold downs.
In the case of the STS-68 cutoff, it was reported that the right engine started a little slowly such that the high pressure oxidizer turbine (HPOT) discharge temperature was slightly over the limit; however, at the time of the cutoff, I believe it was also reported that the limit changes with time and would have increased slightly such that the discharge temp would have been within the limit just a few hundred milliseconds later. (At the time, I believe it was reported that the sensor sample rate was every 20 or 40 milliseconds.)
Regarding the "boattail" water deluge, I believe the system has been in place since the first launch; however, I don't believe it was used in any of the planned or unplanned cutoffs until the 26 June 1984 launch attempt for STS-41D, where the nature of the shutdown left enough hydrogen gas in the area to help ignite some RTV on the orbiter (I believe) and start a fire. Since that event, I believe the deluge activates automatically in case of a cutoff.
JamesSpaceFlight:
Excellent information. Hats off to you all at KSC for what is an engineering marvel with STS launch ops.
Space101:
Mr Mathews, you don't happen to know how the 02 leak during STS-114 investigation is proceeding?
Long thread on this here http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=989&start=1 - the article by this site was first, then Florida Today and CBS News and Associated "we hate NASA" Press followed three days later. So we're all hoping this place gets to follow it up as no one else is.
Chris Bergin:
There's a subject where you gain nothing more than unanswered e-mails from KSC press relations. Kinda given up on that route (nice people, but don't go asking something you shouldn't apparently know). I think they've been used to crap media, no media, or negative media, so I understand to a level.
I do need to find myself an Orbiter tech who works with SSMEs though.
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