-
#240
by
Rocket Ronnie
on 12 Jan, 2006 12:03
-
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.
-
#241
by
psloss
on 12 Jan, 2006 12:24
-
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.
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.
-
#242
by
JamesSpaceFlight
on 12 Jan, 2006 12:24
-
Excellent information. Hats off to you all at KSC for what is an engineering marvel with STS launch ops.
-
#243
by
Space101
on 12 Jan, 2006 12:31
-
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.
-
#244
by
Chris Bergin
on 12 Jan, 2006 13:25
-
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.
-
#245
by
Launch Fan
on 12 Jan, 2006 17:44
-
A question, if I may, which will sound stupid, so I appologize in advance.
I have read that a team stays at the pad during launch, in case of a pad abort where the astronauts have to escape. Is this right? I know the Red Team do the final checkout of the systems, but I didn't think anyone would be able to stay near the pad, in the RSS I read, during the launch?
-
#246
by
possum
on 12 Jan, 2006 18:19
-
SSME shutdown can happen up to the last millisecond as far as I know. There was one mission where the countdown clock at the press site read 0:00:00 after an engine shutdown and everyone was freaking out thinking the bolts may have released and the Shuttle was teetering on the pad. Of course, that would never happen. As for the O2 leak in the aft, I posted on this thread what I know:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=989&start=131&posts=135
-
#247
by
Avron
on 12 Jan, 2006 19:20
-
rmathews3 - 12/1/2006 2:19 PM
SSME shutdown can happen up to the last millisecond as far as I know. There was one mission where the countdown clock at the press site read 0:00:00 after an engine shutdown and everyone was freaking out thinking the bolts may have released and the Shuttle was teetering on the pad. Of course, that would never happen. As for the O2 leak in the aft, I posted on this thread what I know:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=989&start=131&posts=135
I understand the bolts go first then SRB ignition, So I guess as long as the Piros have not been triggered shutdown is an option.. Was wondering if the hold down bolt trigger where EH.. hardwired to SRB's or was under control directly and independantly from the onboard sequencer
-
#248
by
mkirk
on 12 Jan, 2006 20:11
-
re:
I understand the bolts go first then SRB ignition, So I guess as long as the Piros have not been triggered shutdown is an option.. Was wondering if the hold down bolt trigger where EH.. hardwired to SRB's or was under control directly and independantly from the onboard sequencer
Edited by Avron 12/1/2006 2:21 PM
Hey All-
I am a new user so pardon me if I am not posting correctly,
I dont' understand the second part of your question but regarding the first half: The command to fire the SRB hold down posts and the SRB ignition command are actually sent to both redundant circuits as a fire 1 command, fire 2 command for each system...in that order (seperation then ignition) essentially simultaneously...I don't recall the exact milliseconds. Each system, holdown and ignition has two redundant circuits. The commands are sent via the onboard master events controller (MECs). All events after auto sequence start (T-31 seconds) are conducted by the onbaord general purpose computers (GPCs). Once the command is sent there is no stopping anything...it can not be revoked. You are either going to have a good clean liftoff with two SRBs thrusting or you are going to have a bad day.
-
#249
by
Chris Bergin
on 12 Jan, 2006 20:31
-
Welcome to the site.
-
#250
by
psloss
on 12 Jan, 2006 23:09
-
rmathews3 - 12/1/2006 2:19 PM
...There was one mission where the countdown clock at the press site read 0:00:00 after an engine shutdown and everyone was freaking out thinking the bolts may have released and the Shuttle was teetering on the pad...
Yeah, that was STS-68; the MSFC report is still cached on Google, but I can't get to the original link.
This is a link to the Google cache copy.Excerpts:
STS-68 LAUNCH ATTEMPT REPORT
AUGUST 18, 1994
GEORGE C. MARSHALL SPACE FLIGHT CENTER
Cynthia A. Snoddy
Chairman, MSFC Space Shuttle
Flight Evaluation Team
.
.
.
ON-PAD ABORT DATE: August 18, 1994
LAUNCH WINDOW: 5:54 am - 9:24 am CDT
ON-PAD ABORT TIME: 94:230:10:53:58.157 GMT
5:54 am CDT
NSTS DATABASE T-REF: 94:230:10:54:00.000
SSME#3 START TIME: 94:230:10:53:53.437
SSME#2 START TIME: 94:230:10:53:53.558
SSME#1 START TIME: 94:230:10:53:53.679
SSME#3 SHUTDOWN TIME: 94:230:10:53:58.157
SSME#2 SHUTDOWN TIME: 94:230:10:53:59.358
SSME#1 SHUTDOWN TIME: 94:230:10:54:00.638
.
.
.
1.0 STS-68 LAUNCH ATTEMPT SUMMARY
The scheduled launch of STS-68 on August 18, 1994 was aborted on Launch Pad 39A
(MLP-1) at the Kennedy Space Center (KSC) shortly after the main engine start
command was issued. The on-pad abort occurred at approximately 5:54 A.M.
Central Daylight Time (CDT) (094:230:10:53:58.157 GMT). The abort was executed
because of a ME-3 Failure Identification (FID) due to the High Pressure
Oxidizer Turbopump discharge temperature exceeding a redline. The
investigation of the abort is discussed in section 2.3.
.
.
.
2.3 SPACE SHUTTLE MAIN ENGINE - SSMEs 2012, 2034, 2032
All SSME parameters appeared to be normal throughout the prelaunch countdown
and were typical of prelaunch parameters observed on previous flights. Engine
"Ready" was achieved at the proper time and all LCC were met.
2.3 SPACE SHUTTLE MAIN ENGINE - SSMEs 2012, 2034, 2032 (cont)
The on-pad launch abort occurred because the ME-3 (E2032) High Pressure
Oxidizer Turbine (HPOT) discharge temperature Channel A exceeded a pre-liftoff
redline check resulting in a Failure Identification (FID) and subsequent engine
shutdown. At Engine Start Command (ESC) plus 2.3 seconds through ESC plus 5.8
seconds the HPOT discharge temperature must not exceed 1560 R. The ME-3 HPOT
discharge temperature Channel A was 1576 R. The Channel B measurement was 1530
R which was also higher than predicted. Instrumentation/data appears to be
valid.
ME-3 was commanded to shutdown at ESC plus 4.72 seconds. ME-2 and ME-1
subsequently shutdown at ESC plus 5.80 seconds and 6.96 seconds respectively.
The shutdowns were all nominal and placed the vehicle in a safe status.
The cause of the high turbine discharge temperature is under investigation and
a number of factors could in combination have led to the overshoot temperature
response (e.g. fuel side build-up characteristics, sequencing changes prior to
STS-68, turbopump efficiencies, hardware degradation, etc.). The current plan
of action is to establish investigation teams, perform fault tree analysis,
engine inspections and detailed data and film evaluation.
Note that the last shutdown command occurred after what would have been T-0! That was definitely a heart-stopper for me, even just watching it live on TV.
Philip Sloss
-
#251
by
Jamie Young
on 12 Jan, 2006 23:52
-
Wow, anyone got a link to a video of that?
-
#252
by
Mark Max Q
on 13 Jan, 2006 02:03
-
-
#253
by
Firestarter
on 13 Jan, 2006 03:25
-
Well it's only 15mb, but took an hour to download
I like it how KSC staff are already walking away as if nothing had happened seconds after cut off.
-
#254
by
Avron
on 13 Jan, 2006 03:36
-
mkirk - 12/1/2006 4:11 PM
re:
I understand the bolts go first then SRB ignition, So I guess as long as the Piros have not been triggered shutdown is an option.. Was wondering if the hold down bolt trigger where EH.. hardwired to SRB's or was under control directly and independantly from the onboard sequencer
Edited by Avron 12/1/2006 2:21 PM
Hey All-
I am a new user so pardon me if I am not posting correctly,
I dont' understand the second part of your question but regarding the first half: The command to fire the SRB hold down posts and the SRB ignition command are actually sent to both redundant circuits as a fire 1 command, fire 2 command for each system...in that order (seperation then ignition) essentially simultaneously...I don't recall the exact milliseconds. Each system, holdown and ignition has two redundant circuits. The commands are sent via the onboard master events controller (MECs). All events after auto sequence start (T-31 seconds) are conducted by the onbaord general purpose computers (GPCs). Once the command is sent there is no stopping anything...it can not be revoked. You are either going to have a good clean liftoff with two SRBs thrusting or you are going to have a bad day.
mkirk welcome,
You answered my second part, so we have two circuits independently commanded from the MEC, one for hold down and one for SRB ignition. What is the chance that MEC fails between the two?
-
#255
by
Tahii
on 13 Jan, 2006 06:44
-
-
#256
by
Chris Bergin
on 13 Jan, 2006 09:56
-
Might of taken some people longer as he minute someone linked it up, you'll of seen a number go download it at the same time.
On the video "3, 2, 1 AND....we have a cut off" yikes. Also interesting to see the close up of SSME shutdown, with the center and right engine taking a good second to power down after the left closed off. Both left and right gimbal to launch position and then gimbal back out, was new to see also.
-
#257
by
psloss
on 13 Jan, 2006 11:47
-
Chris Bergin - 13/1/2006 5:56 AM
Might of taken some people longer as he minute someone linked it up, you'll of seen a number go download it at the same time.
On the video "3, 2, 1 AND....we have a cut off" yikes. Also interesting to see the close up of SSME shutdown, with the center and right engine taking a good second to power down after the left closed off. Both left and right gimbal to launch position and then gimbal back out, was new to see also.
The way the live TV cut between cameras and the timing of the cutoff made it a little extra dramatic; the engines are gimballed to launch position after they all reach mainstage and they cut to the wide shot just as they were finishing that -- and also just as the cutoff started with the engines being moved back to start position and the shutdown command going to the center engine.
The video also shows what I mentioned earlier in the thread -- the hydrogen burn igniters stop at T-0, even though the shutdown sequencing is still in progress. That probably contributed to a little extra free, unburned hydrogen before the water deluge started. (Another thing interesting thing to me with the water deluge is seeing how hot the boattail got with the engines running at mainstage -- when the water comes on, look at the steam coming off the tail, etc.)
I believe this event contributed to the choice of a picture in picture for the live liftoff broadcast in many of the subsequent launches.
-
#258
by
Jonesy STS
on 13 Jan, 2006 12:22
-
There never seems to be a lot of people near the countdown clock. Why is this?
-
#259
by
possum
on 13 Jan, 2006 12:35
-
The following two statements are from the Space Shuttle News Reference document which is available to the public:
1)Three signals must be present simultaneously for the PIC to generate the pyro firing output. These signals (arm, fire 1 and fire 2) originate in the orbiter general- purpose computers and are transmitted to the MECs.
2)The solid rocket motor ignition commands are issued by the orbiter's computers through the master events controllers to the hold- down pyrotechnic initiator controllers on the mobile launcher platform. They provide the ignition to the hold- down NSDs.
Let me interpret to clarify that the signal to ignite the SRB's and to release the holddown bolts are one and the same. The signal is actually three signals - arm, fire1 and fire2, all must be present to initiate the pyros. The command comes from the Orbiter computer and goes to the Master Events Controller (MEC). The MEC sends the signal to both the SRB igniter and the holddown post pyros (and other T-0 events). There is probably a few milliseconds difference in the two firing events due to response time and legth of wiring, but it is a single command to initiate both. All signal paths are redundant, there are two for each SRB igniter and two for each of the 16 charges on the holddown bolts (2 each for all 8 bolts). I believe that the MEC sends this same signal for SRB ignition to the 8 holddown bolts, both TSM umbilicals, and the Hydrogen Vent Arm. These are all T-0 events and are all initiated by the same command from the on-board computers and distributed by the MEC to all destinations through redundant electrical paths.
I like it how KSC staff are already walking away as if nothing had happened seconds after cut off.
