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#200
by
input~2
on 27 Dec, 2010 17:41
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#201
by
sanman
on 28 Dec, 2010 03:58
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So these seem to be the sequence of events leading to failure, imho:
1) aerodynamic stresses/vibrations build up as rocket traverses Max-Q
2) stresses/vibrations snap control cables
3) loss of control cable connectivity means engines stop responding to guidance correction commands
4) rocket loses correct orientation and angle of attack
5) rocket suffers structural breakup
Is that a reasonably plausible recap of what's happened, based on the evidence and statements available?
Edit: Wait, that can't quite be right, because I remember reading some statement from ISRO officials that at T+0.2 seconds after liftoff, they lost signal-connectivity to one of the boosters. So the control cable initially snapped during the stress of liftoff, and not at Max-Q. Fair enough?
In which case, why would stress of liftoff cause such a failure? Would it more likely be due to unaccounted vibration modes, or more likely be due to somebody just carelessly not connecting a cable firmly enough?
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#202
by
isro-watch
on 28 Dec, 2010 05:40
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So these seem to be the sequence of events leading to failure, imho:
1) aerodynamic stresses/vibrations build up as rocket traverses Max-Q
2) stresses/vibrations snap control cables
3) loss of control cable connectivity means engines stop responding to guidance correction commands
4) rocket loses correct orientation and angle of attack
5) rocket suffers structural breakup
Is that a reasonably plausible recap of what's happened, based on the evidence and statements available?
Edit: Wait, that can't quite be right, because I remember reading some statement from ISRO officials that at T+0.2 seconds after liftoff
where did u get this from...Can you please provide any link...because this is new
, they lost signal-connectivity to one of the boosters. So the control cable initially snapped during the stress of liftoff, and not at Max-Q. Fair enough?
How come the rocket run for 45 seconds with cable snapped...the flight seemed perfect till 45 seconds....your first 5 point summary looks the possible explanation...snapping should have taken place at max-Q
In which case, why would stress of liftoff cause such a failure? Would it more likely be due to unaccounted vibration modes, or more likely be due to somebody just carelessly not connecting a cable firmly enough?
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#203
by
cd-slam
on 28 Dec, 2010 05:41
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So these seem to be the sequence of events leading to failure, imho:
1) aerodynamic stresses/vibrations build up as rocket traverses Max-Q
2) stresses/vibrations snap control cables
3) loss of control cable connectivity means engines stop responding to guidance correction commands
4) rocket loses correct orientation and angle of attack
5) rocket suffers structural breakup
Is that a reasonably plausible recap of what's happened, based on the evidence and statements available?
Edit: Wait, that can't quite be right, because I remember reading some statement from ISRO officials that at T+0.2 seconds after liftoff, they lost signal-connectivity to one of the boosters. So the control cable initially snapped during the stress of liftoff, and not at Max-Q. Fair enough?
In which case, why would stress of liftoff cause such a failure? Would it more likely be due to unaccounted vibration modes, or more likely be due to somebody just carelessly not connecting a cable firmly enough?
The quote from The Hindu below, if correct, would seem to suggest your sequence 1-5 above is correct.
ISRO Chairman K. Radhakrisnan said at a press conference: “The controllability of the vehicle was lost after 47 seconds because we found that the command to control it did not reach the actuator system in the first stage of the vehicle… We suspect that a connector chord, which takes the signal down, has snapped.”
http://www.thehindu.com/sci-tech/science/article979052.ece
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#204
by
isro-watch
on 28 Dec, 2010 05:43
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#205
by
sanman
on 28 Dec, 2010 06:59
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where did u get this from...Can you please provide any link...because this is new
Nah, forget about it - I seem to have misread an article which itself is based on further misinterpretations.
http://economictimes.indiatimes.com/news/politics/nation/isro-teams-analysing-data-to-pinpoint-gslv-failure/articleshow/7166441.cmsThe FAC to be formed is expected to be similar to the committee set up after the failure of GSLV-D3, primarily for the flight testing of indigenously developed Cryogenic Upper Stage (CUS), on April 15 this year.
The FAC comprising multi-disciplinary experts concluded at the time that the primary cause for the failure was the sudden loss of thrust in one out of the four liquid propellant strap-on stages (S4) immediately after lift-off at 0.2 sec.
Obviously that article is talking about the GSLV-D3 launch on April 15th, and the article itself mis-remembers those events by claiming that the Cryogenic Upper Stage failed 0.2secs after liftoff, when it probably failed 0.2secs after CUS-ignition (ie. well into the flight).
Oops, sorry about that.
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#206
by
Jim
on 28 Dec, 2010 13:20
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Can it be that the rocket was aerodynamically unstable...and that isro is just covering tracks...as suggested in the above article.
All major launch vehicles are aerodynamically unstable
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#207
by
Jim
on 28 Dec, 2010 13:22
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How can the connectors be connected in such a delicate fashion that they snap...? Have rockets failed with this connector snapping stuff before ?
They can come apart.
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#208
by
kevin-rf
on 28 Dec, 2010 13:33
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Well, they do have to come apart when staging events occur...
It sounds unlikely to me that four cables would snap at once (but not impossible), I personally would be looking upstream somewhere before the cable harness separates into four separate harnesses.
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#209
by
jimvela
on 28 Dec, 2010 14:24
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How can the connectors be connected in such a delicate fashion that they snap...? Have rockets failed with this connector snapping stuff before ?
They can come apart.
US launches have failed when critical cables were either not mated or were mated but the retaining hardware not tightened.
A recent example had a fairing fail to separate...
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#210
by
Lee Jay
on 28 Dec, 2010 14:54
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How can the connectors be connected in such a delicate fashion that they snap...? Have rockets failed with this connector snapping stuff before ?
They can come apart.
US launches have failed when critical cables were either not mated or were mated but the retaining hardware not tightened.
A recent example had a fairing fail to separate...
I wasn't aware that the OCO failure investigation came to that conclusion. The executive summary doesn't seem to state that:
http://www.nasa.gov/pdf/369037main_OCOexecutivesummary_71609.pdfDo you have a source confirming what you have said?
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#211
by
pradeep
on 28 Dec, 2010 14:59
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So these seem to be the sequence of events leading to failure, imho:
1) aerodynamic stresses/vibrations build up as rocket traverses Max-Q
2) stresses/vibrations snap control cables
3) loss of control cable connectivity means engines stop responding to guidance correction commands
4) rocket loses correct orientation and angle of attack
5) rocket suffers structural breakup
Is that a reasonably plausible recap of what's happened, based on the evidence and statements available?
I have seen the video here:
which shows a pretty good full vehicle picture when the failure occurs.
Notice that the payload fairing region crumbles first which points to aerodynamic failure since as I understand it these are at the nose of the vehicle. I think the explosion is really the Range Safety Officer pressing the self-destruct after the loss of payload.
Comments are welcome.
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#212
by
sanman
on 29 Dec, 2010 13:04
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#213
by
Danderman
on 29 Dec, 2010 13:16
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Hmmm .. perhaps the heavier C15 upper stage generated loads at the second stage/third stage interface that were not expected.
Or else, some leaking propellant got onto the connectors.
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#214
by
Art LeBrun
on 29 Dec, 2010 13:31
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Isn't there a better term than snapping connectors? Are connectors suspended within conduit or attached to frame?
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#215
by
Jim
on 29 Dec, 2010 14:11
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Isn't there a better term than snapping connectors? Are connectors suspended within conduit or attached to frame?
disconnected, unmated, unplugged,
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#216
by
edkyle99
on 29 Dec, 2010 16:16
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Hmmm .. perhaps the heavier C15 upper stage generated loads at the second stage/third stage interface that were not expected.
Or else, some leaking propellant got onto the connectors.
Other possibilities might include aerodynamic loads created by the larger diameter payload fairing or a mangled umbilical disconnect sequence at liftoff. Wouldn't these "connectors", or at least the cables tied to them, be located in a cable tunnel mounted on the outside of the rocket?
I think that umbilical connectors are visible in this image of the third stage. This is the general area of the described failure.
http://upload.wikimedia.org/wikipedia/en/a/a2/GSLV_Mk2D3_Cryo_Engine.jpgOf course workers would have been into this area during the leak investigation.
- Ed Kyle
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#217
by
Antares
on 30 Dec, 2010 03:40
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This quad failure isn't credible to me, unless it was a progressive failure (1 then another then the other 2) and it was able to fly through 1 of them.
I suggest we wait for the investigation.
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#218
by
Danderman
on 30 Dec, 2010 03:51
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I think that umbilical connectors are visible in this image of the third stage. This is the general area of the described failure.
http://upload.wikimedia.org/wikipedia/en/a/a2/GSLV_Mk2D3_Cryo_Engine.jpg
Of course workers would have been into this area during the leak investigation.
- Ed Kyle
The image is of a MKII upper stage, the indigenous Indian stage. In this particular failure, the Khrunichev upper stage was used, ie the MKI stage.
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#219
by
seshagirib
on 30 Dec, 2010 04:35
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Isn't there a better term than snapping connectors? Are connectors suspended within conduit or attached to frame?
disconnected, unmated, unplugged,
Maybe the fact that they used the word "snapping" indicates they suspect the cables snapped rather than the mating connectors. - though it is even more difficult to imagine how this could happen.
May be a umbilical chord failed to unmate and somehow pulled at the cable assembly at launch.
