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#680
by
DaveS
on 24 Feb, 2008 21:54
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Each SRB uses 4 Solid Rocket Motor(SRM) segments and these can be a real mix of really old segments that may be dating back to STS-1 and new segments that only dates back to STS-95.
So no SRB is ever identical as it's made up of many different components(SRM segments, forward and aft skirts, frustrum, nose caps etc).
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#681
by
kneecaps
on 26 Feb, 2008 14:09
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DaveS - 24/2/2008 10:54 PM
Each SRB uses 4 Solid Rocket Motor(SRM) segments and these can be a real mix of really old segments that may be dating back to STS-1 and new segments that only dates back to STS-95.
Can the segments date back that far since they were redesigned post Challenger?
Also I wonder what the oldest segments still in use actually are!
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#682
by
GLS
on 26 Feb, 2008 14:18
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Only half? of the segments were redesigned (new). Only the segments that are the tang (top) in the field joint had to be replaced, because of the addition of the capture feature. The clevis (bottom) segments are the same. Not sure right now if the aft dome was also new... anyone???
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#683
by
Jim
on 26 Feb, 2008 14:56
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GLS - 26/2/2008 10:18 AM
Only half? of the segments were redesigned (new). Only the segments that are the tang (top) in the field joint had to be replaced, because of the addition of the capture feature. The clevis (bottom) segments are the same. Not sure right now if the aft dome was also new... anyone???
That't what I was lead to believe. The old segments still could be used
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#684
by
ChrisGebhardt
on 26 Feb, 2008 20:51
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Jim - 26/2/2008 10:56 AM
GLS - 26/2/2008 10:18 AM
Only half? of the segments were redesigned (new). Only the segments that are the tang (top) in the field joint had to be replaced, because of the addition of the capture feature. The clevis (bottom) segments are the same. Not sure right now if the aft dome was also new... anyone???
That't what I was lead to believe. The old segments still could be used
Has to be. I remember durinig the launch countdown coverage for STS-118, Diller spoke about how one of the SRB segments on that flight dated back to STS-3.
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#685
by
psloss
on 26 Feb, 2008 21:03
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There's tang vs. clevis, but there's also field vs. factory joints. I believe at the time of the redesign, only the case-to-case field joints added the capture feature; the case-to-case factory joints did not. Not sure if/how that changed over time.
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#686
by
Lee Jay
on 27 Feb, 2008 02:28
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I know there have been a number of RSLS aborts in Shuttle program history. What I'm wondering is if there's a list or document somewhere that provides a summary of the root cause determination of each of those events. I've spent the last half-hour searching to no avail. What I'm really wondering is if they all ended up being sensor-related issues, or if there have been actual SSME failures during those events that would have caused a shutdown post launch if they had happened a few seconds later than the did.
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#687
by
Jim
on 27 Feb, 2008 11:11
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Lee Jay - 26/2/2008 10:28 PM
I know there have been a number of RSLS aborts in Shuttle program history. What I'm wondering is if there's a list or document somewhere that provides a summary of the root cause determination of each of those events. I've spent the last half-hour searching to no avail. What I'm really wondering is if they all ended up being sensor-related issues, or if there have been actual SSME failures during those events that would have caused a shutdown post launch if they had happened a few seconds later than the did.
One I know was for a slow moving valve
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#688
by
Lawntonlookirs
on 27 Feb, 2008 17:19
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#689
by
Jim
on 27 Feb, 2008 17:27
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#690
by
GLS
on 27 Feb, 2008 18:02
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psloss - 26/2/2008 10:03 PM
There's tang vs. clevis, but there's also field vs. factory joints. I believe at the time of the redesign, only the case-to-case field joints added the capture feature; the case-to-case factory joints did not. Not sure if/how that changed over time.
The factory joint doesn't need the capture feature. It has insulation over it on the inside and then the propellant, so if that joint rotates at all it's harmless.
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#691
by
GLS
on 27 Feb, 2008 18:28
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Lee Jay - 27/2/2008 3:28 AM
I know there have been a number of RSLS aborts in Shuttle program history. What I'm wondering is if there's a list or document somewhere that provides a summary of the root cause determination of each of those events. I've spent the last half-hour searching to no avail. What I'm really wondering is if they all ended up being sensor-related issues, or if there have been actual SSME failures during those events that would have caused a shutdown post launch if they had happened a few seconds later than the did.
NTRS doc about RSLS abort on STS 51
http://hdl.handle.net/2060/19940021727(there's more but you have to buy them... :angry: )
On ignition, the SSME (and probably other engines) is very sensitive to valve position errors. I think it's like 1 or 2% error in the position of some valves and you've ruined the start sequence, some sensor will soon violate it's redline and then you hear the PAO saying "3, 2, 1... and cutoff!!". Most were valve position (41-D, 51-F, 55). 51 was a flow sensor and on 68 the engine apparently didn't have any problem. It died because the discharge temperature of the HPOTP was over the redline by 3ēR, and just a few milliseconds later that same redline would be increased... so it was just bad luck!
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#692
by
psloss
on 27 Feb, 2008 19:02
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GLS - 27/2/2008 2:28 PM
51 was a flow sensor and on 68 the engine apparently didn't have any problem. It died because the discharge temperature of the HPOTP was over the redline by 3ēR, and just a few milliseconds later that same redline would be increased... so it was just bad luck!
I believe the engine HPOTP on 68 going over the redline was attributed to more than one factor, including a "slow start"; I can still hear Brewster Shaw saying something along the lines of "a stack up of tolerances." FWIW, the engine was sent to Stennis after the cutoff and started fine.
Also is the three-degrees-over-the-redline info from NTRS? At the time I believe the spread was stated a little differently, though those numbers would have been from very shortly after the cutoff. This preliminary Marshall report used to be on one of NASA's servers, but at least there's still a copy of a Usenet post. It quotes Channel A as indicating 16 degrees over the 1560R limit:
http://groups.google.com/group/sci.space.shuttle/msg/4aaa1b8c09597d78?dmode=source
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#693
by
kneecaps
on 27 Feb, 2008 19:36
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psloss - 27/2/2008 8:02 PM
Also is the three-degrees-over-the-redline info from NTRS? At the time I believe the spread was stated a little differently, though those numbers would have been from very shortly after the cutoff. This preliminary Marshall report used to be on one of NASA's servers, but at least there's still a copy of a Usenet post. It quotes Channel A as indicating 16 degrees over the 1560R limit:
http://groups.google.com/group/sci.space.shuttle/msg/4aaa1b8c09597d78?dmode=source
I have a faint memory that the HPOT OPV was slow to open/move.
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#694
by
psloss
on 27 Feb, 2008 20:05
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kneecaps - 27/2/2008 3:36 PM
I have a faint memory that the HPOT OPV was slow to open/move.
FWIW, in the post-cutoff briefing, Boyce Mix (the MSFC SSME project rep) said that at least the quicklook data showed the prevalve positions were as commanded. I'll see if I can post some audio from the STS-64 pre-launch press conference later on.
Edit -- just to note, it was the preburner valves; I screwed up and translated that to prevalves.
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#695
by
nathan.moeller
on 27 Feb, 2008 20:55
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Lee Jay - 26/2/2008 9:28 PM
I know there have been a number of RSLS aborts in Shuttle program history. What I'm wondering is if there's a list or document somewhere that provides a summary of the root cause determination of each of those events. I've spent the last half-hour searching to no avail. What I'm really wondering is if they all ended up being sensor-related issues, or if there have been actual SSME failures during those events that would have caused a shutdown post launch if they had happened a few seconds later than the did.
If memory serves me right, a ruptured hyrogen valve started a fire in one of Discovery's main engines that lead to the RSLS abort of STS-41-D in June 1984.
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#696
by
kneecaps
on 27 Feb, 2008 21:14
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psloss - 27/2/2008 9:05 PM
kneecaps - 27/2/2008 3:36 PM
I have a faint memory that the HPOT OPV was slow to open/move.
FWIW, in the post-cutoff briefing, Boyce Mix (the MSFC SSME project rep) said that at least the quicklook data showed the prevalve positions were as commanded. I'll see if I can post some audio from the STS-64 pre-launch press conference later on.
Ah!!! My mistake! I meant to write 'HPOT OPOV' as in HPOT Oxidiser Preburner Oxidiser Valve....where as OPV would refer to Oxidiser Pre Valve....but I mean't OPOV.
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#697
by
jeff122670
on 27 Feb, 2008 21:18
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what do you mean you have to buy them? you mean on L2 or on a pay site?
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#698
by
jeff122670
on 27 Feb, 2008 21:19
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i thought the 41-D fire was from residual hydrogen in the area after shutdown.....remember, they didnt use the "firex" water until WAY after the shutdown.
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#699
by
psloss
on 27 Feb, 2008 21:33
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kneecaps - 27/2/2008 5:14 PM
psloss - 27/2/2008 9:05 PM
kneecaps - 27/2/2008 3:36 PM
I have a faint memory that the HPOT OPV was slow to open/move.
FWIW, in the post-cutoff briefing, Boyce Mix (the MSFC SSME project rep) said that at least the quicklook data showed the prevalve positions were as commanded. I'll see if I can post some audio from the STS-64 pre-launch press conference later on.
Ah!!! My mistake! I meant to write 'HPOT OPOV' as in HPOT Oxidiser Preburner Oxidiser Valve....where as OPV would refer to Oxidiser Pre Valve....but I mean't OPOV.
Well, I screwed up, too -- he said preburner valves, not prevalves.