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#700
by
psloss
on 27 Feb, 2008 21:38
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jeff122670 - 27/2/2008 5:19 PM
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.
Right; I realize we're drifting away from Lee Jay's question, but for those who are interested in this, there's already at least one thread on the 26 June 1984 41-D abort:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=2788&start=1
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#701
by
kneecaps
on 27 Feb, 2008 21:44
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psloss - 27/2/2008 10:33 PM
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.
[/QUOTE]
, I'm pretty sure there was an RSLS abort due to a slow moving valve and with the with the high HPOT TDT mentioned I figured it was this!
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#702
by
psloss
on 27 Feb, 2008 21:57
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kneecaps - 27/2/2008 5:44 PM
, I'm pretty sure there was an RSLS abort due to a slow moving valve and with the with the high HPOT TDT mentioned I figured it was this!
Nice way of bringing this back to Lee Jay's question.
(In addition to the cases that GLS noted earlier of aborts due to expected vs. indicated valve positioning, the first attempt to do the FRF prior to STS-26 was cutoff before main engine start due to a "sluggish" fuel bleed valve.)
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#703
by
Lee Jay
on 27 Feb, 2008 22:23
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This discussion is fascinating. It seems the answer to my question is "no, we don't know of a document that describes these events".
Nevertheless, the bits and pieces all of you are able to recall seem to point more to the complex and touchy nature of the SSME startup sequence as the cause of most of the RSLS events. I've read about that procedure in detail and, frankly, I'm now amazed they ever get them started at all!
The only in-flight failure was due to a pair of faulty temperature sensors, which led the controller to shut down a perfectly working engine. Fortunately, that was late enough to lead to an ATO, and the successful completion of the mission. STS-93 had engine nozzle damage that led to a LOX eco shut down, and the safe completion of the ascent. Bottom line, from the incomplete picture we have of the RSLS aborts, and the rest of the flight history, it seems that once these engines are running, they are pretty darned ultra reliable.
I'm still wondering if any of these valve position and speed problems could have led to an in-flight shutdown had they not been detected during that touchy startup sequence. Anyone have any ideas?
Thanks for all the comments!
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#704
by
brahmanknight
on 28 Feb, 2008 20:27
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Whyare the SSMEs pointed at an angle away from the stack ( appears to be 5 degrees ) instead of straight down like the SRBs?
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#705
by
DaveS
on 28 Feb, 2008 20:30
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brahmanknight - 28/2/2008 10:27 PM
Whyare the SSMEs pointed at an angle away from the stack ( appears to be 5 degrees ) instead of straight down like the SRBs?
Center of Gravity(CG). The CG is in the External Tank, so to maintain the CG, the engines thrust through it, keeping things balanced.
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#706
by
Jim
on 28 Feb, 2008 20:33
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brahmanknight - 28/2/2008 4:27 PM
Whyare the SSMEs pointed at an angle away from the stack ( appears to be 5 degrees ) instead of straight down like the SRBs?
to point thru the center of gravity of the whole stack. If they were straight down, it would induce a downward pitch to the stack
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#707
by
kneecaps
on 28 Feb, 2008 21:21
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Lee Jay - 27/2/2008 11:23 PM
Nevertheless, the bits and pieces all of you are able to recall seem to point more to the complex and touchy nature of the SSME startup sequence as the cause of most of the RSLS events. I've read about that procedure in detail and, frankly, I'm now amazed they ever get them started at all!
It's not fair to call it touchy or that there is anything wrong with the procedure. It's all about the redlines...they vary depending on the different phases of the start. During the start the redlines have are very tight, this is because its far safer to shut an engine down prior to SRB Ignition and simply try again another day that it would be to launch with an engine possibly misbehaving.
I'm sure if the redlines were more relaxed then there would have been fewer RSLS cutoffs but potentially some of those RSLS cutoffs could have lead to engine trouble while heading uphill.
Found a link to some kind of list of aborts (
http://www.shuttlepresskit.com/STS-93/REF89.htm)
they are pretty darned ultra reliable.
Given the complexity of them it's fantastic!
If your on L2 and have a real interest in the engines, the booster systems brief on the SSME and the Booster console handbook is highly recommended. It talks redlines, goes through lots of possible perfomances cases including fuel flowmeter shifts (which caused the STS-68 RSLS cutoff) and many more.
I'm still wondering if any of these valve position and speed problems could have led to an in-flight shutdown had they not been detected during that touchy startup sequence. Anyone have any ideas?
STS-68 certainly may have..but who knows, there isn't much actual data/analysis available (That I know of), the thing about the engine is its closed loop..so it can 'run away' trying to correct problems..which lead to problems...which lead to a correction etc etc (just look at the engine diagrams to imagine how, the problem with most engine diagrams is they don't show you the location of everything like temp probes and flow meters).
The extra usage of LOX on STS-93 is a prime example of this (although it didn't run away!).
P.S.: There are some good links (google them I can't remember off hand, try 'uncontained failure ssme' that kind of thing...found some
http://ildp.nasa.gov/nasasearch/llis/search/search.jsp?nasaInclude=ssme+test)
Stennis stuff that deals with failures (catastrophic in some cases) of engines during test firings. They go into some detail and really help to glean understanding into how the engines work.
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#708
by
Lee Jay
on 28 Feb, 2008 22:03
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kneecaps - 28/2/2008 3:21 PM
Lee Jay - 27/2/2008 11:23 PM
Nevertheless, the bits and pieces all of you are able to recall seem to point more to the complex and touchy nature of the SSME startup sequence as the cause of most of the RSLS events. I've read about that procedure in detail and, frankly, I'm now amazed they ever get them started at all!
It's not fair to call it touchy or that there is anything wrong with the procedure.
I didn't say there was anything wrong with it, just that it's "touchy" as in very sensitive to precise valve positions and timings, which I believe is a true statement (but am happy to be corrected if I am wrong).
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#709
by
brahmanknight
on 29 Feb, 2008 00:53
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Are there any rules or procedures for what to do if a spacewalker vomits? It would seem to be a dangerous situations since he could inhale it.
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#710
by
rdale
on 29 Feb, 2008 01:34
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Per the press conference after the illness thread came up - you get the spacewalker inside ASAP.
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#711
by
gavsto2006
on 29 Feb, 2008 02:52
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What am I seeing in this video at 03:40 (point of seperation just after). . Looks like some sort of atmospheric effect? Are we seeing an engine fire, if so are we seeing the SSME or RCS?
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#712
by
Lee Jay
on 29 Feb, 2008 03:25
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Broken link, but from your description, I'm guessing OMS assist. The OMS engines are used during ascent at around that time.
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#713
by
DaveS
on 29 Feb, 2008 08:02
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Lee Jay - 29/2/2008 5:25 AM
Broken link, but from your description, I'm guessing OMS assist. The OMS engines are used during ascent at around that time.
Here's the correct link:
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#714
by
Jim
on 29 Feb, 2008 11:00
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DaveS - 29/2/2008 4:02 AM
Lee Jay - 29/2/2008 5:25 AM
Broken link, but from your description, I'm guessing OMS assist. The OMS engines are used during ascent at around that time.
Here's the correct link:
that one is wrong too
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#715
by
gavsto2006
on 29 Feb, 2008 11:09
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Proper link, sorry about that
Effect can be seen throughout 8 minutes and at ET SEP
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#716
by
Jim
on 29 Feb, 2008 11:31
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The effect at 8 minutes is the plume of the SSME's decreasing as the engines are throttled down and then shutting down. Anything after 9 minutes is RCS jets firing.
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#717
by
kneecaps
on 29 Feb, 2008 11:41
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Lee Jay - 28/2/2008 11:03 PM
It's not fair to call it touchy or that there is anything wrong with the procedure.
I didn't say there was anything wrong with it, just that it's "touchy" as in very sensitive to precise valve positions and timings, which I believe is a true statement (but am happy to be corrected if I am wrong).[/QUOTE]
Don't worry i'm not rebuking you, I'm just trying to dispel the notion that the SSME's are like a car engine in the winter or something, difficult to start
You are quite right, the redlines are very tight (on the grounds of safety of course) and this means that even slight off-nominal readings can cause a shutdown T-0.
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#718
by
Lee Jay
on 29 Feb, 2008 13:30
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How are the PRSD levels (the "fuel" remaining in the fuel cell H2 and O2 tanks) determined on orbit? With 0g, a rigid set of tanks, and a liquid, I'm having trouble figuring out how the ground can determine the precise number of hours remaining near the end of the flight.
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#719
by
kneecaps
on 29 Feb, 2008 16:41
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Lee Jay - 29/2/2008 2:30 PM
How are the PRSD levels (the "fuel" remaining in the fuel cell H2 and O2 tanks) determined on orbit? With 0g, a rigid set of tanks, and a liquid, I'm having trouble figuring out how the ground can determine the precise number of hours remaining near the end of the flight.
There is a capacitance probe running through the centre of a tank. This system is very much like what was found in the Apollo SM cryo tanks. Also it's cryogenic 'slush' in the tanks more than liquid in the traditional sense.
How many hours remaining from each tank is calculated on the ground based on power usage and other factors.
, I'm pretty sure there was an RSLS abort due to a slow moving valve and with the with the high HPOT TDT mentioned I figured it was this!