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#320 by psloss on 09 Dec, 2007 18:45
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Zachstar - 9/12/2007 1:57 PM
I'll pick fixing the sensor system instead. Incredibly useful for avoiding cryo pump cavitation when you run out of prop, which has happened twice.
Now that we have a chance to take a breath. Let me throw in my call to disable the entire ECO sensor system.
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#321 by Lee Jay on 09 Dec, 2007 19:03
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Integrator - 9/12/2007 12:29 PM
Believe it or not, cryo liquid tanks sensors is one area that could stand some technology improvement. Another is cryo mass flow, that allows determination of what part is liquid, what part is boiling. Turbine flow meters fail in this respect. Delta IV Heavy encountered this on first launch attempt and had an early shutdown, preventing attainment of desired orbit. The problem is rocket engineers are never sure exactly how much fuel and oxidizer their systems are using in flight, so they compensate for uncertainty by overtanking propellants and depend on ground test and derived measurements, such as those from these ECO sensors to determine cutoff criteria. True mass flow through the engine is unknown. Anyone with new sensor technology ideas in these areas should promote them and the various companies that produce liquid rocket engines should investigate integrating these new technologies. It's like driving a car on a long trip with no gas gage.
It seems to me that if you know the precise time between when the 100% sensors go dry and when the 5% sensors go dry, and the throttle command curve between those two points, that you should be able to make a mighty-accurate prediction of when the ECOs would be uncovered. -
#322 by Avron on 09 Dec, 2007 19:03
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psloss - 9/12/2007 2:45 PM
QuoteZachstar - 9/12/2007 1:57 PM
I'll pick fixing the sensor system instead. Incredibly useful for avoiding cryo pump cavitation when you run out of prop, which has happened twice.
Now that we have a chance to take a breath. Let me throw in my call to disable the entire ECO sensor system.
and something that you can use moving forward... there are lessons to be learned here... -
#323 by Avron on 09 Dec, 2007 19:04
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Lee Jay - 9/12/2007 3:03 PM
It seems to me that if you know the precise time between when the 100% sensors go dry and when the 5% sensors go dry, and the throttle command curve between those two points, that you should be able to make a mighty-accurate prediction of when the ECOs would be uncovered.
That be one 5% sensor I think... so if its gone now what? -
#324 by rdale on 09 Dec, 2007 19:14
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Lee Jay - 9/12/2007 3:03 PM
It seems to me that if you know the precise time between when the 100% sensors go dry and when the 5% sensors go dry, and the throttle command curve between those two points, that you should be able to make a mighty-accurate prediction of when the ECOs would be uncovered.
But as we saw - engines can run richer or leaner than anticipated, or system leak can use more than anticipated... -
#325 by Lee Jay on 09 Dec, 2007 19:16
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rdale - 9/12/2007 1:14 PM
QuoteLee Jay - 9/12/2007 3:03 PM
It seems to me that if you know the precise time between when the 100% sensors go dry and when the 5% sensors go dry, and the throttle command curve between those two points, that you should be able to make a mighty-accurate prediction of when the ECOs would be uncovered.
But as we saw - engines can run richer or leaner than anticipated, or system leak can use more than anticipated...
Right...but tank volume change is ground truth. -
#326 by psloss on 09 Dec, 2007 19:18
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Avron - 9/12/2007 3:03 PM
Well, maybe. It's a much more straightforward thing if you know what root cause is. So far, they've had a much tougher choice/risk trade without knowing root cause and they may be faced with it again.
and something that you can use moving forward... there are lessons to be learned here...
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#327 by svenge on 09 Dec, 2007 19:38
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Maybe Congressman Weldon introduced his bill because he psychically forsaw that the sensors will require until 2015 to work properly...
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#328 by Zoomer30 on 09 Dec, 2007 19:47
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The system may be flawed and has a few sneaky gremlins, but its needed. Is it possible that testing them "dry" may damage them? If it does, it would be a nasty paradox. You need to know if they can sense a "dry" condition but in doing so they may not be able to sense a dry condition the next time. I'm thinking of heat build up.
If I read it right, when the cryo gets below the sensor level, the heat cant disapate as quick, this tells the computer that the cyro is low. -
#329 by Jorge on 09 Dec, 2007 19:49
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ShuttleDiscovery - 9/12/2007 1:43 PM
Quotekimmern123 - 9/12/2007 7:24 PM
Will this delay in any way influence the ISS crew exchanges? Leo seems to get a mighty short stay if he goes up on 122 and down again on 123.
I mentioned that way back in the thread, but no one responded. One month after so much training isn't really fair, especially as he is an ESA astronaut so he has a lower chance of flying again.
They may have Leo come down on 124, and everyone else bumped down one flight, but who knows? We'll ahve to wait and see!
That would mean no Americans on ISS between the next Soyuz and 124.
Won't happen. -
#330 by ShuttleDiscovery on 09 Dec, 2007 20:06
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Jorge - 9/12/2007 8:49 PM
That would mean no Americans on ISS between the next Soyuz and 124.
Won't happen.
Or maybe not, then!
It would just be more hassle to swap the FE2s around anyway, I suppose. I'm sure Leo will be grateful no matter how long he gets on ISS.. -
#331 by hobson911 on 09 Dec, 2007 20:25
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Something intresting on the KSC camera feeds. Look at channel 13 which is currently on camera 61..they have it zoomed in on the top part of the tank looking at something. It looks like there may be a crack but I really cannot tell. Maybe someone else can elaborate as to what they may be looking at?
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#332 by Avron on 09 Dec, 2007 20:31
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Zoomer30 - 9/12/2007 3:47 PM
The system may be flawed and has a few sneaky gremlins, but its needed. Is it possible that testing them "dry" may damage them? If it does, it would be a nasty paradox. You need to know if they can sense a "dry" condition but in doing so they may not be able to sense a dry condition the next time. I'm thinking of heat build up.
If I read it right, when the cryo gets below the sensor level, the heat cant disapate as quick, this tells the computer that the cyro is low.
We know its an open circuit, the question is where and why... -
#333 by jmjawors on 09 Dec, 2007 20:32
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hobson911 - 9/12/2007 3:25 PM
Something intresting on the KSC camera feeds. Look at channel 13 which is currently on camera 61..they have it zoomed in on the top part of the tank looking at something. It looks like there may be a crack but I really cannot tell. Maybe someone else can elaborate as to what they may be looking at?
Sure is closed in tight...
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#334 by hey you on 09 Dec, 2007 21:08
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Did a google search on something like:
eco sensor design failure space shuttle
One of the url returned was:
www.nasa.gov/pdf/160763main_NESC%20Update,%20Volume%204.pdf
[Ok, hope I cut and pasted that correctly.]
The title of the document found there is:
STS-114 Engine Cut-off Sensor Anomaly Technical Consultation Report
Lets just say that there is material there that I find appalling. If the report is accurate, and
the results are so eye-catching that some independent check needs to be done that the
report found is indeed authentic, there are, at least based on my perspective, unbelieveable
problems.
For starters, look at the possibility mentioned for noisy power supply. In that seems to be
the distinct possibility that the power supply/converter is oscillating. In addition 741 op amps
are apparently subject to overvoltage possibilites). It certainly seems that the erratic behaviour
has odds at least one to two orders of magnitude greater to be found in the point sensor box
than in the sensor or the wiring.
The apparent design flaws with the PSB are in all boxes. It is hard to believe that the wiring
and/or sensors are the culprit. Having said that, it is possible that, if the PSB design is marginal
or has negative margin (a phrase "borrowed" from a different context from the CAIB), small legitimate
wiring changes to the sensors (stray capacitance, wire inductance) could affect the operation of
the PSB.
I have heard nothing about a redesign of the PSB box since STS-114. Personally, if the report is
accurate, the design is not acceptable for non-man-rated applications, let alone a manrated one.
Just my perspective. (Reminds me of the temp sensor problems that were known prior to 51-F, but
they kept flying. It seems to be that the troubleshooting effort if barking at a shadow and not at the
root cause. Oh well, ..........
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#335 by Bruce on 09 Dec, 2007 21:26
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There's lots of different rocket designs being used. OK, not many that are man-rated, but surely someone else has solved this problem of eco sensors. Is it something that can be bought elsewhere? Presumably the whole system would need to be changed, and that's not going to happen quickly.
Maybe there's more to this 2015 extension. Maybe NASA have said there's too much pressure to get ISS complete AND finish by 2010. Maybe someone has finally realised that NASA will look just a bit silly with a 5 year must-rely-on-soyuz plan.
Either design to fly safely without eco sensors. Or install a system that works. Wayne Hale's comment/excuse about them being borrowed technology from the Saturn programme is about as close to an admission of "not fit for purpose" as we'll ever get.
All IMHO of course
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#336 by jimvela on 09 Dec, 2007 21:30
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hey you - 9/12/2007 3:08 PM
Did a google search on something like:
eco sensor design failure space shuttle
One of the url returned was:
www.nasa.gov/pdf/160763main_NESC%20Update,%20Volume%204.pdf
[Ok, hope I cut and pasted that correctly.]
I'll do the same search, but the document pulled up by your URL above includes only the following:QuoteThe NESC was part of a team to determine the root cause of the anomalous behavior
observed in the Space Shuttle Engine Cut-Off (ECO) sensor system during External
Tank (ET) tanking tests and launch attempts on STS-114. A theory was developed
that would explain how a sensor could show an apparent failure on first exposure
to liquid hydrogen (LH2), but show no indication of anomalous behavior when
returned to ambient temperature or on subsequent exposure to LH2.
The team performed cryogenic cycling of 50 fully instrumented recent vintage
(2002-2003) flight grade sensors between ambient and LH2 temperatures to determine
the validity of the theory. It was noted that the STS-114 ECO sensors
were of an earlier vintage. Both non-destructive and destructive physical analysis
techniques were employed to characterize the sensors. While all sensors behaved
nominally, nondestructive and destructive physical analysis indicated some issues
with the material selection and process variability used in the fabrication of a swaged
circuit board terminal connection that could be highly sensitive to human factors in
the assembly process and result in lot-to-lot variability.
I don't see anything particularly damning in that text...
Have a better link? -
#337 by ChrisGebhardt on 09 Dec, 2007 21:31
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Ok.... a couple questions that haven't been asked yet...
1. Will they offload the PRSD fuel cell load given the standown?
2. Will they execute a complete countdown backout and start a whole new countdwn from the T-43hour mark once they're back in a launch posture? -
#338 by jimvela on 09 Dec, 2007 21:38
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jimvela - 9/12/2007 3:30 PM
I'll do the same search, but the document pulled up by your URL above includes only the following:
I re-ran your Google search adding one search term:
eco sensor design failure space shuttle NESC
Note the addition of NESC...
The second link down returns the following url:
http://www.nasa.gov/pdf/160734main_STS-114%20Engine%20Cut-off%20Sensor%20Anomaly%20Technical%20Consultation%20Report.pdf
This document has a great deal of analytical detail, I'll go study it. Most designs, if put under intense scrutiny yield lots of critical observations even for things with lots of flight heritage.
Maybe someone more qualified that myself will look this over and comment...
{edit to correct obvious typo} -
#339 by Jim on 09 Dec, 2007 21:58
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Trekkie07 - 9/12/2007 5:31 PM
Ok.... a couple questions that haven't been asked yet...
1. Will they offload the PRSD fuel cell load given the standown?
2. Will they execute a complete countdown backout and start a whole new countdwn from the T-43hour mark once they're back in a launch posture?
yes and yes
