Author Topic: "Truth, Lies, and O-rings"  (Read 39764 times)

Offline bholt

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Re: "Truth, Lies, and O-rings"
« Reply #20 on: 04/07/2009 10:20 pm »
I thought the book was very thorough and informative. At times, I could not put it down. If I had to recommend 3 books on the Challenger accident, I would list the following: (In no particular order)

1. Truth, Lies, and O-rings- Inside the Space Shuttle Challenger Disaster
2. The Challenger Launch Decision
3. The Report of the Presidential Commission on the Space Shuttle Challenger Accident

There are some other good books as well, but these give a pretty good view of the accident.

Brent
"We choose to go to the Moon! We choose to go to the Moon in this decade, and do the other things, not because they are easy, but because they are hard."
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Offline russellis

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Re: "Truth, Lies, and O-rings"
« Reply #21 on: 04/07/2009 10:27 pm »
McDonald says on page 101 the o-ring temperature of the coldest static test of the original SRM was estimated to be 47F.  On page 47, he states the o-ring temperature of the coldest previous flight was 53F.  After the failure, the redesigned RSRM was static tested at a mean bulk propellant temperature of 39F (page 538) with some skin temperatures at 29F before the RSRM was considered flight qualified.  Even in January in Utah it took over a month at a conditioning temperature of 30 F to get the mean bulk propellant temperature below 40F (the design minimum for both the original and RSRM); perhaps that is why there was not an original design tested at that low a temperature.

Offline Art LeBrun

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Re: "Truth, Lies, and O-rings"
« Reply #22 on: 04/07/2009 10:33 pm »
Thanks, Russ. I was thinking about the o-ring cold soak; I have no clue on propellant cold soak effects. Yes, that would take awhile I am sure!
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Offline russellis

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Re: "Truth, Lies, and O-rings"
« Reply #23 on: 04/07/2009 10:39 pm »
And for the RSRM, o-ring heaters were added as a belt and suspenders.

Offline DerekL

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Re: "Truth, Lies, and O-rings"
« Reply #24 on: 04/07/2009 10:46 pm »
I wouldn't call lack of sharing a conspiracy theory.  Much information is not shared between competitors, or between Government agencies.  But is this enough to place partial blame on Titan people, when the real cause - in my mind - was operating at a temperature far below both previous experience and design limits?

When you have a faulty design - the fact that you're operating outside of some ill defined and only dimly understood limit is all but irrelevant.  We could have lost one in July almost as easily as we did lose one January.

The root cause lies in the design of the field joint.

And for the RSRM, o-ring heaters were added as a belt and suspenders.

The O-ring heaters were suspenders at best - the belt was the redesigned joint.  Redesigned to prevent the actual cause of blow by... joint rotation.

Offline russellis

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Re: "Truth, Lies, and O-rings"
« Reply #25 on: 04/08/2009 12:08 am »
I cannot agree with your speculation that temperature was not a factor.  This field joint worked in 48 flight SRBs (24 launches) plus a half dozen or so static tests. 54 successful motor operations is statistically significant.  The failure was in a booster whose temperature of 9 F was 14 F cooler than the other booster on Challenger (p. 269) and 44 F cooler than any previous flight.  The lower temperature reduces the stiffness of the o-ring, and - possibly more important - increases the time it takes for the primary o-ring to move across the gap and seat.  Remember the leak check displaces the primary o-ring to the other side of its groove.  Physics cannot be ignored.

Offline Antares

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Re: "Truth, Lies, and O-rings"
« Reply #26 on: 04/08/2009 03:40 am »
The issue seems to be that Titan o-ring erosion experience "was not shared".

For the sake of discussion, I think there's a point to be made here.  Civil servants should protect proprietary data at all costs; but in a case like this, the role of civil servants - 1) having wide access to data and 2) being the last line of mission assurance - calls for them to blur the line and share the data.  Frankly, in such a case I would not care what was legal: it is the right thing to do.

I was amazed that the SRB firings in Utah never had an extreme cold soak test? Can anyone verify this? For a vehicle that was to have a high rate of flights this is surprising if true.

No, but recall that the Thiokol staff were not advocating using the SRM outside of its qualified temperature range.  That fault sits with NASA.

I have no clue on propellant cold soak effects.

Solids have more impulse when it's hot.
If I like something on NSF, it's probably because I know it to be accurate.  Every once in a while, it's just something I agree with.  Facts generally receive the former.

Offline sbt

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Re: "Truth, Lies, and O-rings"
« Reply #27 on: 04/08/2009 10:51 am »
The issue seems to be that Titan o-ring erosion experience "was not shared".

For the sake of discussion, I think there's a point to be made here.  Civil servants should protect proprietary data at all costs; but in a case like this, the role of civil servants - 1) having wide access to data and 2) being the last line of mission assurance - calls for them to blur the line and share the data.  Frankly, in such a case I would not care what was legal: it is the right thing to do.

Unfortunately Darwin operates here. Civil Servants who have a tendancy to do things like that get weeded out (sacked, jailed or reassigned to places where they don't have access to propriety data) before they get to the point where they can influence history by 'doing the right thing'.

And the government, contractors and the public expect us to do what they consider the 'right thing' until situations like this turn up - that is not share the data.

Rick
I am not interested in your political point scoring, Ad Hominem attacks, personal obsessions and vendettas. - No matter how cute and clever you may think your comments are.

Online Blackstar

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Re: "Truth, Lies, and O-rings"
« Reply #28 on: 04/08/2009 12:31 pm »
I hope this is not a conspiracy subject. We're not interested in allowing the promotion of such things here.

Doesn't sound like it.  I was an investigator on the CAIB and this is exactly the kind of information that is important for any investigation.

The recent articles on STS-27 raised similar issues of information that might have been ignored prior to an accident, although in that case the incident took place about 15 years earlier.

Offline Herb Schaltegger

Re: "Truth, Lies, and O-rings"
« Reply #29 on: 04/08/2009 12:58 pm »
I cannot agree with your speculation that temperature was not a factor.  This field joint worked in 48 flight SRBs (24 launches) plus a half dozen or so static tests. 54 successful motor operations is statistically significant.  The failure was in a booster whose temperature of 9 F was 14 F cooler than the other booster on Challenger (p. 269) and 44 F cooler than any previous flight.  The lower temperature reduces the stiffness of the o-ring, and - possibly more important - increases the time it takes for the primary o-ring to move across the gap and seat.  Remember the leak check displaces the primary o-ring to the other side of its groove.  Physics cannot be ignored.

The O-rings were not meant to be directly exposed to combustion gases.  Joint rotation is what allowed that to happen.  THAT is the key to the physics.
« Last Edit: 04/08/2009 12:58 pm by Herb Schaltegger »
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Offline Gov't Seagull

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Re: "Truth, Lies, and O-rings"
« Reply #30 on: 04/08/2009 11:33 pm »
This is an entirely appropriate topic for discussion in any respectable forum. Al McDonald was a central figure in the actual events who demonstrated considerable integrity during the failure investigation. About the only thing you can fault him for is not having protested more during the launch decision, although as has been noted, there were considerable pressures against doing so. Russ Ellis is a highly respected solid rocket engineer, not some amateur with an opinion. His views ought to be valued and welcomed by anyone interested in this subject.

It's interesting that the question of proprietary data versus safety came up in relation to Challenger, because the exact same thing happened in the TRW whistleblower case that was just settled. You know something's not right but you aren't allowed to speak up without violating an NDA. How sure do you have to be before you risk your career and your money breaking the NDA? If you thought there was a 1-in-10 chance of a failure, that would be totally unacceptable from a program point of view and you would be completely justified in speaking up, yet if you did so there would be a 90% chance of no failure. Then it would be a battle of opinions, and you would probably lose. The only reason the TRW guy won is that there actually were failures. It's a classic problem in engineering ethics.

The O-rings were not meant to be directly exposed to combustion gases.  Joint rotation is what allowed that to happen.  THAT is the key to the physics.

I don't agree. A certain amount of O-ring erosion was expected by the time Challenger happened. It was a known condition that, although not anticipated in the initial design, was accepted subject to (we now know insufficient) constraints on operation. That sort of thing happens all the time in engineering. The problem was that the likelihood of failure was grossly underestimated by those who controlled the budget and schedule, and therefore not enough money and time were spent on thoroughly understanding the temperature effects. After the failure, the harmful effect of cold was proven.

 

Offline DerekL

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Re: "Truth, Lies, and O-rings"
« Reply #31 on: 04/09/2009 07:05 am »
I cannot agree with your speculation that temperature was not a factor.  This field joint worked in 48 flight SRBs (24 launches) plus a half dozen or so static tests. 54 successful motor operations is statistically significant.

Only so long as you (incorrectly) define 'successful' as 'does not blow up',

Quote
The failure was in a booster whose temperature of 9 F was 14 F cooler than the other booster on Challenger (p. 269) and 44 F cooler than any previous flight.  The lower temperature reduces the stiffness of the o-ring, and - possibly more important - increases the time it takes for the primary o-ring to move across the gap and seat.

Look up the other flights that had failed O-rings, and note the temperatures at which they failed.

The O-rings were not meant to be directly exposed to combustion gases.  Joint rotation is what allowed that to happen.  THAT is the key to the physics.

I don't agree. A certain amount of O-ring erosion was expected by the time Challenger happened.

And that's the problem - a failure condition came to be treated as an expected condition.

Quote
It was a known condition that, although not anticipated in the initial design,was accepted subject to (we now know insufficient) constraints on operation.

The initial design suffered from blow by, so the joint was redesigned (the back up O-ring added), and even though blowby continued to appear was accepted for flight.

Even though the specification stated that blowby and O-ring erosion was not acceptable.

Quote
That sort of thing happens all the time in engineering.

Accepting a design with a known dangerous flaw and which also fails to meet specifications happens all the time?

Quote
The problem was that the likelihood of failure was grossly underestimated by those who controlled the budget and schedule, and therefore not enough money and time were spent on thoroughly understanding the temperature effects. After the failure, the harmful effect of cold was proven.

They did not grossly underestimate in a vacuum.  If there exists a document in which those who controlled the budget and schedule were clearly warned of the dangers by those responsible for the engineering, it's never surfaced.

Offline Herb Schaltegger

Re: "Truth, Lies, and O-rings"
« Reply #32 on: 04/09/2009 01:49 pm »
The O-rings were not meant to be directly exposed to combustion gases.  Joint rotation is what allowed that to happen.  THAT is the key to the physics.

I don't agree. A certain amount of O-ring erosion was expected by the time Challenger happened.

And that's the problem - a failure condition came to be treated as an expected condition.

Derek is exactly right.  We saw the same exact phenomenon with regard to foam shedding and resultant TPS damage prior to STS-107, as explicitly noted by the CAIB (and for that matter, the Rogers Commission report). 

"Well, something's wonky with our design 'cause [unexpected stuff] happens, but we think it'll be okay . . ." is a terrible attitude for a manned space program. 
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Offline Gov't Seagull

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Re: "Truth, Lies, and O-rings"
« Reply #33 on: 04/09/2009 07:27 pm »

Derek is exactly right.  We saw the same exact phenomenon with regard to foam shedding and resultant TPS damage prior to STS-107, as explicitly noted by the CAIB (and for that matter, the Rogers Commission report). 

"Well, something's wonky with our design 'cause [unexpected stuff] happens, but we think it'll be okay . . ." is a terrible attitude for a manned space program. 

I'm familiar with the argument -- I think it was the Challenger investigation that labeled it with the fancy phrase "normalization of deviance." But if every unexpected observation required a redesign, no vehicle would ever fly again. Criteria and requirements are written in a state of partial knowledge that improves with each flight provided people are willing to observe carefully and learn. Surely you will agree that the SRBs can provide the required thrust even with some o-ring erosion. If every full-duration firing had shown exactly 5% erosion regardless of temperature or loads, there would have been a good case for accepting it even though it was not originally anticipated. The problem was that it wasn't 5% - it was 0% in some flights and a lot more than 5% in others, and there was a failure to act on that information. A relatively modest constraint on temperature could have saved this supposedly "fatally flawed" design. 

« Last Edit: 04/09/2009 07:49 pm by Gov't Seagull »

Offline psloss

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Re: "Truth, Lies, and O-rings"
« Reply #34 on: 04/09/2009 07:59 pm »
I'm familiar with the argument -- I think it was the Challenger investigation that labeled it with the fancy phrase "normalization of deviance."
That was Diane Vaughan; well after the official investigations ended.

Offline Herb Schaltegger

Re: "Truth, Lies, and O-rings"
« Reply #35 on: 04/09/2009 08:54 pm »

Derek is exactly right.  We saw the same exact phenomenon with regard to foam shedding and resultant TPS damage prior to STS-107, as explicitly noted by the CAIB (and for that matter, the Rogers Commission report). 

"Well, something's wonky with our design 'cause [unexpected stuff] happens, but we think it'll be okay . . ." is a terrible attitude for a manned space program. 

I'm familiar with the argument -- I think it was the Challenger investigation that labeled it with the fancy phrase "normalization of deviance." But if every unexpected observation required a redesign, no vehicle would ever fly again.


The problem is, blow-by was not just any old "unexpected observation."
I've designed spaceflight equipment with elastomeric seals.  By and large, elastomers don't do well with exposure to hot combustion gases, let alone combustion gases with particulate matter in them.  The SRB field joint was designed to absolutely prevent such exposure, and failed in its design due to the unexpected nature of the joint rotation.  Given the history of prior occurrences which were less than catastrophic, this "deviation" was "normalized" (to massively sanitize the FUBAR'd mental process involved) and essentially forgotten about as a serious concern.

That is absolutely wrong.  The SRB field joint was not behaving as expected - this on a motor which produces some 3,000,000 lbs of thrust and is located next to a cryogenic fuel tank - and NASA essentially said, "Don't worry about it."  Cold or lack thereof shouldn't matter.  Elastomers may not be perfectly homogenous and are subject to all sorts of chemical and mechanical damage after manufacture - assuming they can always do the job they were never intended to do just because they always had is dangerous at best and fatal at worst. 
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Offline Gov't Seagull

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Re: "Truth, Lies, and O-rings"
« Reply #36 on: 04/09/2009 11:03 pm »
The problem is, blow-by was not just any old "unexpected observation."

On that we certainly agree. I'm just saying that the process by which that observation was addressed was at least as flawed as the design itself. That process has to walk a fine line sometimes.There's never enough money to fire up the CAD scope every time something flaky happens, and even if there was, your design would always be floating around and you wouldn't be able to build up an experience base. But conversely, you can't brush off erosion and blowby without a thorough understanding of what causes it.

Offline russellis

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Re: "Truth, Lies, and O-rings"
« Reply #37 on: 04/10/2009 02:40 pm »
New information (post Roger's Commission report) in the book is that accumulation of GOX vapors, drifting down from the vent near the top of the ET to the base of the right-hand SRB, likely supercooled the area of the booster where the field joint that later failed was located.  This is discussed in chapter 36.  At the time of the hearings, it was not understood why IR guns measured 9F minimum on the right hand booster and 23F minimum on the left SRB.  Such a difference (and such low readings) had never before been observed.  These low readings - below the launch commit criteria (LCC) of 31F minimum - were not reported to the overall team prior to launch (Chapter 20). Later, NASA - citing a calibration error - "corrected" the readings, raising them by 19F, close to, but still below, the LCC.

In 1987 MTI modeled the configuration of the launch pad with the best available information on wind direction and speed the morning of the launch.  The model supported the uncorrected IR gun readings. NASA and Rockwell initially did not believe the MTI model, but eventually performed their own CFD analysis, and agreed GOX vapor accumulation could be a problem.  The LCC was changed to 42F minimum with winds of < 5 knots, 33F if greater, even though joint heaters had been added in the redesign.

Offline rich_columbia

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Re: "Truth, Lies, and O-rings"
« Reply #38 on: 04/11/2009 12:17 am »

It's interesting that the question of proprietary data versus safety came up in relation to Challenger, because the exact same thing happened in the TRW whistleblower case that was just settled. You know something's not right but you aren't allowed to speak up without violating an NDA. How sure do you have to be before you risk your career and your money breaking the NDA? If you thought there was a 1-in-10 chance of a failure, that would be totally unacceptable from a program point of view and you would be completely justified in speaking up, yet if you did so there would be a 90% chance of no failure. Then it would be a battle of opinions, and you would probably lose. The only reason the TRW guy won is that there actually were failures. It's a classic problem in engineering ethics.


Please see "18 U.S.C. § 1905. Disclosure of confidential information generally"

http://www.nasa.gov/offices/ogc/commercial/18usc1905.html

-or-

http://www4.law.cornell.edu/uscode/18/1905.html for

Rich
« Last Edit: 04/11/2009 01:34 am by rich_columbia »

Offline Gov't Seagull

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Re: "Truth, Lies, and O-rings"
« Reply #39 on: 04/11/2009 03:01 pm »
Please see "18 U.S.C. § 1905. Disclosure of confidential information generally"

http://www.nasa.gov/offices/ogc/commercial/18usc1905.html

-or-

http://www4.law.cornell.edu/uscode/18/1905.html for

Rich

Thank you for the links. I am not sure whether you had a point to make in relation to whistleblowing, but 18 U.S.C. § 1905 is so broad that it calls into question a good fraction of public discussion on spaceflight. Much of the information published in, for example, the Rogers Commission report, is clearly a disclosure of confidential information. How did they work that? Did they tell Thiokol, et al, that either they permit the release of the information or lose the right to future NASA business? I may have to put a lawyer on retainer to review my future posts!

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