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  STS-51L: Root cause of the Challenger accident (Page 1)

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Author Topic:   STS-51L: Root cause of the Challenger accident
PetesParkingLot
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posted 02-20-2013 11:37 AM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
Gerry Griffin, Apollo Flight Director, asserted in a NASA interview from 1999 that the cold was not the root cause of the Challenger solid rocket booster failure. There is some evidence to support his claim.

Five of the six SRB field joints exposed to the cold of the launch successfully sealed themselves. Clearly, other factors were involved. Mr. Griffin seems to imply that there was a assembly defect which lead to the failure of the right SRB seal. If he is correct then the entire discussion about launching below 32 degrees is a red herring.

In addition, NASA management is not guilty of a flawed launch decision, but guilty of a lack of quality control, a much different failure. The same lack of quality control that lead to the Apollo 13 failure.

Would a properly packed O-ring have survived the STS-51L launch and made the entire discussion of cold temperature launch a footnote in history?

garymilgrom
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posted 02-20-2013 11:54 AM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
Sorry but your post mimics the NASA thought processes that caused the accident - "if 5 of 6 joints are safe then prove why the vehicle is unsafe to fly". Whereas the proper question would have been "why is a field joint failing?"

There is no doubt that the inability of the O-ring to properly seal the field joint was the root cause of this accident.

However, while the stiffness of the O-ring(s) was due to low temperatures, the stack also experienced the strongest wind shear on any launch to date. That meant the SRB's flexed more than what was experienced before. The combination of the stiff O-ring and flexing booster likely caused the accident to worsen, ending with the destruction of the machine.

The field joint was designed to reduce the size of a leak during operation when in fact launch experience showed it enlarged the leak. This flawed design was known for years. Why THAT was not corrected before 51-L is part of the NASA culture criticized by the accident report.

PetesParkingLot
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posted 02-20-2013 12:02 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
Why did the left lower SRB seal, exposed to the very same cold temperature, seal?

There had to be more going on than simply launching at below 40 degrees. From the facts of the launch you could expect the seals to work 5/6 of the time even below 40 degrees. Was the true failure an assembly failure, as Gerry Griffin asserts?

If not what was the root cause of the right SRB O-ring failure? Gerry Griffin states in his NASA history interview that he believes the 51L accident would have happened on a warm summer day.

Robert Pearlman
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posted 02-20-2013 12:03 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Gerry Griffin, Apollo Flight Director, asserted in a NASA interview from 1999 that the cold was not the root cause of the Challenger solid rocket booster failure.
To be fair to Griffin, he didn't so much assert, as suggest.
...this is based strictly on a gut feel. I think the temperature aspects were probably overdone. I have a feeling we would have lost that vehicle on a summer day.

I think there was a bad seal. We knew the design was close. It was marginal, and we were working on an improved interface between the segments. But we had flown lots of things and, gosh, clear back to — in my timeframe, Gemini and Apollo, Skylab, we had flown things that we knew design was — you know, we wish it was beefier — we wished it was — but we thought it was okay. And so I really think, you know, they had trouble making that seal at the Cape.

PetesParkingLot
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posted 02-20-2013 12:24 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
The wind shear had nothing to do with the initial breach of the O-rings on the pad.

The theory is that after the initial O-ring failure and "puffs of black smoke" the breach sealed itself until later in the flight when the wind shear fractured the "artificial" seal of alum oxides and lead to a flame leak after 65 seconds of flight.

It seems that both right and left lower SRB O-rings were exposed to the same forces, one failed one did not. If the root cause of the right hand SRB failure was not the cold temperature by itself, then NASA management was not guilty of a "flawed" launch decision based upon temperature. Clearly any flight decision which results in a loss of crew is flawed, no one is arguing that fact.

The question I raised is whether NASA was wrong to launch 51L below 40 degrees. Absent the single failure of the right hand lower SRB seal on 51L, where is the evidence that cold alone would lead to SRB seal failures? Again, 5 of the 6 seals on that stack worked, something more must have been involved in that failure.

garymilgrom
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posted 02-20-2013 12:24 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
Here is the original design and it is easy to see how the seal opens as pressure rises on the propellant side of the booster.

SRB joint rotation

garymilgrom
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posted 02-20-2013 12:30 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
It seems that both right and left lower SRB O-rings were exposed to the same forces,

I do not agree with this. The booster is a huge article and could easily have different forces at different locations. Do both boosters receive the same steering commands? Do both experience the same wind loads during ascent? If the wind shear is coming from the right or left does it matter? I don't know.

PetesParkingLot
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posted 02-20-2013 12:50 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
Your point is well taken, but what we also don't know is whether a flaw in the packing of the right SRB seal (or even better a bit of FOD left behind similar to the Apollo 1 tool) could be the true cause of the failure.

If so then the focus on cold temperature launch is totally misplaced and is simply a way to complete the story and attach blame in a most dramatic way.

It seems to me that anyone who is willing to accept that the cold temperatures was the root cause of the 51L failure needs to at least offer an explanation as to why 5 of the 6 seals didn't fail in the cold.

There is no evidence that I am aware of for a packing failure, but I accept it as a reasonable hypothesis to explain why one SRB joint failed and the other 5 did not. I have more trouble accepting that the cold by itself impacted one SRB field joint and left the other 5 functional.

Greggy_D
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posted 02-20-2013 01:14 PM     Click Here to See the Profile for Greggy_D   Click Here to Email Greggy_D     Edit/Delete Message   Reply w/Quote
I wouldn't say the cold temp was the root cause, but more of a contributing factor to the failure.

garymilgrom
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posted 02-20-2013 01:38 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
This seems like a witch hunt without purpose. Before the 51-L flight about half the field joints had exhibited O-ring blow by. Why did the other half not show any? We don't know why. We do know the data proved the design deficient and at least partially failed about 50% of the time. That's a FACT.

Why did the other 5 field joints not fail? We don't know why. They may have partially failed but the evidence was destroyed. The one FACT not in disupute is cold weather reduced the rings' ability to seal - proven by the data collected by other flights in low temperatures. Why did the lower joint on the right side SRB fail completely - it didn't, it partially failed, seated again, then failed to fill the gap created by wind shear.

This accident had multiple, maybe thousands of small causes. What were they all? We don't know. Why do some things fail and others don't? We don't know. But that is not a reason to discount what we do know about cold and rubber.

The biggest contributor to the 6th O-ring failing to seal was the cold weather. The biggest contributor to the accident was that failure to seal. This has no bearing on why the other 5 did not fail. As I said above they may have been in the act of failing. We have no data to say without doubt they would have worked until SRB burn out.

PetesParkingLot
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posted 02-20-2013 02:04 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
If the design was deficient and cold weather was not the root cause then NASA either had to ground the shuttle flights until it was fixed or continue to fly while trying to isolate the root cause. Since no clear root cause was forthcoming and the cold weather was not in and of itself the root cause then the mistake was not to ground the shuttle completely.

That decision has never been fully questioned because we seem lost in focusing on the "flawed" launch decision of 1/28/86. The true failure of STS-51L lies with those in senior management who continued to permit flights with a an O-ring that could fail either at 40 degrees or 90 degrees.

Was the choice to fly below 40 degrees truly a flawed decision or was the decision to fly any further flights with this design the "flawed" decision? Is part of spaceflight making "flawed" decisions and getting away with them?

Robert Pearlman
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posted 02-20-2013 02:17 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
...we seem lost in focusing on the "flawed" launch decision of 1/28/86.
It depends on who the "we" is you're talking about. It really doesn't matter if "we" — space history enthusiasts (and even professionals) — focus on one aspect of the launch decision, so long as the engineers who worked the recovery and who are making the choices for future vehicles concentrate(d) on all the aspects.

The decision made on Jan. 28, 1986 wasn't to ignore the temperature or the design of the o-ring; it was to waive an existing flight rule, which was based on both. Understanding why that decision was flawed is the crux of the matter — and I believe most working the investigation and recovery understood that.

Tykeanaut
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posted 02-20-2013 02:18 PM     Click Here to See the Profile for Tykeanaut   Click Here to Email Tykeanaut     Edit/Delete Message   Reply w/Quote
If you really want the root cause then it was a lack of funding in the early 1970's that lead to a compromised shuttle design.

Jim Behling
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posted 02-20-2013 02:18 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Why did the left lower SRB seal, exposed to the very same cold temperature, seal?

There had to be more going on than simply launching at below 40 degrees. From the facts of the launch you could expect the seals to work 5/6 of the time even below 40 degrees. Was the true failure an assembly failure, as Gerry Griffin asserts?


Wrong, because the same conditions did not exist on all six joints. The same reason blow-by did not happen on all joints of same boosters on other flights, where blow-by did occur on one of the joints.

Building an SRB was labor intensive and use some "craftmanship" in laying up the insulation and putty between joints.

Example: Take a bricklayer and have him build three identical walls. The three walls will have some minor differences in them. But they are not flawed and will meet the same standard "requirements." However, when subjected to extreme forces, they will fail at different values.

quote:
Originally posted by PetesParkingLot:
Was the choice to fly below 40 degrees truly a flawed decision or was the decision to fly any further flights with this design the "flawed" decision? Is part of spaceflight making "flawed" decisions and getting away with them?
Both were flawed decisions, one on top of the other.

The last question is nonsense.

Jay Chladek
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posted 02-20-2013 03:45 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
I've met Gerry Griffin in person and I respect his opinions a lot.

One factor that Gerry isn't taking into account with his statement though was a set of readings taken by an ice team member with a temperature gun on the pad. He got a very cold reading from the vicinity of the aft field joint on the SRB that had the failure. At the time it was dismissed as an erroneous reading, but the IR guns had never given improper readings before, so a few years after the accident, some weather data was plugged into a computer program to simulate conditions that day. Apparently with the cold temperatures on the pad and the relatively light wind (I believe combined with a temperature inversion), the aft field joint was apparently super cooled a bit due to gaseous oxygen vapor coming from the LOX vent hood (the beanie cap) cooling the air. Rather than it blowing away, the chilled air sunk down towards the base of the pad and collected in that spot along the SRB resulting in the colder than expected temperature readings and that MAY have been a factor in why the O-ring failed the way it did (i.e. not necessarily saying that is the cause, but it likely contributed).

The Allan McDonald and James R. Hansen book "Truth, Lies and O-Rings" talks about it in a lot more detail (and with a bit more accuracy than my repeating of it) and brings up other topics from the time as well concerning the investigation into what happened. If you haven't read that book, I URGE you to do so as it is IMHO the best text to date on Challenger and explains the engineering behind what happened very well. Anyone who has studied Challenger in depth should have this in their library.

Regardless of whether the cold weather was a factor or not, the original shuttle SRB field joint design had a few weaknesses as they were susceptible to joint rotation (meaning the casings would flex more than they should have when SRB ignition pressurized the casings internally) and the O-rings were having to work harder and do more than they should have. Ultimately, the exact same O-rings were used in the SRB joint re-design while the field joints themselves were redesigned with better redundancy (with joint heaters being used to keep the O-rings within their tolerance range). Thiokol (now ATK) never utilized a replacement O-ring compound which had better cold temperature tolerance until they began work on the Constellation/Ares SRMs (which will be used in the SLS rocket I believe).

The one thing to keep in mind about ANY engineering disaster is it is a chain of events with A LOT of factors at play. Change any one factor, no disaster. That is true of the decisions made by management, by engineers and the random factors nobody has control over (weather being the main one in Challenger). So while one knows they can't control the random factors, they can do something about the human ones. Those that choose not to or delude themselves into believing the random factors aren't important enough and end up spinning the revolving mechanism of the giant gun of chance should not be at all surprised if once in awhile it ends up with a bullet in the chamber in this game of engineering Russian roulette.

Headshot
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posted 02-20-2013 04:51 PM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
A diagram in the Feb 24, 1986 issue of Aviation Week and Space Technology illustrated how that morning's prevaling winds swirled around the shuttle to make the right SRB temperature lower than the left SRB.

PetesParkingLot
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posted 02-20-2013 06:58 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
So it looks like the right SRB launched at a temperature of 9 degrees and the left SRB flew at 23 degrees. Somewhere between those two numbers is the real information as to what temperature you could successfully fly an SRB.

Clearly you could fly at 23 degrees, making the entire argument of the Thiokol engineering team from the night before not relevant. They proposed not flying below 40 degrees and it appears that you could safely fly down to 23 degrees temperature on the SRB O-rings.

Somewhere below 23 degrees was the point at which the O-ring failed to seal. Now, we have a real root cause. Was NASA Management aware of this IR gun data prior to the launch decision?

Greggy_D
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posted 02-20-2013 07:02 PM     Click Here to See the Profile for Greggy_D   Click Here to Email Greggy_D     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
So it looks like the right SRB launched at a temperature of 9 degrees and the left SRB flew at 23 degrees. Somewhere between those two numbers is the real information as to what temperature you could successfully fly an SRB. Clearly you could fly at 23 degrees...

NO! You cannot make that assumption! As noted above, temps were one factor out of MANY (both human and technical) that caused the failure.

PetesParkingLot
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posted 02-20-2013 07:15 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
We are dealing with the facts of 51L on 1/28/86. I am in no way expressing the opinion that one should launch at these temperatures.

The issue I want to nail down is what was the reality facing the launch team that day. Can one not assert that the reality was that if you launched with a SRB field joint temperature of 23 degrees or higher you would not get a breach. Five field joints successfully flew that day at 23 degrees or higher, even with the wind shear and all the other factors. One field joint failed with a launch temperature of 9 degrees.

Isn't the root cause of the Challenger disaster the launching of a SRB field joint at a temperature below 23 degrees? None of the other factors lead to a Criticality one failure that day...

Robert Pearlman
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posted 02-20-2013 09:49 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Five field joints successfully flew that day at 23 degrees or higher, even with the wind shear and all the other factors.
That statement, I believe, is introducing facts not in evidence. I don't believe you can say for certain that the other joints weren't also in the process of failing but hadn't progressed as far as the sixth when the vehicle was lost.

Ronpur
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posted 02-20-2013 10:02 PM     Click Here to See the Profile for Ronpur   Click Here to Email Ronpur     Edit/Delete Message   Reply w/Quote
Without digging out my Challenger Report... how much of the other field joints were recovered? If 100% of those were not recovered, then we can never assume the remaining joints were sealed.

Jim Behling
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posted 02-21-2013 07:29 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Isn't the root cause of the Challenger disaster the launching of a SRB field joint at a temperature below 23 degrees? None of the other factors lead to a Criticality one failure that day...
Wrong, again you can not make that assumption. Temperature was only one of the factors. Due to variables inherent in all non elemental material, that particular o-ring, while still meeting specs, could have been slightly smaller and a little stiffer. Same goes for the casing joints, with larger groove in that spot and a little more flex. It is factors like this that add up and make an event happen in one place, while under seemingly the same conditions not happen in another.

An engineering lesson: Two "identical" objects (materials, systems, etc) will act the same way while operating within margins. The exact behavior of the object is unpredictable outside the margins.

quote:
Can one not assert that the reality was that if you launched with a SRB field joint temperature of 23 degrees or higher you would not get a breach. Five field joints successfully flew that day at 23 degrees or higher, even with the wind shear and all the other factors. One field joint failed with a launch temperature of 9 degrees.
No.
  1. Not enough data points to draw that conclusion.
  2. Different set of boosters on the same day may have had no joint failures or a different joint fail.
There is insufficient data to make any conclusion.

PetesParkingLot
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posted 02-21-2013 11:08 AM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
I begin to understand the dilemma faced by NASA management that day. Even after the fact with all the real data of the flight in front of us, we cannot agree on the lower bound of temperature for a safe flight. No wonder management struggled with this decision!

For me, my interest is not in reliving the technical details of a engineering failure. I want to understand the choice that was faced that day by management.

I assume that NASA had the best and the brightest managers in the industry and they were all dedicated to crew safety. Yet they made a decision to fly a SRB in a temperature range that did not permit the O-rings on the SRB to seal and lead to crew death. What factors were weighed improperly to lead to this choice?

Again, it appears to me that the choice to fly below 40 degrees was not the cause of the accident. Had the right hand SRB been 39 degrees it is likely it would have sealed.

What information could you use on 1/28/86 to make this choice and what would the parameters of a correct choice? It is easy to criticize the bad choice, but what was the correct call that a day? Was it as simple as "We will not fly below 51 degrees"?

Jim Behling
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posted 02-21-2013 11:25 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
I assume that NASA had the best and the brightest managers in the industry and they were all dedicated to crew safety.
Bad assumptions.
quote:
Yet they made a decision to fly a SRB in a temperature range that did not permit the O-rings on the SRB to seal and lead to crew death. What factors were weighed improperly to lead to this choice?
It has been gone over many times and in the commission report, schedule pressure.
quote:
Again, it appears to me that the choice to fly below 40 degrees was not the cause of the accident. Had the right hand SRB been 39 degrees it is likely it would have sealed.
Unsupported conclusion. You can not say that based on the available data. the exact temp which would cause the failure is unknown. And it was a confluence of many other factors. But in all, it was a bad design.
quote:
What information could you use on 1/28/86 to make this choice and what would the parameters of a correct choice? It is easy to criticize the bad choice, but what was the correct call that a day? Was it as simple as "We will not fly below 51 degrees"?
The proper answer would not to fly any missions (especially after 51-C) and fix the joints.

Headshot
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posted 02-21-2013 01:27 PM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Jim made a comment about "schedule pressure." What many do not remember is the intense public pressure brought on by the media.

I am not a media basher by any means, but I recall the broadcast media just ridiculing NASA mercilessly during Challenger's many scrubbed launch attempts for the 51-L mission.

They positively went nuts with scathing commentary when a bolt securing the removable handle to Challenger's hatch got stripped. Technicians had to locate a drill and bring it up to the white room to drill the damn bolt out. When the drill's battery lost power and another drill had to be found newscasters positively went nuts. More than one talking head commented that NASA could not do anything right anymore.

You know that kind of crap had to mess with managers' heads.

PetesParkingLot
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posted 02-21-2013 02:06 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
For me the evaluation process is relatively simply. My job as a manager is to minimize the "unknowns". I can manage the "known" risks and I assume that if I have a good team we are doing the best we can with the known risks. The managers job is to weigh the number of unknowns I am introducing by going ahead with a task vs the benefit that I derive. In this case flying outside of the experience base introduce a whole bunch of unknowns, what was my benefit from flying below 51 degrees? Could I expect to avoid all the temperature unknowns by waiting? If I have to fly in January have I done all I can to make the unknowns known?

Like everyone else on this forum, I am certain I would not have made the choice to fly on 1/28/86. I would have done so not because I knew that we couldn't safely fly in "cold" temperatures(the prior discussion shows that their is no definitive data to that effect). I would have objected to it because to do so would uneccesarily exposed 51L to a large number of temperature unknowns with no real benefit.

That to me was the mistake of the NASA management, they accepted a large number of temperature unknowns into the flight with no real benefit to the mission. This mistake of doing a poor job of managing the unknowns was made by Apollo management as well, they just got luckier. (Apollo 12 didn't need to launch with rainstorms in the Cape area.

AJ
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posted 02-21-2013 05:27 PM     Click Here to See the Profile for AJ   Click Here to Email AJ     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Like everyone else on this forum, I am certain I would not have made the choice to fly on 1/28/86.
There is way too much hindsight involved in this comment and a hell of a lot of hubris.

The blame game involving 51-L has been played since the day it happened. To say that you, in retrospect, would do anything differently or would somehow be capable of a better decision is pretty insulting.

We all know mistakes were made, but to say that you would not have made them is, in my opinion, inappropriate.

PetesParkingLot
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posted 02-21-2013 05:36 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
At this point I hope to learn from the mistakes made by NASA management and to learn you must understand the mistake. I am somewhat insulted by the attitude taken by so many that it was obvious that 51L should not have flown. I suspect that many of those who claim to now see the obvious might not have been so clairvoyant on the morning of 1/28/86.

Again, I make the assumption that NASA management was good and dedicated to crew safety. To understand why it made sense to them to launch 51L is to learn from their mistake. Otherwise we are simply just reviewing the facts, something that is better done with the written materials as opposed to communicating on this forum.

Headshot
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posted 02-21-2013 06:04 PM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
We have shifted from the technical root cause of Challenger's destruction to discussing the launch decision. One cannot do this without discussing the management culture prevalent at the time.

This is a very complex issue. I will just say that I hope most readers are aware of a book that is used in many university courses titled The Challenger Launch Decision written by Diane Vaughan.

I believe that the author was interviewed by the CAIB during the Columbia accident investigation as well.

Orthon
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posted 02-21-2013 06:53 PM     Click Here to See the Profile for Orthon   Click Here to Email Orthon     Edit/Delete Message   Reply w/Quote
Would the decision have been as difficult had there not been a State of the Union address scheduled for that evening?

Jim Behling
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posted 02-21-2013 07:06 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
Again, I make the assumption that NASA management was good and dedicated to crew safety.
Bad assumption.

p51
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posted 02-21-2013 07:11 PM     Click Here to See the Profile for p51   Click Here to Email p51     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Headshot:
You know that kind of crap had to mess with managers' heads.
Too true. And you just know that politicians were feeding into the same frenzy.

NASA had, for better or worse, sold the nation on a '18-wheeler to space' that would run like clockwork. If anything, they were a victim of their own PR. When they didn't get a shuttle up regularly, the press, public and lawmakers also went bonkers. I'm just as guilty as anyone in that regard, I went to KSC to watch three launches along the causeway and all were scrubbed within a few minutes of going up. I never did see one go up from less than 100 miles away and I still get ticked just thinking of that.

I'm reading, "Dragonfly" right now and the comparison between the 'don't tell the press that the Russian situation is a goat rope' admonishments to NASA underlings and the 'we gotta get these shuttles up no matter what' go-fever of the shuttle era is so easy to make. Like in most other government agencies, NOBODY wants to be that guy who says, "we shouldn't do this" because nobody wants to hear that.

PetesParkingLot
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posted 02-22-2013 01:02 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
I do not accept the idea that NASA management succumbed to pressures to launch. Despite the pressure there was not a suggestion anywhere in the Rogers investigation that anyone at NASA tried to knowingly stretch launch criteria in order to avoid a scrub. The idea that NASA management was just weak or flawed is in my mind a way to avoid a deeper truth.

Even after Challenger accident, when it was clear that one flight a month wasn't going to happen, NASA repeated this type of "flawed decision" with the foam problem. One cannot argue that NASA ignored the foam issue because of launch pressures. Just the opposite, by 2003, it was clear that a serious vehicle failure was more likely to end the program than a failure to launch regularly.

I recall a scene from the "Spider" episode of From the Earth to the Moon. In it a failure of the LM strut is found to have been traced to an engineering error. The guilty engineer comes to Tom Kelly and immediately reports the error. The response by Tom Kelly is appropriate pointing out that the engineer did not attempt to "cover your ass" but instead came forward with the reality. Without such complete openness with regard to the reality of failures, a complex program "won't get to New Jersey, let alone the Moon". What I see as the fundamental change in NASA was the lack of openness about the reality of the system performance.

The mission for Morton Thiokol became building and selling SRB and keeping the contract. The mission was no longer getting to the moon by the end of the decade or even flying safely.

When questions were raised about the unknowns of cold weather performance of the SRB seals, instead of passing the reality of the unknowns up to NASA management so they could truly weigh the risks, the organization "covered their ass." For me that is the lesson that I take from the "flawed decisions" of Challenger and Columbia. The lesson is that if your organization fails to pass to the decision makers a true picture of what we DON'T KNOW as well as what we do know then we should not blame decision makers when they do a poor job of managing the risk of the unknown.

What would it have hurt for Thiokol to pass the following information along to NASA Senior management?

"We know that at some temperature below 51F the O-rings will fail to seal and we will have a criticality one failure. We simply do not know what the lower limit is on temperature for the O-rings to seal. Our best estimate based upon very limited data is that it will be safe to fly the O-rings above the launch commit criteria of 31F."

With that honest statement of reality from the engineering team would 51L have flown on 1/28/86? Or would it have been scrubbed until NASA management could limit the temperature unknowns.

Robert Pearlman
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posted 02-22-2013 01:15 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
You're assuming such a discussion between Thiokol and NASA never took place.

A flight rule regarding temperatures at launch existed for a reason — in part because Thiokol and NASA had reviewed the safety margins for the solid rocket motors.

I tend to dislike pointing people towards books, but this is a topic that has been thoroughly researched. So I feel it is appropriate to ask, have you read "The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA" by Diane Vaughan (as mentioned previously in this thread), as well as "Truth, Lies, and O-Rings: Inside the Space Shuttle Challenger Disaster" by Allan McDonald with James Hansen?

328KF
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posted 02-22-2013 10:52 PM     Click Here to See the Profile for 328KF   Click Here to Email 328KF     Edit/Delete Message   Reply w/Quote
I think we see in some of these arguments a classic case of what is known as "hindsight bias." It is simply impossible to put ourselves in the position, and mindset, of those involved without the knowledge we all now have that their decisions led to a loss of vehicle and crew.

The books Robert mentions clearly detail the decision making processes that took place. The one core piece of data none of the engineers and managers had was the experience of a manned spacecraft failing in flight. It simply had never happened before, therefore, how could it?

The SRB's had shown a tendency to have O-ring erosion, even hot gas blow-by, yet had never completely failed or exploded. I think there was an organizational thought process (group think) to accept the damage and maybe even consider the joint design to be resilient enough to withstand the damage observed. Years later, in the discussion of the Columbia accident, the term "in family" came along to describe understood and accepted quantities of damage. The same thinking was applied on launch day of 51-L.

One of the better known quotes from the engineering meetings in deciding whether or not to launch Challenger was "My God, Thiokol, when do you want me to launch? In April?" So the pressure, real or imagined, was there. The flight previous, 61-C, with Congressman Bill Nelson aboard, was delayed a record number of times, I believe it was seven or so. Then the landing was delayed by several days on the back end of the mission. This led to the shortest time between a shuttle landing and a shuttle launch in the program's brief history. Sure there was pressure.

1986 had a record number of missions on the books. NASA's ambitious plans were on the cover of several magazines, fueled by the media frenzy over Christa McAuliffe's flight. Several high profile missions were scheduled - Galileo to Jupiter, Magellan to Venus, and the Hubble Space Telescope. All of these missions were to follow Challenger's departure from Pad 39-B. Sure there was pressure.

We're not going to go back and find some long missing needle in a haystack that tells us we've been wrong all along about Challenger. It's history. Unfortunately it's often repeated history. As long as there are humans making the decisions, building the machines, and flying them, we will continue to make the same mistakes. You can't engineer them all out and history shows us that hard lessons can be forgotten as new generations come into the business without having had that defining experience of lethal failure.

jasonelam
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posted 02-23-2013 11:09 PM     Click Here to See the Profile for jasonelam   Click Here to Email jasonelam     Edit/Delete Message   Reply w/Quote
One of the biggest issues with the shuttle program at that time (and at the time of STS-107) concerned complacency. O-ring erosion issues had been seen on several flights before 51L, and yet NASA continued flying, as if it were commonplace for these things to happen. During the investigation of the Challenger accident, investigators learned that STS 51-B had a similar issue that could have resulted in the loss of vehicle and crew. Did NASA stop and look at the situation? No. It became simply, "Let's press on." There were clearly enough warning signs that there were issues with the O-rings, and NASA failed to see them.

Schedule pressure was part of the situation as well, I believe. Given there were 16 flights planned for 1986, there was no margin for delays in the program. From "Encyclopedia Astronautica":

Prior to Challenger's launch, NASA was stretched to the limit. It had advertised the shuttle was providing cheap access to space, but this could only be achieved if the flight rate reached 20 per year, or one every two weeks. But the shuttle turned out to be a maintenance nightmare. Every one of the 28,000 tiles had to be checked before each flight, software for each mission had to be individually written, tested, debugged, and certified; the engines had to be thoroughly inspected and replaced or rebuilt. The result was that there were insufficient staff, time, and spare parts to sustain a rate over 10 per year. But headquarters pressed. Decision-making centered on justifying why a mission should go rather than why it should not. Challenger lifted off a record 16 days after Columbia. The ground crews were exhausted, working massive overtime and weekends. The push to achieve the necessary flight rate to make the shuttle 'economical' finally took the ultimate toll.
Something had to give, and unfortunately it was 51L.

At the same time the O-ring issue was being looked at, another issue was rearing it's ugly head: External Tank foam shedding. Starting from STS-7 there were incidents of foam shedding. Original ET requirements were for a tank that did NOT shed foam, hence any shedding events were safety related and had to be investigated. However, NASA eventually decided that the events were "inevitable and unresolvable" with the rationale they were not a threat. Even when a piece dented a SRB near its electronics box on STS-112, they simply kept going.

There is a saying we have at work: "There are NO accidents." In these two cases, these were simply a combination of different things that, when combined, resulted in two orbiters being lost and loss of 14 astronauts, a "perfect storm" of human, environmental and engineering errors. O-rings and Foam Shedding were most obvious answers, but there was much more involved.

pterodactyl
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posted 02-24-2013 06:57 AM     Click Here to See the Profile for pterodactyl     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Robert Pearlman:
...have you read "The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA" by Diane Vaughan
Vaughan was the first to coin the phrase "normalization of deviance." This describes the condition where an organization (NASA in this case) becomes so conditioned to an unsafe and abnormal condition that it begins to discount its accident potential.

In the case of Challenger the Primary O-ring blow-by was a known safety problem, but the assumption was the secondary O-ring would always seal. Bad assumption given the temperatures that morning.

In Columbia, "normalization of deviance" was applicable to the ET foam shedding problem which was assumed to have little damage potential, even after clear evidence to the contrary from several missions that sustained serious damage.

If you want a root cause from an organizational perspective, NOD is a good candidate.

Dietrich
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posted 02-24-2013 04:13 PM     Click Here to See the Profile for Dietrich   Click Here to Email Dietrich     Edit/Delete Message   Reply w/Quote
To my understanding (after reading A. McDonald's first-hand book, and others) the initial statement by Thiokol was not to launch based on engineering assessment of the out-of-spec temperature predictions for the field joint. Then NASA expressed some urgency (at least it was perceived as such by Thiokol) and Thiokol, as the design responsible of the hardware, came back with a recommendation to launch. Obviously, this gave NASA management the assurance that it was okay to launch if the best-knowledgeable of the design recommended to do so.

Imagine that Thiokol would have stated something like "we cannot be sure that the field joint will properly work at low temperatures. The data are inconclusive and not justifying correct operation at those temperatures. Thus, the probability of failure may be high, while the severity of a failure is immense (loss of human life) so we opt for waiting for temperatures inside the experience basis. Alternatively, dedicated tests could be run at low temperatures." Would NASA management have overruled Thiokol? To my understanding a main part of the wrong decision was rooted in the inability of Thiokol's engineers to get their concerns directly up to the relevant management and engineering decision makers at NASA. But it was not their fault, but the necessary direct communication lines did not exist. The management was obviously in-between.

Worse is that the problem was well known to Thiokol and NASA before 51L, but was not put at high enough priority to have a solution applied in good time. A solution was proposed well before, see e.g. A Fundament Flaw in SRM Joint Design.

What I do not fully understand is that McDonald, who was at KSC, was very surprised by this change of mind, but did not call back to his engineering colleagues at Thiokol to understand their reasons (he obviously assumed they had some) for the positive launch recommendation.

PetesParkingLot
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posted 03-30-2013 08:59 PM     Click Here to See the Profile for PetesParkingLot     Edit/Delete Message   Reply w/Quote
First, thank you to Gene Kranz and to those of you who gave me suggested sources for material to answer the question of the root cause of the 51-L launch failure. I was very bothered by the explanation that the cold was the cause of the right hand aft SRB joint to fail, when the left hand aft SRB performed without failure, as did 4 other SRB joints exposed to the cold temperature that day. There had to be a better explanation than simply the cold temperature.

Having reviewed the evidence again, I fully agree with Gene Kranz that the temperature variable is greatly over emphasized. Thanks partly to the public demonstration by Professor Feynman and to the fact that the public could easily grasp the cold temperature "explanation" the real root cause of the Challenger launch failure has been obscured.

The root cause of the failure of the aft SRB joint was an "out of round" condition which narrowed the gap into which the O-ring seal had to move through to seal.

Below freezing temperature was merely a contributing factor which was present in all six SRB field joints but failed to impact 5 of the 6 field joints.

To quote the findings of the Rogers Commission on page 70 of Volume one:

Launch site records show that the right Solid Rocket Motor segments were assembled using approved procedures. However, significant out-of-round conditions existed between the two segments joined at the right Solid Rocket Motor aft field joint (the joint that failed).
  1. While the assembly conditions had the potential of generating debris or damage that could cause O-ring seal failure, these were not considered factors in this accident.
  2. The diameters of the two Solid Rocket Motor segments had grown as a result of prior use.
  3. The growth resulted in a condition at time of launch wherein the maximum gap between the tang and clevis in the region of the joint's O-rings was no more than .008 inches and the average gap would have been .004 inches.
  4. With a tang-to-clevis gap of .004 inches, the O-ring in the joint would be compressed to the extent that it pressed against all three walls of the O-ring retaining channel.
  5. The lack of roundness of the segments was such that the smallest tang-to-clevis clearance occurred at the initiation of the assembly operation at positions of 120 degrees and 300 degrees around the circumference of the aft field joint. It is uncertain if this tight condition and the resultant greater compression of the O-rings at these points persisted to the time of launch.
Significant is the fact the the narrowest point in the "out of round" field joint was at the 120 degree and 300 degree points. The joint was estimated to have leaked between the 296 degrees and 314 degrees centered on the 307 degree point.

This is the root cause of the Challenger launch failure. None of the other joints on the 51-L flight were assembled with a .004 gap. All were exposed to temperatures below freezing. Both the left and right hand SRB aft field joints were cooled to an estimated 28 degrees +/- 5 degrees. Only the right hand SRB aft joint failed.

Even more telling is the fact the the right hand SRB sealed and did not leak everywhere but the point between 296 and 314 degrees, the exact point at which the "out of round" condition created the narrowest gap.

The temperature variable had only a marginal impact, NASA may very well have been able to fly brand new (perfectly round) SRBs in 28 degree temperatures for the entire flight manifest without any launch failure.

I wonder if the apparent inconsistent relationship between temperature and joint leakage can be more readily explained by examining the joint gap after assembly as the primary factor.

The focus on temperature while missing the major variable of the gap size at launch, left a reasonable doubt as to the relationship between temperature and joint erosion on prior flights. Had the Thiokol engineers better analyzed their data they might have convinced the management of both NASA and Thiokol.

More to come if I can find a relationship between joint erosion and number of flights a SRB segment flew.

Robert Pearlman
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posted 03-30-2013 09:21 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by PetesParkingLot:
This is the root cause of the Challenger launch failure.
I believe your certainty is misplaced. If I can quote from the same section of the Rogers Commission report:
Other joints on the left and right Solid Rocket Boosters experienced similar combinations of tang-to-clevis gap clearance and temperature. It is not known whether these joints experienced distress during the flight of 51-L.
(Emphasis mine.) Without knowing what the condition of the other seals were at the point of the breakup, you are going to have a hard time defending a single root cause.

As you are basing (at least part of) your analysis and conclusions on the Rogers Commission report, then its other findings are equally relevant, such as:

Of 21 launches with ambient temperatures of 61 degrees Fahrenheit or greater, only four showed signs of O-ring thermal distress; i.e., erosion or blow-by and soot. Each of the launches below 61. degrees Fahrenheit resulted in one or more O-rings showing signs of thermal distress.
Thus, the foundation does not exist to rule out a multi-factor root cause, as the Commission reported:
The failure was due to a faulty design unacceptably sensitive to a number of factors. These factors were the effects of temperature, physical dimensions, the character of materials, the effects of reusability, processing, and the reaction of the joint to dynamic loading.


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