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> Challenger: no gasses were supposed to make it past the o-rings no matter what, > but when it became clear that gasses were escaping and the o-rings were bei

> Challenger: no gasses were supposed to make it past the o-rings no matter what, > but when it became clear that gasses were escaping and the o-rings were being > damaged, there was a push to suggest that it's an acceptable level. Interestingly, the article<https://docs.google.com/document/d/1ddi792xdfNXcBwF8qpDUxmZzIksrs0jy/edit?pli=1 https://docs.google.com/document/d/1ddi792xdfNXcBwF8qpDUxmZz...> by heat shield expert and Shuttle astronaut Charles Camarda, the former Director of Engineering at Johnson Space Center, asserts that it was *not* the O-rings: "The Challenger accident was not caused by O-rings or temperature on the day of launch; it was caused by a deviant joint design which opened instead of closed when loaded. It was caused by mistaking analytical adequacy of a simplified test for physical understanding of the system. The solution, post Challenger, was the structural redesign of the SRB field joint and the use of the exact same O-rings." I find that highly surprising, because "it was the O-rings" explanation seems universally believed and sanctified by no lesser authority than the Nobel prize laureate Richard Feynman.

voidUpdate 6mo ago
Using the same o-rings afterwards is surprising, I've heard that the manufacturer was surprised that they were being used for that purpose because they weren't rated for that. Also I'm not sure the assertion is correct. If the sealant and O-Rings were adequate, the joint would not have failed. It was suboptimal, and increased risk, sure, but it in itself wasn't the reason for the accident. It was the joint and the o-rings in combination. The holes in the swiss cheese model lined up that day, and a lot of small problems combined into one big problem
- Mikhail_K 6mo ago
  > If the sealant and O-Rings were adequate, the joint would not have failed. That assertion requires some reasoning and evidence to back it.
  - voidUpdate 6mo ago
    The sealant and O-rings were meant to keep the hot gasses inside. Simply making a joint slightly wiggly will not keep hot gasses inside. The hot gasses did not stay inside. The sealant and O-rings did not succeed in keeping the hot gasses inside (evidence: Challenger). They were not adequate
    - Mikhail_K 6mo ago
      > The sealant and O-rings did not succeed in keeping the hot gasses inside (evidence: Challenger). They were not adequate No. The whole assembly --joint, sealant and O-rings, -- failed. "They were not adequate" - yet, after the redesign, they kept those same O-rings and declared that boosters are safe to fly, in manifest contradiction to your assertion. So your reasoning is clearly flawed.
      - john_strinlai 6mo ago
        >"They were not adequate" - yet, after the redesign, they kept those same O-rings presumably "redesign" means some stuff changed. why is it not possible that the O-rings were inadequate for the old design, but adequate for the new design?
        buildsjets 6mo ago
        Exactly. They re-designed the tang and clevis joint so that the metal parts of the joint did not spread under gas pressure and the o-ring did not lose compression. They added a heater to ensure that the o-ring remained in it's usable temperature range. And added a superfluous third O-ring. Speaking of which, has anyone ever adequately explained why Challenger's Right SRB joint temperature was measured as -13 deg C using infrared pyrometers, when the lowest ambient temperature that night was -5.5C, and the Left SRB was measured -4 C? What subcooled the right SRB? Allan McDonald's "Truth, Lies, and O-Rings" is mandatory reading for anyone who wants to discuss the details of this particular bit of corporate and government malfeasance. It's 600 pages of technical detail and political intrigue. He suggests that a plume from a cryo vent could have impinged on the field joint and cooled the o-ring to lower than ambient temperatures. No proof though.
- inaros 6mo ago
  >> Using the same o-rings afterwards is surprising, I've heard that the manufacturer was surprised that they were being used for that purpose because they weren't rated for that. Not surprising if you understand what the real cause was: https://news.ycombinator.com/item?id=47585889 https://news.ycombinator.com/item?id=47585889
- sidewndr46 6mo ago
  Surprised? One of the engineers was literally on the phone with NASA the morning of the disaster begging them not to launch. He was overruled by management.
  - randomNumber7 6mo ago
    Surprising for the management. If you are a spoiled brat who always got what it wanted if you just asked/cried you don't expect reality to come and hit you.
    - LorenPechtel 6mo ago
      Actually, not surprising. The engineering was clear: don't fly. But given political realities had they said that they probably would have lost the contract to build the rockets--and that was a big part of their business. They made the human choice: chose the option with a chance of success vs the option that was a certain failure.
      - randomNumber7 6mo ago
        They had already failed earlier and are just too selfish to accept it. This is not human, its a disgusting subset of the species.
        LorenPechtel 6mo ago
        The failure was pretty much forced. This was a cost plus contract, if NASA didn't want to dig into the blowby issue they weren't really in a position to do so.
rob74 6mo ago
Without being too familiar with the subject - another commenter referred to the "swiss cheese model": the O-ring design, the temperature etc. weren't the single cause, they were contributing factors, and the more contributing factors you eliminate, the more certain you can be that you won't have a repeat accident. AFAIK there weren't any more Shuttle launches at such low temperatures after that anymore either?
- pfdietz 6mo ago
  That's right, the accident launch was by far the coldest. They also added joint heaters.
mikkupikku 6mo ago
It's the same explaination. When the SRB joints flexxed the o-rings were meant to stay in place, but the joints were defective and NASA knew the o-rings were moving. However NASA also believed the o-rings could still take the abuse, because although they were moving they were getting shoved deeper into the joint, in a way that wasn't intended but was nonetheless at least marginally effective at stopping exhaust blow-by shortly after it began. But when the o-rings were cold and stiff... they didn't move the same way, exhaust blew by them longer and cut right through. At that point the SRB turns into a cutting torch (the SRBs didn't actually explode until after the shuttle broke up and range safety sent the signal to kill the boosters.
- Mikhail_K 6mo ago
  > However NASA also believed the o-rings could still take the abuse, because > although they were moving they were getting shoved deeper into the joint, Why would they be "shoved deeper," when the problem is that the joint opens wider under load?
  - anonymars 6mo ago
    See here: https://www.researchgate.net/profile/Scott-Post/publication/268078377/figure/fig3/AS:667784442826775@1536223626438/Schematic-of-SRB-joint-showing-rotation-17.png https://www.researchgate.net/profile/Scott-Post/publication/... What would happen "normally" (i.e. the normalization of deviance) was that the rotation (from the SRB joints bowing--essentially "ballooning") would create a gap, and the O-rings would get blown into that gap and ultimately seal in there With Challenger, it was too cold, so the O-ring rubber was not malleable enough to seal into that space (like the O-ring towards the right of the diagram), so the hot gases were allowed to blow by and erode the O-ring. If they had sealed in (like the one on the left) it would have just taken the pressure but not worn away
    - pdonis 6mo ago
      > What would happen "normally" (i.e. the normalization of deviance) was that the rotation (from the SRB joints bowing--essentially "ballooning") would create a gap, and the O-rings would get blown into that gap and ultimately seal in there But data from previous Shuttle flights showed that even that wasn't happening, at temperatures up to 75 F. And the Thiokol engineers had test stand data showing that it wasn't happening even at temperatures up to 100 F. In short, that joint design was unacceptably risky at any temperature. It is probably true that the design was somewhat more unacceptably risky at 29 F. But that was a relatively minor point. The reason the cold temperature was focused on by the Thiokol engineers (who were overruled by their own managers in the end, as well as NASA managers) in the call the night before the launch was not that they had a good case for increased risk at cold temperature; it was that the cold temperature argument was the only thing they had to fight with--because NASA had already refused to listen to their much better arguments the previous summer for stopping all Shuttle flights until the joint design could be fixed.
inaros 6mo ago
>>I find that highly surprising, because "it was the O-rings" explanation seems universally believed and sanctified by no lesser authority than the Nobel prize laureate Richard Feynman. Essentially you are mischaracterizing what Feynman did or say, although this is also Feynman fault :-), by doing the famous public demonstration, with the ice water in a glass [2], although even there he only said it has "significance to the problem...". In other words, we should not simplify, even for the general public, what are complex subtle engineering issues. This is also the reason why current AI, will fail spectacularly, but I digress... Feynman documented the joint rotation problem in his written Appendix F, but his televised demonstration became the explanation...[3] Camarda is correct here. There was a fundamentally flawed field joint design, meaning the tang-and-clevis joint opened under combustion pressure instead of closing. This meant the O-rings were being asked to chase a widening gap something the O-ring manufacturer explicitly told Thiokol O-rings were never designed to do. Joint rotation was known as early as 1977, a full nine years before the disaster. The cold temperature made things worse by stiffening the rubber so it could not chase the gap as quickly, but O-ring erosion and blow-by were occurring on flights in warm weather too and nearly every flight in 1985 showed damage. The proof is how they fixed. NASA redesigned the joint metal structure with a capture feature to prevent rotation, added a third O-ring for redundancy, and installed heaters but kept the exact same Viton rubber. If the O-rings were the real problem, you would change the O-rings. They did not need to. The report [1] is public for everybody to read...but not from the NASA page... who funnily enough has a block on the link from their own page, so I had to find an alternative link... [1] - https://www.govinfo.gov/content/pkg/GPO-CRPT-99hrpt1016/pdf/GPO-CRPT-99hrpt1016.pdf https://www.govinfo.gov/content/pkg/GPO-CRPT-99hrpt1016/pdf/... [2] - https://youtu.be/6TInWPDJhjU https://youtu.be/6TInWPDJhjU [3] - https://calteches.library.caltech.edu/3570/1/Feynman.pdf https://calteches.library.caltech.edu/3570/1/Feynman.pdf
- Mikhail_K 6mo ago
  That's valuable, detailed explanation, thanks.
- LorenPechtel 6mo ago
  Yeah--people don't get it that while it was the failure of the O-rings that doomed that flight that they failed because they were subjected to forces they were never designed to take. The fact that they got that many flights before it blew actually says they were doing an admirable job of covering up the design flaw.
oritron 6mo ago
My recollection is that a rocket design was scaled up from one that worked, by people who didn't consider how an o-ring should be loaded in order to function properly. They inadvertently changed the design rather than simply scale it. I don't think Feynman got this wrong either. His demo was because the justifications for flight were based on the fact that failure had a temperature correlation, and they had a model representing how damaged the o-rings would be. The o-ring failure was a measurable consequence of the joint design failure. The data behind the model didn't go down to temperatures as low as that at Challenger's launch date. For more inappropriate extrapolation to justify a decision: the data for the heat shield tile loss model was based on much less damage than sustained by Columbia (3 orders of magnitude IIRC). Now they are looking at the same style of fallacy and don't even have a model based on damage sustained in flights. Another parallel I haven't seen discussed here yet, though I haven't read all comments: I recall Feynman feeling like he was on the investigation panel as a prop, that the intention of the investigation was to clear NASA of any wrongdoing. They used a model, considered risks, etc. Feynman recognized the need for a clear and powerful visual to cut through an information dump and pull it to front page news. The invitation of Camarda to a presentation with a pre-determined conclusion has the same feeling. I don't know what Camarda can do to put it on a (non-HN) front page today.
nritchie 6mo ago
Both things can be true. A better O-ring with the same joint might have prevented the disaster. A better designed joint with the same O-ring might also. Feynman knew that a little theater would go a long way. The O-ring explanation, albeit a partial explanation, made for good theater.
acranox 6mo ago
There’s a pretty good explanation here: https://exrocketman.blogspot.com/2021/12/the-seal-failure-in-srb-that-doomed.html https://exrocketman.blogspot.com/2021/12/the-seal-failure-in...
pdonis 6mo ago
> "it was the O-rings" explanation seems universally believed and sanctified by no lesser authority than the Nobel prize laureate Richard Feynman. If you read Feynman's account in the book What Do You Care What Other People Think?, you'll see that he realized afterwards that he was prompted to make the demonstration he made at a NASA press conference--putting a piece of O-ring material in a glass of ice water, clamped with a C-clamp, and then taking it out and releasing the clamp to show that the material did not spring back--to get public attention focused on problems with the joint in a way that could not be ignored. But, as has been pointed out downthread, when the joint was redesigned, the new design did not change the O-rings at all. So the specific issue that was shown in Feynman's demonstration was not the issue that actually needed to be fixed. It was just a convenient way to show the public that there were problems with the joint, with a simple demonstration that everyone could understand. Trying to show the actual problem--that the entire joint design was fundamentally flawed and needed to be changed--would not have worked in a context like that.

voidUpdate 6mo ago

Using the same o-rings afterwards is surprising, I've heard that the manufacturer was surprised that they were being used for that purpose because they weren't rated for that. Also I'm not sure the assertion is correct. If the sealant and O-Rings were adequate, the joint would not have failed. It was suboptimal, and increased risk, sure, but it in itself wasn't the reason for the accident. It was the joint and the o-rings in combination. The holes in the swiss cheese model lined up that day, and a lot of small problems combined into one big problem

Mikhail_K 6mo ago
> If the sealant and O-Rings were adequate, the joint would not have failed. That assertion requires some reasoning and evidence to back it.
- voidUpdate 6mo ago
  The sealant and O-rings were meant to keep the hot gasses inside. Simply making a joint slightly wiggly will not keep hot gasses inside. The hot gasses did not stay inside. The sealant and O-rings did not succeed in keeping the hot gasses inside (evidence: Challenger). They were not adequate
  - Mikhail_K 6mo ago
    > The sealant and O-rings did not succeed in keeping the hot gasses inside (evidence: Challenger). They were not adequate No. The whole assembly --joint, sealant and O-rings, -- failed. "They were not adequate" - yet, after the redesign, they kept those same O-rings and declared that boosters are safe to fly, in manifest contradiction to your assertion. So your reasoning is clearly flawed.
    - john_strinlai 6mo ago
      >"They were not adequate" - yet, after the redesign, they kept those same O-rings presumably "redesign" means some stuff changed. why is it not possible that the O-rings were inadequate for the old design, but adequate for the new design?
      - buildsjets 6mo ago
        Exactly. They re-designed the tang and clevis joint so that the metal parts of the joint did not spread under gas pressure and the o-ring did not lose compression. They added a heater to ensure that the o-ring remained in it's usable temperature range. And added a superfluous third O-ring. Speaking of which, has anyone ever adequately explained why Challenger's Right SRB joint temperature was measured as -13 deg C using infrared pyrometers, when the lowest ambient temperature that night was -5.5C, and the Left SRB was measured -4 C? What subcooled the right SRB? Allan McDonald's "Truth, Lies, and O-Rings" is mandatory reading for anyone who wants to discuss the details of this particular bit of corporate and government malfeasance. It's 600 pages of technical detail and political intrigue. He suggests that a plume from a cryo vent could have impinged on the field joint and cooled the o-ring to lower than ambient temperatures. No proof though.
inaros 6mo ago
>> Using the same o-rings afterwards is surprising, I've heard that the manufacturer was surprised that they were being used for that purpose because they weren't rated for that. Not surprising if you understand what the real cause was: https://news.ycombinator.com/item?id=47585889 https://news.ycombinator.com/item?id=47585889
sidewndr46 6mo ago
Surprised? One of the engineers was literally on the phone with NASA the morning of the disaster begging them not to launch. He was overruled by management.
- randomNumber7 6mo ago
  Surprising for the management. If you are a spoiled brat who always got what it wanted if you just asked/cried you don't expect reality to come and hit you.
  - LorenPechtel 6mo ago
    Actually, not surprising. The engineering was clear: don't fly. But given political realities had they said that they probably would have lost the contract to build the rockets--and that was a big part of their business. They made the human choice: chose the option with a chance of success vs the option that was a certain failure.
    - randomNumber7 6mo ago
      They had already failed earlier and are just too selfish to accept it. This is not human, its a disgusting subset of the species.
      - LorenPechtel 6mo ago
        The failure was pretty much forced. This was a cost plus contract, if NASA didn't want to dig into the blowby issue they weren't really in a position to do so.

rob74 6mo ago

Without being too familiar with the subject - another commenter referred to the "swiss cheese model": the O-ring design, the temperature etc. weren't the single cause, they were contributing factors, and the more contributing factors you eliminate, the more certain you can be that you won't have a repeat accident. AFAIK there weren't any more Shuttle launches at such low temperatures after that anymore either?

pfdietz 6mo ago
That's right, the accident launch was by far the coldest. They also added joint heaters.

mikkupikku 6mo ago

It's the same explaination. When the SRB joints flexxed the o-rings were meant to stay in place, but the joints were defective and NASA knew the o-rings were moving. However NASA also believed the o-rings could still take the abuse, because although they were moving they were getting shoved deeper into the joint, in a way that wasn't intended but was nonetheless at least marginally effective at stopping exhaust blow-by shortly after it began. But when the o-rings were cold and stiff... they didn't move the same way, exhaust blew by them longer and cut right through. At that point the SRB turns into a cutting torch (the SRBs didn't actually explode until after the shuttle broke up and range safety sent the signal to kill the boosters.

Mikhail_K 6mo ago
> However NASA also believed the o-rings could still take the abuse, because > although they were moving they were getting shoved deeper into the joint, Why would they be "shoved deeper," when the problem is that the joint opens wider under load?
- anonymars 6mo ago
  See here: https://www.researchgate.net/profile/Scott-Post/publication/268078377/figure/fig3/AS:667784442826775@1536223626438/Schematic-of-SRB-joint-showing-rotation-17.png https://www.researchgate.net/profile/Scott-Post/publication/... What would happen "normally" (i.e. the normalization of deviance) was that the rotation (from the SRB joints bowing--essentially "ballooning") would create a gap, and the O-rings would get blown into that gap and ultimately seal in there With Challenger, it was too cold, so the O-ring rubber was not malleable enough to seal into that space (like the O-ring towards the right of the diagram), so the hot gases were allowed to blow by and erode the O-ring. If they had sealed in (like the one on the left) it would have just taken the pressure but not worn away
  - pdonis 6mo ago
    > What would happen "normally" (i.e. the normalization of deviance) was that the rotation (from the SRB joints bowing--essentially "ballooning") would create a gap, and the O-rings would get blown into that gap and ultimately seal in there But data from previous Shuttle flights showed that even that wasn't happening, at temperatures up to 75 F. And the Thiokol engineers had test stand data showing that it wasn't happening even at temperatures up to 100 F. In short, that joint design was unacceptably risky at any temperature. It is probably true that the design was somewhat more unacceptably risky at 29 F. But that was a relatively minor point. The reason the cold temperature was focused on by the Thiokol engineers (who were overruled by their own managers in the end, as well as NASA managers) in the call the night before the launch was not that they had a good case for increased risk at cold temperature; it was that the cold temperature argument was the only thing they had to fight with--because NASA had already refused to listen to their much better arguments the previous summer for stopping all Shuttle flights until the joint design could be fixed.

inaros 6mo ago

>>I find that highly surprising, because "it was the O-rings" explanation seems universally believed and sanctified by no lesser authority than the Nobel prize laureate Richard Feynman. Essentially you are mischaracterizing what Feynman did or say, although this is also Feynman fault :-), by doing the famous public demonstration, with the ice water in a glass [2], although even there he only said it has "significance to the problem...". In other words, we should not simplify, even for the general public, what are complex subtle engineering issues. This is also the reason why current AI, will fail spectacularly, but I digress... Feynman documented the joint rotation problem in his written Appendix F, but his televised demonstration became the explanation...[3] Camarda is correct here. There was a fundamentally flawed field joint design, meaning the tang-and-clevis joint opened under combustion pressure instead of closing. This meant the O-rings were being asked to chase a widening gap something the O-ring manufacturer explicitly told Thiokol O-rings were never designed to do. Joint rotation was known as early as 1977, a full nine years before the disaster. The cold temperature made things worse by stiffening the rubber so it could not chase the gap as quickly, but O-ring erosion and blow-by were occurring on flights in warm weather too and nearly every flight in 1985 showed damage. The proof is how they fixed. NASA redesigned the joint metal structure with a capture feature to prevent rotation, added a third O-ring for redundancy, and installed heaters but kept the exact same Viton rubber. If the O-rings were the real problem, you would change the O-rings. They did not need to. The report [1] is public for everybody to read...but not from the NASA page... who funnily enough has a block on the link from their own page, so I had to find an alternative link... [1] - https://www.govinfo.gov/content/pkg/GPO-CRPT-99hrpt1016/pdf/GPO-CRPT-99hrpt1016.pdf https://www.govinfo.gov/content/pkg/GPO-CRPT-99hrpt1016/pdf/... [2] - https://youtu.be/6TInWPDJhjU https://youtu.be/6TInWPDJhjU [3] - https://calteches.library.caltech.edu/3570/1/Feynman.pdf https://calteches.library.caltech.edu/3570/1/Feynman.pdf

Mikhail_K 6mo ago
That's valuable, detailed explanation, thanks.
LorenPechtel 6mo ago
Yeah--people don't get it that while it was the failure of the O-rings that doomed that flight that they failed because they were subjected to forces they were never designed to take. The fact that they got that many flights before it blew actually says they were doing an admirable job of covering up the design flaw.

oritron 6mo ago

My recollection is that a rocket design was scaled up from one that worked, by people who didn't consider how an o-ring should be loaded in order to function properly. They inadvertently changed the design rather than simply scale it. I don't think Feynman got this wrong either. His demo was because the justifications for flight were based on the fact that failure had a temperature correlation, and they had a model representing how damaged the o-rings would be. The o-ring failure was a measurable consequence of the joint design failure. The data behind the model didn't go down to temperatures as low as that at Challenger's launch date. For more inappropriate extrapolation to justify a decision: the data for the heat shield tile loss model was based on much less damage than sustained by Columbia (3 orders of magnitude IIRC). Now they are looking at the same style of fallacy and don't even have a model based on damage sustained in flights. Another parallel I haven't seen discussed here yet, though I haven't read all comments: I recall Feynman feeling like he was on the investigation panel as a prop, that the intention of the investigation was to clear NASA of any wrongdoing. They used a model, considered risks, etc. Feynman recognized the need for a clear and powerful visual to cut through an information dump and pull it to front page news. The invitation of Camarda to a presentation with a pre-determined conclusion has the same feeling. I don't know what Camarda can do to put it on a (non-HN) front page today.

nritchie 6mo ago

Both things can be true. A better O-ring with the same joint might have prevented the disaster. A better designed joint with the same O-ring might also. Feynman knew that a little theater would go a long way. The O-ring explanation, albeit a partial explanation, made for good theater.

acranox 6mo ago

There’s a pretty good explanation here: https://exrocketman.blogspot.com/2021/12/the-seal-failure-in-srb-that-doomed.html https://exrocketman.blogspot.com/2021/12/the-seal-failure-in...

pdonis 6mo ago

> "it was the O-rings" explanation seems universally believed and sanctified by no lesser authority than the Nobel prize laureate Richard Feynman. If you read Feynman's account in the book What Do You Care What Other People Think?, you'll see that he realized afterwards that he was prompted to make the demonstration he made at a NASA press conference--putting a piece of O-ring material in a glass of ice water, clamped with a C-clamp, and then taking it out and releasing the clamp to show that the material did not spring back--to get public attention focused on problems with the joint in a way that could not be ignored. But, as has been pointed out downthread, when the joint was redesigned, the new design did not change the O-rings at all. So the specific issue that was shown in Feynman's demonstration was not the issue that actually needed to be fixed. It was just a convenient way to show the public that there were problems with the joint, with a simple demonstration that everyone could understand. Trying to show the actual problem--that the entire joint design was fundamentally flawed and needed to be changed--would not have worked in a context like that.