SpaceX Falcon 9 - AMOS-6 - (Pad Failure) - DISCUSSION THREAD (2)

[Ben the Space Brit]

https://twitter.com/jeff_foust/status/780893099501326336

Musk: F9 anomaly investigation still top priority; “most vexing and difficult thing.” Ruled out all the obvious possibilities. #IAC2016

I find this reassuring as to the viability of Falcon-9. It implies strongly that whatever went wrong was a low probability event that may relate to an unpredictable and near one-off interaction of causes.

[MarekCyzio]

I thought the helium system was supercritical, i.e. neither liquid nor gaseous, but both.

There is a line item in the Falcon 9 countdown that references liquid helium loading.

No, it is 5000 psi gaseous helium.

Isn't helium at 5000 PSI supercritical?

It's more about temperature than pressure. Yes at subcooled lox temperatures and 5000 PSI helium is supercritical but still much closer to a gas than a liquid. It needs to be cooled down to a few K to become more like a liquid. And if you cool it down below supercritical temperature it will become liquid. But at subcooled LOX temperatures it is still gas, just much denser gas.

[rsdavis9]

I'm guessing what other sources of problems in the He system could cause the accident besides a previously damaged COPV. SpaceX previously had problems with parts of the second stage freezing. They rectified this by adding insulation around the cold pipes in the stage. Could the insulating not be sufficient for the subcooled LOx or RP-1? With less space in the second stage, too cold of an environment might cause valves to stick, seals to fail, or other problems. Sticky valves might show up on telemetry, but what other problems are possible that wouldn't show up? Could LOx leak into the He pipes?

wasn't the freezing the tea/teb system during the coast phase for s2 after launching and releasing something(?) they did  a test restart and it failed.

[Proponent]

At (even sub-cooled) lox temperatures, yes.

[Mike_1179]

There's something fishy about the most recent update anyway. Is there anyone here who didn't already know that the helium system was breached? Put in another way, would you have believed an update that said thankfully the helium system was not breached?

I remember many people in the first thread 'knowing' that there was some kind of mysterious fuel-air explosion outside the rocket that was caused by whatever was the person's favourite. And many other theories. Now many of the same people who seemed very sure about their now-discredited theories have moved to 'knowing' how exactly the helium system breach happened. Often wrong, but never in doubt...

I think some of that motivation for the fuel-air explosion external to the stage was that it would mean the problem wasn't with the Falcon 9 but with the GSE - that way you don't indict the fancy rocket that already had one failure from it's compressed He system with another, unrelated failure of the same system.

[jpo234]

Is the theory "COPV suddenly decides to go boom" off the table with Musks answer at the press conference? What are "obvious" and "less probable" possibilities?

We’ve eliminated all of the obvious possibilities. So what remains are less probable.

[kevin-rf]

Honestly, they have the debris. If they have located all the COPV's and they all are intact, then it's off the table. If one is in pieces they need to decide if it's a cause or effect.

So did they recover all the COPV's intact? That would be an interesting question.

[Kabloona]

Honestly, they have the debris. If they have located all the COPV's and they all are intact, then it's off the table. If one is in pieces they need to decide if it's a cause or effect.

So did they recover all the COPV's intact? That would be an interesting question.

That's a good question, and quite possible since we've seen pics of several that have survived reentry.

[Jim]

Is the theory "COPV suddenly decides to go boom" off the table with Musks answer at the press conference? What are "obvious" and "less probable" possibilities?

We’ve eliminated all of the obvious possibilities. So what remains are less probable.

Helium system breach has not been eliminated and it has been the leading possibility since day one

[jpo234]

Is the theory "COPV suddenly decides to go boom" off the table with Musks answer at the press conference? What are "obvious" and "less probable" possibilities?

We’ve eliminated all of the obvious possibilities. So what remains are less probable.

Helium system breach has not been eliminated and it has been the leading possibility since day one

That's not really helpful. We know that it was a "Helium system breach", but that's not very specific.

[cscott]

Yes, the "improbable" part is referring to the *cause* of the helium breach, presumably.  The "cause of the explosion" is the helium breach, which as Jim notes is not an improbable consequence of a large helium breach.

[Jim]

Is the theory "COPV suddenly decides to go boom" off the table with Musks answer at the press conference? What are "obvious" and "less probable" possibilities?

We’ve eliminated all of the obvious possibilities. So what remains are less probable.

Helium system breach has not been eliminated and it has been the leading possibility since day one

That's not really helpful. We know that it was a "Helium system breach", but that's not very specific.

There are many obvious things that could go wrong in the helium system that have not been eliminated
Line burst, valve failure, fitting failure, attach fitting failure, pass through failure, sensor installation failure, etc

[vanoord]

Honestly, they have the debris. If they have located all the COPV's and they all are intact, then it's off the table. If one is in pieces they need to decide if it's a cause or effect.

So did they recover all the COPV's intact? That would be an interesting question.

It might be fair to assume that if they had all but one COPVs intact and a few fragments of the other one then that would be a sufficiently smoking gun?

The public statements - including Elon's comment yesterday - suggest that SpaceX don't yet know the exact cause; and that could indicate that there's nothing obvious from the condition of the COPVs that implicates them specifically.

[kevin-rf]

That's a good question, and quite possible since we've seen pics of several that have survived reentry.

My guess is they are sorting through all the debris trying to build up a picture of what is intact and what is missing or broken to find what failed. I am worried it was a certified component that failed well below it's rating. Just like the strut. They just have to find the broken part.

[Kabloona]

That's a good question, and quite possible since we've seen pics of several that have survived reentry.

My guess is they are sorting through all the debris trying to build up a picture of what is intact and what is missing or broken to find what failed. I am worried it was a certified component that failed well below it's rating. Just like the strut. They just have to find the broken part.

Problem with that is, a relatively small component (regulator, valve, tubing section) that bursts at 5000 psi and then (maybe) falls into a giant lake of burning RP-1 may not have much left of it, if it didn't get blown a mile away into the scrub forest. They may as well be looking for a strut fragment somewhere in the Atlantic.

Hope I'm wrong, though.

[kevin-rf]

Problem with that is, a relatively small component (regulator, valve, tubing section) that bursts at 5000 psi and then (maybe) falls into a giant lake of burning RP-1 may not have much left of it, if it didn't get blown a mile away into the scrub forest. They may as well be looking for a strut fragment somewhere in the Atlantic.

Hope I'm wrong, though.

At those pressures, would it be fair to assume stainless, meaning if the fragments of the failed part fell into the fuel fire they are still around. The trick will be finding the fragments in the scrub.

[JasonAW3]

      The thing that bothers me the most about the Helium tank failure scenario is; What was the initial ignition source that caused the fire?

      A Helium / LOX mix, by itself, wouldn't self-ignite.  It might have caused the LOX tank to rupture, but there SHOULD have been a few seconds before the LOX would have been able to find an ignition source.

      If the initial ping heard four seconds before the conflagration WAS the puncture of the tank, what was it that actually set off the fire?

[JasonAW3]

Problem with that is, a relatively small component (regulator, valve, tubing section) that bursts at 5000 psi and then (maybe) falls into a giant lake of burning RP-1 may not have much left of it, if it didn't get blown a mile away into the scrub forest. They may as well be looking for a strut fragment somewhere in the Atlantic.

Hope I'm wrong, though.

At those pressures, would it be fair to assume stainless, meaning if the fragments of the failed part fell into the fuel fire they are still around. The trick will be finding the fragments in the scrub.

      I'm surprised that no one is using the same magnetic imaging technology that NASA developed to map the magnetic fields of other worlds, to map out the area for possible debris from the conflagration.

      Sure, it was developed to be used at an altitude of a few hundred to thousand miles in altitude, but at lower altitudes, (of a few hundred feet) the resolution should be MUCH sharper.

[Jim]

      I'm surprised that no one is using the same magnetic imaging technology that NASA developed to map the magnetic fields of other worlds, to map out the area for possible debris from the conflagration.

      Sure, it was developed to be used at an altitude of a few hundred to thousand miles in altitude, but at lower altitudes, (of a few hundred feet) the resolution should be MUCH sharper.

it doesn't work that way.  It is not magnetic imaging.  And it can't be used that this levels.
Also, there is too much iron in the TEL, launch mount and rebar.   And stainless is not magnetic.

[fthomassy]

https://twitter.com/jeff_foust/status/780893099501326336

Musk: F9 anomaly investigation still top priority; “most vexing and difficult thing.” Ruled out all the obvious possibilities. #IAC2016

I find this reassuring as to the viability of Falcon-9. It implies strongly that whatever went wrong was a low probability event that may relate to an unpredictable and near one-off interaction of causes.

I get just the opposite impression.  It says the "thing" is not yet understood.  So you have no idea if this is a rare event that was unlucky to occur early or a common event where the first occurrence happened late.  Until it is understood it can't be eliminated and your "viability" is unknown.
_{Edit: Or a unique event that can never happen again.}