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

[woods170]

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

Nice going there Jim. Contradicting Elon Musk like you know his rockets better than he does.

[JasonAW3]

      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.

     True for the center of the zone, but it could help find stuff further out, say, a hundred meters from the initial conflagration zone.

     And which stainless steel alloy are you referring to?  Most stainless steel alloys I've worked with are capable of having a magnetic field induced in them remotely.  Much like how magnetic mine detectors work.

     Proper radio frequencies, such as from many ground search radars, can likewise induce such magnetic fields, although briefly.

     Many times, when steel is heated to fairly high temperatures in a fire, a low level of magnetic field effect can and often is induced as well.

     Obviously, this won't detect all of the debris, but it may help in finding anything blown further away, say a quarter mile or so.

[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

Nice going there Jim. Contradicting Elon Musk like you know his rockets better than he does.

How is that?  That statement does not contradict Musk in anyway.  Like he says, they are stumped.  I just listed many parts of the helium system that could potentially fail.  Nothing on this thread or what had been announced has eliminated them.  I did not describe how they could fail and what signatures would be seen.

[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.

     True for the center of the zone, but it could help find stuff further out, say, a hundred meters from the initial conflagration zone.

     And which stainless steel alloy are you referring to?  Most stainless steel alloys I've worked with are capable of having a magnetic field induced in them remotely.  Much like how magnetic mine detectors work.

     Proper radio frequencies, such as from many ground search radars, can likewise induce such magnetic fields, although briefly.

     Many times, when steel is heated to fairly high temperatures in a fire, a low level of magnetic field effect can and often is induced as well.

     Obviously, this won't detect all of the debris, but it may help in finding anything blown further away, say a quarter mile or so.

NASA magnetometers look for magnetic fields, they don't induce them.

There is debris from other launches and such all around.

[kevin-rf]

Don't forget bits from the explosive demolition of the Titan launch tower. They should have 100% cleaned it, but I bet you could find metal bits here and there.

I do not think there had been any prior pad failures at LC-40.

[Jimmy_C]

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.

Ya you are right. The point, which I'm poorly trying to make, is that the subcooled LOx temperature could affect other systems. I suppose LOx can't leak into the He system, since it's under too much pressure.

Does anyone know of they perform a visual inspection for Foreign Object Debris before the static fire? I think I recall a cleaning rag being left in an engine for another company, which caused a RUD.

[Kabloona]

Does anyone know of they perform a visual inspection for Foreign Object Debris before the static fire? I think I recall a cleaning rag being left in an engine for another company, which caused a RUD.

They'd have to remove engines and/or feed lines, which isn't normal preflight procedure in the field. That type of check should happen in the factory during final assembly.

[Herb Schaltegger]

Does anyone know of they perform a visual inspection for Foreign Object Debris before the static fire? I think I recall a cleaning rag being left in an engine for another company, which caused a RUD.

They'd have to remove engines and/or feed lines, which isn't normal preflight procedure in the field. That type of check should happen in the factory during final assembly.

Yep. And if there was true "foreign" object debris in the tank/plumbing, it would've shown itself during the tanking and static firing in McGregor before it got to LC40. If debris of any kind is involved in this, it would almost certainly be debris from the very incident itself: a piece or pieces of the rupturing helium system (fitting, sensor, flow control valve or orifice, mounting fixture, whatever).

[yokem55]

What would contamination of the HE supply do? Say water contamination on the order of less than .01%? Could ice buildup in one of the helium lines and cause a problem? Is such contamination possible?

[hrissan]

What would contamination of the HE supply do? Say water contamination on the order of less than .01%? Could ice buildup in one of the helium lines and cause a problem? Is such contamination possible?

I know the following is just very stupid idea - but if the contractor supplies several He bottles and by mistake one bottle is filled with hydrogen instead of He? Would result in several percent hydrogen contamination in helium. Due to different joule-Thompson coefficient during COPV filling the gas heats up unusually, until some fitting fails. The hot gas containing hydrogen is violently mixed into LOX...

The theory is easily disproved by checking helium purity in the pad tanks. Hope they survived?

[Space Ghost 1962]

What would contamination of the HE supply do? Say water contamination on the order of less than .01%? Could ice buildup in one of the helium lines and cause a problem? Is such contamination possible?

I know the following is just very stupid idea - but if the contractor supplies several He bottles and by mistake one bottle is filled with hydrogen instead of He? Would result in several percent hydrogen contamination in helium. Due to different joule-Thompson coefficient during COPV filling the gas heats up unusually, until some fitting fails. The hot gas containing hydrogen is violently mixed into LOX...

The theory is easily disproved by checking helium purity in the pad tanks. Hope they survived?

... or a cause for embrittlement cracks that could accelerate routine metal fatigue.

[starsilk]

      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.

     True for the center of the zone, but it could help find stuff further out, say, a hundred meters from the initial conflagration zone.

     And which stainless steel alloy are you referring to?  Most stainless steel alloys I've worked with are capable of having a magnetic field induced in them remotely.  Much like how magnetic mine detectors work.

     Proper radio frequencies, such as from many ground search radars, can likewise induce such magnetic fields, although briefly.

     Many times, when steel is heated to fairly high temperatures in a fire, a low level of magnetic field effect can and often is induced as well.

     Obviously, this won't detect all of the debris, but it may help in finding anything blown further away, say a quarter mile or so.

saw an interesting technique used for treasure hunting on a TV show recently - they were flying a drone with sensitive IR cameras onboard after dark, scanning the ground. metal heats up from the sun during the day, then cools off more slowly than the ground after sunset.

they were claiming to be able to find metal pieces under a foot or more of dirt. GPS tagging using the drone, then searching the location using hand held metal detectors.

[Steven Pietrobon]

The helium is not cooled before loading into the stage. The COPV tanks however are immersed in the very cold LOX, so the helium in the stage is colder and takes up less space.

That's news to me. When I hear "cryohelium loading" in the SpaceX webcasts I assumed the Helium was cryocooled before loading. My assumption is that the Helium is cooled to a similar temperature to the LOX. If not, I think it will take a long for the Helium to cool in the tanks.

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.

Helium that is the above critical point of 5.2 K and 226 kPa is supercritical. As supercooled LOX is at 66 K and a pressure of 34,000 kPa is more that 226 kPa, that means the Helium that SpaceX is using is supercritical, which means it is neither a gas or a liquid.

http://bbradu.web.cern.ch/bbradu/cryogenics.php

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?

After the first explosion, some or all of the COPVs could have exploded since they would have quickly warmed up from the fireball. If the Helium gas could not escape fast enough, these COPVs would explode. You can hear quite a few popping sounds after the main explosion. These could be the COPVs exploding. We know these popping sounds are not from the tank farm since SpaceX has said that the tank farm is in good condition. This could make determining if the initial explosion was caused by a COPV difficult.

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

The ignition source is most likely the kinetic energy of the exploding COPV if that was the cause of the failure. That should be high enough to ignite the mixture of LOX, Aluminium and carbon fibre that would be generated in the explosion.

[Jet Black]

After the first explosion, some or all of the COPVs could have exploded since they would have quickly warmed up from the fireball. If the Helium gas could not escape fast enough, these COPVs would explode. You can hear quite a few popping sounds after the main explosion. These could be the COPVs exploding. We know these popping sounds are not from the tank farm since SpaceX has said that the tank farm is in good condition. This could make determining if the initial explosion was caused by a COPV difficult.

What else could make such sounds? has anyone counted them?

[kevin-rf]

After the first explosion, some or all of the COPVs could have exploded since they would have quickly warmed up from the fireball. If the Helium gas could not escape fast enough, these COPVs would explode. You can hear quite a few popping sounds after the main explosion. These could be the COPVs exploding. We know these popping sounds are not from the tank farm since SpaceX has said that the tank farm is in good condition. This could make determining if the initial explosion was caused by a COPV difficult.

What else could make such sounds? has anyone counted them?

That assumes the tanks have shutoff valves in them and did not depressurize when the plumbing attached to them was destroyed.

[Herb Schaltegger]

After the first explosion, some or all of the COPVs could have exploded since they would have quickly warmed up from the fireball. If the Helium gas could not escape fast enough, these COPVs would explode. You can hear quite a few popping sounds after the main explosion. These could be the COPVs exploding. We know these popping sounds are not from the tank farm since SpaceX has said that the tank farm is in good condition. This could make determining if the initial explosion was caused by a COPV difficult.

What else could make such sounds? has anyone counted them?

That assumes the tanks have shutoff valves in them and did not depressurize when the plumbing attached to them was destroyed.

Even if the COPVs don't have shut offs or flow control orifices, flow rate of high pressure helium escaping from the plumbing will be choked at sonic for the fluid conditions. What's the speed of sound in cold helium?

Tl;dr - there might still be greater than ambient pressures inside one or more of the COPVs even after the system itself failed.

[spacekid]

Florida Today is reporting that SpaceX has requested Nov 17 on the Cape Canaveral range for a launch from pad 39A. It's for planning purposes but doesn't sound real serious. I suspect they'll use it to make sure they have everything ready and to test out GSE.

http://www.floridatoday.com/story/tech/science/space/2016/09/29/spacex-targeting-launch-ksc-soon-nov-17/91210636/

[Patchouli]

      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?

The only way I can see an explosion happening they way it did is if the common bulkhead failed first.

[warddw]

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'm not sure I agree with that assessment at all - if its a QA issue with a helium vessels we might be looking at the same sort of issue as was encountered on the strut. A logical next step will be to start looking at whatever vessels are on the shelf and perhaps doing a destructive test on some of them to insure they are in fact up to specification. Might be nothing wrong with the design - it may simply be part QA again. That would include all the parts associated with the tank...

[watermod]

saw an interesting technique used for treasure hunting on a TV show recently - they were flying a drone with sensitive IR cameras onboard after dark, scanning the ground. metal heats up from the sun during the day, then cools off more slowly than the ground after sunset.

they were claiming to be able to find metal pieces under a foot or more of dirt. GPS tagging using the drone, then searching the location using hand held metal detectors.

40+ years ago there was a farmer in central Nebraska tired of old iron working it's way (freeze thaw) through his long drive and puncturing his expensive tractor and implement tires.   He just made a giant electromagnet and bought a military surplus generator truck.   His magnet could pull old nails from out of 1 foot deep soil.  Every spring he would run it down his drive and get  a few pounds of old iron.   Much simpler than trying to ID pieces and dig for them.