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

[RDoc]

In past technical broadcasts you can hear SpaceX calling our "cryohelium loading" during the count. I don't know what temperature the cryohelium is at though. If the cryohelium was below the LOX freezing point, that might be a contributing factor to oxygen crystals forming.

Interesting comment.

Perhaps the He loading temperature was at or near the O2 loading temp, ie near freezing. However, if the supply line to the COPV was small enough and the loading pressure high enough, the initial He loading into a nearly empty tank might expand enough to lower its temp below the freezing point of O2 in the COPV overwrap. Then, perhaps the whole failure scenario played out too rapidly for the subsequent He loading to pressurize the tank enough to start dumping heat through the walls to thaw the O2.

[RDoc]

Nitrogen has a lower freezing point than Oxygen.

-210degC is lower than -218degC?  Really?? 

Agh, you're right, I read the table wrong, sorry.

[Fred Bonyea]

Perhaps the He loading temperature was at or near the O2 loading temp, ie near freezing. However, if the supply line to the COPV was small enough and the loading pressure high enough, the initial He loading into a nearly empty tank might expand enough to lower its temp below the freezing point of O2 in the COPV overwrap. Then, perhaps the whole failure scenario played out too rapidly for the subsequent He loading to pressurize the tank enough to start dumping heat through the walls to thaw the O2.

This certainly fits Elon's "When you have eliminated the probables, you have to start looking and the improbables' statement.

Whenever you move gases across high pressure gradients, there can be rapid cooling and/or rapid heating. I have seen valves freeze and crack during venting, I have seen high pressure nitrogen vented into a line with atmospheric gases (and valve grease) in it, and cause a diesel explosion: -40deg C at one end of the line, and over 250 deg C at the other!

[Jet Black]

Well very sad to hear my initial thinking was correct. Material failure due to intrusion/delam as a result of operational errors, more likely design failure due to overstress as a result of operational mistakes.


Basically the worst case for spacex this justifies most of the criticisms recently levied against them specifically that their lower cost access approach is resulting in unintended higher risks to payloads and flight rationale.

That said it's entirely fixable, but it will be harder than just changing a few parts out. Gotta change the methodology.

Nothing here is correct until SpaceX confirms it. Since all SpaceX have said is that they have some suspicions and are narrowing things down, it's much too early to be claiming anything, especially a design fault (since they have over 20 successful launches that did not show the issue and the design is the same)

There haven't been 20 launches with subcooled LOX.

[JamesH65]

Well very sad to hear my initial thinking was correct. Material failure due to intrusion/delam as a result of operational errors, more likely design failure due to overstress as a result of operational mistakes.


Basically the worst case for spacex this justifies most of the criticisms recently levied against them specifically that their lower cost access approach is resulting in unintended higher risks to payloads and flight rationale.

That said it's entirely fixable, but it will be harder than just changing a few parts out. Gotta change the methodology.

Nothing here is correct until SpaceX confirms it. Since all SpaceX have said is that they have some suspicions and are narrowing things down, it's much too early to be claiming anything, especially a design fault (since they have over 20 successful launches that did not show the issue and the design is the same)

There haven't been 20 launches with subcooled LOX.

True, but there have been over 20 launches with this design(as far as we know). So, possibly not a design fault, but perhaps the wrong design. But I'll wait for SpaceX to determine cause before claiming anything concrete.

[spacekid]

could they put the whole COPV inside of another aluminum cylinder with some nitrogen in the space between?

To do this, you'd not only be increasing weight (the cylinder) but have issues with maintaining nitrogen supply and associated plumbing and then there's the possibility of the nitrogen freezing..

A vacuum bottle with an internal oxygen alarm sensor might be a better idea.

This whole line of thought would be a typical trade off performed. You add one thing to prevent something and it can cause other problems (added weight or other failure mechanisms).

Usually engineers want to go with the simpler method because you have to produce it, analyze it and test it. Also previous history of designs provides additional confidence although changing that previous design would counter some of that previous experience. When problems creep up, you try to deal with it making the smallest alteration you can. When you do that a lot to a design, it's usually time for a better overall design.

Any modification done now would require re-qualification and the more divergent, the longer the qualification. Trying something that's never been done before would undoubtedly take years to get comfortable with.

[gongora]

SpaceNews: SpaceX’s Musk says sabotage unlikely cause of Sept. 1 explosion, but still a worry

New article on SpaceNews talks about the comments we saw from Reddit that were attributed to Musk speaking at the NRO, and also has a lengthy discussion about the COPV's.

[Semmel]

Very interesting article. The part about COPV's comes from a very knowledgeable person with lots of experience in the field. Sounds almost like HMXHMX.

[Jim]

Well very sad to hear my initial thinking was correct. Material failure due to intrusion/delam as a result of operational errors, more likely design failure due to overstress as a result of operational mistakes.


Basically the worst case for spacex this justifies most of the criticisms recently levied against them specifically that their lower cost access approach is resulting in unintended higher risks to payloads and flight rationale.

That said it's entirely fixable, but it will be harder than just changing a few parts out. Gotta change the methodology.

Nothing here is correct until SpaceX confirms it. Since all SpaceX have said is that they have some suspicions and are narrowing things down, it's much too early to be claiming anything, especially a design fault (since they have over 20 successful launches that did not show the issue and the design is the same)

There haven't been 20 launches with subcooled LOX.

True, but there have been over 20 launches with this design(as far as we know). So, possibly not a design fault, but perhaps the wrong design. But I'll wait for SpaceX to determine cause before claiming anything concrete.

Nor 20 since the last accident and there have been changes

[HMXHMX]

Very interesting article. The part about COPV's comes from a very knowledgeable person with lots of experience in the field. Sounds almost like HMXHMX.

Just to go on the record, it wasn't me.  But I pretty much agree with what the anonymous interviewee said.

[HVM]

That was awful article, with reddit rumors and 'anonymous-experts', blah.
Total hack job even for SpaceNews standard. More close to ParabolicArc...

[Comga]

HMV =X= HMXHMX /2

That was awful article, with reddit rumors and 'anonymous-experts', blah.
Total hack job even for SpaceNews standard. More close to ParabolicArc...

Did you consider the expert opinion of the post immediately preceding yours?

Very interesting article. The part about COPV's comes from a very knowledgeable person with lots of experience in the field. Sounds almost like HMXHMX.

Just to go on the record, it wasn't me.  But I pretty much agree with what the anonymous interviewee said.

[Fred Bonyea]

That was awful article, with reddit rumors and 'anonymous-experts', blah.
Total hack job even for SpaceNews standard. More close to ParabolicArc...

I have a LOT of experience in the field, and although speculative, (since the public fault tree is still very large) it is an excellent essay on composite bottle failure modes.

I am a little troubled by the statement by Shotwell: “The more than likely — the overwhelmingly likely — explanation is that we did something to that rocket,” Shotwell said. “And we’re going to find it and we’re going to fix it.”

Oh?  You don't know the root cause, you haven't reproduced the failure mode, and you yet you feel you can assign a probability to the likelihood of an operational *mistake* rather than a design problem? This contradicts Elon's statement that the usual suspects have been eliminated and that now they must look for something unexpected. Yes, it may be as simple as changing the fueling sequence; but unless and until testing confirms this, it is premature to assign probabilities.

[1]

I am a little troubled by the statement by Shotwell: “The more than likely — the overwhelmingly likely — explanation is that we did something to that rocket,” Shotwell said. “And we’re going to find it and we’re going to fix it.”

Be fair. Shotwell was directly answering a question pertaining to the probability of sabotage vs something happening on their own end. From:
http://spacenews.com/spacexs-shotwell-on-falcon-9-inquiry-discounts-for-reused-rockets-and-silicon-valleys-test-and-fail-ethos/

Could you address a recent story that SpaceX suspected that a nefarious actor might have been a contributor to the Sept. 1 failure? I know you can’t eliminate anything in an inquiry, but…

That’s right: You cannot eliminate anything, especially if there are some data points that say it’s possible, but not likely. The more than likely — the overwhelmingly likely — explanation is that we did something to that rocket. And we’re going to find it and we’re going to fix it.

Not that you're wrong about premature statements in general, but Gwynne and Elon were addressing two different audiences in two different locations at two different times.

[Fred Bonyea]

Be fair. Shotwell was directly answering a question pertaining to the probability of sabotage vs something happening on their own end. From:
http://spacenews.com/spacexs-shotwell-on-falcon-9-inquiry-discounts-for-reused-rockets-and-silicon-valleys-test-and-fail-ethos/.

Yes, in this context, she was taking responsibility for the failure. My bad.

[woods170]

Be fair. Shotwell was directly answering a question pertaining to the probability of sabotage vs something happening on their own end. From:
http://spacenews.com/spacexs-shotwell-on-falcon-9-inquiry-discounts-for-reused-rockets-and-silicon-valleys-test-and-fail-ethos/.

Yes, in this context, she was taking responsibility for the failure. My bad.

Yup, context.

Or: the difference between a meal and a road-kill.

(From HBO's "From the Earth to the Moon")

[docmordrid]

Road kill can be free food it you retrieve it quick enough

[CyndyC]

http://www.waff.com/story/26340259/explosion-sends-metal-flying-at-cimarron-in-huntsville  (August 21, 2014)

A Cimarron employee said they had performed the procedure hundreds of times before.

[CyndyC]

http://m.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

(July 14, 2016) Their main product are the helium tanks used on SpaceX's Falcon 9 rocket, the one that made headlines when it landed its booster stage after launching a payload.

[docmordrid]

http://www.cimarroncomposites.com