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

[Patchouli]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?
Both of these may create more opportunities for small defects and leaks.

[jpo234]

It seems that sabotage is considered
https://www.washingtonpost.com/business/economy/implication-of-sabotage-adds-intrigue-to-spacex-investigation/2016/09/30/5bb60514-874c-11e6-a3ef-f35afb41797f_story.html

[guckyfan]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?
Both of these may create more opportunities for small defects and leaks.

We know no liner for sure. There are photos from inside. Autoclave-less is a quite safe bet at this size.

[Johnnyhinbos]

Wait, there's been endless conversation of liner separation, changing liner material, liner characteristics in cryo LOX, etc etc etc - and now it's said there isn't a liner?

Is this based on the pictures of the charred remains of a re-entered COPV recently making rounds? Do you have a picture or link you can share with definitive proof of this statement?

I'm just not a fan of statements such as, "we know for sure that..." Maybe YOU are sure of this, but I'm not. But am willing to be shown the proof and get on board the we train.

[Echium]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?
Both of these may create more opportunities for small defects and leaks.

We know no liner for sure. There are photos from inside. Autoclave-less is a quite safe bet at this size.

Very few COPV's are autoclaved, simple hot air is generally used for curing.  The thermal expansion of the metallic liner during the oven cure tensions the carbon fibers and consolidates the laminate.  CTE for the CF is almost zero. Sometimes (disposable) polymer shrink tape is used for additional compaction during the cure.  For polymer lined COPVs ('Type-4s'),  air pressure is used to stretch the liner to achieve the same effect as thermal expansion works for metallic liners ('Type 3s').  Linerless COPV's are 'Type 5''s and have the temporary mandrel washed out afterwards or pulled out if it is a bladder.  Linerless COPVs can be vulnerable to gas permeation and chemical attack from some pressurized / liquified gases.  Hence can be expensive / tricky to make perform successfully.

[Herb Schaltegger]

1.How does stress-fractured aluminum helium tank bleeding through a composite overwrap that is in another tank, much less immersed in LOX make such sound?

I described the sound as being similar to the rapid release of very high pressure through a fluted burst disk - I wouldn't expect the sound of such an event to survive for 4 km, so I am looking for something that might.

I have heard composite bottles burst many times ...

For all the folks new to NSF and these AMOS-6 threads, this tweet of Elon's and the sounds heard on the US Launch Report video have been discussed in nauseating detail. Please review the prior threads in two weeks after the incident for details. And as you do, please remember two things: #1) SpaceX has access to many more audio and video recordings of this incident from their own pad-area cameras than we do; #2) any sounds referred to by Elon in an abbreviated tweet are almost certainly NOT the same sound(s) recorded from 4km away by a private company.

[Jim]

"At this stage of the investigation, preliminary review of the data and debris suggests that a large breach in the cryogenic helium system of the second stage liquid oxygen tank took place. All plausible causes are being tracked in an extensive fault tree and carefully investigated. Through the fault tree and data review process, we have exonerated any connection with last year’s CRS-7 mishap."

cryogenic helium system>COPV.  There is much, much more to the system

[Jim]

but a diminishing screech only a few ms long is exactly what I would expect to see/hear in a very rapid decompression due to a filament wound bottle failure, regardless of the medium.
 

Not inside a liquid.  Anyways, the signature of that that would have been detected.  Since it hasn't been detect, that is not the cause, since they are still perplexed.

They had a COPV go on an earlier mission during tanking.

[Jim]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?

Then they are no longer CPOV's

[HMXHMX]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?
Both of these may create more opportunities for small defects and leaks.

We know no liner for sure. There are photos from inside. Autoclave-less is a quite safe bet at this size.

The tanks are designed by SpaceX, liner's supplied by SpaceX (aluminum) and over-wrapped by Cimarron Composites in Huntsville.  This is all public information: http://www.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

[Rocket Science]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?
Both of these may create more opportunities for small defects and leaks.

We know no liner for sure. There are photos from inside. Autoclave-less is a quite safe bet at this size.

The tanks are designed by SpaceX, liner's supplied by SpaceX (aluminum) and over-wrapped by Cimarron Composites in Huntsville.  This is all public information: http://www.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

"an aluminum liner about as thin as a soda can" Thank you for this information...

[Johnnyhinbos]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?

Then they are no longer CPOV's

That's interesting news Jim. Would you mind expanding? Maybe on L2?

[Kryten]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?

Then they are no longer CPOV's

That's interesting news Jim. Would you mind expanding? Maybe on L2?

I'm pretty sure he's just saying that if they didn't have liners, they wouldn't be COPVs. COPV=Carbon fibre Overwrapped Pressure Vessel; if there's no liner, nothing is overwrapped.

[Johnnyhinbos]

I wonder if they been manufacturing their COPVs with the new autoclave-less process and are they linerless as in there is no metal core?

Then they are no longer CPOV's

That's interesting news Jim. Would you mind expanding? Maybe on L2?

I'm pretty sure he's just saying that if they didn't have liners, they wouldn't be COPVs. COPV=Carbon fibre Overwrapped Pressure Vessel; off here's no liner, nothing is overwrapped.

Lol - yep, I didn't see the "then" part. Thanks.

[andy_l]

I don't like quoting my own posts, because it implies I believe they have credibility. As I have no expertise in the fields of composites, cryogenics or rocket propulsion, clearly they do not. However as this is a very long thread it is worth referring back once in a while.

Way back here https://forum.nasaspaceflight.com/index.php?topic=30981.msg1578155#msg1578155 I linked to a 2008 NASA Constellation study on cryo-immersed COPV's (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080009730.pdf). Later, I called out some pertinent points (and yes, I'm aware the test articles had a lower design MOP than SpaceX, and utilised LN2 for tests):

"The test articles will consist of vessels lined with Inconel 718 and Al-2219. Inconel 718 has been selected since it is LO2 compatible and it provides excellent corrosion resistance and provides good material fracture toughness at cryogenic temperatures.2 Al-2219 has been selected since it is lighter in weight and it can be used if the risk of exposure to LOX is acceptable based on the propulsion system design ... The 31-43B resin has been selected based on previous research and development work performed by ARDE’, Inc. The Toray T-1000 carbon fiber by Torayca has been selected since NASA plans to use it for the fabrication of the flight vessels."
...
Following are the test procedures to be performed on the series of test articles.

Ambient
1. Perform 2 proof pressure tests hydrostatically to 1.25 X MOP = 5625 psig.
2. Perform 100 pressure cycles from 0 to 4,500 psig with water.
3. Perform hydrostatic burst pressure tests using Digital Imaging Correlation (DIC) equipment to measure the strain as the pressure is increased to the rupture event.

Cryogenic
1. Perform 2 proof pressure tests to 1.25 X MOP = 5625 psig at -320°F where LN2 is in the COPV and GN2 is the pressurant.
2. Perform thermal cycle testing 5 times where the COPV is filled with and submerged in LN2 with no applied pressure.
3. Perform 100 pressure cycles charging to 4,500 psig at -320°F using LN2 where GN2 is the pressurant while the COPV is submerged in LN2.
4. Perform burst pressure tests with LN2 at -320°F.
...
These results for the burst tests for both Inconel 718 and Al-2219 show that the minimum burst pressure was met where the smallest burst pressure is 2.36 X MOP or 10,620 psig for the cryogenic burst tests of Inconel 718. Comparisons of the Al-2219 versus the Inconel 718 show that the Al-2219 provided higher burst pressures at a lower vessel weight than the Inconel 718. The Al-2219 vessels have more overwrap due to the reduced tensile strength of Al-2219 but the results show that Al-2219 can provide the required burst pressures after proof tests, pressure cycles and thermal cycles.
...
The remaining risk for COPVs that needs to be tested regards stress rupture life at cryogenic conditions.

For Kevlar® COPVs, the manufacturer can compute the stress rupture reliability using a Weibull model because a large, robust database exists. Un- fortunately, as of the writing of this paper, there is not a similar database for carbon. Two NASA independent stress rupture test programs are currently under way that should provide additional data availability in 2013 for analysis. Until that time, the NESC and JSC Engineering recommend that the carbon fiber strain remain at or below 50% of the ultimate strength. Based on industry- wide experience, the risk of stress rupture at a strain ratio of 50% is minimal for short-duration space missions.

Given the short lifespan of the second stage, stress rupture is probably a failure mode of more relevance to the first stage vehicle. Nevertheless, by now the White Sands long-term carbon COPV test programme should have produced significant stress rupture data on these types of vessels. Therefore whilst SpaceX might be the only company flying cryo-immersed COPV's, there is recent analytical and empirical data on this application - they are not 'flying blind'.

There is significant interest in the COPV's on this thread - understandably so - however as Jim keeps pointing out, they are only one of the many components that form the He system.

[ZachS09]

Cross-posting from AMOS 6 Update Thread:

https://www.washingtonpost.com/business/economy/implication-of-sabotage-adds-intrigue-to-spacex-investigation/2016/09/30/5bb60514-874c-11e6-a3ef-f35afb41797f_story.html

[Jim]

Grasping for straws comes to mind

[SWGlassPit]

I think the implication is all the Post's. Really irresponsible journalism for how much respect the paper gets...

[pobermanns]

It seems that sabotage is seriously considered
https://www.washingtonpost.com/business/economy/implication-of-sabotage-adds-intrigue-to-spacex-investigation/2016/09/30/5bb60514-874c-11e6-a3ef-f35afb41797f_story.html

It seems incredible that someone might try to sabotage a rocket, especially on the Cape Canaveral launch complex. Maybe there will be a simple cause found; from my background in Naval Aviation, I could cite various examples where strange accidents were ultimately explained by obscure causes. So, probably the idea of sabotage as the cause of the AMOS-6 explosion is just BS.

BUT, what if it's not?

[kevin-rf]

Can we keep the conspiracy posts, even if they come from SpaceX on the conspiracy thread?

That said, aliens