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

[Steven Pietrobon]

Tanks are pressurized at more than 1 atm, let's say 3 atm, so you need 3x helium more than you counted. 350 liters instead of 113.

The pressure can vary quite a bit. The Saturn V used a pressure of about 175 kPa in the first stage, 300 kPa in the S-II LH2 tank, 380 kPa in the S-II LOX tank, 320 kPa in the S-IVB LH2 tank and 400 kPa in the S-IVB LOX tank (information from Apollo 14 Flight Evaluation Report). This variation may have to do with the inlet pressures required for the engines. Since the F-1 and M-1D are both kerolox gas generator cycle engines, perhaps only 175 kPa is required. That increases the required volume by only 75%, to say 200 L. That requires a tank 0.726 m in diameter. That should still be able to fit at the base of the second stage, which is 3.66 m in diameter.

Liquid helium tank is neither small nor lightweight. See specs here http://www.cryofab.com/products/spec_sheets/Cryofab_CMSH_Series_Specs_350.pdf

That's a ground based tank where there is no need to save mass. Flight tanks can be made much lighter. Here's a superfluid Helium tank that can hold 1332 L and which weighs only 224 kg. A 200 L tank could weight about 40 kg.

http://www.airliquideadvancedtechnologies.com/en/our-offer/space/flight-equipment-for-storage/liquid-helium-tanks.html

[CameronD]

COPV's seem to (generally speaking) survive re-entry often enough.. what are the changes they'd survive this fire relatively intact?  Could SpX reasonably expect to find fragments of a failed COPV in the wreckage.. or at least account for those that didn't fail??

[woods170]

If it was a COPV, don't you think Spacex would have come forward with that vs just He system?

COPV is not ruled out at this point. SpaceX simply stated that a large breach in the cryogenic helium system has apparently occurred. As to what the cause of this breach is, or what part of the cryogenic helium system actually breached, is publically unknown at this time. (see their latest anomaly update) So, COPV is not off the hook at this time. Neither is is the rest of the cryogenic helium system.

"I'm not saying it was the COPV, but it was the COPV".  ;-)

[Stranger]

If it was a COPV, don't you think Spacex would have come forward with that vs just He system?

They might like to know a bit more about the event first.  eg. If it was a COPV, did it explode or implode?  There's a big difference in root cause but a similar outcome.

COPV's is not going to implode.

Under any conditions?  Faulty weld + brittle fracture? High/sudden pressure differential/pressure shock??

Okay... if Jim says so it must be true.   

imho, Jim denies that COPV exploded by itself, but it does not negate the fact that COPV could be destroyed, and this has led to an explosion

[Stranger]

If it was a COPV, don't you think Spacex would have come forward with that vs just He system?

COPV is not ruled out at this point. SpaceX simply stated that a large breach in the cryogenic helium system has apparently occurred. As to what the cause of this breach is, or what part of the cryogenic helium system actually breached, is publically unknown at this time. (see their latest anomaly update) So, COPV is not off the hook at this time. Neither is is the rest of the cryogenic helium system.

"I'm not saying it was the COPV, but it was the COPV".  ;-)

in 2015  broke fasteners COPV
in 2016 COPV  jumped from durable fasteners in place of the weld, IMHO

[Rocket Science]

I would just like to make a point about various opinions about SpaceX's approach to it's LVs. IIRC they stated that Falcon was designed from the onset to be a "human rated" vehicle, thus from my perspective one should hold their feet to the fire to the standards they set for themselves... 2017 is not that far away for there to be "unknown, unknowns" for a vehicle to begin tests with crew aboard IMHO... Years back I stated that "I would strap my back onto an Atlas V today" given the chance to fly. Nothing has changed my opinion so far...

If only a launch vehicle was all that was needed.

So what's your point, because they have to design Dragon as well? No point talking about landing of Mars if you can't get to orbit reliably much less off the pad. If you want to play in the "big leagues" you have to put on and "wear the big boy" pants... Years ago on a thread titled "Who will compete with SpaceX" I said "SpaceX" because they may become a victim of there own success taking on too much too fast, spreading themselves too thin...Their wounds are self-inflicted...

[Alastor]

COPV's seem to (generally speaking) survive re-entry often enough.. what are the changes they'd survive this fire relatively intact?  Could SpX reasonably expect to find fragments of a failed COPV in the wreckage.. or at least account for those that didn't fail??

Given the energy of the reentries they survive, it is very likely that they found COPVs as part of the wreckage. Either intact or damaged.

If they found damaged COPVs, that wouldn't mean that they are part of the root cause of course.
On the other hand, if they found all of them intact, that would definitely rule them out.

[Rocket Science]

COPV's seem to (generally speaking) survive re-entry often enough.. what are the changes they'd survive this fire relatively intact?  Could SpX reasonably expect to find fragments of a failed COPV in the wreckage.. or at least account for those that didn't fail??

Given the energy of the reentries they survive, it is very likely that they found COPVs as part of the wreckage. Either intact or damaged.

If they found damaged COPVs, that wouldn't mean that they are part of the root cause of course.
On the other hand, if they found all of them intact, that would definitely rule them out.

Yeah, the problem seems to be keeping them "in" the LV  from pad to orbit, intact or otherwise... Just sayin'...

[Mike_1179]

in 2015  broke fasteners COPV
in 2016 COPV  jumped from durable fasteners in place of the weld, IMHO

In 2015, the COPV strut failed when the buoyancy forces due to acceleration exceeded what it could hold. This was not found in ground firings because there was not the additional forces from 3G acceleration at that time.

For AMOS-6, there were no additional forces on the stage and its internals that were not present in the static fire at McGregor. So, why did that fastener hold for a full-duration firing at McGregor but failed early in the filling at LC-40?   

[Stranger]

in 2015  broke fasteners COPV
in 2016 COPV  jumped from durable fasteners in place of the weld, IMHO

In 2015, the COPV strut failed when the buoyancy forces due to acceleration exceeded what it could hold. This was not found in ground firings because there was not the additional forces from 3G acceleration at that time.

For AMOS-6, there were no additional forces on the stage and its internals that were not present in the static fire at McGregor. So, why did that fastener hold for a full-duration firing at McGregor but failed early in the filling at LC-40?

thanks for the answer to the beginner

imho, different charging rate LOX in McGregor and LC-40. On the LC-40 refueled faster

[Wolfram66]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

[Mike_1179]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

And this right here is one of the big things we miss from shuttle days. Private companies have no reason to release proprietary information like this, while back in shuttle days these sorts of diagrams, schematics, hi-res images from assembly in Palmdale, high res close-out photos from the Orbiter Processing Facility (all within the confines of ITAR) could be shared here, in L2 and then in an article for the site.

Not complaining, I love that we do get to share in this and have serious discussion about the technical aspects of spaceflight, it's just different with commercial providers.

That being said, I think it's pretty unlikely that anyone here has a schematic of the He system for Falcon. If they did, it's because they work for SpaceX and sharing it publicly would be frowned upon.

[Jim]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

 There are no such schematics publicly available, there are ITAR and propriety issues.
And, it isn't cryogenic, just high pressure.

[Wolfram66]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

 There are no such schematics publicly available, there are ITAR and propriety issues.
And, it isn't cryogenic, just high pressure.

Quoting SpaceX official statement: http://www.spacex.com/news/2016/09/01/anomaly-updates
"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. "

Are you saying that SpaceX doesn't know what systems are used in their OWN rockets?

[Mike_1179]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

 There are no such schematics publicly available, there are ITAR and propriety issues.
And, it isn't cryogenic, just high pressure.

Quoting SpaceX official statement: http://www.spacex.com/news/2016/09/01/anomaly-updates
"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. "

Are you saying that SpaceX doesn't know what systems are used in their OWN rockets?

The LOX they load into the vehicle is cryogenic - it is held at cold temperatures and loaded in cold.

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.

Jim is very correctly stating that they don't load cold helium into the stage - it is not stored in insulated spheres at the pad like LOX, it is stored in those small diameter pressure tubes we've talked about so much lately under ambient temperatures.

[jpo234]

Does anyone have a schematic of the cryogenic helium system on the S2, from the GSE->TEL->S2->LOX tank-> COPV?
Thanks in advance

 There are no such schematics publicly available, there are ITAR and propriety issues.
And, it isn't cryogenic, just high pressure.

Quoting SpaceX official statement: http://www.spacex.com/news/2016/09/01/anomaly-updates
"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. "

Are you saying that SpaceX doesn't know what systems are used in their OWN rockets?

This is what I think is going on:
Jim: Cryogenic = liquid helium
SpaceX: Cryogenic = Submerged in super cooled LOX

[rsdavis9]

Anybody think that they loaded warm helium too fast might be part of the problem? Maybe the copv's were so hot that they vigorously boiled the lox...

[Mike_1179]

Anybody think that they loaded warm helium too fast might be part of the problem? Maybe the copv's were so hot that they vigorously boiled the lox...

That is some of the discussion around was it a (1) problem in the stage or a (2) problem in the GSE that caused the stage to fail.

The GSE is different for each site and the GSE at LC-40 is now destroyed. If the telemetry they recovered does not rule something like what you described out, then it would be likely that aspects of filling would be tested in McGregor to see if there are similar signatures to what they saw in LC-40.

However, there are more factors to consider beyond flow rate of He; that's what the investigation is likely doing - identify potential failure modes that can be supported by the data they have in hand, get data to rule out some assignable causes, repeat.

[mfck]

...

No point talking about landing of Mars if you can't get to orbit reliably much less off the pad.

This is just an empty rhetoric, sorry

If you want to play in the "big leagues" you have to put on and "wear the big boy" pants...

EM does not want to play the "big leagues". He will play there only as long as he has to, which is not long now. He's in the business of building his own league. Look at ULA trying to redesign their pants to fit their shortened legs :-)

[Pete]

Anybody think that they loaded warm helium too fast might be part of the problem? Maybe the copv's were so hot that they vigorously boiled the lox...

Considering that the COPVs, the helium in them, and the whole aluminium LOX tank starts at more-or-less ambient temperature, **of course** the lox will vigorously boil when contacting it. There is a temperature difference of some 200K between the boiling point of LOX and the container you are putting it in.

This is normal.
This is expected.
This is ludicrously unlikely to be the cause of failure.