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

[yg1968]

No, they are not changing how they load LOX but how they load the helium.   They are just going to load it slower.

What tradeoff(s) are associated with varying he loading times?   

Was shorter he load part of an effort to be get back to having multiple shots in a ~1hr launch window (while retaining super-densified prop)?   

Window management apparently. See below:

Yes but there is also this part:  "as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads."

What does this mean?

They were apparently testing a new, faster loading procedure.

It is also understood that SpaceX was testing modifications to the countdown sequence on the Static Fire Test for the previous Falcon 9 mission with JCSat-16 to introduce window management capabilities for the FT version of Falcon 9 that initially had to launch very shortly after propellant loading finished in order to avoid the chilled propellants warming up inside the tanks.

[Oersted]

Does anyone have an idea what size buckling we are talking about? Fractions of millimeters? Millimeters? Centimeters?

The COPV's (and their attachments) have truly been nefarious for SpaceX. Hope they won't step into such troublesome technology choices in the future.

Anyway, we should be thankful this was discovered now, before it would have caused loss of life.

[RDoc]

Does anyone have an idea what size buckling we are talking about? Fractions of millimeters? Millimeters? Centimeters?

The COPV's (and their attachments) have truly been nefarious for SpaceX. Hope they won't step into such troublesome technology choices in the future.

Anyway, we should be thankful this was discovered now, before it would have caused loss of life.

Also, what caused the buckling? Presumably it was some compression force on the liner which sounds like it may be contraction of the overwrap. That sounds like the underlying problem.

[HMXHMX]

Does anyone have an idea what size buckling we are talking about? Fractions of millimeters? Millimeters? Centimeters?

The COPV's (and their attachments) have truly been nefarious for SpaceX. Hope they won't step into such troublesome technology choices in the future.

Anyway, we should be thankful this was discovered now, before it would have caused loss of life.

Also, what caused the buckling? Presumably it was some compression force on the liner which sounds like it may be contraction of the overwrap. That sounds like the underlying problem.

The CTE of the liner and the overwrap are grossly mismatched.  Aluminum shrinks away from the overwrap as temperatures drop.  Steel liners would have less of a problem, but I understand Elon decided he didn't want to use them due to cost and weight.

[Robotbeat]

Is linerless an option?

[HMXHMX]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

Indeed.  Perhaps out of scope for this thread, but certainly related, since warm/hot GOX and their current composite materials are not a good combination.  There are ways to make that work but to my knowledge they are not implementing them.

What would you suggest they do?

I charge for engineering solutions.    Though I have hinted at possible remedial actions in prior posts.

[HMXHMX]

SpaceX said the following" The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations.​"  You feel there is more that can/should be done?  Would these changes be short/long term and what would be the affect on operations/cost, etc?

I expect "long term", means moving COPV production in-house.

They already do COPV production in-house.  And they make all the liners for the outside vendor. That's part of the problem.

[CriX]

So an ignition of the carbon or perhaps the aluminum created the rupture?  Why the subsequent fireball?  I would think the LOX hose would maybe just pop off the rocket or something.  I guess we assume there was a microdetonation which caused the COPV to fail like popping a balloon and the shock from this ruptured both the the kerosene and lox tanks which allowed the fireball.  I'm trying to trace the path to the kerosene.

[shooter6947]

So an ignition of the carbon or perhaps the aluminum created the rupture?  Why the subsequent fireball?  I would think the LOX hose would maybe just pop off the rocket or something.  I guess we assume there was a microdetonation which caused the COPV to fail like popping a balloon and the shock from this ruptured both the the kerosene and lox tanks which allowed the fireball.  I'm trying to trace the path to the kerosene.

Once the COPV's rupture, then the total pressure inside the LOX tank skyrockets.  The LOX tank fails, sending shards out in every direction at high speed.  One of these punctures the fuel tank, leading to its failure. Maybe.

[HIP2BSQRE]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

Indeed.  Perhaps out of scope for this thread, but certainly related, since warm/hot GOX and their current composite materials are not a good combination.  There are ways to make that work but to my knowledge they are not implementing them.

What would you suggest they do?

I charge for engineering solutions.    Though I have hinted at possible remedial actions in prior posts.

Even if you charge for engineering solutions and the cost is $10,000, is that not peanuts compared to the potential cost of a rocket and the lost revenue?  Approx. how much is the weight penalty  and cost of using steel bottles? Have you offered your services to SpaceX?

[jpo234]

YouTube video explaining what happened:

[HMXHMX]

I can't seem to successfully reply to message #1209 for some reason.  So here's the response without quotes:

"Even if you charge for engineering solutions and the cost is $10,000, is that not peanuts compared to the potential cost of a rocket and the lost revenue?  Approx. how much is the weight penalty  and cost of using steel bottles? Have you offered your services to SpaceX?"

Yes.  Small, on the order of a hundred pounds mass.  No.

[HIP2BSQRE]

I can't seem to successfully reply to message #1209 for some reason.  So here's the response without quotes:

"Even if you charge for engineering solutions and the cost is $10,000, is that not peanuts compared to the potential cost of a rocket and the lost revenue?  Approx. how much is the weight penalty  and cost of using steel bottles? Have you offered your services to SpaceX?"

Yes.  Small, on the order of a hundred pounds mass.  No.

You don't think SpaceX will take the weight penalty? Would it make it safer or just introduce another area of risk?  I hope that you offer your services at some point.   

[dglow]

If this has been addressed elsewhere in this thread, apologies in advance. Pointers to previous posts are welcome.

With the AMOS explanation now official I find myself wondering whether, and for whom, this may change the thinking about CRS-7. The strut-as-culprit rationale is, of course, very different than that presented for AMOS. COPVs are a common thread in both of these incidents, as well as another on-pad incident (discussed here).

Let me pose a specific question: do we think the use of densified LOX is a requisite for the AMOS failure or merely a contributing factor?

I recall that Elon hit the 'Solidified oxygen, OMG!' note hard in his personal communication following the event. By contrast today's anomaly update casts it more as a contributing factor which may have 'exacerbated' already existing conditions.

Is it possible that some of the COPV issues discovered with AMOS also contributed to CRS-7?

[launchwatcher]

If this has been addressed elsewhere in this thread, apologies in advance. Pointers to previous posts are welcome.

With the AMOS explanation now official I find myself wondering whether, and for whom, this may change the thinking about CRS-7. The strut-as-culprit rationale is, of course, very different than that presented for AMOS. COPVs are a common thread in both of these incidents, as well as another on-pad incident (discussed here).

Let me pose a specific question: do we think the use of densified LOX is a requisite for the AMOS failure or merely a contributing factor?

I recall that Elon hit the 'Solidified oxygen, OMG!' note hard in his personal communication following the event. By contrast today's anomaly update casts it more as a contributing factor which may have 'exacerbated' already existing conditions.

Is it possible that some of the COPV issues discovered with AMOS also contributed to CRS-7?

An alternate failure analysis for CRS-7 would have to include an alternate explanation for this:

The telemetry data also, somewhat confusingly, shows a drop in the helium pressure system, which you would expect if there was a breach in the helium system, and then, somewhat strangely, a rise in the helium system back to approximately its starting pressure. This is obviously quite confusing, but we think what may have happened is that as the helium bottle broke free and twisted around it may have pinched off the line to the helium manifold and restored pressure in the helium system, but released enough helium into the liquid oxygen tank to cause the liquid oxygen tank to fail. This is somewhat speculative, but that's the best explanation we can think of right now. So it's a really odd failure mode.

(Source: http://shitelonsays.com/transcript/elon-musk-talks-failed-crs-7-dragon-mission-2015-07-20 )

[Jim]

So an ignition of the carbon or perhaps the aluminum created the rupture?  Why the subsequent fireball?  I would think the LOX hose would maybe just pop off the rocket or something.  I guess we assume there was a microdetonation which caused the COPV to fail like popping a balloon and the shock from this ruptured both the the kerosene and lox tanks which allowed the fireball.  I'm trying to trace the path to the kerosene.

Its not hard. The LOX and kerosene tanks share a common bulkhead.  Also, it is not the shock of the COPV, it is the pressure from its contents that ruptured the tank

[Jim]

Is linerless an option?

No, can't hold He.

[Fred Bonyea]

Is it possible that some of the COPV issues discovered with AMOS also contributed to CRS-7?

From the article:

"Specifically, the investigation team concluded the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner, leading to ignition and the subsequent failure of the COPV,” added SpaceX."

Assuming this is very carefully worded, they suspect either a void or a buckle. So the challenge is to avoid rapid pressure changes where expanding O2 could rip apart the case in a shear zone, like a phone book.

Also in the article:

 "In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations. ”

This likely means that not everyone involved in the investigation is satisfied that returning to the slower, less-chilled loading cycle will eliminate all failure modes for the COPV; but there have been enough successful bottles  to continue launching with the existing system until a redesign can be implemented.

If I were wearing SpaceX shoes, I would make the same choice, but it is not without risk -and Yes, there could be a common bottle failure mode underlying both the pad mission failures: Hence, the redesign.

[Steven Pietrobon]

A way to avoid the SOX problem alltogether is to use liquid Helium in an external bottle, like what Arianespace do for Ariane 5. That should also be a much lighter solution as well as providing more propellant volume. I'm surprised SpaceX did not choose to do this. I think any plan that loads Helium at below the freezing point of LOX is just asking for trouble.

[kevinof]

Agreed but do they have the room in the S2 to mount the bottles externally? Would appear to be a better and safer solution but only if they don't have to stretch the stack any more.

A way to avoid the SOX problem alltogether is to use liquid Helium in an external bottle, like what Arianespace do for Ariane 5. That should also be a much lighter solution as well as providing more propellant volume. I'm surprised SpaceX did not choose to do this. I think any plan that loads Helium at below the freezing point of LOX is just asking for trouble.