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

[RotoSequence]

I'll take that bet.  I'm equally confident they will fix what they've got, not throw it out and try something completely different and lower-performance.

My personal take would be to eat the performance penalty from doubling their weight to gain simplicity in manufacturing on an expendable upper stage and simply dispense with some catastrophic failure modes altogether. Two launch vehicle failures in two years from the same systems family doesn't seem worth it.

[Negan]

Seems to me one sliver of silver lining in this happening now. SpaceX has unequivocally stated this incident has no relation CRS-7, but people seem almost desperate to dispute that finding. I could see the same thing happening with a reused stage. There would be tons of theories and innuendo on the forums and in the media trying to link it to the cause of the accident.

[Herb Schaltegger]

I'll take that bet.  I'm equally confident they will fix what they've got, not throw it out and try something completely different and lower-performance.

I agree they'll fix what they've got (especially since they're still not certain of the actual root cause (the proximate cause they know - a failure of the LOX pressurization system involving the helium subsystem). They don't yet know what caused the helium system itself to fail.

That said, IF they rule out GSE as a proximate cause, I think whatever fix(es) they apply will almost necessarily eat into performance. That said, the hit might well be a few tens of kilograms rather than a major fraction of the payload capability.

[NaN]

I'll take that bet.  I'm equally confident they will fix what they've got, not throw it out and try something completely different and lower-performance.

My personal take would be to eat the performance penalty from doubling their weight to gain simplicity in manufacturing on an expendable upper stage and simply dispense with some catastrophic failure modes altogether. Two launch vehicle failures in two years from the same systems family doesn't seem worth it.

A redesign comes with its own set of new risks, perhaps more than you would retire with your old design which has, by this point, significant testing and flight heritage. Two launch failures in two years are water under the drawbridge, all that matters is future risk.

[RotoSequence]

A redesign comes with its own set of new risks, perhaps more than you would retire with your old design which has, by this point, significant testing and flight heritage. Two launch failures in two years are water under the drawbridge, all that matters is future risk.

While true, all-metal tanks are well understood systems in cryogenic environments, and can be pressure tested below their yield strengths an indefinite number of times. COPVs still have at least one catastrophic failure mode without an identifiable root cause, if I recall correctly?

[yokem55]

What about moving the common bulkhead up by the volume of the COPVs in the LOX tank and putting all the COPVs in the RP1?

Part of the point of putting the helium in the lox tank is that it reduces the helium's temperature and increases its density at a given pressure. In the RP1 tank, it wouldn't be as cold, so they would need more bottles to get the same amount of helium to backfill the stage.

[NaN]

A redesign comes with its own set of new risks, perhaps more than you would retire with your old design which has, by this point, significant testing and flight heritage. Two launch failures in two years are water under the drawbridge, all that matters is future risk.

While true, all-metal tanks are well understood systems in cryogenic environments, and can be pressure tested below their yield strengths an indefinite number of times. COPVs still have at least one catastrophic failure mode without an identifiable root cause, if I recall correctly?

Ah, I thought you were talking about moving the entire helium system outside the propellant tanks as others were, which would be a major change. Still, SpaceX were aware of COPV characteristics when they made their design decision. If a COPV was at fault this time, and they're not confident they can identify cause and prevent a recurrence, switching the tank design would certainly have to be on the table. But they would have to be pushed into such a change by the investigation, IMO.

[AncientU]

I'll take that bet.  I'm equally confident they will fix what they've got, not throw it out and try something completely different and lower-performance.

I agree they'll fix what they've got (especially since they're still not certain of the actual root cause (the proximate cause they know - a failure of the LOX pressurization system involving the helium subsystem). They don't yet know what caused the helium system itself to fail.

That said, IF they rule out GSE as a proximate cause, I think whatever fix(es) they apply will almost necessarily eat into performance. That said, the hit might well be a few tens of kilograms rather than a major fraction of the payload capability.

There are failure mechanisms that require zero hardware change on the vehicle... last thing you want to do is start Easter-egging the solution (changing something that might be a cause of the problem, but with perfect knowledge would be understood to not have been the problem).  This not only leaves the real issue untouched, but introduces new variables into the situation.

Too rapid of pressurization, for instance, could have caused excessive vibration, as could excessive boiling of LOX from rapid heating.  Liquid in the system could cause water hammer. Oils in an oxygenated system could result in diesel effect which could detonate affected lines/tanks when rapidly pressurized (submariners know this one well -- it sunk several boats before being fully understood).  Any of these issues would require procedural changes or minor modifications such as flow-limiting orifices.

Best to dive deep enough to ID the root cause before anything is changed.

[alang]

I'll take that bet.  I'm equally confident they will fix what they've got, not throw it out and try something completely different and lower-performance.

I agree they'll fix what they've got (especially since they're still not certain of the actual root cause (the proximate cause they know - a failure of the LOX pressurization system involving the helium subsystem). They don't yet know what caused the helium system itself to fail.

That said, IF they rule out GSE as a proximate cause, I think whatever fix(es) they apply will almost necessarily eat into performance. That said, the hit might well be a few tens of kilograms rather than a major fraction of the payload capability.

There are failure mechanisms that require zero hardware change on the vehicle... last thing you want to do is start Easter-egging the solution (changing something that might be a cause of the problem, but with perfect knowledge would be understood to not have been the problem).  This not only leaves the real issue untouched, but introduces new variables into the situation.

Too rapid of pressurization, for instance, could have caused excessive vibration, as could excessive boiling of LOX from rapid heating.  Liquid in the system could cause water hammer. Oils in an oxygenated system could result in diesel effect which could detonate affected lines/tanks when rapidly pressurized (submariners know this one well -- it sunk several boats before being fully understood).  Any of these issues would require procedural changes or minor modifications such as flow-limiting orifices.

Best to dive deep enough to ID the root cause before anything is changed.

The thing being described: two different cryogenic liquids at different temperatures being loaded fast into  two pressures vessels via pipes, with one vessel inside the other and the inner vessel being a composite.
Is it at all realistic that all the potential turbulent flow and differential heating will be understood, unless they use similar techniques as they've been using to model combustion and reentry.
What are the costs of loading more slowly - more boiling off of liquid oxygen and He ? Less dense liquid oxygen ?

Edit: boiling off of not boiling of

[Rocket Science]

If they are RTF in November IIRC, those stages are either close to final assembly, about to be tested or have been. That would tell me that they are not changing anything at this point... If anyone in the know what point the LV's are in the flow please post...

[Herb Schaltegger]

If they are RTF in November IIRC...

That's the thing. They're almost certainly NOT returning to flight that quickly. One "best case scenario" tweet taken out of context.

[Rocket Science]

If they are RTF in November IIRC...

That's the thing. They're almost certainly NOT returning to flight that quickly. One "best case scenario" tweet taken out of context.

I'm not putting any money on it... My eyebrows are still stuck in the "up-position" since they said it...

[kevin-rf]

Thought about moving the COPV's outside of the LOX tank.

All the speculation assumed COPV burst because they are not compatible with a LOX environment. What if one failed for other reasons. They will be at the same pressure inside/outside the LOX tank. To blame LOX we have to assume the material is weaker/more brittle at LOX temps or LOX worked it's way inside and ignited. 

[rabe0070]

If they are RTF in November IIRC...

That's the thing. They're almost certainly NOT returning to flight that quickly. One "best case scenario" tweet taken out of context.

IIRC it was an actual sentence uttered by Shotwell at some seminar/Q and A thing. Not one tweet taken out of context. Although, I agree that November seems pretty optimistic.

[Herb Schaltegger]

If they are RTF in November IIRC...

That's the thing. They're almost certainly NOT returning to flight that quickly. One "best case scenario" tweet taken out of context.

IIRC it was an actual sentence uttered by Shotwell at some seminar/Q and A thing. Not one tweet taken out of context. Although, I agree that November seems pretty optimistic.

Yes, standing alone it's out of context. Because the context was provided by the next statement she made (also widely reported on Twitter), that they had not determined the root cause, and November was a best-case scenario. Friday's statement underscores that point, in fact.

[Colodie]

I believe that exact quote is "as early as November."  There's a difference between that and "we plan to ..."

They could absolutely go and launch in November.  It would be an... *interesting* decision... but there is nothing physically preventing them from doing it.

[jpo234]

If they are RTF in November IIRC...

That's the thing. They're almost certainly NOT returning to flight that quickly. One "best case scenario" tweet taken out of context.

IIRC it was an actual sentence uttered by Shotwell at some seminar/Q and A thing. Not one tweet taken out of context. Although, I agree that November seems pretty optimistic.

Yes, standing alone it's out of context. Because the context was provided by the next statement she made (also widely reported on Twitter), that they had not determined the root cause, and November was a best-case scenario. Friday's statement underscores that point, in fact.

Friday's statement reiterates RTF for November and strengthens that target from "our best hope" to "we anticipate".

[jpo234]

I believe that exact quote is "as early as November."  There's a difference between that and "we plan to ..."

They could absolutely go and launch in November.  It would be an... *interesting* decision... but there is nothing physically preventing them from doing it.

Nothing physical, but they need FAA clearance and the customer needs to be aboard.

[Wolfram66]

SpaceX has had experience with plumbing failures in rockets back to Falcon 1. Hubris led them to use braided flexible plumbing for the M1C engine rather than decades of experience. Harmonics with the flexible lines lead to failure.

[Robotbeat]

It would probably depend upon whether Space X can conclusively determine the exact cause of the failure. If they can, then probably the COPVs can stay where they are. If, on the other hand, it’s a bit nebulous as to what happened or multiple issues are identified, then maybe a larger redesign is warranted — or needed to keep key customers happy — that includes relocating the COPVs. Time will tell.

I dunno. The engineer in me just doesn't like the idea of putting tanks pressurized to hundreds or thousands of pounds inside a tank that's built for 30.

Yeah, it was a cool idea but so were a lot of my FUBARs, too. Sometimes you just have to backtrack.

Honestly, what difference would it make in flight? If the pressurization system fails in flight, you're screwed anyway. Maybe in a less dramatic fashion, but so what? (The difference I would suggest: DON'T do static fires with the payload attached! Just don't!)

They're not going to put the tanks outside. There's nowhere to put them.

The suggestions here are to make essentially an entirely new stage. No way in heck that's going to happen before return to flight.

No, they'll find the root cause, hopefully find a belt-and-suspenders way of preventing it from happening again (such as double inspections, 1.5x current FoS on the tank, plus an inert sealant on the COPV, if that's the root cause), then move on.

Hopefully this will spur development of a reusable methane upper stage since it uses a different technique entirely. But SpaceX isn't going to abandon the entire design like people are suggesting.