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

[Oersted]

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.

Aren't those two sentences somewhat contradictory?

[garidan]

The RP-1 COPV's are in the RP-1 tank

Are you certain? Since the helium has to exchange heat with the engines anyway (going all the way down and back up) before going into the propellant tank, I would think they'd stick both in the LOx since you could fit like 4x as much Helium in the same tank due to the much colder temperature of LOx.

But I guess you should know.

And you would get SOME of the benefit from cooling due to the supercooling of the kerosene, I suppose.

I wonder how much weight all the COPV have, RP1 and LOX ones. If say they are 25Kg, I would be happy to pay the 75Kg difference for 4x the number and have them in the "hotter" RP1 tank. I know, they have data and all, but better safe than sorry and if the payload difference is not that much, a less stressing environment for so energy rich components would let me feel a little better, especially after so many problems on that he system :-) .

One question though, for a Raptor second stage methane would be itself its pressurization gas, but wouldn't LOX need He (and COPVs) anyway ?

[Lar]

What are the odds of them pointing a tiger team at developing an autogenous pressurization system for the F9/FH LOX tanks? Just to retire the cLOX v He issue once and for all. Implement as "v1.2.1"

I don't know the odds, think they are low, but it would be neat.

[Jim]

One question though, for a Raptor second stage methane would be itself its pressurization gas, but wouldn't LOX need He (and COPVs) anyway ?

No, LOX can be used like Methane too

But also upperstages have different requirements than boosters.  Boosters can be pressurized by GSE before launch and then bootstrap for flight.  The upperstages have to contend with coast periods and boiloff

[Thorny]

For the record CRS7 was the last of the previous design and the next flight was always going to be FT, that was a done deal long before the failure.

JASON 3 was.

[SWGlassPit]

COPV burst test...

As violent as that was, I'm pretty sure that was a hydro burst test. A gas-filled tank would be orders of magnitude more violent.

[JamesH65]

... . They have done this in the past after failures, CRS 7 included (IE upgrading to FT ect, using the time to just redesign things all the way around before flying again).

For the record CRS7 was the last of the previous design and the next flight was always going to be FT, that was a done deal long before the failure.

FT would have used the same struts and same material for the struts more likely than not had that failure not happened. Additionally, I (and I am not alone) remain unconvinced a strut failing was the actual failure mode as opposed to the liner or part of the COPV where the strut attached failing because it de-laminated.

We will never know because it would produce almost exactly the same readings on flight instrumentation, but we do know some struts in the same batch were found to have material defects in post accident investigation.

Here is why it doesn't matter though: the bottom line was the helium pressurization system failed due to quality control lapse. The same thing happened again here though its probably for a very different technical reason.

The issue being the event chain and result were the same and have a very common problem even though actual failure/material failure is different.

But respectfully, as much as you and others may be unconvinced that a failed strut caused CRS7 , I doubt that you have access to the data that is required for coming to a rational conclusion. As I understand it, there was a fluctuating pressure signal that was incompatible with a catastrophic COPV failure and which could only be explained in terms of a broken strut allowing the strongly buoyant COPV to bend a pressure line. If you have evidence or knowledge to the contrary, please share it - please don't just declare it unsatisfactory in your judgement if you have no data to base your judgement on.

I'm also unconvinced by your declaration that there was a quality control lapse in this latest anomaly. Where is your evidence that there was no design flaw, no mishandling, no environmental factor...?

I was going to write pretty much the same post. FF's posts are full of conjecture based on no evidence whatsoever. He doesn't have access to the reports from the SpaceX engineers on CRS7 (The accident report states it was a strut failure - I tend to believe the actual official report on the subject), or any view SpaceX quality control process, so his claims are absolute conjecture, and bad conjecture at that.

If of course there is evidence that the report is wrong, or that SpaceX quality procedures are ineffective, then please cite them. Whilst I won't be happy of bad news like that, if the citation is valid then there is no argument.

[mn]

For the record CRS7 was the last of the previous design and the next flight was always going to be FT, that was a done deal long before the failure.

JASON 3 was.

Correct. Forgot about that one.

Thank you

[john smith 19]

As much as the COPV's are being beaten to death here, engineering logic says they're a primary suspect.

They are potentially very dangerous but the question is how many have actually failed?

I have, however, seen a 1000 psi Helium line blow out and almost take someone's head off. I was working on my Masters thesis in a high-pressure solid propellant combustion lab. A friend and I were pressurizing a shock tube with Helium when one of the stainless steel Helium line fittings let loose, and a section of stainless tubing went ballistic and almost hit my fellow student in the head. Instead it dented the corrugated steel wall right next to him.

Now what if that wall was the side of a COPV? Obviously the COPV id deeply involved but not in fact the root cause.

[john smith 19]

I'm pretty sure the Saturn LOX tanks were Ti in LOX because their was a cost  reduction project to switch to SS "blown up" using LN2 (Autofrettage?) to put the walls in permanent compression. IIRC they were 1/18 the cost at the same weight.

The Saturn LOX tanks were aluminium;

During the countdown, pressurization was supplied by a ground source, but during flight, a helium pressurant was supplied from elongated bottles stored, not on the fuel tank, but submerged in the liquid oxygen (LOX) tank. In this medium, the liquid helium in the bottles was in a much more compatible environment, because the cold temperature of the liquid helium containers could have frozen the RP-1 fuel. There were additional advantages to their location in the colder LOX tank. Immersed in liquid oxygen, the cryogenic effect on the aluminum bottles allowed them to be charged to higher pressures.

http://history.nasa.gov/SP-4206/ch7.htm

I stand corrected, but it makes no sense to run a project to replace Titanium tanks as a cost saving measure if you're not using them somewhere

IIRC both stages of the Titan 2 did this. The trick is to burn the propellant either fuel rich or just on stociometric and use the reaction products to pressurize the tank. However unless you strip the water vapour you get ice in the tank. Worked fine for a 1 shot system, probably not what you want for a reusable system.

That was only the fuel side, the ox side just heated the N2O4.

Much in the same way you might heat a part of the LOX flow from the F9 main tanks and use that?

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

Well...

Musk is know for his best-case optimism but that's when Pad 39 is due to be finished.

In that sense SX would be ready for flight, but not necessarily returning to flight.

Given the schedule the only way to achieve this would be that all mods are either
a) Software and procedural changes or b) simple go/no go tests that can be added to parts which can be readily removed or added to a built stage.

Assuming of course they have found an exact root cause and by extension an exact fix for it.

I have no idea how plausible such a chain of events is.

[Rocket Science]

For RTF I'm really less interested in SpaceX "making the rush" but rather "making it right"...

[Robotbeat]

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.

Aren't those two sentences somewhat contradictory?

...not if you hadn't cut off the context.

I think SpaceX will get the existing design working again for return to flight, but failure of this stage will still perhaps spur efforts to do a methane upper stage (which won't be ready for years).

[glennfish]

There's a thought that's been going around in my head for the past three weeks about the two LOV events when it comes to the structural differences between S1 and S2... I call it simply, "what's the same, what's different"... S1 solid bird from launch to landing, S2 cantankerous... Why is this "if" there is so much commonality in materials, production technique, tooling, employees assembling them, handling and transportation, testing...etc?

[rnataraja]

As much as the COPV's are being beaten to death here, engineering logic says they're a primary suspect.

They are potentially very dangerous but the question is how many have actually failed?

I have, however, seen a 1000 psi Helium line blow out and almost take someone's head off. I was working on my Masters thesis in a high-pressure solid propellant combustion lab. A friend and I were pressurizing a shock tube with Helium when one of the stainless steel Helium line fittings let loose, and a section of stainless tubing went ballistic and almost hit my fellow student in the head. Instead it dented the corrugated steel wall right next to him.

Now what if that wall was the side of a COPV? Obviously the COPV id deeply involved but not in fact the root cause.

What are the chances that this is a manufacturing defect in the tank?
With re-usability reducing costs, can the tanks be built with costlier and lesser weight alloys? Assuming second stage will eventually be re-usable?

Ps : Pardon naive questions.

[mme]

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.

Call it cherry-picking if you prefer, but Shotwell was clear in the very same Q/A that SpaceX does not know the root cause and that November RTF is best case.

[Rocket Science]

There's a thought that's been going around in my head for the past three weeks about the two LOV events when it comes to the structural differences between S1 and S2... I call it simply, "what's the same, what's different"... S1 solid bird from launch to landing, S2 cantankerous... Why is this "if" there is so much commonality in materials, production technique, tooling, employees assembling them, handling and transportation, testing...etc?

Then the question Glen would be what happens during the integrated test that would cause two S2 failures, one in flight, one on the pad and are those unrelated?

[glennfish]

There's a thought that's been going around in my head for the past three weeks about the two LOV events when it comes to the structural differences between S1 and S2... I call it simply, "what's the same, what's different"... S1 solid bird from launch to landing, S2 cantankerous... Why is this "if" there is so much commonality in materials, production technique, tooling, employees assembling them, handling and transportation, testing...etc?

Then the question Glen would be what happens during the integrated test that would cause two S2 failures, one in flight, one on the pad and are those unrelated?

Well, my career involvement in rocketry advanced as far as Estes Rockets, so take my thoughts with a grain of salt,

but, based on having built complex systems that sometimes get simplified because the customer didn't need EVERYTHING...

It would seem to me like S1 is like the absolute attention getter from an engineering perspective.  9 times as many engines, bigger tanks, more He systems, grid fins, landing legs, precision landing guidance, has to do re-entry and fly a gazillion times.  It's a complex beast and the best and the brightest engineering goes into that.

The S2 is a scaled down copy, 1 engine extended nozzle, small tanks, carries a tiny payload...  It's really boring by comparison.

I can easily picture a case where the senior engineer says, here, take this, it's validated on S1, it should work on S2, and the junior engineer does exactly that. 

I try to imagine simply the He fill system for S1 and compare it to the same system for S2.  Should be exactly the same, except, not as much He gets loaded, not as much plumbing, not as many COPVs.  Would it really be that the He process is the same in both cases, except S2 gets less He than S1?  Would the couplings be the same, the flow rates, the target load pressures, the expected COPV & plumbing temperatures, etc. etc.?

S2 is a totally different rocket than S1 albeit shares as many parts as possible with S1.  Sharing parts is good economics.  Do they share the same processes and do they have equal validation and oversight and QA?  Certainly your brightest engineers did the work on S1.  Did the same engineers do the work on S2?

In the fault tree analysis, is there a little box next to each item that says, "same as S1" and did that mean it didn't need the same analysis, design review that it got when it was defined for S1?

I don't claim any knowledge of the root cause, or even of the possible process failures that lead to it, but I know from personal experience, it's very easy to assume a working subsystem will work in a different context and end up being very surprised when it doesn't.

[Rocket Science]

There's a thought that's been going around in my head for the past three weeks about the two LOV events when it comes to the structural differences between S1 and S2... I call it simply, "what's the same, what's different"... S1 solid bird from launch to landing, S2 cantankerous... Why is this "if" there is so much commonality in materials, production technique, tooling, employees assembling them, handling and transportation, testing...etc?

Then the question Glen would be what happens during the integrated test that would cause two S2 failures, one in flight, one on the pad and are those unrelated?

Well, my career involvement in rocketry advanced as far as Estes Rockets, so take my thoughts with a grain of salt,

but, based on having built complex systems that sometimes get simplified because the customer didn't need EVERYTHING...

It would seem to me like S1 is like the absolute attention getter from an engineering perspective.  9 times as many engines, bigger tanks, more He systems, grid fins, landing legs, precision landing guidance, has to do re-entry and fly a gazillion times.  It's a complex beast and the best and the brightest engineering goes into that.

The S2 is a scaled down copy, 1 engine extended nozzle, small tanks, carries a tiny payload...  It's really boring by comparison.

I can easily picture a case where the senior engineer says, here, take this, it's validated on S1, it should work on S2, and the junior engineer does exactly that. 

I try to imagine simply the He fill system for S1 and compare it to the same system for S2.  Should be exactly the same, except, not as much He gets loaded, not as much plumbing, not as many COPVs.  Would it really be that the He process is the same in both cases, except S2 gets less He than S1?  Would the couplings be the same, the flow rates, the target load pressures, the expected COPV & plumbing temperatures, etc. etc.?

S2 is a totally different rocket than S1 albeit shares as many parts as possible with S1.  Sharing parts is good economics.  Do they share the same processes and do they have equal validation and oversight and QA?  Certainly your brightest engineers did the work on S1.  Did the same engineers do the work on S2?

In the fault tree analysis, is there a little box next to each item that says, "same as S1" and did that mean it didn't need the same analysis, design review that it got when it was defined for S1?

I don't claim any knowledge of the root cause, or even of the possible process failures that lead to it, but I know from personal experience, it's very easy to assume a working subsystem will work in a different context and end up being very surprised when it doesn't.

Or is it the case that S1 is overbuilt with increased structural margins for re-usability and S2 is pushing the minimal margins to extract maximum performance to make up for it...

[gosink]

Does any of this make autogenous gas generation a reasonable alternative to He?   I picture a couple of large heating elements inside the tank and a couple of Tesla's worth of batteries outside the tank.  Could you rig enough batteries in series to deliver the required power in 2-3 minutes?  How would the numbers work out for the mass, ie: 

delta_weight ~  (batteries + heating coils + unburnt autogenous gas) - (COPVs + mounting hardware + He + He piping) ?

Even if the numbers are reasonable, I'm sure this would never happen as they are way down the He path, but I'm curious if the numbers might be close.

[Jim]

Does any of this make autogenous gas generation a reasonable alternative to He?   

Autogenous would have heat exchanger on the turbo pump exhaust, that takes some of the LOX and turns it into gas

You don't want to heat up the bulk of the LOX and there is no sense for batteries and heaters.