Musk: SpaceX Has Theory on Falcon 9 Firexplanomaly; Sabotage Unlikely
Credit: USLaunchReport.com
Remarks attributed to Elon Musk in which he discussed a possible cause of SpaceX’s Falcon 9 launch pad firexplanomaly leaked out to the public last week after his his presentation before officials at the National Reconnaissance Office (NRO).
“We are close to figuring it out. It might have been formation of solid oxygen in the carbon over-wrap of one of the bottles in the upper stage tanks. If it was liquid it would have been squeezed out but under pressure it could have ignited with the carbon. This is the leading theory right now, but it is subject to confirmation,” Musk is reported to have said.
Musk was reportedly referring to carbon composite overwrapped pressure vessels (COPVs) that hold helium inside the Falcon 9’s second stage liquid oxygen (LOX) tank.
Elon Musk (Credit: SpaceX)
The remarks were briefly posted on Reddit before they and the entire thread were deleted. SpaceNews reports that a SpaceX spokesman “declined to confirm or deny that the statements, published anonymously online, conformed exactly to what Musk said.”
The Reddit post also attributed the following remarks to Musk concerning the prospect of sabotage of the rocket.
“The other thing we discovered is that we can exactly replicate what happened on the launch pad if someone shoots the rocket. We don’t think that is likely this time around, but we are definitely going to have to take precautions against that in the future. We looked at who would want to blow up a SpaceX rocket. That turned out to be a long list. I think it is unlikely this time, but it is something we need to recognize as a real possibility in the future.”
A long list, indeed. As SpaceNews points out, it’s not clear whether Musk volunteered the information about possible sabotage or whether he was asked to comment upon it by a member of the audience.
A source with contacts at Cape Canaveral tells Parabolic Arc that people there believe SpaceX is spending a bit too much focusing on a sabotage angle they don’t see as very credible. But, since SpaceX is in charge of investigating its own failure, the company is going to proceed as it sees fit.
What’s really interesting is that SpaceNews asked several experts in the field to comment on the report anonymously and summarized the results in its story. The experts found the theory reportedly offered by Musk to be “perfectly credible.” The story also raises the following issues.
SpaceX’s Use of COPVs. The composite helium bottles are not new, but the way SpaceX is using them is. And that might go to the core of the problem.
“It has been used at least since the 1980s on several launchers and spacecraft. But to my knowledge they have never been used in such a cryogenic, unsteady environment. In a cryogenic environment you have thermal gradients that are not always oriented in the same way from the interior to the exterior of a structure, or the exterior toward the interior.
“The difficulty is reproducing the thermal demands applied to the wound exterior of the bottle against the interior side. If wound or wrapped layers slide even a little bit, you get shear de-lamination. This can cause a catastrophic result.”
Did a Burst Helium Bottle Bring Down Another Falcon 9? A SpaceX investigation into the explosion that destroyed a Falcon 9 rocket in flight last year blamed a defective strut provided by a supplier that broke under pressure, causing a helium bottle to shoot up to the top of the second stage LOX tank. The company says a strut was not involved in the launch pad accident last month.
Dragon capsule separated from Falcon 9 launch vehicle.
But, is that what actually happened last year? SpaceNews experts raised serious doubts.
“The question is whether the strut was really the origin of the June 2015 failure. The struts were of below-specified quality, but it was not demonstrated that this was the root cause of the failure.
“It remains possible that a helium bottle burst in June 2015 and that, in parallel, the struts supporting it were of poor quality….
“But there is always the risk of correcting things that are not the real cause, such as correcting a badly built strut, which might not have prevented the June 2015 failure…”
Parabolic Arc has heard reports for about a year that experts didn’t buy SpaceX’s conclusion. Sources believe the accident was more complicated than a defective strut breaking under flight pressure.
A separate investigation by NASA’s Launch Services Program (LSP) did not find a probable cause for the accident. An audit by the NASA Office of Inspector General released last June summarized the program’s findings as followed.
“LSP did not identify a single probable cause for the launch failure, instead listing several ‘credible causes.’ In addition to the material defects in the strut assembly SpaceX found during its testing, LSP pointed to manufacturing damage or improper installation of the assembly into the rocket as possible initiators of the failure. LSP also highlighted improper material selection and such practices as individuals standing on flight hardware during the assembly process, as possible contributing factors.
The SpaceX investigation board included 11 company employees, including its chairman, and a long FAA representative. The final report was signed by the 11 SpaceX employees only.
The Falcon 9 that failed in June 2015 was carrying a Dragon supply ship to the International Space Station for NASA’s Commercial Resupply Services-1 (CRS-1) program. Eight months earlier, an Orbital Sciences (now Orbital ATK) Antares rocket carrying a Cygnus supply ship to the station for the same program exploded shortly after liftoff.
The NASA IG audit criticized NASA’s practice of allowing SpaceX and Orbital ATK to conduct their own investigations in the failures.
“NASA’s official policy for investigations requires all official Mishap Investigation Boards to be independent. NTSB and USAF have similar requirements. In contrast with these best practices, the CRS-1 contract and FAA license requires SpaceX to conduct its own investigation but does not require company investigation boards to screen for conflicts of interest or maintain independence. FAA officials stated NASA can implement additional independence requirements for contractor-led investigations through its contracts as long as they do not conflict with FAA regulations….
“We acknowledge SpaceX’s investigation was transparent and the observers from FAA, ISS, LSP, NTSB, and USAF had access to the investigation’s data and analysis. However, an investigation led by the employee responsible for the SPX-7 launch and run by the contractor responsible for the failure raises questions about inherent conflicts of interest.”
Why Did SpaceX Bring Helium Bottle Production In-house? The helium bottles used by SpaceX during its early years were supplied by Cimarron Composites of Huntsville, Ala. However, SpaceX brought production of these bottles in house in 2014.
At the time, there was a general belief that SpaceX made the change due to its preference for vertical integration. The company felt it had learned everything it needed to learn from Cimarron and could proceed on its own.
However, SpaceX ended up delaying multiple launches due to helium leaks in 2014. Instead of launching 11 Falcon 9’s as planned that year, the company achieved only six flights. So, maybe SpaceX hadn’t learned everything about how to manufacture these bottles.
The SpaceNews article suggests another reason for bringing COPV production in house.
“In 2014 Cimarron Composites suffered an explosion which caused extensive damage. My understanding is that after this event, SpaceX decided to bring in-house the production of these vessels.”
Space — and COPVs — are Hard. Not only is manufacturing the composite helium bottles challenges, but producing them consistently for the “cryogenic, unsteady environment” SpaceX uses them in creates additional risks.
Fiber- or tape-, or strip-wound “overwrapped” technology is not something you can learn in a day or two. But SpaceX did it. They have many good technicians and engineers and equipment.
But this kind of multilayer, resin-coated winding is never totally reproducible. The big problem in serial production of this kind of manufacturing is to be able to identify the drift and defects, during quality control inspections, in an operating mode that is representative of the intended use — with margin, as necessary. That is not easy for severe cryogenic uses.
In cryogenic geyser cycling environments, such as SpaceX’s rapid filling of a LOX tank at 66 Kelvin, you have violent variations of temperature between the interior and exterior. The thermal gradient is deeply heterogeneous from one location to another.
Can SpaceX Begin Flying Again in November?
SpaceX President Gwynne Shotwell have expressed confidence Falcon 9 can be returned to service in November and fly a couple of missions by the end of the year. She has suggested the the September accident was caused by operational issues rather than a flaw in the COPV design.
The verdict from SpaceNews’ experts on such a rapid return to flight is a definite maybe.
“There are lots of ways they could proceed, depending on how acceptable risk is assessed. For example, they could launch a mission that does not need the rocket’s full performance, and so they can pressurize the helium tank to a much lower extent. But it’s difficult to move forward without demonstrating a root cause and corrective actions.”
33 responses to “Musk: SpaceX Has Theory on Falcon 9 Firexplanomaly; Sabotage Unlikely”
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Carbon in a pure Oxygen environment is highly flammable. Heat up a diamond with a small butane torch and drop it into a flask of liquid Oxygen and it will burn until gone.
“Heat up a diamond … and it will burn until gone.”
But don’t heat it up and it doesn’t.
Steel will burn in pure oxygen if you heat it above its ignition point (it’s even a type of cutting torch), and yet we happily store oxygen in steel tanks.
Yes, burn, not explode. It heats the LOx which excites the atoms and it converts into GOx which reacts with the carbon. But the Liquid Oxygen portion remains inert until it reaches that conversion to GOx. When you look at the remnants of the COPV very little of the carbon fiber is missing. You have a big furball of the carbon fiber and most of the resin that used to hold it together is missing, or if it is there it is difficult to see. Also missing from your argument is the heat source to get the carbon to the appropriate temperature especially when submerged in LOx. Drop your diamond into LOx without heating it up. Pretty boring. Same thing happens with burning coal by the way.
I was illustrating that even tightly bonded carbon, in the form of diamond, will burn under the right conditions. I am not making a guess about what initiated the fire. I’m not sure what resin is being used on the COPV’s, but regular epoxy is a petrochemical. Again, a material that is going to be very flammable when saturated with liquid Oxygen. The guess that I will make is there was a hot enough spark or other heat source that got something to burn and burn very vigorously in an almost pure Oxygen environment. If something like that happens, the rest is inevitable.
Pressure tanks get hot when being filled. The more rapidly they are filled, the hotter they get. With COPV’s it’s important to regulate the fill rate or refrigerate the gas before it goes into the tank.
The chain of the accident looks like a fire and then a rupture of main fuel and oxidizer tanks. Is TEA/TEB used to ignite the second stage?
If the sounds a few seconds before the fire could be triangulated to the craft, I could be convinced that some structural component was stressed and then broke. That could have caused a leak in the fuel system which lead to more badness.
Ok this is going to be hard to convince you about but there are a couple of things that should be easy to sort out if you check out what I say before you curse the day I was conceived. Nothing burns in liquid oxygen. It has to be converted into a gaseous form before it burns. The diamond you used in an earlier example only burns in the presence of liquid Oxygen because the temperature is able to quickly boil enough of the LOx and convert it into GOx to be able to burn. Secondly the Helium tank actually chills down when it is pressurized. I was converted about this fact a couple of hours ago. Evidently Neon, Helium and Hydrogen all get colder as you compress them and if you do it quicker the chilling effect is even more noticeable. That is why EM said that he thought Frozen LOx became an issue as the already close to freezing LOx actually got colder as it encountered the pressurizing helium tank. It has to do with the basic properties of helium which are different than all the other gases we are accustomed to. The noise a couple of seconds before the explosion have not been triangulated yet at least publicly. I am very curious/concerned about where that noise originated and what it was. There was also some sort of microphone feedback heard a second or two before the quieter bang that has not been sufficiently explained yet either.
“If I recall correctly, the NASA report on the June 2015 failure said the strut issue was a probable cause, but not a definitive root cause. You said it wasn’t 100 percent sure, but 99 percent sure. Is it possible that the second-stage composite helium bottle, immersed in the LOX tank, might have been an actor in the 2015 failure and again in what happened on September 1?
[Gwynne Shotwell] Until we complete the investigation and get through all the data, and all the scenarios, you can’t say it wasn’t this or it wasn’t that. I can tell you that the signature for this particular failure was substantially different from the one we saw last June. It’s incredibly unlikely that the scenario that we saw last June was the same as this one. It’s extremely low on the possibility list right now.”
http://spacenews.com/spacex…
Emphasis (italics) mine.
That’s answered in the SpaceX story.
Q. SpaceX has said that while they have not yet determined the root cause for the Sept. 1 explosion, they know enough to conclude it is not related to the June 2015 Falcon 9 failure.
A: “I read that to mean they cannot explain the Sept. 1 anomaly by the failure of a strut, which is understandable. Quality defects were found in the struts, and corrections were made. It seems logical that what happened Sept. 1 is not tied to a strut failure.
“The question is whether the strut was really the origin of the June 2015 failure. The struts were of below-specified quality, but it was not demonstrated that this was the root cause of the failure.
“It remains possible that a helium bottle burst in June 2015 and that, in parallel, the struts supporting it were of poor quality.”
In other words, the strut didn’t give way in the accident last month. That’s all SpaceX is saying. At least that’s the opinion of the experts SpaceNews interviewed.
Actually, the Shotwell quote above is really interesting. Shotwell was asked directly whether the helium bottle could have been the root cause of the June 2015 accident. In other words, did it burst and that caused the defective strut to break free and shoot up to the top of the LOX tank? That is the scenario posed by the experts in the SpaceNews story. That it was a combination of the bottle breaking and the strut being defective.
She didn’t seem to address the question directly. She didn’t say, in June 2015 the helium bottle wasn’t the root cause. She simply said the two accidents are different.
Tell that to Musk. He’s the one who called it a theory. I understand he likes being corrected on his mistakes.
I stand corrected regarding the possible cause of the Sept. 1st incident.
However I do not think that I “attacked you sharply” in any way. I did not use any rude words or insulted you in any way. I simply stated that I did not like the FUD (= Fear, Uncertainty and Doubt) you were spreading about related (carbon composite) rocket projects and asked you what qualified you to claim that a number of companies did not understand the problem that you brought up.
So I see no reason for an excuse.
PS: As far as I know, you can “ping” another user using the “@” sign like o twitter -> @snofruchufu
So there is no need to make off-topic comments like the one you made (and deleted, but by the time the notification had already reached my inbox ;)) on the Antares Launch thread or you simply could have made another reply to my original comment.
Put the helium tanks in the kerosene tanks. Must be a good reason not to and I am sure someone has commented on doing this, but I do not remember. Not enough room or cryogenic allows smaller tanks. Have to make a new rocket. Maybe in the inter-stage.Sounds like a bad idea the way they are doing it from what the expert says. Seems to work ok out of cryogenic. Simple but a bullet in water slows down rapidly. In LOX if it does the same thing it would never reach the helium tank. Of course if the tank was empty. The same with shrapnel hitting the common bulk-head. A bullet would puncture the tank and cause a LOX leak is all I can see. Musk seems to disagree with Shotwell that it is business, not technical. She may be thinking far out that a business competitor to get more launches somehow caused the helium rupture.
You need the helium cooled down to LOX temperatures to make it dense enough so that there’s enough expanded volume to handle all the various tasks that require helium. (It’s not just for tank pressurization; it’s used in chilldown and various purging operations as well.)
There are also Helium COPV tanks in the RP-1 tanks, both need to be pressurized as they are drained of fuel to maintain structural integrity.
I think the (supposed) reaction with the COPV wall and LOX could be considered negligible in comparison with the pressure force of the helium contained within. I say the bottle failed (burst) catastrophically, the high pressure helium bubble pushed the common bulkhead and lots and lots of LOX down into the RP-1 tank, and you all have seen what happened next. Gone in milliseconds.
“I think you mean ‘hypothesis’. “
“I’m pretty sure he must be at the theory”
Make up your mind.
People have mentioned the weird thermal properties of GHe at these temperatures. Apparently at the intended operating temps, GHe temperature rises as it expands. (A “negative Joule-Thomson coefficient”, to repeat-without-understand.) Hence as you let He out of the bottle, the walls warm slightly instead of cooling, and hence there’s no risk of LOx freezing.
But only slightly below the normal operating temps (it’s “Joule-Thomson inversion temperature”), GHe reverts to the more expected behaviour, cooling as it expands, hence venting GHe would cool the bottle walls.
The speculation is that this might have happened if the cryo-cooler systems were mis-set – such as a mismatch between the actual vs expected rate-of-flow – leading to an unintentional loading of extra-cold He into the bottles. The technicians wouldn’t have been aware of the risk.
The suggestion is that the super-cooled bottle walls may have frozen out any LOx that seeped into the carbon overwrap. This higher-density solid then causes cryo-pumping which pulls in more LOx. The heat of solidification warms the He back above critical temp, the next venting warms the bottle above the melting point of SOx, and the now-liquid Oxygen expands inside the carbon-overwrap too fast to bleed out, causing a sudden and catastrophic delamination. That breaches the bottle, which creates enough force to blow out the side of the LOx tank, creating the initial plume. “Ignition is free” – tear-static could be enough – so the subsequent fireball is mundane.
The reason it hasn’t been seen before is because there’s normally no delamination from a small amount of LOx leaking or absorbing into the overwrap, and at those temperatures no risk of the carbon igniting. It took a bad setting of the external cryo-cooler to pull the trigger.
The bad things is that it’s a fundamental design flaw.
The good thing is that it’s predictable and measurable, so they might be able to work around it with the right combination of sensors and procedures, avoiding a costly and time-consuming redesign.
Gwynne Shotwell’s remarks seem to indicate that it was a problem that could be solved by changing procedures. That’s why she is talking about flying again next month. So you might be right in what you say in the last paragraph.
SpaceX desperately wants to avoid having to redesign the system. It would be very costly. Not just in the redesign, but the lack of revenue from launches. SpaceX’s burn rate is very high. The rocket being grounded for a long time would be very bad. A redesign would require a number of tests to prove the system will work in flight. And they’d have to admit they have a fundamental design flaw in their rocket.
What really worries me is human spaceflight. Blow up a Dragon cargo ship or a communications satellite, that’s one thing. But, the idea of putting the crew aboard a Dragon and then fueling the rocket after what we’ve just seen is scary. Nobody’s done that with human spaceflight before because of the risks involved.
This is very useful. I’d done the computation assuming helium was an ideal gas (it’s here), and it looked like you needed a whopping big pressure drop to get down the O2 freezing point. The negative μ-jk makes that even more unlikely.
A few things:
1) I confirmed that the inversion temps for helium stay low at high pressures, so your theory holds there.
2) LOX @ 66°K has a density of 1.23 g/cm^3. γ-phase SOX is about 1.36 g/cm^3;, so if we cryo-pump, we’re going to have about an 11% increase in volume from the pre-freezing when everything melts.
3) I don’t think the expansion behavior is completely reversible here, and I’d expect that super-chilled GHe would warm on compression, not cool. (The negative μ-jk results from frictional forces overwhelming the adiabatic expansion, and compression doesn’t eliminate those.) So you’d have to have the input temperature set really, really low to freeze the LOX near the COPV walls. But, as you say, there might be naive operational reasons for doing that if you didn’t expect the super-chilled GHe to cause any problems.
4) From Elon’s statement, I inferred that the issue wasn’t so much the overwrap failing as igniting. Presumably, if you suddenly put 11% more volume on a localized segment of carbon fibers, that’s going to put terrific strain on the fibers, which should heat them. I’m clueless on where the ignition temperature is. Most of the literature I brainlessly googled says that the prinicpal fire risk from carbon fiber composites is from the resin, but things will be really weird at cryo temps.
5) I wonder if the kind of de-lamination behavior you’re envisioning could also lead to a non-explosive failure of the COPV. (You’re not going to get very much crack propagation.) If so, that sounds like something that you could put closer to the root of a strut failure tree, but which might have acoustic properties that would escape detection. I like it when there’s only one underlying cause for a couple of disparate failures.
Gotta get all of our speculation in before SpaceX releases a report!
“That breaches the bottle, which creates enough force to blow out the side of the LOx tank, creating the initial plume.”
But the initial plume already had RP-1 and LOX mixed. The only way that could happen is if the common bulkhead gave way and the resulting mixture of the propellants ignited (and perhaps detonated) in the ullage space of the RP-1 section of the tank.
Fuel and LOx. Not necessarily RP-1. The carbon/resin from the destroyed He bottle might have provided enough material for the initial plume.
The He bottles are at the bottom of the LOx tank, near the common bulkhead, so the release of RP-1 fuels the second, larger fireball.
There must be a reason for the abruptness of the initial plume, with no prior warning. If there was a prior mixing of the RP-1 and LOx – after the He bottle breached, but before the mix ignited and blew out the side – there would have been a drastic rise in the pressure of the LOx (and then RP-1) tanks which would have produced a sudden increase in venting. Even if just for a frame or two.
That didn’t occur, which means you needed the fuel-source pre-mixed with the LOx at the same time as the breach. And in the scenario I described, the obvious candidate is the He bottle itself.
(Remember, the initial flare is too bright to make out structure. Part of what we see is reflection off the rocket, the T/E, and the vapour clouds caused by previous venting. The size of the plume doesn’t need to be “an explosion”, it could be mostly LOx/GOx propelled by the suddenly released GHe, with a relatively small proportion burning with the fragmented bottle itself illuminating the rest, like a filament in a frosted bulb. A moment later and the RP-1 tank is spilling out and the slower main deflagration starts.)
[If you look at videos of COPV bottles failing, they tend to shatter into dust/filament clouds. That’s a lot of surface area to burn.]
The failed COPV bottles I have witnessed failing turned into what looked like a huge fur ball. Not dust/filament clouds. The GOx is mostly located at the top of the LOx tank above the surface of the LOx and very little or none of it would have been mixed with super chilled LOx. I can imagine those small bits of resin shattered loose from the carbon fiber filaments and burning like a shower of sparks as they fly outward but I can not imagine them exploding like RDX, HMX or PETN. Nor can I imagine them flaring like an arc welder when submerged in a bath of super chilled LOx. or in a cloud of LOx atomized with a mixture of GHe. Something flared dramatically during the first few milliseconds of this explosion and that forms a signature that needs to be replicated if they want to prove a given theory about what happened and when. Furthermore, looking at still frame by frame of the explosion it looks like it starts at the bulkhead between the Lox tank and the RP1 tank. so if the He tank exploded inside the LOx tank you would think that the RP1 would be blown downward, and the LOx would be blown upward with similar horizontal blowout on each. Thus mixing should have occurred primarily between the two clouds and combustion should have occurred here. But we don’t see that. We see almost exactly the same amount of flame upwards as we see downwards and more horizontal burning flame front than vertical up or down but again the left and right hemisphere seems exactly the same even though the center of the explosion seems closer to the side of the rocket. Then several frames later we see unburned Ox clouds and unburned RP1 clouds expanding outward. This is exactly the opposite sequence of events I would have expected. I expected unburned LOx cloud going upwards and outwards away from the burst tank and Unburned RP1 clouds pushed downwards and outwards then a flame and fire from the center burning the downward flowing RP1, but what is burning in that upward moving column of Ox vapor that is equally hot as the mixture of RP1 atomized with normal air? What is burning to the right side of the rocket that has equal amount of flame producing authority as the left side where all the fuel and LOx has been thrown? The symmetry of the initial burst is very confusing unless, …. unless there is a high explosive element to this mess. Could the pressure wave from the bursting GHe have caused a sympathetic detonation of the range safety explosives? I don’t have enough data. What kind of explosives are the range safety squibs made from, where are they located on the rocket chassis? How many are there chained together? How many chains of them are there? I am so jealous of those investigators who get to chase down these issues and have access to those classified details.
I’m talking about the moment of failure, not the end result afterwards. The point is the rapid increase in surface area, mixed with pure oxygen.
My “cloud of LOx/GOx” reference is to some of the LOx turning to gas when released, not to pre-existing gaseous O2 in the tank. (I also believe that finely aerosolised LOx mist will happily allow a fast deflagration, unlike bulk LOx.)
Again, remember that you aren’t seeing just the actual flame-front, the camera is also overwhelmed by the reflection off the surrounds. We don’t see the actual flame-front until it expands significantly and the “surface” cools below the saturation point of the camera pixels.
We really shouldn’t draw too much inference from the video (or the audio).
The specific HE chosen for range-safety ordinance is designed to not be able to be detonated by a shock applied to one side of the HE packs. They can’t even by set off by their own detonators, until they are properly inserted.
And the triggers are mechanically separated from the main HE. That is, the detonators are physically withdrawn from the main HE until the RSO engages them, which, according to the timeline and subsequent reports, they weren’t at the time of the accident.
Like all stable explosives, they will happily burn, but even that occurs fairly slowly. More like a particularly vigorous fire-lighter than an explosive device. Nothing fast enough to be useful in explaining the events.
They are in three vertical strips running up the sides of the tanks. They are intended to “unzip” the tanks. (Also, AIUI, they are not on or near the He bottles.)
Remember, the range-safety ordinance is not meant to “destroy” a rocket, but merely to deprive the engines of fuel/oxidiser. The danger of an out-of-control rocket is that it will fly itself outside of the exclusion zone and into a populated area (or into other facilities.)
They can’t set each other off. It’s mechanically impossible.
Have you seen some COPV’s? They can be porous as heck! And I’m not talking about the micro level either, this is the macro level. The windings are usually helical, so they don’t sit particularly close to the tows next to them. The polar bosses are the worst though. A small little gap with be instantly infiltrated with any liquid. I haven’t seen SpaceX’s particular design (I last visited their facility before they brought that in house), but they are all made by similar processes.
That’s the advantage of this theory (as a solvable flaw), it is not based on random “thermal stresses” that depend on potentially unique momentary characteristics, but on a very specific behaviour of GHe at the critical temps. That’s what’s repeatable/testable/preventable. The only “unique” part was simply reaching the critical temps on that specific day.
Isn’t he saying the overwrap is porous, rather than the totality of the vessel itself. I don’t know either way, but that is how I read it.
Here’s an interesting question for all of you. The SuperDraco engines also use helium spheres. Is this a concern as well?
http://aviationweek.com/spa…
Other highlights noted by Musk included the composite overwrapped
titanium spheres containing the pressurized helium for the propulsion
tanks for the SuperDraco engine. The engines operate at a chamber
pressure of around 1,000 psi and are fed from propellant tanks located
around the base of the vehicle.
The issue seems to be the location of the He bottles inside the LOx tank, combined with something unique to supercooling, not merely having COPVs somewhere-on-the-vehicle. COPV He tanks are routine in the launch industry, they don’t cause issues. But they are usually (like on Dragon) outside the other tanks.
‘If the LOx tank blows out, what is igniting exactly that resembles that blast?”
Exactly right Thomas. The rapid decompression of the Helium is an inert explosion. Even if the fibers of the helium tank ignite, there is just so much mass there to combust and that combustion would be just sparks burning as they find small amounts of gaseous oxygen to react with. Eventually the ruptured RP1 tank would allow RP1 to be atomized enough to start reacting with the gaseous oxygen and a conflagration would quickly happen, but it would take (IMHO) several seconds for all these things to happen. The explosion we witnessed on the video was hot like an arc welder and just as bright judging by the way background items and the payload fairing lit up in the first 1/30th of a second. (thats how long one video frame is from the next). This is a signature of the explosion that needs to be replicated if this scenario is to be true. I am going to be a call me Kansas kind of skeptic until I see a video of a replication of the event. The only example of an explosion similar to this one where the size and speed of the explosion are any where similar is when the range safety explosive squibs are triggered on a wayward rocket. I am going to be a “doubting Thomas” on this one for quite a while.
My “vision” of how things proceeded is:
1. The COPV integrity fails catastropically (the COPV “blows”).
2. Everything around the high pressure helium bubble immersed in the LOX “feels” the force, the closer to the bubble the higher the force per unit area.
3. Outer tank wall next to the helium bubble deforms.
4. The weld between the outer tank wall and the common bulkhead fails below the high pressure helium bubble.
5. LOX begins to gush into the ullage space of the RP-1 tank.
6. The the weld between the common bulkhead and outer tank wall continues to detach, driven by the pressure of the helium bubble above.
7. More and more of LOX gets pushed into the RP-1 section of the tank.
8. High pressure stream of LOX causes a lot of splashing and mixing with the RP-1, by it’s kinetic energy and because of flash boiling of LOX to GOX when it meets the “hot” RP-1.
9. Eventually some of the mixture finds its way to the still failing weld.
10. Ignition happens.
11. The end.
Remember, the time frame here is measured in milliseconds. Definitely not seconds.
What do you think?
The assumptions I made in the above assesment are:
1. The level of the LOX in the tank was relatively high at the moment of the COPV rupture (the dense LOX above the COPV would “stem” the sudden release of pressure).
2. The common bulkhead between the LOX and RP-1 sections of the tank is not designed to hold differential pressure between the tank sections (you can have almost equal pressure in both sections of the tank). This is just a guess on my part, but it could save some mass which is very important in rocketry. 🙂
He already said that while the bullet theory is not likely the issue this time, it is enough of a possibility that they would take steps to insure it was not a possibility in the future. It is October surprise time. Maybe Hillary did it and it remains to be proven. Even with a bullet breaking the COPV and exploding both tanks almost simultaneously the resulting fireball is very symmetrical in both its Hemispherical lobes and its vertical lobes. How could that happen if the tank is located at the bottom of the LOx tank the LOx would mostly be blown upward and outward, the RP1 would have been blown downward and outward, the mixing and flame front sandwiched between the two non-flammable clouds. Since the explosion seems centered on the side of the rocket most of the fuel and LOx should have been pushed out to the left of the video frame. But the initial flame of the explosion seems equal in left and right lobes. But there is not nearly as much fuel and LOx available over there on the right. How is that possible. ….. I think that maybe the decompression bomb type of event might have created enough of a pressure wave to cause a sympathetic detonation of the range safety explosives. …. That may explain the symmetry of the explosion and lack of data to support an accidental detonation of the range safety squibs.
Me too, but I am exploring sympathetic detonation of explosives right now. The idea that the COPV blew out and caused a chain reaction of sympathetic detonations of the range safety explosives intrigues me.
LOL I only wish I knew. I had not and still have not seen anything I have confidence in that says they also hit the tank with a bullet. That is news to me. I’ll go research it for a bit.
Its going to be a gonner for sure. The question at hand is if it actually did blow because of a failure of those high pressure tanks, or if the tanks were blown, or if something else blew. Its a great and fun job speculating about it.