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SpaceX says Crew Dragon capsule exploded due to exotic titanium fire
- thrill 7y ago"Rockets are tricky."
- vikramkr 7y agoOoh a titanium fire - that would be really cool to see. I wonder if it's possible to make titanium thermite as easily as aluminum thermite?
- AndrewBissell 7y agoThe titanium fire could be fun but the problem is you don't want to be anywhere near that hydrazine when it goes. https://www.latimes.com/business/la-fi-spacex-crew-dragon-escape-system-fuel-20190423-story.html https://www.latimes.com/business/la-fi-spacex-crew-dragon-es...
- CaliforniaKarl 7y agoFor a 'fun' watch, check out NASA's "Toxic Propellant Hazards" video, from ~1966. https://www.youtube.com/watch?v=Zha9DyS-PPA https://www.youtube.com/watch?v=Zha9DyS-PPA
- kevin_thibedeau 7y ago4:46: Let me just move this beaker of rocket fuel over a foot while I aim a syringe of oxidizer.
- CaliforniaKarl 7y ago> titanium (a technically flammable metal similar to magnesium) Yeah, it didn't click with me immediately. I saw "titanium fire" but my brain substituted "magnesium fire". The idea that titanium can catch on fire in a similar way, is…concerning. … and of course there's a small-scale YouTube video: https://www.youtube.com/watch?v=cH76ObzYIxc https://www.youtube.com/watch?v=cH76ObzYIxc
- RaceWon 7y ago> "titanium fire" but my brain substituted "magnesium fire". Ditto.
- xkcd-sucks 7y agoEh all metals like to burn, which is why so many are found as oxides in nature. For example, a "thermobaric lance" used to punch holes through reinforced walls is just a bunch of iron metal burning in excess oxygen, the colors in fireworks are diverse metals, etc. It's an example of "kinetically driven" versus "thermodynamically driven" in that metals all want to burn and give off tons of heat, but in everyday human circumstances the ambient temperature is cold enough to prevent the metaphorical ball from rolling down the hill. It's rather surprising that any metals at all can withstand the remarkably unhappy oxidizers used in modern rocket fuels! Probably the metal part in contact is an oxide layer that's easily abraded by big chunks of crap.
- FreeFull 7y agoGold is very resistant to any sort of oxidation (the oxides are less stable than the metal), but of course using gold for a rocket wouldn't be very practical.
- andrewflnr 7y agoThat's why we need to bring down that giant gold asteroid! Gold fuel tanks for everyone!
- RyJones 7y ago
- jandrewrogers 7y agoMost metals can be used to successfully make thermite when paired with appropriate metal oxides. It is a very simple thermodynamics equation that determines which combos work well. The main considerations are the net energy release of the reaction, which can vary widely, and the amount of energy required to bootstrap the reaction, which can be extremely high. Classic thermite -- aluminum and iron oxide -- is a middling combo but has the large benefits of being dirt cheap and low density. Designing exotic thermites is a literal direct application of the elementary reaction thermodynamics that you learn in basic chemistry classes. Bootstrapping ignition is a bit more involved and often multi-stage.
- DonHopkins 7y agoThe article says: "Rather, the cause lies in a more exotic and unanticipated chemical/material interaction between a plumbing valve, liquid oxidizer, and a helium-based pressurization system." How can chemical interactions be "exotic"? Or did they mean "exothermic" or "exciting" or "esoteric"? Is "exotic" a technical term, or did the chemicals simply come from a distant foreign country, and how does that affect their physical properties? https://www.quora.com/What-are-exotic-compounds-in-chemistry https://www.quora.com/What-are-exotic-compounds-in-chemistry Is there such a thing as non-baryonic titanium? https://en.wikipedia.org/wiki/Exotic_matter https://en.wikipedia.org/wiki/Exotic_matter >Hypothetical particles and states of matter that have "exotic" physical properties that would violate known laws of physics, such as a particle having a negative mass. I can understand why you'd want to fill a rocket with exotic matter of negative mass: to make it lighter! ;)
- asark 7y agoI'd take it to mean "not supposed to be there; from outside (the place where the reaction happened)". Webster's 1913 for "exotic" includes: extraneous. Same source for "extraneous" includes: without or beyond a thing; not essential or intrinsic; foreign.
- jandrewrogers 7y agoThe term "exotic" in a chemistry context means one of two things. First, it can mean observed chemistry that is seen neither in nature nor the lab under ordinary conditions. In other words, it is theoretically possible but the required conditions are so atypical that the expected probability of it occurring unintentionally are very small. I'm guessing this is the case that applies here. Second, "exotic" can mean engineered chemistry that is far outside the standard industrial spectrum, typically because there is a unique application with very special requirements. Industrial chemistry is all about price performance of the chemistry not absolute performance, but some use cases are more performance sensitive than price sensitive so people will design bespoke and unusual ("exotic") chemistry for the purpose. It is a curve. Everyone uses the cheapest chemistry that still does the job adequately.
- nine_k 7y agoIIRC, titanium fires were a problem during the development of SR-71, too.
- lutorm 7y agoWhen you ignite metals in the presence of pure oxidizer, though, the result is not so much a "fire" as an explosion. It doesn't really "look" different than any other explosion...
- Gibbon1 7y agoI read some of the early experiments with termite reactions involved heating crucibles filled with metal oxides and aluminum power in a furnace. Results were surprising as they were unfortunate.
- throw20102010 7y agoI haven't tried it, but I would make a somewhat educated guess to say, no. Not that it can't be done, but that it probably isn't as easy to get the reaction going as regular thermite. Thermite made from aluminum and iron can start with a child's firework sparkler, so it is pretty easy to make and use. Titanium, while not a noble metal, is more resistant to heat and corrosion than aluminum and is just generally less reactive. You might call it "less un-noble" than aluminum. I expect that you'd have a much harder time getting thermite started using titanium. Just look at how much it took to get the titanium fire going on the Crew Dragon- a chunk of NTO had to slam into a valve at really high speed. Edit: Since you piqued my curiosity, I decided to see if it had been done before. It has: http://developing-your-web-presence.blogspot.com/2008/10/on-titanium-thermite-bronze-age-and.html http://developing-your-web-presence.blogspot.com/2008/10/on-... You replace iron oxide with titanium oxide (since titanium pieces oxidize only on a thin outer layer I expect you would need a very fine mesh), and keep the aluminum. This seems to need a little work but it has been done.
- jandrewrogers 7y agoThermite reactions only happen at extremely high temperatures. Your intuition based on room temperature chemistry is incorrect. Sparklers (i.e. the fireworks) sometimes use titanium to make the sparks, but the primary thing you are igniting is a conventional oxidizer salt (nitrates) and an organic binder. Basically weak rocket fuel with some particles of flammable metal in it to throw off sparks. This is not a thermite reaction. The surface areas of the metals have a huge impact on practical flammability, hence why fine powders are easy to ignite. Iron is also quite flammable as a fine powder but I don't expect my skillet to spontaneously combust on my stove.
- benj111 7y agoI think you're misreading the parent. They're implying you can start the reaction with a sparkler, not that the sparkler reaction is the same.
- jandrewrogers 7y ago
- Gibbon1 7y agoI obtained back you could just order this stuff, 100g of titanium powder. Toss a teaspoon on a camp fire and it makes pretty silver sparks.
- accrual 7y ago> To do this, helium is rapidly pushed through a check valve - designed with low-molecular-mass helium in mind - to physically pressurize the propellant systems. Unintentionally, the NTO that leaked 'upstream' through that valve effectively was taken along for the ride with the high-pressure burst of helium. In essence, picture that you crash your car, only to discover that your nice, fluffy airbag has accidentally been replaced with a bag of sand, and you might be able to visualize the unintended forces Dragon’s check valve (the metaphorical airbag) was subjected to when a "slug" of dense oxidizer was rammed into it at high speed. This paragraph really drove the point home for me. I was able to easily visualize the event.
- wizardforhire 7y agoClassic Water Hammer! https://en.wikipedia.org/wiki/Water_hammer https://en.wikipedia.org/wiki/Water_hammer
- lutorm 7y agoWell "classic" water hammer doesn't involve the water igniting with the pipe material... ;-)
- wizardforhire 7y agoTotally! You get a water hammer and thermite reaction all in one go! Eeeek!
- gpm 7y agoIs metal burning with a non-metal-oxide oxidant a thermite reaction?
- TheSpiceIsLife 7y agoAren't all these thermite oxidisers metals or metalloids? Bismuth(III) oxide, boron(III) oxide, silicon(IV) oxide, chromium(III) oxide, manganese(IV) oxide, iron(III) oxide, iron(II,III) oxide, copper(II) oxide, and lead(II,IV) oxide. https://en.wikipedia.org/wiki/Thermite https://en.wikipedia.org/wiki/Thermite
- phkahler 7y agoDoesn't their solution preclude restarting the engines? Maybe that was never intended.
- gvb 7y agoNo restarts. The incident was with "fire once" thrusters for use only in the event of a launch escape.
- ravedave5 7y agoIt was originally intended but now these are one time use escape engines.
- manicdee 7y agoThe Super Dracos are only intended to be ignited once, either for a launch abort or a propulsive landing.
- jessriedel 7y agoIs it the case that, if used for propulsive landing (which is speculative at this point), each of the Super Draco engines would be turned on and then left on -- presumably, with variable non-zero thrust -- until landing has completed? It's not obvious to me that they wouldn't need to be throttled down to zero. Or is that not relevant so long as the pressure from the helium remains on throughout engine usage?
- ansible 7y agoThe latest I've heard on /r/SpaceX is that the propulsive landing is completely off the table for this vehicle. I suppose they might retain the ability in case of a chute failure, but that would be it. I'd still like to see them try it.
- jessriedel 7y agoMusk says it's still on the table as a backup plan "pending NASA approval". Different commenters on /r/SpaceX have greatly varying estimates about how realistic that is. https://twitter.com/iamkostmos/status/1104510464627625984 https://twitter.com/iamkostmos/status/1104510464627625984 I hadn't heard any thing from official channels since then.
- mholt 7y agoDirect link to SpaceX press release: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation https://www.spacex.com/news/2019/07/15/update-flight-abort-s...
- inamberclad 7y agoAs someone on reddit pointed out: "The following metals have been found to be incompatible with nitrogen tetroxide and must not be used: Aluminum 2024, Zinc, Aluminum 7075, Silver, K-Monel, Titanium, Brass Cadmium, Bronze Hastelloy, Copper, EZ Flow 45 Braze."[0] [0]: Materials Compatibility with Liquid Rocket Propellants, https://apps.dtic.mil/dtic/tr/fulltext/u2/866010.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/866010.pdf
- yborg 7y ago>Boeing report published 1970 >SpaceX: "It is worth noting that the reaction between titanium and NTO at high pressure was not expected." SpaceX did not expect a reaction known to Boeing almost 50 years ago. My guess would be that this is actually known by a lot of people in rocketry, since UDMH/NTO is a standard propellant - the Proton is entirely fueled with it. I also guess that the titanium component of the valve is not normally exposed to the oxidizer, and only came in contact with it when the valve broke. It would seem that the simple issue of shattered valve fragments flying down the oxidizer line would have been sufficient to destroy the thruster irrespective of a titanium fire...
- russdill 7y agoI think for the fire to start, there has to be titanium fragments, not smooth, solid titanium
- lvs 7y agoNot hard to achieve during unscheduled disassembly. But the same report also notes: "Nitrogen tetroxide with a water content in excess of 2.5 percent can accelerate titanium intergranular corrosion to the point of violent reaction."
- DuskStar 7y ago> Not hard to achieve during unscheduled disassembly. I think the assumption is that by the time a RUD starts you no longer care about whether the various parts of your fuel system are going to explode, since the fuel is a far larger concern and it's going to go up anyways.
- PhantomGremlin 7y agoBased on what just happened, this is somewhat alarming: For the time being, NASA has published a tentative target of mid-November 2019 for Crew Dragon’s first crewed launch to the International Space Station I'd rather fly 1,000,000 miles in a Boeing 737 MAX than risk one ride in this contraption. It surely needs quite a bit more unmanned testing before it can honestly be considered to be "man rated". Of course, NASA has a long and sordid history of pushing spaceflight while playing down many potential catastrophic problems. The Shuttle problems prove that. And there's no need to belabor Musk's shortcomings. As someone on HN recently quipped, in response to Musk's claim of full driving autonomy by 2020: Tesla has an advantage here in that they don't feel the need for their autonomy to be particularly safe.
- freehunter 7y agoLuckily you’re also 1,000,000 times more likely to fly 1,000,000 miles in a 737 Max than to ever fly in one of these contraptions. So you don’t need to worry about it.
- lutorm 7y agoWell, flying paying passengers in scheduled airline traffic and taking astronauts to space have different definitions of "man rated". As they should.
- mikeash 7y agoAirliners are the safest form of transport ever devised. You’re safer in an airliner than you are in the shower. Space travel is one of the most dangerous forms of transport ever devised. Even the most insane, wildly optimistic estimates for the safety of the Shuttle were orders of magnitude more dangerous than an airliner. Comparing the two does not make sense. If airliners are your standard of safety for space travel, you might as well take a shortcut and just say “don’t launch humans into space.”
- PhantomGremlin 7y agoComparing the two does not make sense. If airliners are your standard of safety for space travel, you might as well take a shortcut and just say “don’t launch humans into space.” It most certainly makes sense. A lot of sense. The Dragon capsule spectacularly blew itself to smithereens. Now is not the time to bring out some duct tape and baling wire to slap the thing back together so that it can attempt to fly astronauts into space before the end of the year. Now is the time for careful and considered testing. Not rushing. This thing needs to be safe. I can guarantee you one thing. If American astronauts die this year because of inadequate testing, that will be the last time you see American astronauts being launched into space on a NASA sponsored platform. If Americans die because this was rushed, you can kiss NASA's manned space efforts goodbye. We'll pay the Russians what it takes to keep going to ISS. And when ISS ends, NASA will be out of the manned space flight business. The operative word going forward will be "robotics".
- black6 7y agoFTA: “...instead of a mechanical check valve (simple but still not 100% passive), the barrier between pressurant and oxidizer (as well as fuel, most likely) will be replaced with something known as a burst disk.” A burst disk comes from a different concept than a check valve. With a check valve, one presumably desires a fluid flowing in one direction—in this case the pressurant for the oxidizer vessel—and no back flow. In the rocket engine industry this setup tends to be used to maintain cleanliness. A burst disk, however, embodies the same concept as a relief valve—it prevents the pressurization of a system above its rated capacity. I fail to see how replacing a check valve with a burst disk fixes the problem and maintains the same system capability.
- lutorm 7y agoI think the idea is that the system is never intended to be depressurized once it's pressurized, so you don't need a check valve, you just need something to prevent backflow before the system is pressurized.
- black6 7y agoAha. I have a better understanding after reading the actual SpaceX presser[0]. The SuperDraco thrusters are to be used only for a launch escape scenario, so they would only be used once before a ground refit of the capsule. That being the case, a burst disk does make sense as a replacement for a check valve. 0: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation https://www.spacex.com/news/2019/07/15/update-flight-abort-s...
- Mvandenbergh 7y agoThe reason why they have a check valve is that the design was originally designed to be re-lightable for purposes including but not limited to abort. At this point, NASA only wants them used for abort so a burst disk is a simpler design but I guess they never updated the design to reflect the restricted purpose. That would fit with SpaceX's general design philosophy of building re-usability in well before the systems are actually due to be re-used.
- deleted 7y ago[deleted]
- Kye 7y agoExotic Titanium Fire would make a great band name.
- RyJones 7y agoToo bad "Some Birds Don't Fly"[0] is so expensive these days; interesting read on the early days of misslecraft [0] https://www.amazon.com/Some-birds-dont-Gary-Paulsen/dp/B0006BU29W https://www.amazon.com/Some-birds-dont-Gary-Paulsen/dp/B0006...
- DuskStar 7y agoOoh, I'll have to keep an eye out! Have you read Ignition! [0] to give a comparison? 0: https://www.amazon.com/Ignition-informal-history-liquid-propellants/dp/0813507251 https://www.amazon.com/Ignition-informal-history-liquid-prop... EDIT: archive.org appears to have it: https://archive.org/details/somebirdsdontfly00paul https://archive.org/details/somebirdsdontfly00paul
- RyJones 7y agoI have not! Thanks!
- caf 7y agoRelevant to this story is this passage from Ignition!: On December 29, 1953, a technician at Edwards Air Force Base was examining a set of titanium samples immersed in RFNA, when, absolutely without warning, one or more of them detonated, smashing him up, spraying him with acid and flying glass, and filling the room with NO₂. The technician, probably fortunately for him, died of asphyxiation without regaining consciousness. There was a terrific brouhaha, as might be expected, and JPL undertook to find out what had happened. J. B. Rittenhouse and his associates tracked the facts down, and by 1956 they were fairly clear. Initial intergranular corrosion produced a fine black powder of (mainly) metallic titanium. And this, when wet with nitric acid, was as sensitive as nitroglycerine or mercury fulminate. (The driving reaction, of course, was the formation of TiO₂.) Not all titanium alloys behaved this way, but enough did to keep the metal in the doghouse for years, as far as the propellant people were concerned. (RFNA is a mixture of NTO and anhydrous nitric acid).
- temptemptemp111 7y agoScam artists. Happy 50Y Moon Landing anniversary. LOL!!!
- delinka 7y agoI've taken these from other commenters, but can someone rectify these apparently contradictory statements for me? "The following metals have been found to be incompatible with nitrogen tetroxide and must not be used: Aluminum 2024, Zinc, Aluminum 7075, Silver, K-Monel, Titanium, Brass Cadmium, Bronze Hastelloy, Copper, EZ Flow 45 Braze."[0] "Titanium is practically the only metal that can store NTO for long periods of time over a reasonably large temperature range." [1] [0]: Materials Compatibility with Liquid Rocket Propellants, https://apps.dtic.mil/dtic/tr/fulltext/u2/866010.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/866010.pdf [1]: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720019028.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197200...
- delibes 7y agoI think levels of impurities and surface treatment of the metal may cause variation in whether something is considered suitable or not? For example, from [0] (which is declassified from 1974!) : "Titanium can react violently with strong oxidizers if the oxi-dizer penetrates the oxidized surface layer." "Free chloride, ions in nitrogen tetroxide can cause an accelera-tion of intergranular corrosion in titanium."
- VLM 7y agoIts sorta like "seawater will rust steel eventually" vs we make all our ships out of steel. The ancient Boeing report is quoted at length as gospel but the reasoning is not explained. Here's some weird facts: 1) Most metals are not happy with NTO because any moisture turns NTO into concentrated nitric acid and nitric eats lots of metals. 2) Some industrial nitric acid plant components are made of very expensive titanium because its strong and essentially nitric acid corrosion proof. This makes Ti sound fantastic for NTO... however... 3) It is true that titanium is one of the few metals you can dunk in seawater where stress-corrosion does NOT occur. Which makes people even more hyper optimistic about Ti for NTO tanks as per above... however... 4) Unfortunately titanium DOES stress corrode in NTO. Stress corrosion is where essentially microcracks that would normally heal in other metals instead get a higher volume "rust" oxidation in the crack slowly breaking the metal apart after thousands or millions of cycles even if an unstressed part would never wear. Think of a perfectly painted garage that would never have wood rot due the the paint protecting the wood, but if you bend the wood back and forth tiny cracks will form in the paint and the water will soak thru the cracks into the wood and the garage wood will rot eventually even if the paint was theoretically perfect under unstressed conditions. Its actually a little more complicated than this. So from an engineering standpoint if you build something under millions of cycles of repetitive stress like the shaft of a circulation pump in an industrial production NTO tank out of titanium, you're doomed to have it shear in a "sooner than economically viable" amount of time like a couple months of continuous use maybe. On the other hand if you build a valve that will only exist for a little while and only be under a couple stress cycles in its lifetime and only possibly operate once for a few seconds, thats very likely OK. There is also a systems issue where if a life-critical failure occurs upstream resulting in everyone being dead already, it doesn't matter if downstream a system that should never be contaminated fails and burns. Or rephrased if enough stuff upstream broke such that the helium system literally caught fire, the crew are already dead men and the ships already lost so it doesn't really matter much anymore if the helium system burns or does not burn at that point. I mean its technically interesting but if you're gonna lose the vehicle and pax it doesn't matter really in the long run. Kinda like the old line about how we could build jet liners to the same standards as black boxes, but the external G forces of the crash would kill the passengers inside the giant black box so realistically why bother. If something upstream fails badly enough that the helium system is compromised, they're already dead anyway so engineering a theoretically indestructible helium system is a waste of time if the mission, ship, and passengers are already lost, so may as well save the weight and labor.