I haven't tried it, but I would make a somewhat educated guess to say, no. [1]. > Musk says it's still on the table as a backup plan "pending NASA approval". I saw "titanium fire" but my brain substituted "magnesium fire". I think for the fire to start, there has to be titanium fragments, not smooth, solid titanium. 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. This isn't entirely arbitrary: air travel has gotten a lot safer lately. We'll pay the Russians what it takes to keep going to ISS. (I'm not disagreeing with you that on a per-mile basis, air travel is very safe. The titanium component in a check valve failed due to a leak of the liquid oxydiser - nitrogen tetroxide (NTO) - and this caused an ignition within the check valve and then the subsequent explosion. There’s an argument that instead of passenger-miles, most people’s intuitive sense of transportation danger is actually based on passenger-hours, not passenger-miles, which makes buses and trains look better. An electronics analogy is a dude who can't solder at all thinks thru-hole soldering is exotic skills and equipment. If people really do evaluate it that way, it’s an interesting bit of psychology, but irrelevant to actual safety. > "titanium fire" but my brain substituted "magnesium fire". Expecting them to see the 'water hammer' issue is a different story, "Nitrogen tetroxide with a water content in excess of 2.5 percent can accelerate titanium intergranular corrosion to the point of violent reaction.". Eeeek! Can you make a thermite rocket out of thermite and starlite? 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. Then if we extend this fair comparison to space, the amount of miles traveled gets rather large, so that would be interesting to see as well. There will of course still be issues with the residual hypergolics since they are highly toxic and the propellant tanks will need to be decanted: whether than happens before or after crew recovery is another discussion. 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. https://twitter.com/iamkostmos/status/1104510464627625984. Exotic Titanium Fire would make a great band name. Doesn't their solution preclude restarting the engines? Not that it can't be done, but that it probably isn't as. (edit: 99.3% with Laplace's rule.) Copyright © 2020 Elsevier B.V. or its licensors or contributors. Or is that not relevant so long as the pressure from the helium remains on throughout engine usage? Not rushing. Musk says it's still on the table as a backup plan "pending NASA approval". Ooh, I'll have to keep an eye out! 141 safe launches just implies that the probability of success is p^141=0.5 (since I have no idea how likely this outcome was, I default to 50/50), so 99.5%. 4:46: Let me just move this beaker of rocket fuel over a foot while I aim a syringe of oxidizer. SpaceX stated: "It is worth noting that the reaction between titanium and NTO at high pressure was not expected. The average airliner trip is hundreds or thousands of miles. An ordinary sparkler does not generate enough heat to reliably bootstrap a thermite reaction. I just think the specific numbers here are interesting. Is "exotic" a technical term, or did the chemicals simply come from a distant foreign country, and how does that affect their physical properties? "Titanium has been used safely over many decades and on many spacecraft from all around the world. Those guys work 14 to 16 hours a day. If Americans die because this was rushed, you can kiss NASA's manned space efforts goodbye. It is used in the Titan III, 34D, and IV space launch vehicles, the Space Shuttle reaction control system, and in some of the newer satellite … That's why we need to bring down that giant gold asteroid! Metals that burn easily, such as magnesium or calcium, are not necessarily great choices as they will be limited by the thermodynamics of the metal oxide and ease of burning does not imply optimal thermite performance. First, it can mean observed chemistry that is seen neither in nature nor the lab under ordinary conditions. 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. The operative word going forward will be "robotics". While as a ceo and "quick drafting solutions" that works. Your numbers look sound. 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. Which makes people even more hyper optimistic about Ti for NTO tanks as per above... however... 4) Unfortunately titanium DOES stress corrode in NTO. It became the storable oxidizer of choice for many rockets in both the United States and USSR by the late 1950s. [0] to give a comparison? Pic: @Astronut099. >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. Unintentionally, the NTO that leaked 'upstream' through that valve effectively was taken along for the ride with the high-pressure burst of helium. Controlling the particle characteristics would be a bit of a challenge though. Totally! Figure 4.5 shows the spectral normalized effective crosos-section kg for different gases. 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. Trains see a rate of 0.15 per billion passenger miles (not including fatalities of non-passengers). I haven't done a fair comparison where the same metric was used (say, fatalities per mile traveled in both transport types) but it would be interesting to see one. Eh all metals like to burn, which is why so many are found as oxides in nature. probably fortunately for him, died of asphyxiation without With no pressuring remaining there is no way to repeat this anomaly. Luckily 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. However, I assume that NASA was monitoring SpaceX's design from early on, and that if the design was clearly dangerous NASA would have insisted that SpaceX change it. I'm sure airliners would still come out on top against cars, but the ratio would be different. Its sorta like "seawater will rust steel eventually" vs we make all our ships out of steel. If you look at, say, the last decade, terrorism doesn't make any difference. 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. russdill on July 16, 2019 In the SpaceX report, it says that the NTO struck the valve at high speed and pressure, causing it to shatter. Additionally, NTO is often used with the addition of a small percentage of nitric oxide , which inhibits stress-corrosion cracking of titanium alloys, and in this form, propellant-grade NTO is referred to as " Mixed Oxides of Nitrogen " or "MON". What are you going to use to convert titanium into a powder? It is a hypergoli… 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. Space travel is not "safe", period. If you decide to go into space, you should be aware that you're exposing yourself to significant risk. ). It surely needs quite a bit more unmanned testing before it can honestly be considered to be "man rated". The ancient Boeing report is quoted at length as gospel but the reasoning is not explained. The 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. Typical thermite bootstraps are three stage for the simple reason that chemistry that is easy to ignite usually does not generate enough thermal power to bootstrap a thermite reaction. I was able to easily visualize the event. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197200... https://www.spacex.com/news/2019/07/15/update-flight-abort-s... https://www.amazon.com/Some-birds-dont-Gary-Paulsen/dp/B0006... https://www.amazon.com/Ignition-informal-history-liquid-prop... https://archive.org/details/somebirdsdontfly00paul, https://www.youtube.com/watch?v=xHHZtwS9U80, https://www.youtube.com/watch?v=cH76ObzYIxc. I've used titanium shavings, lit by high explosives, to start fires. I wouldn’t quite go as far as stupid. To work with substance X, which is called "exotic", you need an upgrade beyond my lab's equipment and safety gear and training, my suppliers consider it custom work if they can provide at all, and the budget has another couple zeros. Moreover, they also show the problem of interferences between the gases. Measuring by hour is plainly stupid. But we don’t live in that world; planes are better in safety when measuring by passenger hour than cars, so in fact we’ve improved public health. "Even so, the static fire test and anomaly provided a wealth of data. 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. The term "exotic" in a chemistry context means one of two things. If cheap air travel availability as a mode induces people to travel 10x more passenger miles, in a world where airlines were only as safe per passenger mile as cars, there would be a net reduction in public health. 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.
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