So in my mind we have ~100cc of N2O4 liquid which rams up against some solid titanium with enough energy to probably hammer burst the valve or line at that point and to ignite the surface of the valve metal and maybe some wire insulation and paint or whatever the flame and N2O spray up against but at that point its surface combustion with a small volume of N2O4 which within milliseconds will be followed by a flood of fire extinguishing Helium. So far that sounds like about as much energy as crashing a 125cc dirt bike into the side of a barn at 25 mph (to use scientific units) with possibly continuing combustion of the titanium liberating more energy over the next few seconds. That to me doesn't seem nearly energetic enough to blow the entire thing (less the SDs which were miraculously preserved) to smithereens. So something happened subsequently and I assume exceedingly quickly subsequently. Anyone care to elaborate on that? More quickly than say a camp fire acting on the outside of the propellant tanks which would take a minute or so to burst. Perhaps the only scenario that I can envision is that on the tank side of the check valve the inside of the metal N2O4 line, the surface interface between metal and N2O4 detonated all the way back into the N2O4 tank thus pressurizing it (it wasn't to that point pressurized(?)) and bursting it which was the dramatically energetic event.
Quote from: mlindner on 07/15/2019 08:53 pmIt should, Titanium is used everywhere for NTO. The fact it can burn it I don't think is well known. Titanium is generally pretty non-reactive.Interesting tweets on this topic by Ben Brockert:https://twitter.com/wikkit/status/1150855184924336128?s=20QuoteSpaceX update on the disappearing Dragon. (link: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation) spacex.com/news/2019/07/1… “It is worth noting that the reaction between titanium and NTO at high pressure was not expected” is a frightening sentence; titanium is well known to have poor oxidizer compatibility and be easy to set on fire. “resistant to N2O4 except under impact... found that Ti impacts sporadically under reasonably well controlled test conditions; the ignition freq. is increased markedly by Ti filings or glass particles on the impact surface” Compatibility of Materials w/ Rocket Prop and Oxidizers
It should, Titanium is used everywhere for NTO. The fact it can burn it I don't think is well known. Titanium is generally pretty non-reactive.
SpaceX update on the disappearing Dragon. (link: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation) spacex.com/news/2019/07/1… “It is worth noting that the reaction between titanium and NTO at high pressure was not expected” is a frightening sentence; titanium is well known to have poor oxidizer compatibility and be easy to set on fire. “resistant to N2O4 except under impact... found that Ti impacts sporadically under reasonably well controlled test conditions; the ignition freq. is increased markedly by Ti filings or glass particles on the impact surface” Compatibility of Materials w/ Rocket Prop and Oxidizers
As someone who deals with (indirectly usually) burst discs daily, I gotta wonder about the contamination of metal fragments downstream of the bursted disc. Especially if the system is tested (discs replaced) one or more times...
Quote from: mmeijeri on 07/15/2019 08:57 pmQuote from: mlindner on 07/15/2019 08:53 pmIt should, Titanium is used everywhere for NTO. The fact it can burn it I don't think is well known. Titanium is generally pretty non-reactive.Interesting tweets on this topic by Ben Brockert:https://twitter.com/wikkit/status/1150855184924336128?s=20QuoteSpaceX update on the disappearing Dragon. (link: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation) spacex.com/news/2019/07/1… “It is worth noting that the reaction between titanium and NTO at high pressure was not expected” is a frightening sentence; titanium is well known to have poor oxidizer compatibility and be easy to set on fire. “resistant to N2O4 except under impact... found that Ti impacts sporadically under reasonably well controlled test conditions; the ignition freq. is increased markedly by Ti filings or glass particles on the impact surface” Compatibility of Materials w/ Rocket Prop and OxidizersThat tweet was deleted though. Are we sure that's accurate?
Quote from: mlindner on 07/16/2019 01:34 amThat tweet was deleted though. Are we sure that's accurate?The quote is indeed from the source given. But it does not include the context - the very next sentence (just after the quote) says "The ignitions do not spread beyond the impact area."
That tweet was deleted though. Are we sure that's accurate?
Quote from: Chris Bergin on 07/15/2019 07:29 pmSpaceX release:Initial data reviews indicated that the anomaly occurred approximately 100 milliseconds prior to ignition of Crew Dragon’s eight SuperDraco thrusters and during pressurization of the vehicle’s propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.My thought when I read "a leaking component" is that the writer went a bit out of the way to not say it was the check valve referred to in the next sentence, the one that went boom. While not certain it leads me to believe there may be (an)other component(s) in the system that leaked here to there. Not sure what it may be (differential pressure sensor???) but it seems that writing was passed through an intentionally vague filter.edit: or it could be that they don't even know which of a plurality of components leaked, still investigating, though admittedly its a simple system and the number of suspect leak paths / components would be very low.
SpaceX release:Initial data reviews indicated that the anomaly occurred approximately 100 milliseconds prior to ignition of Crew Dragon’s eight SuperDraco thrusters and during pressurization of the vehicle’s propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.
Mars Observer (probably) had a similar failure when NTO migrated slowly over time through a check valve, then got blown into the MMH side of the biprop system upon pressurization.
Quote from: OxCartMark on 07/15/2019 10:10 pmQuote from: Chris Bergin on 07/15/2019 07:29 pmSpaceX release:Initial data reviews indicated that the anomaly occurred approximately 100 milliseconds prior to ignition of Crew Dragon’s eight SuperDraco thrusters and during pressurization of the vehicle’s propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.My thought when I read "a leaking component" is that the writer went a bit out of the way to not say it was the check valve referred to in the next sentence, the one that went boom. While not certain it leads me to believe there may be (an)other component(s) in the system that leaked here to there. Not sure what it may be (differential pressure sensor???) but it seems that writing was passed through an intentionally vague filter.edit: or it could be that they don't even know which of a plurality of components leaked, still investigating, though admittedly its a simple system and the number of suspect leak paths / components would be very low.I found the wording to be odd also, but how many components are capable of introducing an NTO slug into the helium line upstream of the check valve other than the check valve?
QuoteAdditionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability....so nobody's gonna point out how ridiculous this line is?
Additionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability.
Quote from: Kabloona on 07/16/2019 12:22 amMars Observer (probably) had a similar failure when NTO migrated slowly over time through a check valve, then got blown into the MMH side of the biprop system upon pressurization.Actually, there was some work long after the MO failure review that suggested the failure was more likely due to incompatible materials in the helium pressure regulator and not related to migration through the check valve after all. "Propulsion Lessons Learned from the Loss of Mars Observer", Carl S.Guernsey, JPL, 2001, but I can't find a copy online at the moment.
Quote from: jgoldader on 07/15/2019 10:27 pmThis reminds me of the Mars Observer, which was lost (most likely) due to a failed check valve. That case might’ve been discussed upthread.Yes, in fact my first thought after the Dragon failure was the Mars Observer check valve failure mode. We discussed it in Thread 2 some time ago, and also in L2.https://forum.nasaspaceflight.com/index.php?topic=48047.msg1951990#msg1951990
This reminds me of the Mars Observer, which was lost (most likely) due to a failed check valve. That case might’ve been discussed upthread.
Quote from: LouScheffer on 07/15/2019 06:04 pmQuote from: Mandella on 07/13/2019 07:49 pmShort the finger pointing, I suppose this is a good thing, even if that first press conference is going to be a bunch of people with serious looks on their faces going, "No, we don't yet know the root cause of the incident.""No, we really don't know the proximate cause either.""No, we don't know how much this is going to affect the schedule, if at all.""No, I don't know why I'm standing here, except that we don't want the media to be frustrated, I guess."One thing that they could say that would decrease media frustration is "Here is a public domain video of the anomaly". The detailed answers will come later, and the media knows that, but this gives them something to put in their article that will be fascinating to their audience. It also avoids any appearance of a coverup.SpaceX has a lot of powerful enemies that like to latch onto anything they can to sow unjustified fear, uncertainty, and doubt. Releasing a video of a failure just gives ammunition to that kind of unfair treatment. I can understand why SpaceX would not want to do that, particularly at a time when they didn't have the information themselves to authoritatively refute such attacks.
Quote from: Mandella on 07/13/2019 07:49 pmShort the finger pointing, I suppose this is a good thing, even if that first press conference is going to be a bunch of people with serious looks on their faces going, "No, we don't yet know the root cause of the incident.""No, we really don't know the proximate cause either.""No, we don't know how much this is going to affect the schedule, if at all.""No, I don't know why I'm standing here, except that we don't want the media to be frustrated, I guess."One thing that they could say that would decrease media frustration is "Here is a public domain video of the anomaly". The detailed answers will come later, and the media knows that, but this gives them something to put in their article that will be fascinating to their audience. It also avoids any appearance of a coverup.
Short the finger pointing, I suppose this is a good thing, even if that first press conference is going to be a bunch of people with serious looks on their faces going, "No, we don't yet know the root cause of the incident.""No, we really don't know the proximate cause either.""No, we don't know how much this is going to affect the schedule, if at all.""No, I don't know why I'm standing here, except that we don't want the media to be frustrated, I guess."
So in my mind we have ~100cc of N2O4 liquid which rams up against some solid titanium with enough energy to probably hammer burst the valve or line at that point and to ignite the surface of the valve metal and maybe some wire insulation and paint or whatever the flame and N2O spray up against but at that point its surface combustion with a small volume of N2O4 which within milliseconds will be followed by a flood of fire extinguishing Helium. So far that sounds like about as much energy as crashing a 125cc dirt bike into the side of a barn at 25 mph (to use scientific units) with possibly continuing combustion of the titanium liberating more energy over the next few seconds. That to me doesn't seem nearly energetic enough to blow the entire thing (less the SDs which were miraculously preserved) to smithereens. So something happened subsequently and I assume exceedingly quickly subsequently. Anyone care to elaborate on that? More quickly than say a camp fire acting on the outside of the propellant tanks which would take a minute or so to burst. Perhaps the only scenario that I can envision is that on the tank side of the check valve the inside of the metal N2O4 line, the surface interface between metal and N2O4 detonated all the way back into the N2O4 tank thus pressurizing it (it wasn't to that point pressurized(?)) and bursting it which was the dramatically energetic event.What do we suppose these propellant lines and tanks are made from? Stainless steel? Titanium? Any info on flame front speed in these conditions?
Quote from: envy887 on 07/15/2019 11:43 pmQuote from: arachnitect on 07/15/2019 09:31 pmQuoteAdditionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability....so nobody's gonna point out how ridiculous this line is?Not at all. It rules out the SDs as a potential root cause.Agree, this is an attempt to emphasize the fact that the SDs were not involved in the mishap. But it comes off ham-fisted. Pointing out the engines are intact when the rest of the capsule was destroyed? It sounds like something Elon might say at a press conference. (theory: he learned the SDs were found intact and demanded this detail be included)Good intention, sub-optimal communication.
Quote from: arachnitect on 07/15/2019 09:31 pmQuoteAdditionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability....so nobody's gonna point out how ridiculous this line is?Not at all. It rules out the SDs as a potential root cause.
