Quote from: SWGlassPit on 09/01/2016 08:36 pmQuote from: king1999 on 09/01/2016 08:31 pmQuote from: ellindsey on 09/01/2016 08:26 pmAccidentally (or deliberately) activated FTS would have activated the FTS for the entire vehicle, not just the second stage. This failure was too localized to be FTS.That exactly looks like what happened. The whole stack just exploded really fast.It really didn't. There was a localized explosion in the second stage with a relatively slow progressive failure down the stack. If it was FTS, the whole vehicle would have ceased to exist in the span of two or three frames.FTS isn't designed to obliterate the vehicle as much as it is to release the fuel to get rid of its mass, momentum, and explosive potential. When we've seen FTS before it causes a slow conflagration fireball just like we see here after that initial pop at the top of S2. It looked very much like the fireball we saw on GH2, although with a much better vantage point to see details.For those saying FTS wouldn't cause a fireball, well, what other ignition source was there? We didn't see a green flash.
Quote from: king1999 on 09/01/2016 08:31 pmQuote from: ellindsey on 09/01/2016 08:26 pmAccidentally (or deliberately) activated FTS would have activated the FTS for the entire vehicle, not just the second stage. This failure was too localized to be FTS.That exactly looks like what happened. The whole stack just exploded really fast.It really didn't. There was a localized explosion in the second stage with a relatively slow progressive failure down the stack. If it was FTS, the whole vehicle would have ceased to exist in the span of two or three frames.
Quote from: ellindsey on 09/01/2016 08:26 pmAccidentally (or deliberately) activated FTS would have activated the FTS for the entire vehicle, not just the second stage. This failure was too localized to be FTS.That exactly looks like what happened. The whole stack just exploded really fast.
Accidentally (or deliberately) activated FTS would have activated the FTS for the entire vehicle, not just the second stage. This failure was too localized to be FTS.
The vehicle is sitting in a cloud of concentrated, evaporating oxygen and is holding thousands of kilograms more on board. A small leak and a spark is all that is needed to cause an event big enough to rupture the tanks leading the chain reaction. Oxygen is abundant in this scenario - we don't need an explosive to turn the situation bad.
Quote from: Moderas on 09/01/2016 08:43 pmThe vehicle is sitting in a cloud of concentrated, evaporating oxygen and is holding thousands of kilograms more on board. A small leak and a spark is all that is needed to cause an event big enough to rupture the tanks leading the chain reaction. Oxygen is abundant in this scenario - we don't need an explosive to turn the situation bad.Oxygen alone will not cause an explosion. It does not react with itself. You need a fuel source.
I heard from one of the reddit that some believe a hydrazine leak from the satellite may of caused the initial explosion. Given the location of the explosion being close the top of the oxygen tank, and the initial size explosion it seems like this is certainly possible. I know from chemistry that hydrazine is particularly reactive, volatile, and very dangerous. I am not an expert on launch systems and satellites, but what is the likelihood that this was the case.
13,000 gallons of liquid oxygen and a full load of fuel sloshed over the stand and the nearby terrain.
Wonder how the Dragon2 Trunk/Capsule would have dealt with this 2nd Stage RUD in a Pad Abort scenario?
Quote from: ugordan on 09/01/2016 06:06 pmQuote from: leetdan on 09/01/2016 05:59 pmCheck the audio, there's a small pop about 5 seconds before the sound from the actual explosions arrive.I think that's just someone messing around a car or something near the camera.Interestingly enough, the small first bang heard is the original S2 explosion. The big bang 3 seconds later is the fuel-air type explosion when that fireball hit the ground and mixed up the RP-1 and LOX. I hear three distinct "initial" sounds:1:16--a very faint "plonk" like someone hitting a PVC pipe with a hammer in the distance...COPV rupture?1:18--a faint pop/bang... S2 tank rupture?1:23--very loud boom...the LOX/RP-1 explosion?That first sound at 1:16 is unusual and seems to me like it may be the initiating event. A COPV or high pressure line/fitting letting go followed by S2 tank rupture 1-2 seconds later seems consistent.
Quote from: leetdan on 09/01/2016 05:59 pmCheck the audio, there's a small pop about 5 seconds before the sound from the actual explosions arrive.I think that's just someone messing around a car or something near the camera.Interestingly enough, the small first bang heard is the original S2 explosion. The big bang 3 seconds later is the fuel-air type explosion when that fireball hit the ground and mixed up the RP-1 and LOX.
Check the audio, there's a small pop about 5 seconds before the sound from the actual explosions arrive.
Quote from: SWGlassPit on 09/01/2016 08:42 pmQuote from: intrepidpursuit on 09/01/2016 08:37 pmThe biggest thing I don't understand is what is the ignition source? Even if the O2 tank had an overpressure, underpressure, or any other failure mode, why would the first thing we see be blinding fire? Some static or something would probably catch it eventually, but without the engines running you could mix O2 and RP-1 and it would still not self detonate.Am I missing something? I realize my optimism toward SpaceX might make me favor the least damaging outcome, but I just don't see how anything other than an explosive charge could have detonated so quickly. TEA-TEB or hypergolics could easily cause a bad day, but they don't appear to have been involved unless they were being loaded into S2 by the umbilical at the time.If the fuel-oxygen mix is right, it only takes a tiny spark. Electrostatic discharge, a momentary arc from a switch opening or closing, really anything...Indeed. You might call this a *static*fire*. Heh.
Quote from: intrepidpursuit on 09/01/2016 08:37 pmThe biggest thing I don't understand is what is the ignition source? Even if the O2 tank had an overpressure, underpressure, or any other failure mode, why would the first thing we see be blinding fire? Some static or something would probably catch it eventually, but without the engines running you could mix O2 and RP-1 and it would still not self detonate.Am I missing something? I realize my optimism toward SpaceX might make me favor the least damaging outcome, but I just don't see how anything other than an explosive charge could have detonated so quickly. TEA-TEB or hypergolics could easily cause a bad day, but they don't appear to have been involved unless they were being loaded into S2 by the umbilical at the time.If the fuel-oxygen mix is right, it only takes a tiny spark. Electrostatic discharge, a momentary arc from a switch opening or closing, really anything...
The biggest thing I don't understand is what is the ignition source? Even if the O2 tank had an overpressure, underpressure, or any other failure mode, why would the first thing we see be blinding fire? Some static or something would probably catch it eventually, but without the engines running you could mix O2 and RP-1 and it would still not self detonate.Am I missing something? I realize my optimism toward SpaceX might make me favor the least damaging outcome, but I just don't see how anything other than an explosive charge could have detonated so quickly. TEA-TEB or hypergolics could easily cause a bad day, but they don't appear to have been involved unless they were being loaded into S2 by the umbilical at the time.
Quote from: DarkenedOne on 09/01/2016 08:56 pmI heard from one of the reddit that some believe a hydrazine leak from the satellite may of caused the initial explosion. Given the location of the explosion being close the top of the oxygen tank, and the initial size explosion it seems like this is certainly possible. I know from chemistry that hydrazine is particularly reactive, volatile, and very dangerous. I am not an expert on launch systems and satellites, but what is the likelihood that this was the case.Probably near zero. The payload was well above the plane where the first flash occurred, encapsulated in a fairing that remained intact long after the initial explosion. Also there's no way for hydrazine to get *into* the LOX tank, which appeared to rupture, suggesting the event may have started inside the LOX tank.
Crank up the volume, the first sound could be the creak of metal bending. If that's the case, we might be hearing a strut bend and break, a COPV rupturing or helium hose popping, and the loud boom is the visible explosion.
FTS is designed to cease acceleration and disperse the propellants. This is often accomplished by a linear shaped charge running the length of the vehicle. I suspect the Falcon is the same way. You might not see an immediate fireball, but you would see the whole vehicle unzip basically at once if it were FTS, not the several seconds it took to completely come apart.
Quote from: IanH84 on 09/01/2016 07:13 pmCrank up the volume, the first sound could be the creak of metal bending. If that's the case, we might be hearing a strut bend and break, a COPV rupturing or helium hose popping, and the loud boom is the visible explosion.Please... This is an incessant problem on the internet to attribute new failures to previous issues. In engineering its the exception rather than the rule that a new failure is the same failure as before. If something fails its almost certainly something else that failed unless your engineers have no clue what they're doing or root cause was not found. This failure is NOT going to be related to struts. Forget the struts exist. That's a solved problem. Different metal suppliers, different stronger design, additional struts, impossible to be the same problem.
Sorry, but there is oversaturation and then there is oversaturation. According to you, those spikes should simply be as wide as the whited-out region, which is clearly not the case. My point is that it takes even more light intensity to produce spiking than it takes to saturate the detector at a region and that it was reasonable to assume that the highest physical brightness point corresponds to the point of origin. The spikes convey additional useful information about the brightness profile above the whited-out region precisely because they are more tightly constrained.