- #176
Jonathan Scott
Gold Member
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From some of the popular descriptions, people might think that the explosion was directly caused by the COPV overwrap catching fire when solid oxygen was crushed against it. However, that wouldn't have enough energy to do much immediate damage on its own, as there was very little material to burn. All it did was cause the COPV failure (and perhaps provided a source of ignition for the main fire later, although many other things could also have done that). As Scott Manley also mentioned, it isn't even certain that the solid oxygen caused a fire. Perhaps it could have merely created ridges underneath the overwrap layer which overstressed it, causing a split.
The second step of the problem was presumably that the pressure shockwave from the helium released suddenly by the failed COPV split the second stage (probably along some sort of seam), opening up the LOX tank and the top part of the fuel tank, ejecting a LOX-rich mixture. (Note of course that LOX does not burn on its own, and fuel will only burn slowly in the absence of LOX).
Finally, that mixture caught alight outside the second stage, creating a flame front which initially ran through it at very high speed. However, once the flame front had reached the limit of the expanding shower of fuel and LOX, it slowed down significantly. I think this means that at the time the mixture was ejected, it was not on fire and was moving significantly slower than the subsequent flame front. I must admit I can't see any sign of anything being sprayed out in the previous two or three frames, which one might expect from that theory, but there's a lot of cloudy stuff around anyway.
The above is my personal interpretation of the details, which is mostly the same as my initial guess earlier in this thread of a COPV failure. I suggested that buoyancy forces or stresses due to thermal contraction could be responsible for the COPV failing at that point. Obviously the buoyancy forces during launch would be higher, so that didn't seem likely, but I think the thermal contraction idea was close.
Does anyone know of any additional information on this apart from the SpaceX anomaly update on their own website? Was anything interesting posted to those Nasa forums, which I don't have the time to read through?
The second step of the problem was presumably that the pressure shockwave from the helium released suddenly by the failed COPV split the second stage (probably along some sort of seam), opening up the LOX tank and the top part of the fuel tank, ejecting a LOX-rich mixture. (Note of course that LOX does not burn on its own, and fuel will only burn slowly in the absence of LOX).
Finally, that mixture caught alight outside the second stage, creating a flame front which initially ran through it at very high speed. However, once the flame front had reached the limit of the expanding shower of fuel and LOX, it slowed down significantly. I think this means that at the time the mixture was ejected, it was not on fire and was moving significantly slower than the subsequent flame front. I must admit I can't see any sign of anything being sprayed out in the previous two or three frames, which one might expect from that theory, but there's a lot of cloudy stuff around anyway.
The above is my personal interpretation of the details, which is mostly the same as my initial guess earlier in this thread of a COPV failure. I suggested that buoyancy forces or stresses due to thermal contraction could be responsible for the COPV failing at that point. Obviously the buoyancy forces during launch would be higher, so that didn't seem likely, but I think the thermal contraction idea was close.
Does anyone know of any additional information on this apart from the SpaceX anomaly update on their own website? Was anything interesting posted to those Nasa forums, which I don't have the time to read through?