Given that the engine telemetry shown on the broadcast showed the engines going out one by one over a period of some seconds, I could easily imagine some sort of catastrophic failure on a single engine that cascaded.
It could be many things, plumbing to the engines, tank leak, ect. You could see fire on the control flap actuators, so the ship interior was engulfed in fire at the same time the first engine was out.
the flight termination system is sort of a shaped charge that's designed to rupture the oxidizer and fuel tanks. Even if only a few % fuel remains, it'll be a big boom.
That doesn't explicitly say that it wasn't FTS. Activation of the FTS is never scheduled and it results in rapid disassembly. There's speculation that it flew for a significant time after losing telemetry. FTS is designed to activate if it goes off course (if it's still on course, it's better to keep flying).
Yeah, I was wondering if it was FTS. I guess it doesn't really matter as FTS is just designed to intentionally cause the same kind of RUD that happened anyway. The main criteria is a RUD sufficient to ensure pieces small enough to burn up on reentry. From the looks of the explosion from the videos helpfully captured from the ground, the RUD certainly looked sufficient. Given it was 146km up at >13,000 mph, rolling down a window would trigger a sufficient RUD.
At those speeds, temps and pressures exploding into tiny pieces isn't just easy - it's the default. NOT exploding is much harder!
do we know when this video was taken? this could just be ship breaking up during re-entry because it lost altitude control. not necessarily the moment of the primary failure.
Or FOD in the LOx supply lines. The methane would keep following, even with the turbopump shut down, until the valve closes. And the methane turbopump might actually keep running with reduced supply oxygen - Raptors have two turbopumps.
Yeah, most likely engine bay fire taking out systems one by one. Would be interesting to compare the telemetry cutoff with the video of explosion if possible. That could indicate if the fire even triggered an explosion, flight termination being activated or just reentry heating making the tanks explode.
Who knows where it started, but the fire was definitely in the payload bay in front of the header tanks if seen through the flap actuators during ascent, after speration at ~7:45 min
