That’s certainly a big question. As I noted in comment #53, like the Soviet N1, they had only one very short all-engine static test of the first stage to go on, and in that test two engines failed (from Elon’s comment afterward, one at ignition and one shortly afterward). One question is at what moment the first three engines failed. I’d be really surprised if they proceeded to launch commit with three engines out prior to release, so it’s likely they failed after liftoff, which raises the possibility it was due to vibration, acoustic reflection from the ground, debris thrown up by the exhaust plume, or damage during the release process. It is interesting that with the exception of the one engine in the gimbaled core, all of the failures were on the outer ring. This is where the engines are closest to interacting with the quick release mechanism, and the outer ring engines have a different start process than those in the centre, as resources for engine start are supplied by ground support equipment. Engines in the core start using on-board resources, because they need to restart for the boost-back and landing burns, and thus they do not interact with the quick-disconnects on the launch mount.
5 Likes