How does one even go about finding a root cause so exotic?

I'd bet lots of telemetry, comprehensive design and change documentation, along with engineers tacit knowledge.

Something like:

telemetry shows dramatic drop of temperature on this, that given the location of the sensor could only be caused by a specific LOX line leak, and vibration sensors show data compatible with friction as the ignition event and not a short circuit because the relevant telemetry doesn't show any electrical abnormality, so, by exclusion, given no other anomalies, give that computer simulations show it is a feasible scenario, followed by lab work with a physical model, this must be the cause of the accident.

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chasd00 a minute ago | parent | next [-]

Engineering cameras all over the bottom of the pad will probably be what they use. I'm sure they have high speed cameras looking directly up at the bottom of the engines like SpaceX has. They'll watch frame by frame and then confirm with sensor data or the other way around. The propulsion engineers are so intimately familiar with the engines they probably already have a good idea.

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domlebo70 10 hours ago | parent | prev [-]

Yeah, but at the end of the day you can't be sure right? That doubt would eat away at me

	▲	sephamorr 10 hours ago \| parent \| next [-]
		The doubt is supposed to stay with you! You need to make sure there aren't other causes or contributing factors hiding behind 'the obvious'. There have been notorious cases in spaceflight where the issue was 'identified' and 'fixed', only for the same thing issue to happen in the next mission.
	▲	SkyBelow 23 minutes ago \| parent \| prev [-]
		Nothing of the level of rocket failure, but I've tracked down issues where you are never sure of the cause. You keep the doubt and let it drive you. You aren't as much sure of a theory, as you have the theory you most want to disprove and keep failing to do so. The more you fail to disprove a given theory while other people with their own personal 'targets' do end up disproving them, the more you can report that the theory is the reasonable conclusion. But you never given up the idea of looking to disprove it. Eventually others join you and work to disprove your theory. As the group continues to fail to disprove it, it becomes the officially stated cause unless someone can provide evidence otherwise. Sometimes I'll have one that I'm stuck on for a month before finally disproving it, and it is an interesting feeling. There is some level of happiness I succeeded at my goal, but it is very bittersweet because it normally was my last working theory and now I'm simply lost until I can formulate a new one. Sometimes disappointment in myself that I might've missed some easy way to disprove it for so long, but other times the way to disprove it was sufficiently hard enough that I just accept it is what it is.