The crowd loves their stage show.
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The idea behind the Starship seems to be to to build a low technology re-usable vehicle which can be taken to places like Mars and used for a variety of purposes. This sounds great but right now it looks more like SpaceX have to use their best gear (the Dragon capsule and the Falcon launchers) because nothing else will cut it.
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I wonder if Starship ends up being Musk’s Spruce Goose.
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I’m not sure I’d call any part of a 2-stage-to-orbit high-performance methalox-powered rocket capable of autonomous powered descent and landing “low tech”. These prototypes certainly are, but they’re intentionally not pouring huge amounts of money into their construction right now because they’re still at such an early phase of the testing process. They’re testing specific sub-systems and processes at this point and it’ll be years yet before there’s anything approaching a functional launch, so rolling out (relatively) cheap containers to house them in is a smart play.
This is a very different testing model than NASA’s traditional “do as much on paper as possible and only test the whole thing at the end for cost expediency’s sake” approach. But even then, at some point you’ve gotta make a mess.
I can’t recall the video offhand but one of the space youtubers posted an explainer about the Saturn V’s F1 engine that included a lengthy discussion of how they kept blowing up on the test stand due to ignition instability. That’s kinda where SpaceX is with the Starship stuff right now.
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But with computer aided design, modelling, etc we should be doing much better than that now. We really should be able to trust our prototypes not to explode. As long as SpaceX have been building launchers, their ability to safely debug on the pad has been legendary. These explosions are just a terrible look. Suggests they are designing backwards.
While SpaceX hasn’t reported out cause of failure for previous Starship prototypes, the suspicion in the rocket community has been that they were caused by COPV (carbon over-wrapped pressure vessel) manufacturing defects, which they’ve struggled with in the past because it’s a tricky process. Judging by photos of the latest prototype from before the explosion today and footage of the explosion itself, I think it’s possible that there was some form of failure in one of those again. (Note that the COPVs are typically filled with liquid helium, which gets used as an inert substance to pressurize the fuel tanks, and they’re temporary additions for the static tests since the final plumbing for the Raptor engines will be different and not require them.)
This prototype had previously been successfully used in a static fire test a couple of weeks ago and the Raptor engine was reportedly removed and re-installed between then and now. It’s possible there was a failure with something on re-assembly, or something in the engine itself unexpectedly gave out on re-use today. You can do a lot of computer design and test modeling, but materials science sometimes just comes down to learning from unexpected device failures.
Reference material:
(I should also point out that at about 2:49 and again at about 3:04 in the video above, the prototype does seem to vent some kind of material much like it did just before the explosion today, so that may be unrelated to the incident.)
tl;dr, Rocket science is extremely hard, and Starship is a brand new ground-up design that doesn’t borrow much, if anything, from the design of the Falcon, especially in the propellant and engine design departments. Failures at this early stage are honestly part of the process, and SpaceX’s design and testing philosophy means they’re more willing to accept the risk of a failure as part of their more iterative approach.
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I just loved the exquisite timing of the announcers.
“Maybe a hose popped out and were seeing an uncontrolled [unintelligible]”
“That does seem to be oxygen, right?”
“Yeah. I believe… if it was methane it would be igniting in the flare, correct?”
[just exactly then the cloud of escaped gas reaches the flare and, MASSIVE KABLOOEY]
…
“That was NOT nominal…”
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O the Manatee.
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I muted the self appointed “announcers”.
Watch SpaceX’s Starship SN4 prototype accidentally self-destruct in a rocket test burn
Fortunately, nobody appears to have been hurt, other than some feelings at SpaceX. And maybe possibly the US Federal Communications Commission, which this week reportedly granted permission for suborbital Starship test flights.
Nevertheless, the explosion was large enough to be picked up by the radar systems of local weather stations in the US state.
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“…and a high pressure system has formed over…nope it’s gone.”
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Yeah, that’s how you get cost-effective rockets like the SLS. 
We’re not really close enough to that yet. I’m not sure we ever will be. Saturn is the only booster program I am aware of which didn’t suffer a destructive launch failure, and I think we can credit that mostly to the designers and builders, but with a heaping spoonful of good luck.
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I was almost there for this “launch.” I had already seen two Antares launches up close, though, and chose not to attend this one. Kinda regret that decision - would’ve been SPECTACULAR, as a friend who was there confirmed - though from our regular vantage point, probably hazardous.
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Unmanned rocket explosions do look pretty awesome, but I’d much prefer them way, way over there!
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It not perfect system. 
Also the SLS has its own accompanying Congressional meddling and extremely non-optimal mandated design decisions that have ballooned costs. If folks in Congress would leave NASA well enough alone to do its job without treating it like a pork buffet, the agency would be in a much better place right now.
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Scott Manley’s got a breakdown of the event now:
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I’m not an expert by any means, but I think because they are experimenting with new materials and novel manufacturing techniques, they are testing limits that simply can’t be simulated, modeled, etc., In short, this is what they have to do. I get what you’re saying about appearance, but I still think they know what they are doing.
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