I'm not sure where I should begin: 1) the investigation has just started, nobody, including SpaceX, knows what happened. 2) SpaceX uses autonomous flight termination systems, no-one in the control center was "forced" to "activate" it – the rocket does it on its own. 3) SpaceX never uses pyrotechnics, since they are not reusable. 4) the separation system is of a completely novel design that has never been attempted before. 5) Why would you think stage separation was the problem? I mean, 6 engines failed, the hydraulic power units exploded, without the hydraulic power, the vehicle spun out …

… control, isn't any one of those things much more likely to be a problem than a failed stage separation that, as far as anyone can tell, never actually happened?

Do you have any credible reporting/source for the major failure being capsule separation? The live stream seemed to show the rocket taking major damage before leaving the pad, suffer multiple further failures in flight and then lose control and tumble several times before the planned separation. You can question many of the design choice but flight did not get far enough for separation to be an issue.

@GremlinWranger Some articles I read and news reports in Italian TV seemed to imply that was the major cause. I'll add something in the question.

@GremlinWranger see my edit.

@JörgWMittag Please, see my edit for why I was assuming 2 and 5. Your point 3 is part of an answer, so thanks. I assumed they would use pyrotechnics in a way they could reuse the thing anyway, maybe replacing just some joints. I was apparently wrong in this respect.

For what it's worth, I suspect the separation system doesn't activate unless the stack is within certain angle-of-attack/sideslip and rotation-rate limits, and the engine-outs caused too much sideslip. But that's just a wild guess.

my engineering gut feeling was "it smells of sloppy design or sloppy implementation". If this was SpaceX's first ever rocket launch, then you'd be absolutely right. But... SpaceX has successfully launched rockets 230 TIMES. Thus, definitely not sloppy design or sloppy implementation.

"Hubris at thinking they didn't need a flame diverter or trench (or both)" is a much more reasonable answer.

Note: I had to roll-back an edit which erased the original Italian text citation and introduced typos. I explicitly cited the original text because it is needed to prove the consistency with my translation, in case the original link go stale (as it is likely with all news links).

What we do know is that the rocket was at an altitude of about 40km and at about 2000km/h when it started tumbling. That's far too low and slow for normal stage separation (for comparison, Falcon 9 stages at around 70km and 8000km/h), so it's unlikely that separation failure had anything to do with the problem... they never got close to where it would have occurred.

Conversely, I've read comments that the "failure to separate when tumbling" indicates a sufficiently robust structure and attachment mechanism which the operator must be feeling pleased with at this point.

They knew they did need a diverter, but it was not finished in time so they "hoped it would be fine." As Elon said, "that was a mistake" :-)

The "dumb failure" was not having the pad ready for Stage 1, which lead to the complete loss of Stage 2. This does not bode well for the concept of a one Stage lunar lander. The Apollo lander was 2 stages, the first acting as a launch pad for the return vehicle to lunar orbit. Imagine what might get "kicked up" from a lunar landing site. RUD is not an option.

@RonJohn sloppy design doesn't necessarily mean the rocket blows up every time; it could also mean a failure of some little component that should have been accounted for can blow up the rocket

@user253751 which part of my comment hints at saying sloppy design means it blows up every time?

@user253751 getting sloppy doesn't mean it'll blow up every time. Note that I also made a comment about hubris by SpaceX.

@RobertDiGiovanni the booster wont be needed for Lunar/Mars launches, it'll just be the ship which is much less powerful (though even that tore up concrete and damaged engines on early tests)

@AlanBirtles please note the "artists conceptions" have a Starship landing on the moon, engines real close to the surface. Now have a look at the Apollo LEM. I'm rooting for SpaceX. They are bold and innovative. But some very smart people tackled lunar landing more than 50 years ago. I would study their work thoroughly.

@RobertDiGiovanni the artists concepts for the Starship HLS have the landing/takeoff engines 30-40 meters off the surface.

@ChristopherJamesHuff this source mentions "lunar regolith impingement". It also mentions mid body thrusters "may not be needed". More "artists conceptions". Unless you think the Booster should have midbody thrusters too? Do you think they are as powerful as the main engines?

Re reliability: you can't say anything about reliability from a single launch; and given how Starship development is being conducted, it may be risky to draw many conclusions even after a few launches while SpaceX continues to make changes to every prototype. Falcon 9 provides a useful roadmap, as there were a number of design changes even after the rocket was in regular use. But most importantly: F9 launched many, many satellite and cargo payloads - successfully - before it carried people. If Starship follows the same path, that's the point when we can talk about reliability.

@SteveMelnikoff Thanks for this POV. I didn't really follow the development of Starship, so I thought it were in a more advanced state of development. I was misled by the hype Italian media gave to the launch: although they said it was a test launch, from the TV reports seemed to be it was some kind of "final" test before an actual mission.

Remember, there's a reason why we use the term "rocket science" proverbially to mean "thing that's very, very difficult." Trying new rocket technology never works right on the first attempt; just look at how many tries it took NASA to get their first one into orbit!

@MasonWheeler Yep! Definitely!

@RobertDiGiovanni ...impingment is the reason for the elevated landing thrusters, not a problem with them. The booster doesn't have or need such thrusters, because it's not landing on the moon.

@LorenzoDonatisupportUkraine, "from the TV reports seemed to be it was some kind of "final" test before an actual mission": yeah, that's...spectacularly inaccurate. This was the first flight...first full thrust burn of a booster and first launch of a complete stack, and of an already outdated early prototype. The upper stage had been repeatedly modified as a test article for their Starlink deployment system, then welded shut for the test flight. There's at least two more ships under construction that don't even have the heat shields and flaps, they're purely experimental orbital craft.

@MasonWheeler counter example: Sputnik.

@Abdullah: Per Wikipedia, "The first launch of an R-7 rocket (8K71 No.5L) occurred on 15 May 1957. A fire began in the Blok D strap-on almost immediately at liftoff, but the booster continued flying until 98 seconds after launch when the strap-on broke away and the vehicle crashed some 400 km (250 mi) downrange." The next couple attempts failed as well, it only succeeded on the fourth flight. It then had multiple successful flights before being used to launch Sputnik..

@ChristopherJamesHuff Really, I didn't know that ;-). But are not the Spaceship boosters also near the bottom?