[ajross]

The engine failure was minor, true. That's the design point: if engines have a firm ceiling to reliability it's better to design so that one or two can fail than to put all the eggs in a basket. And indeed, the 32/33 engine set was enough to hit the trajectory targets, so that worked great.

But I don't think you can characterize a burned-through flap as minor. Once there's a hole in something like that, the fact that it remains aerodynamically usable is just dumb luck. Clearly the heat shielding failed. If this were a production craft you'd probably have to scrap it even if you recovered it successfully, defeating the whole point to having it be reusable in the first place. The shielding folks have work to do.

But at the same time, the telemetry and control folks are popping champagne. Their stuff worked magically. We literally had live video (albeit through a cracked lens from all the flap debris) all the way through reentry to spashdown, and the landing maneuver looks to have worked perfectly.

[bell-cot]

> But I don't think you can characterize a burned-through flap as minor...

In prod, a localized flap burn-through would be a Major Incident.

Vs. in dev...what competent manager would be bothered if the some bleeding-edge beta code dropped 10% of packets the first time that it faced a full-load test?

[ajross]

That sort of depends on context. If the failure was reasonably expected, like for example your router is running on prototype underclocked hardware or is a debug build that is known not to have the final performance characteristics, sure. But if it fails and you don't immediately suspect why it failed, then that's a sign of a genuine design flaw.

And sure, it's good to find the design flaws in "dev" vs. "prod", but it's still bad to have them.

In this case, we don't really know what the expected performance of that flap shielding was. Maybe it was a kludge and they were just hoping the glue held together, maybe it was a finished design they just thought they were validating. The latter is a much (!) bigger problem than the former.

[bell-cot]

Per Wikipedia, SpaceX's 3 "Get out of Mishap Investigation, Free" cards from the FAA for this test flight were -

Starship burns up during reentry

Flaps lack sufficient control authority

Raptor engines fail to relight

- suggesting that both the flaps and heat shielding were regarded as highly experimental, and failure(s) in them very likely to occur.