SpaceX

Good point. I wasn't really thinking what i meant by "the critical path". I was probably assuming the path to a vehicle & system working (at least qualitatively) as designed - including full reusability.

But now that I think about it, probably the thing that matters most to SpaceX is launching at least one ship during the next Mars transfer window, in order to test their Martian EDL approach. (The critical path to making life multi-planetary?) And for that I guess booster reuse is much(?) more important than ship reuse. Or to put it another way, currently for Starship, Mars EDL is the main goal, and Earth EDL only matters to the extent it helps with that goal.

I should've realized this without your question, because after Flight 4 I decided that it was now likely they would be ready by early 2027 - even if they did struggle with reusability. (I think even after Flight 3 we had grounds to reach this conclusion.)

So I now say that this decision is probably not a mistake.

N.B. When I say I think they'll be ready by early 2027, I mean from an engineering PoV. I'm excluding politics and such. What if a NASA science team decides they don't want Starship to contaminate Mars, and Trump doesn't feel like helping Musk overturn that decision?

No flaps and no heatshield would give a decent payload increase too.

I still remember the press conference before the first F9 booster reuse. The customer CEO(?) was saying that his team was comfortable, and I think even that the insurance company was comfortable too. So I was fairly confident it would work.

In this case, there's no customer or insurance company giving any high level push-back on any concerns.

One possibility I wonder about is that Musk and/or other senior SpaceX ppl might be wanting to 'double down' on how this is a bold & risk-taking programme, for psychological reasons, in defiance of all the naysayers after the Flights 7 & 8 situation. And thus ignoring the 'critical path' argument, and the fact that the only good risks to take are calculated risks.

Do you think the cost of booster production could be a factor in their decision?

Unsure about this topic in general. My guess is that the raw materials and COTS components are relatively cheap, and that most of the costs are labour. So one uncertainty lies in whether the people would be employed at Starbase regardless of whether they had to build an extra booster or not. And just in general, when we hear dollar figures bandied around, what proportion of those are the true 'marginal'(?) cost.

But ultimately I think yes, now you mention it, cost would've been a significant factor in the decision.

Along with maybe production rate? Maybe they can easily shift existing people & factory space from boosters, to ships. And so the full 'critical path' argument needs to take into account how booster reuse could potentially increase the ship production rate.

Well I certainly wouldn't want to launch on an F9 booster on its first flight![1] And NASA recently gave a clear sign that they share that logic to at least some extent.[2] So I'm definitely open to that possibility, for Super Heavy, and maybe SpaceX already believes it.

But as an outsider my guess is that, if nothing else, the 'unknown unknowns' should give us significant concern on the first attempt. I'm guessing a 20% probability that the booster reuse significantly hampers Flight 9.

[1] - Nor on its 2nd actually. My theory is that there could be manufacturing defects in/around the reusability hardware that don't get stressed until after the main stress of the first flight, which the second flight then uncovers. E.g. a landing leg attachment fitted imperfectly causes a crack in the rocket body during the 1st landing, and the crack causes a RUD at max Q during the 2nd flight.

In other words the first section of the bathtub curve might not be as steep as we'd like.

[2] - I think within the last year there was a problem during transport of a brand new F9 booster, and NASA said they were glad to subsequently give it a test flight on a Starlink mission before it was used for a NASA mission.