Sure, SpaceX has been doing first stage reuse for a long time now. But they have demonstrated landing the second stage successfully at sea twice now with the same sort of smoothness that they demonstrated once for the booster before they then caught the booster on the first real try.

A partial list of unbelievably hard things that SpaceX has so far made seem easy:

  - building a rocket from scratch
  - landing Falcon 9 boosters
  - landing Falcon 9 boosters *reliably*
  - 3x weekly launch cadence (Falcon)
  - the bellyflop manoeuver
  - mass manufacturing(!) a rocket engine
  - catching the booster
  - simulated landings of the ship

Anyways, if they can do all those things then it's pretty clear that they can catch-land the ship.

There's still a huge list of crazy-difficult things that SpaceX say they want to do that are hard to believe are possible, except for the fact that SpaceX has already done so many unbelievably difficult things already.

The tiles in combination with ablative materials and the insane robustness of a steel vehicle is sufficient to get Starship through re-entry and soft land in the ocean. We know ceramic thermal tiles worked on Shuttle and X37B and presumably will on Dreamchaser so while the success was an awesome achievement it wasn't unlikely given time to refine their methods.

SpaceX are limited by the properties of real materials, not their ambitions, and we still don't know if rapidly reusability is possible with ceramic tiles or if their fragility will require inspections and refurbishment. They can't do it with ablatives and there aren't many other options. I am optimistic but also realistic about the difficulties of what they are attempting. Sometimes risky projects run into brick walls and you don't know what is possible until you try.

But I imagine that by IFT6 they'll have nailed the flap burn through problem.

IMO a better use for it might be to ferry up large pieces of purpose built craft with less excess dry weight. A single reusable Starship launch can put the entire mass of the Apollo craft needed to make it from LEO to the Moon and back into LEO. Put a craft in two launches and dock it in orbit and you've got a huge capability to put a lot of mass onto the moon and still use the cheap cost to orbit Super Heavy gives.

They could do the same thing with S2 recovery here.

Supposedly they’re working on both a reusable and cost optimised non-reusable second stage at the same time. And they don’t really know yet which one will end up being cheaper.

You also see this kind of thinking with Rocket Labs neutron rocket. Where they focus on making the reusable booster do more, while making the second stage smaller, cheaper and simpler.

I think if it wasn’t for the rocket engine this wouldn’t be a question at all. The tank doesn’t have much value. It’s just a thin shell and probably a fraction of the cost of the fuel.

So I’m thinking, perhaps the optimal solution is something like this: the bottom part of the second stage with the engines separates, and a small engine and fuel tanks places the engines in a stable orbit. The tank itself is deorbited and burns up.

At some point later something like the Starship collects several second stage engines and deorbits them safely to be reused.

Or perhaps just the engines can be immediately deorbited with an inflatable heat shield and parachutes.

Maybe they will have to sacrifice more payload mass for active or passive shielding or more fuel for powered deceleration. That would yield a less impressive lifter but with full reusability.

It was one of the technological breakthroughs of von Braun's team with the V2.

You're way too optimistic. Starship will deliver commercial payloads, with SpaceX phasing out Falcon 9 outside of ISS launches, before anyone has a reusable Falcon 9 equivalent.

It pains me to say this, but SpaceX is in a class all its own.

Blue Origin plans to launch New Glenn in a month, with landing planned. They are a wild card.