Yeah, SpaceX’s reuse is much, much simpler than the shuttle booster refurbishment. At the extreme, Starship is intended to have no refurbishment between flights - refuel and fly again, so that the cost of each flight will be mostly the fuel cost, on the order of single digit millions. Falcon 9 I believe is trickier since its kerosene fuel generates a lot of soot compared to the methane engines of Starship, and can be fouled. If you’ve ever used a camp stove with kerosene vs methane, one leaves your stove covered in black soot.

Note that for the Space Shuttle, the external tank was large proportion of the fuel-carrying capacity of the vehicle, i.e. "most of the rocket". And for the solid rocket boosters they were not fully recovered as they ejected the rocket engine bell just before impact with the water which sank to the bottom of the ocean on each launch.

Additionally, solid rocket boosters are some of the hardest things to re-use as the process of re-filling them is more like re-manufacturing them than actual true re-use. The sections (they had 4 sections) need to disassembled and refilled with the epoxy that is the solid rocket fuel. They were additionally made of steel rather than aluminum so were not substantially valuable components to recover versus the high end aluminum alloys in the external tanks.

Landing the rocket back on the pad requires significantly more fuel for most missions. The reason most Falcon 9s do landing at sea instead of RTLS is due to this. They have to boost up and out over the ocean to the correct insertion coordinates, and then they run out of fuel (for the mission). When they run out of mission fuel, they just use gravity and fall straight downwards to land on a drone ship.

In short, performing RTLS requires additional fuel. This is fuel that can no longer be used to boost the payload into the correct orbital insertion. So all RTLS missions tend to be lower performance missions that don't need the full power of the Falcon 9 / Heavy since they have fuel to spare for RTLS.

Right, for the Space Shuttle the shortest interval on a back-to-back mission was 63 days.

> The innovation here isn't about reusability at all, it's about the economics of reuse.

It's about both.

SpaceX showed that the 1st stage of a rocket can be reliably reused in production. Which is really important from an architecture perspective because 2/3 stage rockets are just more efficient than 1/1.5 stage rockets (mostly due to the propellant mass fraction term of the rocket equation).

To give some examples, the payload mass fraction of some reusable rockets is:

* Shuttle(partial reuse): 1%

* Falcon 9(partial reuse): 4%

* Starship(full reuse, in development): 2%