What is the practical limit on reusable chemical rockets?

Question

With few exceptions, orbit-reaching rocket systems have a service life limited to a single launch.

The Space Shuttle was intended at concept to be highly (and economically) reusable. Although much of the vehicle was reusable, it took a lot of work and money to prepare the vehicle for its next flight. Ultimately, its reusability was not economically advantageous.

The current SpaceX Falcon 9 is claimed to require no refurbishment from soft landing to next launch. Even if the claim is inflated, it is presumably less expensive per unit of payload to re-fly than the Shuttle ever was.

My question is: what is the current state-of the art for reusable surface-to-orbit vehicle systems where reuse actually confers an economic advantage over a non-reusable vehicle of comparable capacity? How many flights until either end-of-life or major refurbishment for the highest-wear components (rocket nozzles, re-entry thermal protection, etc.)? Does it number in the tens, hundreds, or perhaps thousands?

Even if the main structure and systems of a given vehicle are fully reusable, would it be more economic to manufacture high-wear items like rocket nozzles, heat shields, etc. to be "single-use"/disposable than to engineer them for maximum lifetime?

Answer 1

The current state of the art is changing rapidly. SpaceX is the best-known proponent of reusable launch systems, and they're in the middle of developing their first reusable rocket. SpaceX have not yet reused a single rocket, so it's difficult to say with any certainty how economic their approach will turn out to be.
We have a few data points:

1. Heat shields. SpaceX claim their PICA-X heat shield can be reused "hundreds of times" without refurbishment. It remains to be seen how much time and money needs to be spent on inspecting the heat shield to make sure it's safe to reuse. PICA-X looks a lot more resilient than the Shuttle's ceramic tile system. The Dragon's heat shield contains a few dozen tiles, compared to thousands on the Shuttle, so inspection time should be a lot shorter.

2. Engines. The critical, high-wear item in a rocket engine is also the most expensive to manufacture: the turbopump. Compared to this, the nozzle is trivial. SpaceX is developing a new rocket engine that uses methane instead of RP-1; a major reason to do this is the fact that methane will leave no residue inside the engine unlike RP-1.

Until SpaceX publish some real numbers on the cost of reuse vs. manufacturing a new rocket, all we can do is speculate.