[jltsiren]

It's not a solved problem. Surviving the re-entry in a condition that makes reuse economical was always the biggest challenge for the Starship. It's far from certain that they can achieve it without a fundamental change in the concept.

The feasibility of building big rockets was already demonstrated a long time ago. Given the reliability of the Falcon 9, it looked plausible that a big rocket could work with many engines. And SpaceX had already shown that they can reuse boosters economically. But reusing orbital spacecraft – the entire upper stage with engines, fuel tanks, and whatever – without expensive and time-consuming refits is something nobody has done before.

[Dylan16807]

They're saying that one specific part burning off is a solved problem, not the entire reuse process.

[cryptonector]

If that part burning off is a solve problem then returning the orbital ship to the launchpad is too given that they are able to gently put it down on the sea, and that they are able to gently catch the booster. This part is basically the only problem left that is ship-specific. However for reuse (or rapid reuse) they might need to rethink heat shielding to reduce refurbishment time and cost.