>Why is it in general required, to design a new, more heavy rocket - and not "just scale" up an existing design? I'm not a rocket designer, just someone who ha

>Why is it in general required, to design a new, more heavy rocket - and not "just scale" up an existing design? I'm not a rocket designer, just someone who has really enjoyed following it for a long time. Someone in the industry could give more specifics, but the basics are straight forward. Everything about a specific rocket is tightly coupled, from material factors to engines and everything that goes into that. To take an obvious one, how do you drive the bigger rocket? If you choose bigger engines, then you need entire new engines (and there are scaling issues there too). If you choose to use more smaller engines, you need brand new plumbing to feed all those engines (a very complex thing itself, last I checked each Raptor engine consumers nearly 800 kilograms of fuel PER SECOND), you need to deal with harmonics and control of more engines, different fluid mechanics, etc. Even merely construction changes with scale. For example scaling up carbon fiber to huge sizes is incredibly hard and expensive, one of a number of reasons SpaceX dropped it in favor of steel instead. Rocket volume obviously scales with the cube compared to surface area with the square of size, material properties change with thickness of various walls, and on and on. All of this also impacts aerodynamics, center of gravity and a host of other things. So yeah! Knowledge and expertise from existing rocket designs is absolutely very useful in designing a new one, Starship directly comes out of a ton of things SpaceX learned from F9, which itself took important lessons from F1 (and "F9" is a much bigger range much faster then typical rockets, from version 1.0 to Full Thrust Block 5, the current one, they changed more and gained more power then entire new rockets sometimes have). A much bigger Starship v2 may take much more from v1 then typical because they now do have something with more scaling potential (steel construction in particular). And a lot of the software no doubt will be directly evolved, Starship landing of course used F9 landing software and hardware lessons. But still, cannot just "scale up", even without things like completely changing fuel. Edit: In reply, jmyeet points out that I glossed over the manufacturing bit too much as well. There is a huge amount of expertise and institutional knowledge in going from a general design of any big complex machine to actually manufacturing it in a reliable fashion. People and the machines that make the machines and all the processes that go into that is a whole 'nother ball of wax. Can find plenty of stories on HN and elsewhere about merely duplicating "the same thing", like trying to manufacture an aircraft in a different factory. Or the level of work in "simply" copying a fab and the lengths that are gone to in order to try to make sure everything is exactly the same.