TL;DR
Allow configuration of rocket capacity per rocket, instead of globally.What?
Move the capacity configuration for rockets from utility-constants to the rocket silo (or rocket?) prototype.One possible complication is the orbital logistics system - how should requested deliveries be assigned to different rocket types? IMO the best solution would be to give the order to the smallest rocket that can fulfill the whole request. If there are multiple rockets with the same capacity available, if the player has a preference over which to use, he could easily use circuit logic to conditionally enable the "more expensive"(/otherwise less desirable) rocket only when no "cheaper" rocket is ready.
Why?
The capacity of a rocket should be a property of that type of rocket. A Saturn V could push 140 tons to orbit, a Falcon Heavy 50-60 tons, and a Falcon 9 only 5.5 to 8.5 tons.There already are some mods adding different rocket silos to the game, but all of them have the same launch characteristics, which wastes a lot of the potential of such mods.
Unless someone else beats me to it, I'd like to make a mod including both a heavy lift rocket as well as a "MIRV" variant (internally multiple rockets managed with lua that launch in a single animation) allowing delivery of small "restock" cargos to multiple platforms with a single launch, and this would require being able to adjust the capacity of individual rockets.
(For the latter part, being able to control rocket launches via script (incl. destinations) would be pretty helpful for optimal functionality, but I think there is already a separate feature request for that)