Assign rocket-specific payload to avoid wasting space

If you're operating a space station III, using a rocket II for crew transport is just wasting that rocket II.
A cheaper rocket I transports your 4 crewmembers just as well.
But if you otherwise build and use rocket IIs for supply transport, you'll currently have to babysit the correct production order of rockets while estimating if there's a supply-request close enough so that no rocket II will be wasted with crew transport.
Either give players the option to say "use rocket II for rations, station parts and electronics IV, and rocket I for crew" or allow a forced transport