You switch out the 'standart' engine with your athmospheric-engine, but its not fitting in size and fluidboxes.
Here i would suggest to make the engines fit to the standart, at least the ones you switch out, so that present space ships still works.
That's a good point! I'll make that change in the next release - I think I'll keep the SL engine as a new entity that is needed for rocket construction, then keep the vanilla thruster as a basic vacuum thruster, etc.
i think that you should not waste one of your nice rocket-engines in the rocket construction (silo on any planet), as they will not be visible in game other than items on belts.
I sure hope you will add some more engines.
Ion-engine (but here your nuclear engine is somelike similar, but maybe a more effective one using xeon-gas (or hydrogen))
Electromagnetic engine - using electricity
I definitely plan to add more engines in the future. My intention is to keep refining this mod and add compatibility with any popular overhaul mods that wind up being compatible with Space Age (which will allow fuel ingredients to be more accurate and varied).