PROPORTIONED ROCKETS!!
I agree that there needs to be more variations in rockets, both in physical size, transport capability (passengers and cargo), armor and weaponry? (in case of there being a combat aspect of space travel implemented), fuel capacity, speed?, and any other traits or stats that would naturally come along with space ship customization.
What I REALLY want to get back to is the idea of building your own ships block by block. This is an awesome idea, and I agree the Zeppelin mod would be the immediate go-to for inspiration. But also, not necessarily. Take this for example (I'll be using Halo as a common reference here because I think we can all understand the terminology):
I build a tier 1 rocket (or any tier, doesn't matter), I take this rocket and use it to get to the planet selection screen, I then build a space station. I use this space station to become a type of dry dock essentially. Over time I build a cool rendition of the Pillar of Autumn (YES!), now, this is where zeppelin would obviously come in. What true benefit do I get from turning the Autumn into an entity and being able to fly it around in, well, any space dimension? None really, there's no terrain to go whizzing by or sights to see, it's just a bunch of stars and nothingness. Instead I think it would be interesting to (again, similar to the zeppelin mod) "detach" the Autumn from the space ship dimension and press it into a role of a space station around other planets, kind of.
Let me be clearer because I don't think I did a good job of explaining myself. I finish the Autumn in orbit above Earth, I board it from my space station and head to the bridge. On the bridge I go to a navigation type screen where I can detach just the Autumn from the dimension it is in and then scoot on over to other planets with it basically making it a "mobile space station." Really I suppose you could say it would be more of a colony ship at this point. I then use that as a kind of base of operations for that planet/moon avoiding the need to fly back and forth from earth repeatedly which, assumedly, would cost an arm and a leg in fuel costs, and quite possibly would require the use of advanced high-tier rockets. It might be neat! I enjoy the idea of pulling away from my space station on earth, going to a new planet selection screen, appearing in orbit around Europa, for example, and then dropping a few pods filled with supplies, then heading over to the hangar and taking a shuttle/rocket whatever down to the surface and starting a colony.
Ultimately I feel like these are a bit of moot points as from my understanding of this mod the focus is really on the planets and how they can enhance your Minecraft experience.
Shoot: