That sounds interesting :). Have you tried the ΔV: Rings of Saturn demo? It is closer to asteroids than a shooter but is physics based (currently in development with the demo kept updated as well). No dolphins either :( (and I don't think it would fit with the game), although the developers are active on the forums so if you have ideas based on inner space they would likely consider them. The tutorial is minimal so there is a lot to figure out but I played the demo for over five hours without finding any restriction so you don't need to purchase before figuring out how it works.

I agree with everyone saying how bad InfraSpace looks. Aven Colony and Surviving Mars are both much nicer looking, although I didn't like Aven Colony (other than the graphics, which are nice). Both the car-centered layout and the lack of interesting terrain are disappointing. One thing I love about the Roller Coaster Tycoon games is the interesting terrain. Timberborn is the one recent builder with more interesting terrain, although it is square blocks. Hopefully InfraSpace will improve in development, although it doesn't seem off to the best start.