On another note, have you considered adding synergy between your stations and planets? For example, something like a space elevator to give a bonus to the planet based on the number of astropolises orbiting it, upkeeped by your Artifacts.
Here's an idea on that:
1) Give Astropoli an innate Accessibility bonus.
2) Make it so that having a Space Elevator requires an Astropolis station (at least one) as an anchor.
3) Once built, the Accessibility of the planet becomes equal to that of the Astropolis if the latter is a higher score.
Example: Astropolis has an Accessibility of 150. The planet has an Accessibility of 80. Planet builds a Space Elevator, now has an Accessibility of 150.
A second idea on that: If there is a Space Elevator and the planet produces a resource that the Astropolis needs, then that resource is automatically delivered each month without the need of trade fleets.
Example: Planet mines Organics, Astropolis has Light Industry. Space Elevator delivers the Organics automatically.
Pirates and other trade interruptions would have no effect on this.A third idea on that: A Space Elevator would allow both the Astropolis and the planet to combine their ground defense scores so long as least one (regular defense) station was still operational. In other words, the only way to cut off the ferrying off defense forces from one to the other would be to knock out
both the Astropolis defense station
and the planetary defense first. If there is more than one Astropolis they do not stack; just use whichever one is highest.
Example: Kadur tries to invade a planet with a ground defense of 100. The planet has an Astropolis in orbit with a ground defense of 250. So long as either defense station is operational both of them will have an effective ground defense of 350, as ferrying troops and supplies can be done quickly and easily between the two. This would make a wonderful counter to the "Domed Cities" malus - when invaders come, orbital drop troops launch into battle to save the day.