In Galactic Conquest mode (not the Campaign scripted missions as said) you can play the Space Only Mod where each planet is treated like Bespin.
That planet is a gas giant planet with no land map (Lando's cloud city FYI). You simply make each planet in the full game the same way. You can own each planet and still build a space station. Look at Bryant and Greys Demo Mod for proof.
So you can have skirmish only in space, these are the one off games; and you can still play the full Glactic Conquest Mode 'space only' against the AI or MP. All palnets are treated as planets such as Bespin, but each are unique. This eliminated the need for land battles.