Not sure if a traveling camera would do it. But the ships in your game traveling between the planets (ala RTS form of conquest) could constitute the traveling aspect that you need to be 'in theme' for the challenge.

Maybe enforcing the theme into the gaem more by making the player actually 'invade' each of their planets as well? Once their main base / command center is defeated or something? That idea seems win/win because you can stick to the RTS theme with it and by all definition it's still traveling from location to location. Just make sure that you have at least 3 of them