Then maybe have some kind of strike craft on them, but I guess many ships; structures already have that.
Or slow long range missiles. But also feature a medium reach arround it that ensures protection to some phase lines (so the player still have to strategically place the Starbase), that when someone invades it, the firing power is bigger since it could use other weapons like beans that supposedly won't go far has the long range guided missiles. Those missiles or some craft could just serve has an backup for the entire orbit, so that the Starbase don't look worthless when enemy invades the orbit but just keep out of the Starbase main firing range.