With missles or direct fire with sattelite mounts, being on the wrong side of the planet isn't a problem. 100 small sats = 100 CSM's with room for 100 PDC. Even if the enemy has tons of PDC, that gives them something to shoot at and allows your fighters to Last longer and do more damage. Plus if you are talking about the AI, they don't always do a good job of staying out of range of the sat's.
Sats alone aren't impervious, but they are a nice compliment to your fighter/WP defenses.
Layers, planetary defense is all about layers!
Geoschmo