I'm currently in a difficulty 7 game (5.0) against the tank and the one-way doormaster (how I hate the latter, especially when he has an adjacent planet with a raid engine on it). I'm encountering a lot of planets with the Spire shield sphere guard post (which has +300 million health) and I have difficulties dealing with these as it takes ages to take them down (even with bombers mark I-IV, bomber and siege starships). Is there any strategy to take these down efficiently or must I resort to "give it all I've got and just sit back and wait"?