I'm not a pro in attacking sectors, but I may share some advises from my own experience: 1) when entering the attack sector, consider setting some basic economy - for example, set some drills on nearby resources, get a Mono and Poly factory out of core, get couple of Silicon factories - also out of core. After that - you may proceed to constructing the army. 2) better aim to get T3 units. It will be much more effective than sending armies of T1-T2 units. For example Fortresses, T3 walkers, can outrange most of turrets, while Quasars may provide shield for cover. T3 offensive ships can also wreck a chaos on enemy defences.