Death star is ray shielded and has like a few KM thick of special density alloy blast/impact armor. Ig88 is a one of a kind assassin android who killed his programmer after he was turned on. Each droid an astromech has their OWN AI and there are a few hundred thousand on the death star. Star destroyers shields must be dropped FIRST otherwise any incoming projectile with less than 1/3 the mass of the ship WONT get through the shield.