AlienCruise

Story-related; cannot be missed.

This achievement unlocks upon completing the area 'The Counterattack' which becomes available in the upper right corner after clearing those planets. The ships along the top of the screen are actually friendly, so don't shoot their turrets and don't worry about touching their shots. After completing the first level, you'll go into the boss fight, which is extremely short and simple. He just shoots volleys of lasers at you while darting around. Focus on him and he'll be dead very quickly.