Here is the full list of all 11 Oscillatron: Alien Frequency achievements.
Destroy 50 orange spaceships
Destroy 25 orange spaceships
Finish 10 of your tracks
Destroy 100 purple spaceships
Finish 5 of your tracks
Destroy 50 purple spaceships
Destroy 100 red spaceships
Finish your track
Destroy 100 green spaceships
Destroy 50 red spaceships
Destroy 50 green spaceships