It is really not so hard how it seems.
Again use "F-44 Cavalier".
Your mission is simple - destroy all asteroids on each level, before they destroy all your bases.
After each mission your weapon will be refilled, so as soon, as level start shoot all your bulletsrocketslasersmissles.
And one more advise: dont kill the enemys hull when it spawn, because if you kill him, he will spawn with much better hull then before.