Here is the full list of all 49 Galactic Battles achievements.
Destroyed 50 small spaceships
Destroyed 100 small spaceships
Destroyed 200 small spaceships
Destroyed 300 small spaceships
Destroyed 500 small spaceships
Destroyed 50 medium spaceships
Destroyed 100 medium spaceships
Destroyed 200 medium spaceships
Destroyed 300 medium spaceships
Destroyed 500 medium spaceships
Destroyed 1 bosses of spaceships
Destroyed 5 bosses of spaceships
Destroyed 10 bosses of spaceships
Destroyed 15 bosses of spaceships
Destroyed 10 meteorites
Destroyed 25 meteorites
Destroyed 50 meteorites
Destroyed 100 meteorites
Destroyed 150 meteorites
500 points scored
1000 points scored
2000 points scored
5000 points scored
10000 points scored
He made 100 simple shots
He made 200 simple shots
He made 500 simple shots
He made 750 simple shots
He made 1000 simple shots
He made 50 launches of a rocket
He made 100 launches of a rocket
He made 150 launches of a rocket
He made 200 launches of a rocket
He made 350 launches of a rocket
5 mega shots
10 mega shots
25 mega shots
50 mega shots
100 mega shots
The first death
Died 25 times
Died 50 times
Died 100 times
Died 200 times
5 upgrades were collected
10 upgrades were collected
50 upgrades were collected
100 upgrades were collected
200 upgrades were collected