Galactic Trooper is a variant of the arcade game Astro Invader which is a shoot 'em up similar to Space Invaders. The player controls his gun along the bottom of the screen and has to shoot the aliens above him. The main difference from Space Invaders is that the aliens one at a time enter columns where they stay until the columns are full of aliens. Then they start descending towards the player before exploding when hitting the ground. In addition to these regular aliens there are landing crafts that appear at times and the main objective (except for getting the high score) of the game is to stop them from landing on the surface. If the player fails with this he will lose a life. The game can be played in three different skill levels.