The aliens attack in formations, all with a predefined movement pattern. Some move across the screen, while some move straight down, and others follow more complicated routes, spinning and moving around in figure of eight patterns. Some move very slowly, whereas some move quickly.

You must destroy all of the atttacking formation to advance to the next stage. If a ship passes by you and moves off the bottom of the scren, it will reappear at the top. All the time you are playing your fuel level is steadily decreasing, so you can't afford to let too many ships pass by, as all time wasted costs extra fuel.

The stages of attacking aliens are also interspersed with other stages where you must destroy/avoid asteroids as you move forwards through an asteroid field. You don't have to destroy all the rocks on this screen, simply get through them all.

There are also stages where you must destroy missiles falling diagonally down the screen. On these stages you must destroy all the missiles.

Every few stages, you must dock with your mothership by using your left and right movement to steer your ship into the centre docking point. Succeed and your fuel is refilled to prepare you for the continuing conflict ahead. If you run out of feul, your game end immediately

Secret bonuses are awarded for various accomplishments, such as surviving the asteroid fiield, or clearing an attack wave without missing a shot.

You can either start with two or four lives.