Orion is a side scrolling shooter similar to Defender. Marauding aliens are attacking the player's home planet and it's his task to defend it and it's civilians. This is done by controlling a space craft left and right over the planet surface while blasting away at the various enemy forces that both try to take down the player and abduct the people standing on the ground.

If an alien catches a human and drags it to the top of the screen it will mutate and become a dangerous enemy. Humans that fall from a shot down enemy can be saved by flying into them and then carried back to the surface. If all civilians die the planet will explode but the action will continue in deep space against a swarm of mutated aliens. In addition to the regular fire the player also has access to a limited supply of smart bombs that kill all aliens on the screen. There's also a hyperspace button that allow the player to quickly travel to another part of the stage but using it too much might lead to death.