The game begins with the player entering one of seventeen rooms of a gigantic space structure. The structure itself is displayed at the top of the video screen; below that, a closeup of the room the player enters comprises the main playing field.
Inside each room, the player must eliminate enemy particles of matter while simultaneously avoiding contact with the walls of the room as well as the pulsing reactor core in the center. Contact with either means instant death.
At the player’s fingertips are several action buttons, allowing for forward thrust, fire, and engagement of the ship’s shield. Direction is controlled by the central Asteroids-like rotational knob. Since the playing field is obscured at times by the core, substantial control of the ship is mandatory. Control is similar to Gottlieb’s Reactor.
Use thrust sparingly. Keep closer to the walls of the rooms rather than the core itself. Obliteration of the deadly cosmic particles results in the core “heating up” and growing progressively larger. The diameter of the core itself can be systematically reduced by unloading a barrage of fire from the ship. Eliminate particles as rapidly as possible, but don’t neglect the core-otherwise you’ll eventually be squeezed against a wall-and out of existence. Use the core to your benefit whenever possible by “hiding” behind it; then rush out, kill the enemy, and retreat.
After one room has been cleared the player proceeds to another and begins again. Ultimately the central reactor room of the space structure—the Cosmic Chasm itself—must be entered and the nuclear core destroyed. Following that, the player must escape the super-structure before it blows up. Successfully doing all this can result in a hefty point bonus.
It’s not necessary to destroy every room in Cosmic Chasm to reach the central chamber. Players can take the shortest possible route (refer to the diagram above the main playfield), enter the core, and immediately begin blasting away at the main reactor. However, clearing all the rooms first builds up the amount of points a player has (by disposing of the alien particles), and also makes for an easier escape from the central core.
One additional note: since the firing mechanism on the player’s ship is located on either side (rather than the middle as in most games), taking aim at your enemies sometimes requires a second glance. You can compensate slightly for this effect by twisting the directional knob when firing, but it’s best to get yourself accustomed to the way the ship operates and adjust your firing habits accordingly.