In Astroblast There are four types of targets, each of which may move at a range of speeds.
As the game advances, the range of speeds for each type of target increases.
The bulk of the targets are meteors, which come in two sizes and various colors. Both sizes fall vertically when entering the screen. Large meteors may be destroyed with a direct hit, or may split into two smaller meteors, which fall diagonally in opposite directions. Small meteors are destroyed with a single hit.
The player must also shoot spinning bombs, or spinners, which are white, come in two sizes, and spin while falling vertically. Each spinner emits a loud whistling sound, which gradually lowers in pitch as it approaches the ground.
Guided missiles appear occasionally as white dots making a pulsing sound, and may fall diagonally toward the player's initial location, or track the laser cannon as it moves left and right. If a missile reaches the ground, it may disappear, or it may continue to track left or right, and can only be avoided by entering hyperspace. The missile may change directions several times before disappearing.
UFOs may cross the screen occasionally, beginning at level 4, firing non-guided salvos aimed at the player's laser cannon.
The player loses a laser cannon each time it is hit by a falling meteor, a guided missile, a non-guided salvo, or by shrapnel from a nearby explosion, and any time a spinner reaches the ground, even if it does not strike the gun. Each target hit increases the player's score; it decreases by half as much each time a meteor reaches the ground, or a laser cannon is destroyed. An extra gun is awarded each time the player's peak score increases by 1,000 points.
The game has six levels, each of which features increased speed and scoring. Each level is represented by a differently-colored background. Level 1, up to 999 points, is black; level 2, from 1,000 to 4,999 points, is blue; level 3, from 5,000 to 19,999 points, is purple; level 4, from 20,000 to 49,999 points, is turquoise; level 5, from 50,000 to 99,999 points, is gray; and level 6, above 100,000 points, is black again. Speed continues to increase along with the player's peak score, at 200,000, 500,000, and 1,000,000 points.
The player has the option of firing single shots by pressing the fire buttons, or switching to automatic fire at a rate of three shots per second. The hyperspace option moves the gun to a random location, which may or may not be safer than the starting point. The game can also be paused at any time.