Liberator has you piloting 4 space canons attempting to destroy bases on the planets that decide to fire missiles at you. The way the the game works is each corner has a cannon that you use to destroy these red squares (bases) on the planet, before they launch missiles at you (which they will). Once one of your cannons is hit, it's destroyed and you lose that missile for the rest of the levels until you get a certain number of points to regain said cannon. Though regardless its a fine game,
that can get tedious, but still fun, though I wouldn't come back to it personally.
Played on Atari 50.