The object of Star Castle is to destroy an enemy cannon which sits in the center of three concentric, rotating energy shield rings while avoiding or destroying 'mines' - enemies that spawn from the core, pass through the energy rings, and then home in on the player's ship. They can stick back to the shield if the player maneuvers in such a way that a ring is between the ship and the mines. The player-controlled spaceship can rotate, thrust forward, and fire small projectiles. The cannon's shields are composed of twelve sections each, and each section takes two hits to destroy. Once a section is breached, rings beneath it are exposed to fire. Once the innermost ring has been breached, the central weapon is vulnerable to attack from the player. However, the player is also more vulnerable at this point, as with the shield rings eliminated, the gun can fire out a large projectile that hisses with white noise. Moreover, the central core tracks player movement at all times. If the player manages to hit the cannon, it explodes violently, collapsing the remnants of the shield rings, and the player is awarded with an extra ship. The next level then starts with a new gun and fully restored shield rings, with the difficulty increased. If the player completely destroys the outermost shield ring, the cannon will create a new one. The middle ring expands to replace the lost outer ring, the inner ring replaces the middle, and a new ring emerges from the core to become the inner ring. Therefore, in order to penetrate the cannon's defenses, the player must be careful not to completely obliterate the outer ring. The three homing mines will destroy the player's ship on contact. The mines can be destroyed, but they are very small and difficult to fire on, and the player does not receive points for destroying them. Mines are revived when shield rings regenerate. As the player progresses through the levels, the mines get faster and faster, forcing the player to keep moving to avoid them.
Legacy
The development of the game was chronicled in an issue of the magazine Science 80. Atari programmer Howard Scott Warshaw investigated writing a clone of Star Castle for the Atari 2600, but didn't see the game as a good match for the system, technically. He reconfigured the concept into Yars' Revenge, which became Atari's top selling original game for the 2600. A hobbyist-written clone of Star Castle for the Atari 2600 was eventually released in 2012. Jim Nitchals of Cavalier Computer wrote a clone for the Apple II called Ring Raiders . Anthony Weber of Stedek Software wrote a clone for Atari 8-bit computers called Star Island. In the 1986 movieMaximum Overdrive, a Star Castle machine electrocutes a person in the arcade. In 1989, a Star Castle machine appears in the background in an episode of Columbo entitled Murder, Smoke and Shadows. Rogue Synapse's Polybius is heavily based on Star Castle.
