The player has five buttons: two to rotate the ship left or right, one to shoot, one to activate the
thruster, and one for
force field. Shooting all objects on the screen completes a level.
Space Duel,
Asteroids,
Asteroids Deluxe, and
Gravitar all use similar 5-button control system. A key concept of the game was that there were two player ships, not one. At game start, the players could decide whether to play in normal fashion with the one (single player) or two (two player) ships acting independently, or in a second mode where the two were connected together. In the connected mode, one ship firing its thrusters would cause the other to be pulled along, and then continue moving when the thrust was stopped, resulting in them rotating around each other. This mode was mostly used in single-player, as it put two ships on the screen and produced two shots. The downside to the connected mode was that if one of the two ships was hit, there was the possibility that the connection between them would burn like a
fuze and destroy the second ship a short time later. This did not happen every time, so in other cases it allowed the remaining ship to fight on. ==Legacy==