Space Defender

The player controls a laser cannon by moving it horizontally across the bottom of the screen and firing at descending aliens. The aim is to defeat five rows of eleven aliens—some versions feature different numbers—that move horizontally back and forth across the screen as they advance towards the bottom of the screen. The player defeats an alien, and earns points, by shooting it with the laser cannon. As more aliens are defeated, the aliens' movement and the game's music both speed up. Defeating the aliens brings another wave that is more difficult, a loop which can continue without end.

The aliens attempt to destroy the cannon by firing at it while they approach the bottom of the screen. If they reach the bottom, the alien invasion is successful and the game ends. A special 'mystery ship' will occasionally move across the top of the screen and award bonus points if destroyed. The laser cannon is partially protected by several stationary defense bunkers—the number varies by version—that are gradually destroyed by projectiles from the aliens and player.

玩家通过在屏幕底部水平移动并在下行外星人射击来控制激光炮。目标是击败五行十一个外星人 - 一些版本具有不同的数字 - 当它们向屏幕底部前进时，在屏幕上水平来回移动。玩家通过用激光炮射击来击败外星人并获得积分。随着越来越多的外星人被击败，外星人的运动和游戏的音乐都加速了。击败外星人带来了另一波更难的浪潮，一个可以继续无止境的循环。

   当外星人靠近屏幕底部时，他们试图通过向大炮射击来摧毁大炮。如果他们到达底部，外星人的入侵就会成功并且游戏结束。一个特殊的“神秘船”偶尔会穿过屏幕顶部并在被摧毁时奖励积分。激光炮受到几个固定防御掩体的部分保护 - 数量因版本而异 - 逐渐被外星人和玩家的射弹摧毁。