Space Sentinel

arcade shoot'em up game for Commodore 64, 1983

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Use Control Port 2.

A small space ship continuously orbits the Earth, able to fire in 8 separate
directions, but unable to change its course. Alien ships approach from
multiple directions, and fire upon the Earth. As the Earth is hit, pieces of
the Northern Hemisphere begin to disappear into the sea. The player must
defend the Earth from alien assault for as long as possible.

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Some useful keyboard shortcuts
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       [PAUSE] - stop/continue game
          [F9] - quick load game state
         [F12] - quick save game state (still stored after leaving the site)
         [F11] - toggle fullscreen mode
  [ScrollLock] - quick switch control ports
    [PageDown] - make a screenshot (320x200)