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An anti-matter power station on an orbiting asteroid is used by the local star system for energy. The station has been taken over by hostile aliens who are threatening to overload the power system which will turn the reactor into a massive black hole and destroy not only the planetary system, but several nearby stars as well.
The object of the game is to make it to the heavily defended power station and disable it before the reactor reaches critical mass and implodes.
The player may control the hovercraft in either a normal joystick operational mode or with vectored movement. When the player pushes forward on the joystick, the hovercraft accelerates, and when pulling back on the joystick, speed decreases.
-  Critical Mass cassette inlay instructions
- Lesser, Hartley; Lesser, Patricia; Lesser, Kirk (July 1988). "The Role of Computers". Dragon (135): 82–89.