Halley's Comet

Halley's comet is a space-based vertical shoot-em-up, where your spacecraft must defend each of the planets of the solar system (and the sun) from an incoming comet. Accompanying each comet is a wave of alien fighters. The fighters will cause damage to the planet you are defending if you let them past you. If you lose all of your ships, allow too many aliens to attack the planet, or take too long to destroy the comet, then the planet is lost and your game is over.

A comet is defeated in three stages. First, you must destroy aliens and then get past a guardian starship. Secondly, you must reach the comet's surface and shoot holes into the surface. Finally, you must invade the comet and take out the core. A display on the right of the screen shows the comet getting closer and closer to the planet, and the percentage damage done by aliens that were not intercepted.

Your ship starts out slow and with a single puny laser. But there are numerous power-ups which increase your speed, strengthens your main laser, adds spread fire, or add some small ships which fly behind you and supplement your weaponry. A fully upgraded ship packs a lot of firepower, but it is all lost if you run into something. Once all of the planets have been defended in turn, the game starts loops back to the beginning.