A massive asteroid is detected flying through space just entering the solar system. As scientists monitor it they calculate that it will smash through the asteroid belt before steaming straight into Earth....
Since then a space ship has been designed and built capable of heading into deep space and destroying the asteroid. But when the asteroid smashed through the asteroid belt it collided with thousands of other asteroids smashing it apart and dragging lots of them with it.
Now your mission is to pilot the spacecraft through the solar system and destroy all the thousands of asteroids heading for Earth, before they rain down and destroy the planets surface.