Meteor.

After a collision with a comet, a nearly 8km wide piece of the asteroid "Orpheus" is heading towards Earth. If it hits it will cause an incredible catastrophe which will probably extinguish mankind. To stop the meteor NASA wants to use the illegal nuclear weapon satellite "Hercules" but discovers soon that it doesn't have enough firepower. Their only chance to save the world is to join forces with the USSR who have also launched such an illegal satellite. But will both governments agree?