On a whim, I decided to fish out the Japanese Wikipedia's entry on Grid Seeker. While there and feeding bits of text to BabelFish (mostly to find the actual names of the weapons), I think I remember seeing a reference to a bad ending if the military satellite at the very end launches successfully. Can anyone corroborate this?
And of course, it turns out on that page that the satellite has enough power to potentially destroy the world. Probably not the antagonists' plan, though; they probably went to that level to guarantee that the remaining planned annexations would have no hope of successful resistance...
(What is it with potentially world-destroying weapons, anyway?)