Nightwatch: Andrew M. Stephenson

Earth has degenerated to the brink of collapse and self destruction. With total war imminent, mankind's only hope is in colonising the moon...But the international Dvornik Moon-base has another purpose, its resources directed at a very different object: an alien spaceship rapidly approaching Earth's orbit. Robotic forts are positioned for the aliens' route; their orders - communicate or destroy. Only Daniel Frome, their creator, is aware of the control system's one flaw - and whatever the aliens' intentions, the consequences could be equally devastating...Cover art by Peter Jones.