Star's End (The Starfishers Trilogy)

At the edge of the galaxy lay the Fortress known as Stars' End, a mysterious planet bristling with deadly automated weapons systems, programmed to slaughter anyone fool enough to come within range. But who built this strange planet of death, placing it within view of the Milky Way's great lens... and tantalizingly close to the hydrogen-filled feeding grounds of the interstellar dragons known as Starfish and the priceless ambergris they create?