With robotic probes scavenging out the interior of asteroids for fresh materials, military planners of the 24th century escaped the age-old limitations of lifting mass into space. Thus the Space Cruiser came into being. The hull of each Cruiser relied on several yards of superheated steel coated within by a foot of lead for protection from microwave beams. Armed with anti-matter torpedoes or fusion-powered particle accelerators, the Space Cruiser possessed the firepower to level a small moon, let alone a space city.