Space fleets cannot forage, so logistics sets their reach

Unlike an army moving through inhabited land, a space fleet cannot assume it will forage along its route. Stewart imagines interstellar ships able to mine asteroids and fabricate most spare parts, even if recreating a whole ship takes longer than building one in a proper yard. Water and some fuel may be collected or recycled, but losses accumulate, recycled ration bars damage morale, and compatible food becomes a hard limit when local allies are not human. Clarke compares the constraint with a nuclear submarine whose reactor and drinking-water systems can outlast its food supply and crew tolerance. Long missions also require privacy and habitability, making the spacious accommodation of a Galaxy-class ship more defensible than it first appears. A fleet may be able to rebuild machinery yet still be limited by human food, privacy, and morale.