from the introduction:
Space Stations on the Frontier
A frontier world is nothing without a space station of its own. It is a trifling outpost at best, a half-barbarous colony world that can service only atmosphere-capable tramp merchants and shuttlecraft. It can do nothing for the ungainly bulks of mobile asteroid smelters or naval warships. Some starfaring worlds are forced by circumstances or necessity to make do with a strictly planetary starport, but most worlds count it a point of pride that they should have a constant presence in the void above their world.