At Spin Two Swords
Near Orbit Features
Orbital Defense System (ODS)
Chances are that any Imperial system will have an Orbital Defense Line in addition to Planetary Defense Boats. ODSs are rather large affairs. They are designed to shoot at attacking vessels who would make Imperial operations dangerous. Any planet with a TL of 8 or more may have its own PDSs as well. Often ODSs are designed to hone in on anomalies that close in on main worlds. The PDB checks the anomaly out under ODS guard. An asteroid of ELE size, barreling towards the planet at 1,000 miles per hour, is likely to get shot down by a ODS.
Planet-to-Orbit Traffic (P20)
Space Elevators appear at the end of TL 7. At that point, it becomes possible to move large amounts of material from the surface to orbit without the use of 1,000 kg of fuel per kg of material. Once space elevators appear, they tend to multiply. Planets rarely have one or two space elevators, and some planets will have enormous numbers of the tethers surrounding it. These tethers often lead up to orbiting factories, facilities, and cities. An orbiting space station may have hundreds of space elevators dedicated to it.
The long and short of it is that at TL 7, Geo-synchronous orbit (GSO) is filled with free floating satellites. At TL8, these are replaced by anchored orbiters which multiply at higher tech levels, gaining both in multitude and size. At TL 13, these tethers begin to disappear as it becomes easier to just control gravity and float materials up to orbit through free-lifters.
With space elevators in place, travel from GSO to surface happens in lanes which may be defended by orbiting weapons platforms. Nobody wants a ship to run into the tethers.