It was a guessing game, truth be told.  If left to inertia, many of the combating stations would drift into queer oblong orbits around their host stars.  The largest of them, or those maneuvering to a new host, might escape from orbit altogether.  If the engines turned off.  The engines never turned off.  Inertia ment death.  Each station was always under fire, and always firing.  Thought seperated by a trench of 50 or so light years, they are able to predict each other with exceptional accuracy due to the high operating costs of their stations.  They must stay near a host sun to supply their power and they usually need terrestrial planets for ammunition.