Where are you getting these extra ships for your fleet? So far, this discussion has been about once a fleet has orbital superiority, what can the planetary population do about it. The answer is, basically nothing. The planet's defenses are out-ranged by the enemy fleet who can just keep throwing rocks. They do not even have to be planet-destroying rocks. They can be smaller rocks that only destroy a few miles of planetary surface, throw a few hundred of those at once and wait for all resistance to cease. It is about as damaging as massed meson weapon fire, but with much less risk to the fleet, since they are out of range of the planetary weapon emplacemen