How do you Defeat Aliens who control the Orbitals?

How do yoou defeat a race of Aliens who control high orbit and can throw rocks at you down the gravity well?

Unless you can somehow get up to defeat their ships you are always going to be at a enormous disadvantage.

The only way to deal with vessels which control the high orbitals from a planet is to have concealed weapons emplacements capable of destroying those same ships. As for how effective those weapons would be, that depends on the ships and their defences.

It all depends on said aliens' objective. If their aim is to subjugate/enslave the human race, it isn't necessary per se to eliminate their ship(s) immediately. The only threat they pose is the ability to reinforce previously-deployed troops. In the long run, it would indeed be necessary to destroy the fleet, a feat that could be achieved in any number of ways:

- Re-targeting ICBMs

- Kinetic weapons (see the Planetary Defense MACs of the Haloverse)

- Capturing and utilizing an enemy shuttle to board a ship (or several simultaneously) and take it by force.

- Alter satellite orbits to crash into them. Assuming that's possible in sufficient quantities to do actual damage.

These all, however, assume that the xenos want to preserve as much of humanity as possible; if they don't, there's no reason for them NOT to drop Big Rocks on us the moment they start hitting major resistance dirtside.

If that second scenario is the case, the only possible way would be to quickly surrender, and then take however long is necessary to develop and deploy weapons capable of destroying the enemy fleet while also avoiding detection until it's too late for the enemy commander to react, evade, and order a retaliatory bombardment.