[Suicide Junkie]

Another option is to give a wider variety of mounts for the satellite weapons.
There could be varying grades of "Siege Mount" weaponry, which cost more resources and space to get more range.

Another good defense should be mines. The very first episode had a colony protected by mines, so mines must be a decent defense.
I believe the only reason why they were breached so quickly was because the control station was destroyed before they could arm the mines.