The planet could simply be part of the background image. Bombardment is abstracted.
Make a few kinds of planetary facilities. They are a new ship type so orders can be made to target them, etc. Also, like missiles vs PD weapons, they are a unique target type that current GSB weapons DO NOT ATTACK. The atmosphere might be treated as a shield, actually, so perhaps they all get a free shield. If so, space weapons might work if they have the penetration…
Types of facility:
—A. Planetary defense base. Has a silhouette for deployment but is invisible in game. This is in effect a ship with no engines allowed. They can have large armor bonuses. Shields don’t work on planets While designed like normal ships, they are invisible, and cover only a small area on the map (they are “below” the ships).
—B. Cities. Same deal, a silhouette for deployment. Unlike defense bases they might be visible as a web of lights, etc. (they can be partially transparent to blend with the background image below). They might be loaded with dummy modules so they can burn, etc over their area.
—C. Satellites. These are actually a new ship type as they are spacecraft with no engines, so not really planetary facilities. During the short timespan of a battle, they effectively don’t move. They take ship modules—frigate modules would be fine. A new unit type so that orders can be made to prioritize them.
Planetary defense bases would have some special weapons. Most would be close to current weapons, but very short ranged due to having to fire through the atmosphere. Planetary fighter bases might exist with virtually endless supplies. Various weapons might be deemed unable to work from a planet to simplify things.
Add a new class of weapons. “Orbital bombardment weapons.” These weapons ONLY attack planetary facilities. The ranges can be set in their files like other weapons, but the default values should be VERY short ranged. 1-200 or so. The idea is that the ships have to fly right over a facility to attack it, or very close, anyway. Orbital bombardment weapons include:
—A. Deadfall ord (bombs). Range 100 or less, probably less vulnerable to any PD since they can be heavily armored.
—B. Missiles. unlike space missiles, these need to be specifically designed to reenter an atmosphere. Can be very long ranged, actually.
—C. Beam weapons. Specially designed to attack planetary facilities through an atmosphere.
Some new scenario rules that allow one side to be the defender, and have more than total destruction as the victory condition. Alternately, by setting planetary bases as more valuable than they actually cost, it might be impossible to win under the current system without wrecking a large % of those bases.