I look for a system that allows solid control of territory (no planet lost because you moved away your fleet for one second).

I try to find out how all these work together. Feel invited to the discussion :)

I'm thinking of 3 components:

* Fleet - the most mobile branch of your forces, should not be used to sit on a planet orbit "just in case". Purpose - offense and control of space.

* Ground forces (2 types: planetary garrison and space marines (or something) that is quite mobile) - Critical for controlling a planet. Not some weakling addition that can't act and dies due to bombardment because there is one measly enemy frigate on the orbit. The fleet orbiting the planet provides an important bonus to the ground forces and hinders enemy reinforcements but alone the fleet can not eradicate defences. You actually need to land on the planet. I was thinking of a model where fleet have some "control of space" parameter and if high enough it can hinder transporters with troop (no instant "kill all enemy transporters", that's stupid, surely if you have one frigate over a planet most of enemy transporters will land safely); also no planetary bombardment (can't kill ground forces from orbit), maybe some bonus, but the main work is done by ground forces.

* Planetary "defences" (actually planetary offences :D) - typically in 4X you have lame space stations that activate only when someone tries to invide the planet which is, again, stupid :) I was thinking of more aggressive defences (can engage all fleets passing through the system or even affect nearby systems) and harder to destroy (not demolished all the time). For example you have missiles that automaticly engage all enemy forces in the system also you have a garrison of heavy fighters, these have limited warp capabilities and will automaticly help defending any neighbour planert that is one jump away (only if there is not a battle on the current planet, local defence has a priority).

In addition, these are not destroyed but "subdued". Or they can be reapired much cheaper that their construction cost (repair can't be done if planet is under invasion or blockade). So, enemy come in, their fleet subdue the defences making these unoperational, but there was no ground invasion and the fleet lest, the defences became auto repaired within several turns.

Also, I find attractive a concept of inter stellar missiles you can simply launch (up to 3-5 jumps from your planet with a military base let's say and with a chance to being intercepted by planetary defences/fleets) vs an enemy planet :)

What you think? Or do you have something to add maybe?

The map can be broken into three "layers" the universe layer, the system layer and the planet layer.

U-class ships have the range to move from universe node to universe node, but are too large/impractical to maneuver within a system.

There are two types of U Class ships...Carriers and battle ships.

S-Class ships don't have the range to move through the universe on their own, but can be carried from system to system by U-class carriers.

Once a U-Class carrier enters a system it can deploy it's S-class ships, enemy S-Class ships treat these carrier ships as planets for purposes of attacking and such.

S-Class ships are Fighters/bombers and transports.

A planet has a set of nodes, each node can be Defensive/offensive/military/agricultural/civilian/economic...etc. The planet nodes start undeveloped but can be upgraded to the various types, each type doing... something.

For purposes of battles a planet is considered a ship with it's weapons and defenses defined by the quantity/type of offensive defenseive nodes. Bombers are the only type of ship that can engage a planet.

Once the planet has be defeated by the bombers S-Class transports can drop planet side units onto the planet.

Now the planet side units battle for the planet the way S class ships battle for a system as U class ships battle in the universe map.

Just notes about a couple of your types:

• Ground forces - valuable because bombardment can only destroy, not control. For example you could destroy an enemy by carpet bombing the planet, but then you have destroyed all useful assets on the planet.
• Planetary defenses - valuable because they have access to planetary resources, e.g. unlimited ammo and power. High fire and damage rate compared to ships.

I think what you really want is a clear seperation of space and ground combat (duh) as well as some mechanics that tie them back together.

Your "Space Controlled" meter is something that would probably work quite well, maybe you should also count planetary defences into this, so that a defender can really beef up the planet. To that end the bombardement should actually be capable of destroying those defences (maybe at a cost for the bombers or only with high cost long range weaponry or expensive rockets that cost each shot).

The Ground Combat can be handwaved by saying that all Ground Forces are under heavy shields (plenty of room for Power Generators on a planet) or in deep bunkers and attackers will probably want to take over the industry so no bombing that.

Also I think the distinction of the Ground Forces into defensive and marines is quite smart: You can have a defensive strength relative to the planets population times some other factors (drafting? ground force tech) and have the marines as a special buildable unit. That way you always have a strong defensive force and the attacker needs to commit to an attack (in this case planets should be actually valuable).

Also I think the distinction of the Ground Forces into defensive and marines is quite smart:

Actually it seems to be a de facto standard in modern games (Civilization V city defence power, Crusader Kings 2 with like half the forces obligued to be garrisioned, March of the Eagels with ultra slow militia units) and for some unknown reason it was never introduced in space 4x...

Anyway, I wonder about 3 kinds of ground forces: defensive that is tied to the planet, defensive that the player can reallocate (moving them to a system that require additional defences) and elite offensive storm troopers that can invade planets. But I wonder if that's not an overkill...

More mechanics:

I strongly feel combat (doesn't matter if space of ground) should last more than one turn. And therefore you can have military units on a planet owned/controled by another party, also if you "lose" the planet it does not mean your forces were wiped out, the planet just changes the flag and you can try to evacuate your infantry if any is left.

Which also raises a questions like "what owning a planet means", "what happens with your population if it's taken over by the enemy"?

Sensors ?? To get a chance to move the mobile resources back ???

I think you need something similar to this:

http://www.gamedev.net/topic/643468-strategic-defensive-elements-in-a-4x-game/

Probably remember that thread from last year?

Using realistic science, this is easy.

Ground forces always have an advantage in the power of their weaponry (particularly beam weaponry) due to the size of their heat sink (the planet itself). Space forces can't compete on this front, and ground defenses are absolute out to a certain distance from the planet, with one exception:

Relativistic kinetic bombs.

We're talking large asteroids which have been accelerated to very nearly the speed of light, embodying so much energy in their relative velocities that they've become planet crackers.

There's no real defense against those except being in space to deflect it from hitting your planet LONG beforehand (the planet itself obviously can't change its trajectory). Which means controlling a distant orbital shell around the planet.

Here's where this gives you exactly what you want:

Relativistic kinetic bombs take a long time to "charge up" and move into position. In reality, even a pretty advanced civilization would need months or years to achieve this, but in game time obviously it could be whatever you wanted.

And they also require a lot of resources to do, so you wouldn't want to create one unless you already have control of the space around a planet (or else take a real gamble).

Step 1. Gain control of the space around the planet (which doesn't let you take the planet, but lets you begin the process of accelerating a distant body toward the planet).

Step 2. Keep control of the space for X amount of time while your bomb is on its way. If the planet's fleet comes back and beats you away, your bomb will no longer serve any purpose because it will be easily deflected.

Step 3. When your bomb arrives, you can either demolish the planet, or they can surrender. Assuming they don't wall want to die, they surrender, and you deflect the bomb yourself once you have gained control of their ground defenses.

The planet is now yours.

That's how it works in my design, anyway. It might give you some ideas.

I wonder about the relation of fleet to ground forces and transports.

I mean, how it should work? If the fleet destroyed enemy fleet over the planet (or made them retreat), what then? I want the transports of troops to still have the chance to land (with casualities possibly). Especially if you have just one small frigate on the orbit you definitely should not be able to stop reinforcements, that's ridiculous... Some sort of "blockade efficiency" maybe?

Ideas?

I have assessed this in a number of ways.

First, some ships have the ability to simply launch drop pods, which means the troops get tossed through space as soon as they enter orbit. Whether the ship becomes destroyed is then irrelevant.

However, planetary defenses will still seek to destroy troops in-transit. Though these defenses are generally used to fire at incoming ships, or help your own ground troops defend the planet, they also play a key role in destroying drop pods. Depending on the amount, a portion of the invading forces becomes annihilated before touching ground.

That being said, the counter-argument would also be valid. Would it even make sense for a ground force without an established space superiority and logistics to be actually able to take over a world? In my game, ground troops require different types of supplies to maintain their ground presence, and a full planetary offensive takes time. If all of your orbiting ships get destroyed, your ground assault will be short-lived.