I'd say it depends on if you are wanting to be realistic or not.  Landing troops to take over makes more sense than destroying the planet's enviroment from orbit.  If you were just destroying worlds that would be different, but since you are taking the planet then a orbital bombardment is not logical.  Not when you are talking in what it does to the planets health and population.

I am no advocating for either side though.  Merely pointing out if we were being realistic.  If you aren't worried about that stuff then orbital bombardment would be faster.

It just depends...  The Advent and the Vasari do it intelligently.  They use weapons that allow them to destroy critical points, but not just wipe out all population.  Kinetic warheads: power of a nuke, but no fallout.  Beams: directional; the opposite of fallout.  Nukes with "Heavy Fallout" (in other words, probably Cobalt): nuclear winter.

Bombing should wipe out all infrastructure (because that is what will be hit from orbit), while invasion I still think should lower all upgrades by one level (unless Emergency Facilities was upgraded into a tree, at which point, obviously invasions would affect some completely such as land military power)

I dont think we can really say anything about the affect of orbital bombardment on recolonization efforts because theres not enough detail. All that can be said is that if you want to have an easier time recolonizing, you have to be more careful with how and where you bomb and vice-versa. Obviously a successful invasion is going to give you the easiest recolonization efforts. I would say to reflect that you might get a bonus to population growth when you acquire the planet. Upgrades included/time invested would be a matter of balance.

If you're looking for a ship that's weak with little armaments to serve as the troop transport, then I would make it the colony frigate. That makes some sense.

The reason I was suggesting the siege frigate was that I feel that ship isnt used much and would be a primary component of an actual fleet. I would also like to avoid adding a new, underused ship. So, expanding the capabilities of the siege frigate makes sense to me and all 3 races have one. It also makes sense (to me) that it might serve as a troop transport to cover all aspects of sieging in one such specialized ship. That way, the 'siegability' of a fleet is directly proportional to the number of siege ships. It also gives you more tactical options in a fight. You might see more ships coming and decide to switch to razing the planet so that you can cause the most damage to the enemy. On the other hand, maybe you're expecting an epic battle and the opponent runs away. You can then leave your siege ships to take the planet via invasion and get the planet fully populated.

Actually, now that you mentioned culture... the time an invasion takes to take over a planet could be tied to the culture level of the planet. You could invade a planet with strongly hostile culture, but it takes a long time (not drawing parallels! nope!). however, if your culture is strong there, it would be very quick.

I would also change the way the planetary defense upgrade works:

1. increases max planet hp 1500->3000. Adds small garrison of troops.
2. increases max planet hp 3000->4500. More troops. Time to invade increased.
3. increases max planet hp 4500->6000. Shield prevents Invasion.

Now, if you had upgrade #3 and I bombed the planet below 4500 hp, you lose upgrade #3 and are now at #2. This would make a fairly realistic siege campaign where you bomb the planet to take out the shields and then invade. If you dont have the resources to beat the garrison, you're force to bomb them all.

This whole system could be implemented without adding new ships or models. just a few icons for some new abilities, some new variables, a new indicator for how many troops are on a planet, and done deal.

Tying it to fleet points could work, but i think it would be difficult to balance the mechanic against using those fleet points for more ships. If need alot of fleet points to make it work effectively, why bother? on the other hand if it's too low, planets will be filled with troops and you cant invade anyhow.

So here is the core idea:

• There is a new number/capacity for planets known as 'troops'. Could simply add it to the planetary info card, but would be better to see it afar via an icon/meter or something
• Defensive upgrades increase your troops there. You can purchase additional troops to be stationed there.
• Siege frigates have a new ability: 'Invade'. This will attempt to take over the planet, and there is a chance of failure. Bombing is disabled while this is cast (debatable, but I'd hate to invade and have ships auto-bombing the planet im about to take over)
• More siege frigates means faster invasion time. More troops on the planet means slower invasion time.
• Siege frigates must outnumber troops on the planet to stand a chance of success.
• A successful invasion means you take ownership of the planet. Population stays the same (possibly small growth bonus), other upgrades could be included but would be determined by playtest for balance. Possibly takes control of oribital structures, again based off playtest balance.

Secondary mechanics that could enhance the core idea:

• Culture affects invasion speed. Invader's culture dominating = quick invasion. Culture other than Invader's dominating = Very slow invasion. Small/no culture = normal invasion speed
• Bombing a planet removes upgrades. Last defensive upgrade prevents invasion (a conceptual shield is the cause). Can be tweaked what is included/not included in this feature
• Planets have a maximum troop capacity or troops might take up fleet points to prevent unlimited build up
• Various upgrades that are already in the game can be enhanced via modifiers to the invasion speed/cultural influence on invasion/troops-to-siege-frigate ratio. These modifiers could be offensive or defensive, or both to add depth to the mechanic
• Maybe some way to move troops between planets? Maybe capitals can have troops?
• Research could change the effects of defensive upgrades

Something that just occurred to me: There was discussion about the habitability of the planets after bombing them.... This made me think of the rate of population increase and that is fast. What are they rabbits? On the other hand, the nuclear fall out could be causing that....

   I could see something like this work if it was kept simple. With no actual battles.

  Would like to have a choice in what the planet's role is in my empire.  Like a mining planet , improves mining operation effeciency across empire by a percentage, with improved mining yield on the planet. A trade planet , improving income for trading across the empire by a percentage, with improved credit yield.  Could be a military planet as well, improve fleet capacity, boosting defensive/offensive values for structures and fleets in the gravity well.

 Then tie in with the ability to launch a ground attack to take the planet with minimal infrastructure damage.  Or you can bombard the planet, destroy the infrastructure and choose what you want that planet to focus on.

  For the troops, to keep it simple, I would suggest making the infrastructure level of the planet, should be upgradeable with above suggestion, cover civilian population values and change the population level to cover troop levels. Add a drop ship to carriers and add a decent cool down for them.  Make it so that after they deploy they begin the decent cool down to deploy the next wave.   Should be fodder to fighters, flak ships defensive emplacements and somewhat to frigates.  

Edit: Also could add ability to incite rebellion on the planets to help weaken the military presence or remove them all together. Would be based on research invested in something like espionage. Maybe requires training in specialized operatives that are highly studied in the day to operation and personnel for each type of planetary operation, several branches.

    Always felt the research should have many more levels for each field, not just 2 or 3.  Allow more leveling in each area so that you just cant research it all. Just reduce the increase percentages and use diminishing returns a bit so you can't pump up one thing to win, but still have some value for the points invested. 

Yeah, the only time I even acknowledge that button's existence is when I have money to burn when I'm about to make the final deathblow against the AI anyways...

  I noticed the bonuses from the minor artifacts,  is I guess what they are.

   But to have a planet dedicated to that, providing a substantial boost, could be much more beneficial and meaningful. You get it when you build it not at random.

  Imagine a choke point planet being a military planet and getting those bonuses, that would be a tough nut to crack.   So do you take the easy way and bomb it into submission or take over the planet with ground assaults.   If you bomb it into submission you will have to drop a lot of resources to get it back to where it was.

while that would be cool, my suggestion is easier for them to implement and easier for the player to adopt. If you have alot of features, a tree makes more sense. If you have a few, rolling it into the existing setup makes the most sense.

If, magically, the devs decided to implement this.... What else would you have? So far, we have troops, planet health, and shields. To protect your planet (I'm sticking with your idea that it be a planetary defense tree), you will need some of each. The smart move is to take some of each. You said something about planetary based weapons, and im okay with that. I just think it could be something that you research and suddenly your max-defense planets all have guns as well.

All in all, if people want Sins to include land based combat, I dont think you can get it with lots of details. It is a space combat game. The best you could get, in my opinion, would be a secondary feature and not fully implemented. By that, I do not mean half-assed. It wouldn't be something that makes you have to re-learn how to play the game, I think.

And research to unlock this stuff could be another section of the entrenchment screen

Something I've been thinking about for a while now but am just now mentioning...  What happens when you halfway bomb a planet and then decide you want to invade or vice versa because the situation changes?  

Thus far it just seems that the best I've got means bombing destroys civilian infrastructure over time as it decreases planet health whereas invasion just reduces the troop presence.  This way if you decide to do both for whatever reason, you still get the results of both.  Now, if you did expand the emergency facilities into an entirely separate build menu in Sins II or whatever, then invasion would probably take down certain things like surface to orbit weapons, troop support infrastructure and the like.  Things of that sort.

ferry good ideer i like it

If we actually could blow up planets or change their type, then I would love your system.  Terran planets get 50,000 health or what have you (asteroids get like 10,000).  Fortifications get say, 6000.  Both numbers slowly regenerate over time, but planet health regenerates MUCH slower.  It is literally the health of the planet.  Bomb too much on a Terran planet and you get the following progression as the planet's overall quality decreases:

Terran>Desert>Lava>Asteroid>Dead Asteroid>Asteroid Field (aka boom).  In this way, hotly contested planets will eventually degrade.  The feasibility of a terran decaying into a desert is relatively high.  To go from the lava to asteroid on the other hand, you really have to really make the planet go boom and probably the only way to do that is superweapons.

Once you knock a planet down a tier, there is no going back.  It permanently gets its maximum population decreased and cannot go back up above the health of that planet type.  Fortifications on the other hand can be rebuilt to the aforementioned 6000.

Habitability would be a separate factor.  This would be like shield mitigation, simply much slower falling.  As you bomb, the habitability of a planet decreases (faster if using TEC and even faster if using High Yield Warheads).  You will ultimately bomb a planet to uninhabitability.  This factor decreases over time, but after reaching say, 20% (or whatever number and unit system you use) population growth is stunted.  After 40%, population begins to drop with an EoT.

Of course, that's all wishful thinking.

Lol, no, I understood fine.  I just took your idea and ran with it