So, I was thinking about what a space combat simulator involving playable big ships would looks like, gameplay wise, given those premise :

- At the scale of a Solar System (where every combat in the game takes place), FTL speed is nearly instantaneous. However :
1) For in-universe design reasons, only capital ships can have jump-drives (Capital Ships being ships over X tonnage)
2) A jump sequence looks like this :
a/ divert power to jump-drives, wait for them to reach full charge (or abort and go to d/) ;
b/ initiate jump (or abort and go to d/) ;
c/ emerge from jump (not always where you where aiming for ; see point 3) ;
d/wait for all systems to return to nominal power (leaving the ship vulnerable for a little while).
3) You can, theoretically, jump from anywhere to anywhere, the problem is that the more intense the gravity well you're in, the more energy you'll have to spend to jump (and physically, a lot of capital ships don't have the energy to, say, jump less than 1.5 million kilometers away from the center Jupiter's gravity well), and the more uncertain you'll be that you'll reach your target : in ballistic terms, the more intense the gravity field you shoot from, the larger (exponentially so) the CEP at your destination.

- The ships have low sub-light accelerations, compared to most other sci-fi settings : a typical Capital Ship has an acceleration of 0.5 to 2 gee in normal flight conditions, and can go up to 5 – 10 gee in “I don't care if it destroy the ship's superstructure : if we don't get out soon, we'll be dead anyway” flight conditions.

- No artificial gravity.

- The weapons of choices for ship-to-ship engagement are lasers and 50 KT to 1 MT nuclear-shaped-charge tipped missiles. The missiles are mounted on missile buses (think : a combo between a MIRV and an unmanned fighter/bombers equivalent) which are typically able to sustain 30 gee or more of acceleration for a dozen of minutes or so, while the missile themselves have 100+ gee of acceleration for the little time their motor runs. Lasers and projectile-based-weaponry are used for point defence. The ships' defence against lasers are typically clouds of reflective matter (think : chaff) and reflective thermally shielded hulls (think : STS heat shield, but a bit better).

- Out of combat, ships have big-ass radiators, that they retract during combat. The heat generated during combat is "stocked" in coolant vats, which can be vented during a fight (this can also serve as an anti-laser counter measure, but then if you vent all your combat-coolant during combat you'll have other problems than those lasers - like your reactor blowing up from overheating, or stuff like that...)


The reason why there are starships fighting each others in the first place is for planet or space colonies to conserve space-superiority (a.k.a. The Ultimate High Ground). The reason why people fight is not so much for resources, which there are plenty of in space anyway ; than for lebensraum on habitable planet : you see, space colonies are all well and goods, but after a few thousands years in those glorified tin cans, people tend to build a real “mystic” toward living on real habitable planets, and politics makes the rest. It doesn't help that habitable planets are really rare. This also prevent much of the “orbital bombardment” tactics, as it would defeat the purpose of any war in the first place : it's to say, take the planet and its environment as intact as possible.


...

… And then it hit me that to know what kinds of ships will compose the fleets and in which numbers, I have to know what are the likely scenarios of a planetary invasion with such premises. Do you really have to land an army of hundreds of millions of troopers to take a planet of billions of people with a civilization at technological parity ; or are there ways you could use far less troops without fucking up the planet's ecosphere and its suitability to human life ?


So, any ideas ?


Note : the fights will be between human civilizations. No non-humans are involved.

I precise the question :

" How do you invade a planet when said planet has a population counting in the billions, a technological and industrial parity with you, and you want to take the planet as intact as possible and without creating hazards toward its human habitability (bioweapons, uncontrollable nanoplagues, etc...) ? "

1) Secure orbit.

2) Neutralize any meaningful surface-to-space weapon capability on the planet.

3) Set up bombardment platforms in orbit: kinetic weapons a la Thor, or large laser platforms are best, since neither has radiological or other long term side effects if you blow up point targets on the ground

4) Reduce planetary surface to tributary status. You do not garrison the surface, you simply insist that they do certain things for you, and refrain from doing certain other things. If they displease you, you bombard them.

5) Keep a suspicious eye on your tributary states to make sure they don't treacherously prepare an arsenal of weapons and try to overpower you after you beat them and take choice bits of useful territory. As a Frenchman, I'm sure you remember what happens when you let the neighbor get away with that.

Transporting enough troops to occupy the surface is out of the question- successful occupations against an even mildly determined opponent require more than one soldier per 100 civilians, and you can't move that many people with the kind of technology in your setting, even if they can live off the local ecosystem and industrial base rather than relying on supplies from home.

So basically your empire will take the form of places that pay you tribute, allow your nationals to run chunks of their economy, and so on, but in which your military presence is mostly limited to the large, ominous dots created by your targeting lasers.

Honestly, the only hope one would have is that one can call down and explain gently to the planetary government that you're preparing kinetic impactors. If they would like to survive, they can surrender, or you'll drop rocks on their heads. Of course, if they call your bluff you're back to square one...

Otherwise, the best you can do is use orbital bombardment to take out as many military bases as possible, then prepare a conventional bombardment. Looking at your tech setup, though, it's possible that any ground defensive force will have sufficient forewarning to disperse into the cities or other areas that you want to capture intact. Unless you have Magical Sensors of Awesomeness (tm), enough of them are going to be able to evade your orbital bombardment to bleed your ground forces faster then you can transport them in... assuming they have the will to take the massive casualties you'll be able to inflict via orbital bombardment.

I crave a realistic space simulator. There are many simulators which come close, but nothing yet.
I just cut off the first half of this post, because Simon_Jester and Forgothrax wrote the same ideas first.


Make planets "worthless". One you are in space, you can build habs. Newly colonized planets are gravity wells, with the sole purpose of raising children in a place where they don't have to worry about as many hazards. Of course, most young planets will still be under terraforming process. (I recomend Para-terraforming, which means covering the whole thing in large domes until you have one large bubble)
They are like a big suburb. They might not even have many large cities, as the most densce population centers may want to be in space, where it's easy to travel around. Their only worthwhile export, is tourism, niche organics, retirement communities, schools, and young people looking to leave them to seek their fortune. No one will want to conquer a planet for the wealth. It'll be like taking Singapore or Massachusetts, for the mineral rights.

What they will do, is hold the planet hostage. This means threatening to bombard it with asteroids, or colony drops unless they transfer you something of value you can use. For most pirates, it's untraceable money, large sums of pharma, or skilled slave labor. For a future despot, they might want R&D data, skilled slave labor etc.
Oddly, the most likely target for a settled world, will be it's space assets, like comm satelights, weapons, orbital cities, platforms, zero G manufacturing facilities, and refueling station.

If the planet has a space elevator, they might be able to send up more valuables, but the mass you have to transport might be prohibitive.

If you insist on holding the planet, You'll need to use WMD, like bombardment, to hold the defenders at bay,and then use a system of rapid cloning, or mass production of robots to occupy the population. These occupiers may have an impossible task of blending in because of their very alien nature.

You had better hope they didn't get a message off planet, because when you major export is people, they can be rather protective of home.

For FTL, I suggest using big bombs! You use these really massive bombs, like an antimatter casaba howitzer, to create the necessary energy density literally blow open the fabric of space. The bombs will be expensive, dangerous, and heavily controlled.
The wormhole will collapse almost instantly, so your ships have to be on a precise trajectory, a minimum speed, have a maximum diameter to enter. In "civilized" space. Wormholes will follow a schedule, and the ships entering will either line up like a train, or be carried on a dedicated wormhole vehicle. A long spindly thruster.
If you plan on using a wormhole, you won't be able to make evasive maneuvers.
An alternative to the bigass bomb, is the bigass laser, but it's so big you need a space station, and maybe the wormholes are only big enough for comms.
The bomb FTL method is very dangerous and heavily regulated. Which means that in "civilized" space, the local government will try to control them. Far away, in "pirate" space, they will have rogue antimatter or microsingularity factories. Some of these "pirates" could be considered freedom fighters, or rebels, or terrorists.
Bomb based FTL will make invasions possible, but difficult. The cost of invasion is too high to do it often, and when you invade, retreat is hard.

Another FTL option I like is the warp conduit. An artificial region of space, where physics has been altered. Maybe the physics are pure neutonian, inertia is lower, the distance between stars has been compressed to a few au, or the price of cheese is sideways plaid.
What makes warp space conduits fun, is that the area between gateways is warped, but it's not zero. (Stay calm physics folk, I mean only in game terms)
You can leave the conduit before you reach the other side. Maybe you have a pirate base hidden at 53 seconds in. Maybe you force other ships to flee the conduit, and make them pay you large sums to re-enter at your secret pirate gateway.
Warp conduits would be stretched at sub light speed, and at great expense, meaning each star system will be heavily settled by players before the next frontier is opened up.
Because you would want to make money on your conduit, it also makes sense to have conduits between areas of major trade, even within the same star system. Now you can ships with something other than an Orion drive able to navigate within a system, and you don't have to simulate cryosleep, and tell the player to log in again in 12 years.
Of course, if the local gateway is destroyed, the conduit might "snap" to nearest gate, which means an unethical corporation might try to destroy a competing gateway to move the conduit, and milk the trade route.

Now your resource wars are no longer just about planets, asteroids, and orbits. They are about FTL trade routes, taxation, smuggling, and customers.

Another option that is more realistic, but less fun is getting rid of the FTL altogether.
Instead have each player be an AI, or a corporation, or a bunch of clones. You want to "jump", you simply take control of a ship or station you already had in place. Have FTL communication, which allows you to "jump" around and purchase material at large distances without actually moving a ship there.

Thread needs more spacenoid slavers! You'd think a part of controlling a planet would be social and economic policies to encourage integration and identification with the greater state, but now I know it's all about killing civilians - just like in real life.

If the target world has that sort of culture, then it's very likely they possess equal space and military capabilities to your own; sufficient to resist at very high cost any invasion attempt. They will either be able to successfully repel your fleets and possibly be able to launch a counter-attack, or their world will be devastated, perhaps past the point of recovery or even viability, while your own forces would suffer unacceptable losses in the effort. This makes any invasion scenario on those terms a non-starter. You simply do not have either the numbers or material advantage to be victorious in a war against a civilisation which is equivalent to your own.

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When ballots have fairly and constitutionally decided, there can be no successful appeal back to bullets.
—Abraham Lincoln

People pray so that God won't crush them like bugs.
—Dr. Gregory House

Oil an emergency?! It's about time, Brigadier, that the leaders of this planet of yours realised that to remain dependent upon a mineral slime simply doesn't make sense.
—The Doctor "Terror Of The Zygons" (1975)

I agree. That's what you do after you establish puppet states- you integrate them into your empire. The problem is that it doesn't last indefinitely; look at the British Raj. They did about as good a job as I can imagine at trying to make sure the local elites integrated and identified with the British Empire, and it was never really enough to cancel out local resentment at being ruled by distant foreigners.

The whole "gratuitous destruction" thing strikes me as the product of a deeply unbalanced mind.

So why build doom networks and slaughter civilians at all? Just wait a decade until you own their planet and their culture is flooded with yours.

You need a doom network at first. If you just send one guy in a ship to say "Hi, sign over your planet and cultural integrity to us," he's going to get ridden out of town on a rail. You need an "or else" added to that sentence, and orbital gun platforms or whatever are it.

Using the Raj as an example of this (which did work for about 200 years), after East India Company domination of India proved not to work, resulting in what the British call the Indian Mutiny, British troops put down the rebellion brutally... and then rearranged the government to be less antagonistic to the people of India, removing the Company's power. If they hadn't had the troops in the first place they'd have lost their colony right then and there.

But the doom network should be used with extreme restraint, not according to some kind of random bullshit terror tactics like Silvertongue says. You're not trying to constantly turn every day of your rule over the place into a new round of hostage crises; you just need something in place in case things go badly wrong with the "suborn the locals" plan.

A "traditional" planetary invasion would likely require three major stages, at least as far as I can see.

The first two stages have already been pointed out in earlier posts, but I'll include them just for the sake of clarity.

First is achieving space superiority, likely over the entire solar system as well as around the target planet. You'd want to be able to access the resources of the star system to help fuel your invasion.

Second would be to deal with any planetary defense on the surface as well as gaining global air dominance. Missiles bases, boomer subs, space fighters, combat aircraft, the works.

After those parts are dealt with, then you get down to the actual ground invasion. Now yes, I am saying ground invasion since I can't really see any other way of conquering a planet without nuking the hell out of said planet.

Now I think that with proper orbital and air support, you can gain control of a planet with relatively few soldiers, say about a few hundred thousand troops for every billion people on the planet.

Now for the sake of argument, let's assume that your soldiers are all typical, powered armor wearing Space Marine analogues, with the usual perks. IE, Enhanced Strength, speed, resistance to small arms fire, and sensor suit that includes thermal imaging and night-vision. These guys would pretty much be able to mop the floor against any kind of troops that are not similarly equipped. But ideally your troops will not be doing very much fighting, but simply holding strategic assets on the planet's surface.

I would forgo having things like tanks, APC, or other heavy armored vehicles, since maneuver warfare is not really what is called for. Ground convoys also would not likely be necessary as you can just drop supplies and reinforcements from orbit. Helicopters or similar VTOL aircraft would likely be useful for transportation and fire support, while predatoresq drones would help with maintaining control over large areas of land.

Now since you're invading an industrialized world, you need to pick certain strategic targets for your troops to hold. Things like power plants, industrial districts, communications choke points (bridges, canals, ports), etc. If you don't have enough troops to control all these objective, just take the most important or difficult to replace and bomb the rest. I would try to avoid sending your troops into urban centers, for reasons that should be obvious.

Now assuming that you've captured or destroyed all the things that an industrial society needs to function, you're going to find yourself in a classic siege situation. Localities that cooperate get power and supplies, while those that don't get to starve in the dark. Any attempt to mobilize ground units to oust your infantry would be destroyed by attack from air and space.

From there, I think it's just a question of time and dickery. And by dickery I mean how far your forces or any insurgents on the planet are willing to go in order to win.

I'm mostly with Degan on this one. If that planet is at technological/industrial parity and expecting an invasion, they're going to have extensive space defenses, and ground defenses as well (such as ground-to-space interceptors, and large lasers using the heat sink of the planet's crust that can hull your ships in orbit). To make matters worse, the nature of the FTL in the OP means that they'll have to drop out of space thousands of kilometers from the defenses at a minimum, giving the Planet Defense Forces time to get prepared for an assault.

To even have a chance of taking that planet, you would need to whittle down their space forces, then try to wipe out what you can of their ground defenses before they destroy a good chunk of your spaceships. This will probably cause extensive damage to the planet, or at least its population centers.

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"You can't hammer tin into iron, no matter how hard you beat it, but that doesn't mean that tin is worthless."
-Jon Snow, A Game of Thrones

"I prefer my history dead. The dead sort is written in ink, the living in blood."
-Rodrik Greyjoy, A Song of Ice and Fire

Thanks y'all for the pointers, keep 'em coming.

I like Simon's take on the subject. It allow a number of varied missions, and the variations it allow on how a conflict is handled are interesting.

So, to take a planet, an invasion fleet has to be able to do the following things :

- Destroy/subvert enemy space-based assets
- Destroy/subvert enemy Planet-to-Space defences
- Destroy/subvert enemy “spaceports” planetside
- Install and maintain “Doom Network” (Space-to-Ground Guns, be them Lasers or Kinetic Impactors)
- If necessary, be able to drop Shock Troops from orbit, supply and support them once on the ground, and take them back to orbit when the job is done (Starship Trooper's “Mobile Infantry”, book version ?)
- Put in place a supply chain for the Fleet once it enters the system

Anything I'm missing ?

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I'll make a try with the informations already gathered here.

Ships by role :

Inter-System Carrier : Those ships carry the whole fleet in their belly. Once the ships they carry undock from them, they have the responsibility to establish the supply chain for the Fleet inside the system : they become the fleet's base of operation in the system. Typically, they are giant hollowed out asteroids, and are heavily defended.
They include factories, shipyards for advanced field repair of the ships, recreational areas, school for the soldiers' childrens... Basically, they are specialised, FTL capable space colonies.
The most technologically advanced of those ISC, if they have the necessary materials, can build ships on the field, even if those ships will not have most, if any, of the more refined features of the ships built back home.

Engineers : Those ships, or fleet of specialized ships, are responsible for the establishment of various space assets like “orbital mine fields” (antiship defence platform firing missiles at any ship without the proper IFF codes), “doom network”, etc...

Space Superiority Ships : This cover all the ships that are destined to space-to-space combat. Some SSS are equipped with Orbital Bombardment weapons, typically second-wave ships.

Troop Transports : Those ships carry ground troops, their means of transportation (orbital shuttles), and their support assets. Troop Transports are equipped for Space Bombardment.



What would the different classes of Space Superiority Ships looks like ?

Another possibility for the defenders to deny any invasion fleet jumping within a few thousand kilometres of their planet would be a space fortress: Capture an asteroid, plaster it with lasers, kinetic weapons and missiles and tug it into the planet's orbit. Even better: place space fortresses at the Lagrange points L1, L2, L4 and L5 (see image)



The only way i see of how to deal with space fortresses is a relativistic kill vehicle, which turns up the costs of the invasion (depending on how expensive FTL is in relation to accelerating a sufficiently massive body to a high relativistic velocity). And although i'm not the biggest fan of FTL, i like Silvertounge's FTL ideas.

And speaking of a space combat simulator: Do you plan to implement it?

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edit, Space Superiority Ships: I suggest the following division:

- Battleships: The mainstray of the fleet. Like the name suggests, they are big warships with sufficient ammunition, fuel and heat capacity to be an effective threat for the enemy.

- Destroyer: similarly armed as the battleship but with substantially less armor and substantially more powerful engines to perform high-gee maneuvers. Therefore unmanned.

- Recon- and Command ships: Weapons (and a little armor) is sacrificed for loads of antennas, computers and communication gear. They collect data from all of your fleet's sensor platforms and provide vital tactical information for Battleships and Destroyers.

- Engineering Support Ships and Tankers: They can refuel and rearm the combat ships and replace overheated cooling fluid with fresh, cool one. They can also tug damaged battleships out of the combat area or provide basic repairs.

My programming skills are shit not sufficient for such a project, but if some people want to try their hands at it, no problem, it would makes me happy.
Otherwise, when I say "space combat simulator", I don't mean 4X-type gameplay, but more like a combo between a combat aircraft simulator, "Silent Hunter" (never played this one, but I mean the principle of "you command a ship and try to accomplish the missions that are given to you"), and games were you command a fleet as the Admiral of said fleet.



Nein, this word ist verboten here.
However, what you could try I think against a space fortress, is to "motorize" a big asteroid, push it on an high-energy collision course with the Space Fortress, and arm it so it will be next to impossible for the defenders to board it. Ideally, the rock should be big enough that it would be difficult for the space fortress to dodge it.
Ramming speed !




Hmm yeah... some of the ships you propose aren't SSS (recon, command ships, tankers, engineers), but Support & Logistic Ships.

As for the other two classes, I don't know if they are really adapted to the tech background I dropped in the OP. I'll think about it.

Well your ISC sounds a lot like the way the Mother ship worked in Homeworld, basically a mobile space factory. What I would recommend is having an organic fleet of asteroid miners and gas harvesters attached to the ISC in order to gather the raw materials you need to supply your fleet. Assuming that you use fusion to power your ships, especially if you plan on using "clean" He3 for fuel, your invasion fleet would be well served securing any gas giants in the system before moving onto the target planet itself.

For example, if you were to invade the Solar System, your first goal should be gaining control of Neptune and Uranus so that you can start harvesting gas to fuel you thirsty starships. Gas giant this size have surface gravity similar to Earth, so it shouldn't be to hard to have gas miners skim the atmosphere. Saturn and Jupiter sized gas giants would be problematic due to high gravity and radiation belts.

As for material resources, there should be plenty of big rocks floating around that could be exploited.



Well to start, i think there would be battleships. These likely would be built as large as possible while still being able to accelerate at 1 standard g of acceleration. These things would be loaded with as much weapons and armor as possible and would be designed for duking it out directly with planetary defenses and other battleships.

Next are cruisers. These ships would be quicker than battleships but have more firepower than anything else. These would mostly be used to maintain space superiority over the the invaded star system in general, not to engage the planet itself. That's the job for battleships.

You may also want to have classes of even smaller, more specialized warships like destroyers or frigates. These would be cheap, expendable platforms whose main function would be to support larger vessels. For example, missile frigates can add considerable firepower for minimal cost. On the other side, you could have an escort destroyers that are loaded with point defense weapons, whose job would be to knock down any enemy missiles or smallcraft that may threaten your battleships.

And you would likely need to have classes of dedicated carrier warships in your fleet, that are about the same size as your battleships.

Assuming that you use fighters, you could need a "fleet" carrier to house them. The "fleet" carrier would house fighters and bombers for combating enemy space forces. If your fighters are capable of atmospheric flight, or if you have specialized trans-atmospheric combat craft, then the fleet carrier would also support you traditional close air support, interdiction, and air superiority missions associated with "wet" carriers.

If your carrier is carrying drop ships instead of fighters, then you got yourself an "assault" carrier, which would function much like a wet navy amphibious assault ship. That would likely overlap with your troop transport idea.

I think you would also need a fleet of dedicated logistics vessels. Things like tankers and freighters that keep your warships fuel tanks, ammo magazines, and food stores fully stocked. On that note, you may want you ships to have built-in hydroponics and caricature labs for growing food for you troops.


Edit: I didn't read Number Theoretic's post before making my suggestions, so I apologize for any overlap.

Exactly my thoughts about the subject. Making it realistic would be an awful lot of work, though, even if you use a game engine like OGRE together with some suitable multibody physics simulation library. Because phenomena like heat managment, hull deformation and damage et cetera et cetera must be modeled and then we are not even starting with designing AI enemys or nice 3D meshes for ships and weapons . Nevertheless, it would be intriguing.


I see. A pet peeve of yours?


That could work. Just make sure your asteroid is bigger and sturdier than the enemy's fortress or else he'll shoot your asteroid to rubble before it can become useful.


I see. At first i thought you meant something like "what ships do i need in a war fleet as soon as i have arrived in the system" but if i understand you correctly, you mean ships that do actual fighting. Then, i'd agree at not including support and logistics ships in SSS. Recon, on the other hand, is debatable because you simply need it to know well enough where to shoot. I would consider it essential. Recon- and/or Command Ships could furthermore do electronic warfare like for example jamming or attacking the enemy's communication networks.

edit:

No worries, your list is more detailed than mine anyway.

Why are you taking your habs into battle like that? I mean, this is begging to be ambushed and end the entire civilisation than and there. If I may propose an alternative that makes more sense:
Have your homeworld ships (that's how I will call them for reference), like the ones you described be non FTL capable but have a really huge attachment port for your carriers. In turn, have your carriers be just massive space docks with a FTL engine and a connection module for the homeworld ships. When you go to battle, the warships dock with the carrier and jump. When you want to move the homeworld ship have the carrier dock with it, attach and act as the engine for it. That way you can keep civilians out of harms way and make for interesting reading. It would also allow you to move your entire factory complex into a system but to a safe place and than make tactical jumps with just your warships without interrupting production and resource gathering. Just think of it as saucer separation taken to the max.

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No need to apologize : the more data I receive, the more "calculations" I can run on what would be the best answer(s) to my questions.




This setting just doesn't have the technology to shoot something at even "only" 0.05 C ; or, if they could do it, it wouldn't be able to reach such acceleration inside a Solar System, or it's terminal guidance would be so messy it would be likely to miss its target, or it would have to be so elaborate as to be a battleship in its own right set to "Ludicrous Ramming Speed !!!".
So, simply not cost effective in the role you suggest.



Eyuup. But even in this setting, it's still hard to blow an asteroid to dust. But you can always try to fracture it or something, which will totally mess its terminal guidance and make it miss its target. But it'll still be hard to achieve I think ; especially so if the Ramming Asteroid has automated (point- and anti-boarding-) defenses.
Anyway, even if you can't destroy a Space Fortress, you can still relatively easily mission-kill it, and send your ships for a boarding action to mop-up what's left.



Don't worry, I'm planning to integrate these functions. I'm just working on how exactly to integrate them.



Interesting. I don't think I'll use it in this highly hypothetical game (as it's supposed to be centered on space combat), but nonetheless interesting (as it can affect in-game missions). Though I think it is still a helluva target for the planetary Wet Navy, especially subs and the like. And 'sploding a Nuke at sea isn't such as big a no-no as it would be on land, so...
You try to land an asteroid, but I don't think this setting has the technology for.



@ Purple :

Er... I must not have bee clear enough, pardon me, but... This isn't the entire freakin' civilization. Just a forward base and the people necessary to make it run.
And it is supposed to run more or less like you describe it : Some "drydocks", factories, habitations quarters, barracks for the troops, and the facilities to make sure that people don't kill themselves from sheer boredom. Like an aircraft carrier.
I put children care in here because when you have men and women living in promiscuity for extended period of time, some things are inevitable , and it is out of the picture to send the odd starship home just so a child can grow far from the front-line. Or even when it's possible (supply ships convoys from Back Home), some parents prefer having their childrens stay close to them.
Plus those ships aren't on the front-line, they are on the edge of the system : first they arrive in the Oort cloud, then the fleet take an outer planet (be it a gas giant, a pluton, or even an earth- or mars-sized planetoid), and then the ICS makes orbit with this outer planet, and stay there for the duration of the conflict, more or less.
And they are heavily guarded, and have themselves a most impressive armament.

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Additional details :

Most ships are heavily automated, and the human crew reduced to a Captain (the ultimate human authority on a ship that is otherwise run by limited AIs), a vice-captain, some officers (weapon, communication, sensors, etc...), and the few engineers needed when the ship's automated systems fail. The human components of the system are augmented to be able to endure high accelerations when necessary while retaining most of their combat effectiveness (read : they don't pass-out when the gees are high and can more or less continue to work)


About ships ducking it out with each others... As there are no magical "energy shields" in this universe, ship to ship combat will look like this (I think, correct me if I seem wrong) :

- At long distance, you engage the enemy ship with your Lasers, while trying to dodge/disperse the laser the enemy is itself shooting at you. Lasers can severely cripple a ship and inflict a mission-kill, but they are rarely sufficient to destroy them.
- When you really want to destroy a ship, you have to close-in and launch a missile bus, which will accelerate a bunch of thermonuclear-shaped-charges missile toward their destination (the enemy ship), and at the right time it will liberate the missiles, which will themselves accelerate at a very high rate (more than 100 gee) toward their target. As point defenses on most ships are good, you have to saturate those defenses with a missile spam if you want to have reasonable chances to inflict a kill. It generally take a dozen missiles or more flying at the same time toward the target for one missile to reach its destination and inflict a one-hit-kill.

A typical missile bus carry between 5 and 8 (generally 6) 1 MT thermonuclear-shaped-charge (like a cazaba howitzer) missiles. The missile buses themselves are reusable, and can be seen as Drones.


Sub-light propulsion on ships is provided by this kind of drives... :


... But put on steroid by advances on magnetic confinement and optimization of the ignition methods. Plus by using more than one of them on ships.

Since you are using nuclear fusion drives, may I suggest that you replace the tritium-deuterium fusion with an "aneutronic" fuel. My personal preference is for He3 based fusion as I am fond of mining gas giants, but there's a list of fuels that you can choose at the bottom of the page of the link below.

http://www.projectrho.com/rocket/fusionfuel.php

Thanks, I'll check that.

Edit :

The problem with 3He is that you have to separate those isotopes from the rest of the ordinary 4He, and isotope separation is a costly and complicated process ; whilst Tritium can be relatively easily manufactured on the fly by using the neutronic radiation from a fusion reaction to decay 7Li on 3H + 4He (see General Fusion's work on their fusion reactor here).

If you're looking for living space, attacking planets with populations over a billion isn't really a good idea. They're likely to have enough infrastructure and defenses to mount a very ugly and expensive resistance, and if you plan on settling the planet, you may end up having to depopulate it of the people who were there before you. What are you going to to, target all their cities and towns with neutron bombs and orbital x-ray batteries? Biological weapons are probably out of the question if you intend to inhabit the world yourself afterwards. How many people can your space fleet move around, anyway?

You're better off targeting recent colony worlds that have populations in the low hundreds of millions or less; they're likely to have less infrastructure in place and less of a defense budget. If they are being settled by an existing space empire, then either the empire doesn't consider the current level of investment worth heavily protecting and the colonists are on their own, or the empire's own space fleets will be doing patrol, along with protecting whatever trade/settlement/supply convoys are in progress. All you need to do is defeat their convoy defenses and announce to the colonists that you will be taking over administration and supply, and also contributing colonists. If the empire cares enough to send a fleet, you'll need to be prepared to be the defender.

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Every day is victory.
No victory is forever.

Oh I understand the issues involved with He3, I just like it from a purely ascetic point of view (IE, I really like mining gas giants). If you don't want to deal with the issues involved with He3, there's also Proton-Boron fusion, which is still aneutronic but the fuel used is more common and easier to refine. I'm pushing aneutronic fusion fuels because that way our ships aren't irradiating themselves as they accelerate.

Also, given how powerful your drives would have to be in order to achieve the accelerations you desire, those drives will be powerful weapons in their own right. So if you're in the mood for a literal scorched earth campaign, you can just have your biggest ships "hover" over a target and watch it get roasted by fusion exhaust.

Varrus is right: I had intended to mention it, but in a realistic setting, your torch drives are by far the most powerful weapons you have; that should really be taken into account. Also, nitpick, it's aesthetic not ascetic, unless you intend to use gas giant mining to divest yourself of personal possessions so that you can devote your time to more spiritual pursuits.

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Every day is victory.
No victory is forever.

Whoops, sorry. Those are just words I always get confused. My apologies.