UE_Research & Development, on Sep 8 2005, 10:39 PM, said:

A couple more thoughts about 'theoretical space warfare'. I seriously doubt anyone will adopt the classic sci-fi paradigm where a ship is like an onion; the top layer is the armor while the crew sections take up the whole ship. A relatively small breach could doom the whole assembly. Instead, barring artificial intelligence sophisticated enough to fight battles, large ships would probably have a very heavily armored and very small crew section within the main hull. The bulk of the internal volume would be consumed by redundant systems or empty space. If the acceptable tolerances of ship armor were modified so that a puncture (as long as it significantly slowed the kinetic kill vehicle) was acceptable, as opposed to even a puncture causing massive depressurization, crew sections would be much more viable. (Also consider that it would be nearly impossible at long distances to aim a second firing so that it would go through the hole and penetrate the crew section.)
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I would have to disagree with you on this point. Adding empty space only increases your target sillouhette. If it is already hard to hit something at this range, making yourself even smaller would be more valuble than making it such that the ship will survive a direct hit. If there is any chance that the destruction of a redundant system would bring about the destruction of the entire ship (and there would be), why not just remove the system all together and let the shot zip on by?

Im thinking armor in space is not worth it. I doubt we will use much more than milimeter thin titanium skin+structural bracing for any non-atmospheric effect.

There are also important logistical issues. Assuming quantum entanglement ftl communication doesnt pan out, and that relativity is right for all reasonably large dimensions, how would teams determine who was friend and who foe? I would think this would be mighty difficult. Before you say IFF, remember that transmitting to the entire are your location 'because someone asks' is a very, very bad idea.

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I would have to disagree with you on this point. Adding empty space only increases your target sillouhette. If it is already hard to hit something at this range, making yourself even smaller would be more valuble than making it such that the ship will survive a direct hit. If there is any chance that the destruction of a redundant system would bring about the destruction of the entire ship (and there would be), why not just remove the system all together and let the shot zip on by?

To a certain extent. However, a crew space (barring luxury suites) will almost always be much smaller than the other equipment required to power and arm a military spacecraft (unless you can somehow shrink down engines and long-range military lasers to something the size of a Winnebago). The point is that the crew space will always be much smaller than the other systems aboard the ship.

As well, there will probably be awkwards empty spaces left over by placement of systems and components. In this case, the marginal cost of putting a reduced, auxiliary, or redundant system in the unusable space would most likely be less than the benefits gained; i.e. the chances that one component will be hit go up slightly, but the system in question will not immediately go down even if that component is hit, whereas if a non-redundant component is hit it is more likely to take down the whole system. Again, this really depends on how technology develops.

Also note that there are probably many more components that can survive a hit better than a crew compartment (if it depressurizes, say goodbye to the ship's nerve center).

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Im thinking armor in space is not worth it. I doubt we will use much more than milimeter thin titanium skin+structural bracing for any non-atmospheric effect.

Possibly, especially because increased ship size requires increased armor plating just to maintain the same level of protection. At the rate things are going, though, I doubt we'll be seeing space combat before scientists develop new types of armor-type protection.

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There are also important logistical issues. Assuming quantum entanglement ftl communication doesnt pan out, and that relativity is right for all reasonably large dimensions, how would teams determine who was friend and who foe? I would think this would be mighty difficult. Before you say IFF, remember that transmitting to the entire are your location 'because someone asks' is a very, very bad idea.

I'm thinking that the distance between ships in any particular 'fleet' will be much smaller than the distances between opposing 'fleets' (concentrated firepower, even the best lasers losing their power at very long distances, etc.). Even if your vessels broke formation, IFF would probably only become a significant issue if the ships came in much closer to each other.

This post has been edited by UE_Research & Development: 09 September 2005 - 10:54 PM

I never understood why anyone would want to take a big ship to a space battle. The bigger your ship is, the easier it is to hit, correct? And in space you really don't want to get hit because everything is moving so fast and your ship is going to be fairly fragile no matter what.

Until we get some sort of 'Defensive Screens,' it'll be all about the small ships.

Actually, shields aren't pure fiction. I read an article somewhere a few years back that the US were running tests on some sort of electrical charge being run across a tank that could enable it to withstand an RPG hit. Clearly they haven't finished yet, or it didn't work, but it shows that as an idea, it works.

At this point, I hope no one minds if I bombard them with the combat ideas that I'm using in my under-way plugin (the one in the signature, if anyone's interested.)

Here's a quick rundown of the organisation for classes:
Scouts come in various flavours, all with the idea of intel gathering. You've essentially got the ridiculously fast, highly fragile ones and the larger, slower, stealthy ones.
Then you've got Fighters and Bombers - I split those up in EV by making fighters faster, and bombers only have one or two gun slots, but get a special, smaller-than-usual rocket launcher.
Then all the usual rigmarole - Gunships, corvettes, frigates, cruisers, carriers, battleships. To try and make it balance out, the bigger something is, the slower it is (obviously), and to get around the PDS imbalance, you need to make a choice about what you want. You want PDS? Fine, but you'll get pasted by the big guns (which are slow firing, probably have limited firing arcs, and cause lots of damage - not ideal against fighters, in other words). Go the other way, and you're liable to get Trench Run Disease as you simply can't fire enough shots to get rid of the fighters. If you go halfway, you get both problems. For a successful fleet engagement, you need a good mixture of ships.

Carriers aren't the weedy things they are in EVN - the smallest one launches 6 fighters, the largest can spit out 24 at you. On the other hand, to have all this room, they've got very little weaponry, so they need protection.

And then for tactics, each race in the plug has their own special tricks up their sleeve.

Centauri use their capital ships from a distance, bombarding the enemy with Accelerator cannon (read 'Railgun') fire, while their carriers launch their unpleasant cloaking fighters. These fighters and bombers only decloak to fire, so you never know where they are.

Skerathi rely on capital ships with plenty of close-in fire, and use a steady advancing line to drive their enemies back while their carriers and fighters swarm around the edges, preventing a sideways breakout.

Pursk use terrifyingly fast and powerful ships to divebomb enemy lines before withdrawing before they take too much damage - their ships are quite frail.

And finally Tren simply let the enemy come to them if they want to - Tren warships are the slowest in the game, but easily the most powerful, with a nasty array of both long-range and close-in weapons.

(quote)QUOTE(Eugene Chin @ Sep 8 2005, 07:23 PM)
However, the act of firing the weapon requires vast amounts of energy, and would be visible from quite some distance away. It would signal three things to every sentient observer in the galaxy:

The ability to make a weapon of planetary destruction.
The willingness to use such a weapon.
The aggressors position. <--- This is the catch.
(/QUOTE)
Actually, I'd say that the second point is the catch. You can use the age-old tactic of misdirection, and hide who launched it by launching the rock from somewhere in or near someone else's territory, but once anyone uses a planet-destroying weapon, they have left themselves (and the rest of the galaxy) open to retaliation in kind.(/quote)

Quite. In the back story (which is actually a book I'm writing) for the plug, some bright spark worked out how to trigger a supernova. To cut a long story short, someone did, everyone went ballistic and the things got universally banned, with production being considered an act of war against all races.

This post has been edited by Chrome Falcon : 10 September 2005 - 10:23 AM

Easy peasy.

Fleets schmeets, move into the enemy system, drop a few hundred thousand tungsten(For mass to SA ratio, to lessen the destructive effects of moving through atmosphere) sabots at the general area of the enemy planet at .98c ... let's see them stop that.

Of course, they just did the same thing to your homeworld. Space combat is a Bad Thing.

Note: Yes, drop the sabots. Remember, The enemy's gate is down.

FluffyWithTeeth, on Sep 10 2005, 11:28 AM, said:

Easy peasy.

Fleets schmeets, move into the enemy system, drop a few hundred thousand tungsten(For mass to SA ratio, to lessen the destructive effects of moving through atmosphere) sabots at the general area of the enemy planet at .98c ... let's see them stop that.

Let's see you accelerate them to .98c...

A few things that you guys have mentioned that need some correcting.

Conventional explosives are pointless. Once a weapon travels at 3 km/s, it will now do its weight as though it were TNT.

K(e) = .5 * M * V^2

K(e) is kinetik energy in joules
M is Mass in kg
V is relative velocity in meters/sec

So a 100 kilogram slug from a railgun, travelling at a measly 500 km/s, would do 1,250,000,000 joules of damage. A kilogram of TNT has 4,500,000 joules.

Fighters are pointless. In order for a fighter to be effective and NOT a manned one-way kamikaze, it needs enough delta-v to reach its target, enough delta-v to cancel out its movement, enough delta-v to maneuver on target, enough delta-v to get back to its carrier, and enough delta-v to maneuver to land. This would require heinous amounts of maneuvering mass. Much simpler to use a missile bus. May not be re-usable, but you can carry a whole lot more of them than you can carry fighters. Why? Because they need a fuel tank only 1/4 as large, they don't require crew space for pilots and other such fighter-related crews, and they don't require a large cavernous bay to house, launch, and recover them; an enlarged missile launcher will do.

Unless you're fighting within a planet-sized magnetic field with a bit of atmosphere, there will be no EMP.

Nuclear weapons will have their damage fall off very quickly in space. Direct hits are almost necessary; a near miss of a few kilometers will do little more than singe the paint job, assuming megaton-range warheads. Radiation is another matter. A megaton-range enhanced-radiation warhead could deliver a fatal dose of radiation from a couple hundred kilomters away.

Lasers are extremely power inneffecient. In order for them to be useful, a new, highly efficient means of power generation is necessary. As well, they produce an extreme amount of heat that needs to be radiated. Can you say heat-seaking missiles?

Source

Missiles:
Must be able to be unpredictable. Move in random patterns.
Must probably have a good targeting system which does not rely on control from the launcher.
something like air to air missiles today.

Ships:
Must also move in unpredictable ways all the time.
Since anything which can be predicted will fall prey to stuff that moves so fast that there is no observation before it hits.

Fighters:
I do not think fighters will be present, if not to kill incoming missiles, guide larger missiles or similar. Since they can fly a lot closer due to a smaller body to move out of the way if fired at by high speed linear trajectory weapons. But it think a fighter will be mostly weaponless, or have weapons to defend itself against missiles or fighters sent out to kill it.

Actually why will there not be fighters. Of course they will not have the ablity to travel far. But they can be launched from a mothership. And I think the mothership will benefit from having them.

This suddenly became very complicated. I'll post this while I think some more.

This post has been edited by modesty_blaise_us : 10 September 2005 - 01:55 PM

The only thing that keeps habitable planets from being totally screwed in space warfare is the fact that they're so damn valuable. I mean, they're in a prtty hefty gravity well, so any defenders on the surface will have to expend energy to get their lasers/projectiles/what have you out into space, while the aggressors pretty much have only to drop large rocks. I expect wepaons designed to destroy or damage planetary populations will be much as nuclear weapons are now, well, I guess that's what nuclear weapons ARE right now.

Anyway, the only truly limited resource is dominance over other peoples, as we expand into space we'll have ridiculous quantities of energy at our disposal, and plenty of other resources. So the battles would be to destroy other nations' spacefaring capabilities and cut off resources. Spacecraft manufacturing facilites would almost have to be in space for reasons mentioned above- i.e. dragging a ship out of a planet's gravity well would be a big waste of energy. And would probably be in defensible locations: asteroid belts (which would also be near resources), orbiting moons, in the debris ring around planets, etc.

Any ship inhabited by humans could not be very maneuverable, since more than a few g's would be fatal, which isn't very much in space really. So fighters would probably be out unless they used sophisticated AI, as even remote controlled ones could simply be jammed. So warships are going to be fairly large. Another advantage of size is that the surface area increase less than the volume when you scale something up, so a bigger ship could have more armor or defenses. I expect armor would mainly be for protecting the crew from radiation, and radiation based weaponry. The disadvantages of size are, well, size, which really isn't that big a deal, since a quadrupling of aspect ratio means you have 8 times the ship, and the fact that engine damage could more easily inhibit maneuverability, since there would be greater sheer stress since the strength of the ships hull would be proportional to the cross section of the supports, whereas the mass to be moved would be proportional to the mass, which increases at a rate of r^3 instead of r^2.

In battle, smaller ships would most likely have to serve a stealth role.

As for weapony, even lasers will take time to hit in interstellar distances, so at longer ranges, a ship that knows it's being fired on can dodge simply by moving erratically. However, it must be noted that the location the beam is firing at can change faster than the speed of light, since it is not an actual physical object and can convey no information from one firing location to the next, meaning that a sweep could be made to hit all probable locations the ship could dodge to. Furthermore, lasers require mirrors in order to operate, so anyone capable of firing a laser will be able to reflect it. This could be alleviated by having arrays of the most powerful lasers possible, but this would be a heavy weapon, most definately. The other disadvantage of lasers, is that they're energy weapons, and so have a significant wave function, causing defocusing over long ranges. Their main advantage is that they cannot be detected before they hit, however, it may well be detectable whether the weapon is powered up before it fires.

Particle beams would not have this defocusing problem, and could be fired at near c, making them almost as undetectable as lasers, but as I said before, the powering up of the weapon system may be detectable.

Unguided projectiles would have to use stealth of some sort. Which in space is pretty easy if you cover it in radar absorbent black paint. They would require some sort of active defense more complex than a simple magnetic field, perhaps something like the active defense system currently being developed which some referred to earlier, which essentially tears the projectile apart with an electromagnetic pulse the moment it contacts the armor, reducing its ability to penetrate.

Guided projectiles would probably see heavy use, as they are the only weapons that can have any sort of accuracy at stellar distances, since they don't have the relativistic time delay when aiming. The best way would probably be to set them up as stealth unguided projectiles set to activate and hit the nearest target after a certain flight time, since once they fired any sort of manuevering thruster, they'd be detected.

Chemical explosives would be far underpowered, so any explosivs would have to be fission, fusion, or even antimatter. They would work quite well as some sort of fragmentation bomb, as there is no air in space to slow the fragments, so they'd probably be made for shredding smaller objects - missiles, stealth fighters, that you only know the general area of.

Battles themselves would probably take place in interplanetary space, since the moment an enemy fleet gets in weapons range of a stationary target, it doesn't have long to live, and ships could be detected long before they arrived anywhere useful. Stealth ships could be a problem, as anything powered down, with light/radar absorbent coating is nigh undetectable. Anything important would probably have satellite grids out at significant range, peroidically sending enerrgy pulses back towards detector stations so to show any object moving throught that space in silhoutte. Warfare would probably be conducted by guided weapons at very long ranges, and any ships trying to move anywhere without gettign hit would have to be flying in rather erratic flight paths, so as to avoid them.

After World War II most everyone thought that the next war would be decided by nuclear weaponry. It certainly seemed like it, once the Soviet Union tested their first atomic bomb. We went through two wars/police actions, and, surprise surprise, nobody used atomic weaponry. The Korean and Vietnam wars were both fought with conventional weaponry, most types of which prototypes had existed during World War II or before.

There are thousands of nuclear weapons extant today, held by a variety of nations, but practically nobody considers actually using them. We don't live in fear of nuclear war today. Every conflict since the end of World War II has been decided by conventional weapons.

Are nuclear weapons impractical? In terms of winning a war, not really. If you really, really wanted to win a war, you could easily reduce a country's major cities and destroy a large portion of their armed forces with ICBMs. If we flattened Baghdad (and the rest of Iraq) with nuclear weapons, our Iraqi insurgent problems would disappear real quickly. Why haven't they been used, then? One reason is MAD, but another one is that people consider the use of nuclear weapons, especially against a civilian populations, to be a repulsive thing to do. Oh, yes, and if we destroyed Iraq like that the place would lose all economic value. It would be hard to drill for oil in the middle of a radioactive wasteland, and most of the population would be dead or dying.

Dropping asteroids/metal slugs/whatever upon a planet in order to eliminate all human life upon the surface is tantamont to nuclear war. It's also rather inefficient in the long run unless you're interested in mineral resources, and you could probably get plenty of those elsewhere. If there is space warfare between two relatively evenly matched (human) factions, nobody will actually resort to this for the same reason nobody's used nuclear weapons in war since the end of WWII: too many ramifications (including the aforementioned MAD), and redundant mining rights aren't (or shouldn't) worth half your civilian population dead.

Of course, it's not impossible, but it's not something people will casually take to, either. We'll fight wars with this method once and everyone will lose, or we'll see it happen and realize that we never want to deal with it again. It would be similar to asking 'what would happen if someone invented a weapon orders of magnitudes more powerful than the nuclear bomb ten years from now?' It sure wouldn't make people more eager to fight long-range nuclear, or antimatter, or whatever war.

This post has been edited by UE_Research & Development: 10 September 2005 - 05:38 PM

Keldor Sarn, on Sep 10 2005, 09:50 PM, said:

<snip>
Particle beams would not have this defocusing problem, and could be fired at near c, making them almost as undetectable as lasers, but as I said before, the powering up of the weapon system may be detectable.
<snip>
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What charge are the particles?

If they're charged, they'll defocus pretty quickly. If they're uncharged, how are you accelerating them?

Only if you're chunking out a lot of particles at relatively low velocities. Fire say one alpha particle at a time at nearly the speed of light, and the kinetic energy will more than make up for the low particle density.

EDIT: By a single particle at a time, I mean generating a single file beam of particles, so that the repulsion will only push forward and backward, and won't push particles off to the side and defocus the beam.

And the fact that you could reduce the focus if you wanted could be an advantage if you wanted to hit a less armored and more maneuverable target.

This post has been edited by Keldor Sarn : 11 September 2005 - 02:36 PM

Antimatter is pure science fiction and should not enter into any equation whatsoever.

The larger problem to worry about is that firing a particle beam may cause your ship to become charged. Ever see two ships arc-weld themselves together? As well, the linear accelerators required for a particle beam would be masive.

You guys keep mentioning "erratic maneuvering." You seem to not understand that this "erratic maneuvering" expends horrendous amounts of fuel, and it would take a large amount of time to get that much mass moving in the direction you want it to.

Radar-absorbent paint is all well and good until they start using LIDAR on you. Besides which, the moment you light up your drive, they'll know without a doubt where you are. Any ship drive capable of moving a large vessel will produce terrawatts of energy.

It is impractical to cover your ship in mirrors fine enough to reflect enemy lasers. In order for your mirrors to not melt, you would need to have mirrors better than the mirrors utilized in an enemy's offensive laser system. Why? Because the enemy can use a focusing mirror larger than the spot size of the laser once it hits your vessel. Thus the heat from the laser will be distributed across a large surface for them, and a small surface for you.

It all depends on what reality you are basing your combat in.

Space combat, as extrapolated solely from current technology, with no major breakthroughs (there will be some, but there's a 95% chance that any you predict will be wrong), would be fairly boring. Interstellar combat will be nonexistant, and even intra-system combat will be slow, with a major home-team advantage to the target planet. Deep-space piracy may occur, although the fuel costs of matching speeds at inter-planetary velocities would likely make it unprofitable.

In my opinion, the question you should ask is not so much "what will space combat look like?" as "what can I do to the universe to make space combat to look like this?"

Edwards

Most definitely, which is why a lot of good science-fiction franchises or stories invent their own supplementary 'physics' or other sorts of meta-scientific explanations that enable them to create a coherent 'why' for what occurs between dueling spacecraft (or whatever).

Human nature, we can however reasonably safely assume, short of institutionalized mind-control techniques or something else comprising a horrible violation of free will, will remain constant into the middle (and possibly even far) future.

Admiral Benden, on Sep 11 2005, 09:45 PM, said:

Antimatter is pure science fiction and should not enter into any equation whatsoever.

...

Radar-absorbent paint is all well and good until they start using LIDAR on you. Besides which, the moment you light up your drive, they'll know without a doubt where you are. Any ship drive capable of moving a large vessel will produce terrawatts of energy.

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Ok, first of all, as student studying A-Level physics, I can tell you that Anti-matter is reality (by an odd coincedence, I'm studying particle physics at the moment). Scientists have managed to create it (admittedly in small quantities), and recent discoveries suggest that antiparticles are popping into reality all the time. The only reason no-one notices them is that a ) they get neutralised by contact with normal matter almost instantly and b ) the energy release is too small to be immedietly noticeable.

The main problem with using antimatter as a weapon is containing it - as I'm sure you all know, the moment it gets into contact with normal matter, they destroy each other and release huge amounts of energy. At this point its necessary to verge into sci-fi technojargon to get force fields and so on, but the idea is sound in theory. To give an example of how it might work, in the aforementioned plug, 'torpedoes' consist of a force field generator at the back which creates a little dome of energy that contains (for the sake of argument) antimatter.

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Guided projectiles would probably see heavy use, as they are the only weapons that can have any sort of accuracy at stellar distances, since they don't have the relativistic time delay when aiming. The best way would probably be to set them up as stealth unguided projectiles set to activate and hit the nearest target after a certain flight time, since once they fired any sort of manuevering thruster, they'd be detected.

At that point, I think that we're talking about the next generation mine.

Can I just ask how we got to this idea of combat taking place with distances between ships being measured in AUs? Yes, there is advantage in being so far apart (you have time to react to incoming fire), but surely this will eventually lead to some bright spark creating stealth ships that sneak up to the enemy and hammer them before they can react - the interstellar equivalent of submarines. Everyone else will be relying on long-range weapons, so they'll be stuffed. Then everyone goes to short range weapons, and then people rediscover long range stuff... I suppose that it goes much the same as that argument of fighters and PDS.

Can I also ask what LIDAR is?

Admiral Benden, on Sep 11 2005, 04:45 PM, said:

Antimatter is pure science fiction and should not enter into any equation whatsoever.
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...he posted on a webboard decated to a pure science fiction computer game.

Gravity and magnetism behave the same (or symetrically) with antimater as with matter, so you could suspend anti-iron filings in a magnetic field if you so desired, thats not too far into unreality. (If you had a strong enough magnetic field, you could probably keep antihydrogen relatively stabile).

Chrome Falcon, on Sep 12 2005, 06:46 AM, said:

The main problem with using antimatter as a weapon is containing it - as I'm sure you all know, the moment it gets into contact with normal matter, they destroy each other and release huge amounts of energy. At this point its necessary to verge into sci-fi technojargon to get force fields and so on, but the idea is sound in theory. To give an example of how it might work, in the aforementioned plug, 'torpedoes' consist of a force field generator at the back which creates a little dome of energy that contains (for the sake of argument) antimatter.
At that point, I think that we're talking about the next generation mine.

Can I just ask how we got to this idea of combat taking place with distances between ships being measured in AUs? Yes, there is advantage in being so far apart (you have time to react to incoming fire), but surely this will eventually lead to some bright spark creating stealth ships that sneak up to the enemy and hammer them before they can react - the interstellar equivalent of submarines. Everyone else will be relying on long-range weapons, so they'll be stuffed. Then everyone goes to short range weapons, and then people rediscover long range stuff... I suppose that it goes much the same as that argument of fighters and PDS.

Can I also ask what LIDAR is?
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Well, the reason we are discussing AUs is because if you can win at AU, they never get to the close combat. Same reason we dont discuss karate versus ninjitzu in modern warfare, we discuss tanks and guns and so on, because if you have superior long range capabilities, short range is totally moot.

Also note that space is (nearly) completely empty and (nearly) completely dark, so there is almost no way to hide yourself. Its like a gigantic empty field, you at one end, them at the other. They have a rifle and you are, given current technology, advocating using a bayonette. Bad idea.

Though, alternately, you are saying that it would make sense to dig a tunnel underneath the field, pop up behind them and stab them in the back. This would certainly be awesome, but we have that little matter of burrowing through real space to deal with. It all depends on how tightly wrapped the extra 6 dimensions are, if string theory is even true (hell... its not even a proper theory yet. No testable predictions).

That said, I still mantain my point that it would be a war of intelligence and misdirection.

Lidar:
http://en.wikipedia.org/wiki/Lidar
I dont see how that has to do with much, we are already operating at relativistic speeds.

There is always the question of how much energy you can pack into anytihng but kinetics. If you simply lunge towards your opponent, dodging randomly, he would be hard pressed to hit you with anything that wasnt guided, and that precludes any sort of kinetic impact. Are nuclear weapons really as impotent in space as people claim? I know inverse squares runs you out of energy really, really fast.

If you accept that Superman can fly, it shouldn't be that big of a stretch for you to accept he can turn back time as well.

By which I mean that if you accept hyperspace in the game it shouldn't be too hard for you to accept cloaking devices either. Furthermore, it shouldn't be too hard for you to accept that there can be weapons in the game that behave however the scenario designer wants them to.

A lot of the way space combat would be fought would have to depend upon the method of Faster-Then-Light travel.

For instance, if FTL travel is achieved via Tachyonic conversion, (switching out STL particles for ones that already travel FTL) then a whole realm of FTL combat would possibly be opened up. However, due to the fact that you are traveling faster then light, all your sensors would be useless, and fighting would be like shooting blind. Even then what would you fire? Faster tacyhons? If you could create a missile that would convert into tachyons with a pre-set timer to un-tachyonize the instant it reached the target... Time paradox problem.

If FTL is accomplished through a black hole or gravity drive, then surely such a device must have incredible potential for shielding. Every projectile fired at the ship would simply fall into the black hole, and the gravity distortion would bend lasers. Perhaps a style of ramming... Two colliding black holes... Yikes! That would not be fun.

If it is accomplished via wormholes/stargate/teleportation/entanglement then every system would have a few select choke-points that would be the main centers of combat. There would probably be a heavy focus on orbital forts, and jump-capable missiles. I liked what David Webber had in "The Shiva Option" for this style of conflict. The attacking side pours heavy amounts of self-guiding missiles through the gate followed by the heavier hitting battleships while the stations are still trying to sort out the missile mess.

As for higher dimensions, it would be interesting to see how combat would play out, with the fleets of each side scattered through several dimensions, phasing in and out. It would be a very disorienting and confusing experience.

I don't know if in the future cloaking will be necessary. Since I am assuming that in the future fleets will travel at rather high velocity themselves, maybe even up to .2-.3c. Laser range finding would be like searching for a needle in a haystack with all the empty space. Probably the best method of locating other ships is when their energy signature reaches you. Given the lag time, adding a sufficient amount of randomness to the flight pattern would make you very difficult to pin down and track. Maybe cutting off the drives and drifting silent for a second or two. Maybe if gravity sensors are created, the capability for accurate enough sensors will make the need for more drastic cloaking measures.

Marine(Ground Troop) transports.
The anti-ground vessels would probably have very heavy armor belly plating, combined with some sort of shockwave causing weapon. The shockwave weapon would probably be highly adjustable, allowing for the ship to knock everyone unconscious within a km radius, or focus the wave to destroy small targets. Railguns and weapons used by ordinary warships would probably be overkill due to the atmosphere of the planet.

The landing zone would probably be within a city, and from there on out urban warfare would be the game. I say that the attackers would probably land in a city, because if they landed in a remote place or enemy military base, the defenders would probably use a nuke to save their planet. (If aliens landed in some part of Russia, I don't think we would mind using a nuke too much.)