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Let's assume 150 years from now Mankind has really made the leap to space, and there are a bunch of colonies spread perhaps over a radius of 2 to 3 solar systems (where Sol is the center, i.e. a total of 6 to 8 solar Systems with 1-3 colonized planets each, well developed (i.e. current Earth-Level + 50 years ish).

For whatever reason, the various star systems are controlled by one faction each and not split up, and these factions are at war with each other.

There is no shielding tech in general. It's only armour plating, bulkheads and/or ship-based interception.

Ships are using conventional engines based upon either nuclear fission or fusion (which is basically the upper end of the tech here), inter-stellar travel is achieved by wormholes located at the outer rim of each solar system. Travelling from the center of a system to the rim takes a few weeks (to give context to engine power).

Ships in general are more clunky and brick-like (maneuver-wise) compared to being sleek and agile (i.e. no Star Trek, Star Wars, Mass Effect, you name it. Closest would be B5 Earth Alliance). Maneuvering IS possible, but is cumbersome.

Realistically, what would be the weapon of choice for starships in this setting and why?

  1. Missiles (guided delivered conv. explosives)
  2. Torpedos (unguided delivered conv. explosives)
  3. Kinetic weapons (i.e. Gauss/Railgun-ish)
  4. Lasers ? (my favorite)
  5. 1 or 2 but with fission/Fusion warheads ?
  6. Strikecraft (i.e. carrier-based) with 1-5 ?
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    $\begingroup$ "clunky and brick-like" => missiles. Fighters in space are unrealistic in the age of drone combat. $\endgroup$ – AndreiROM Aug 8 '16 at 12:19
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    $\begingroup$ I'd suggest extending your time frame a little. In 150 years time, your colonies are likely to still include a number of early-generation colonists; children and grandchildren of the original pioneers. And that's for the oldest colonies. The planets colonised later may still be populated by the original colonists. Given this, I don't think they'll have had time to develop populations or infrastructure large enough to be self-supporting enough to go to war with each other. I'd suggest pushing it out to 250 years. You can slow the rate of technical development to compensate. $\endgroup$ – Simba Aug 8 '16 at 13:48
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    $\begingroup$ @AndreiROM Indeed, the drones from Andromeda or the Very Dangerous Array from "Schlock Mercenary" are far more realistic than BSG- or Honorverse-style fighters. I'd design them to be able to fire cutting lasers as they approach the enemy, then attempt to make contact and when the laser fails just blow up. If that happens inside a hole the laser cut earlier, so much the better. $\endgroup$ – Monty Harder Aug 8 '16 at 17:39
  • $\begingroup$ @montyHarder - I went into more detail in my answer, below $\endgroup$ – AndreiROM Aug 8 '16 at 17:44
  • $\begingroup$ #2, 3, and 4 could only be effective at short-range. In a dynamic long-range situation, they cannot reliably hit their targets. $\endgroup$ – RBarryYoung Aug 8 '16 at 20:15

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I'd go for the rail-gun because you have power to spare and it is economic.
Since maneuvering is cumbersome and not easy, you can fire a bunch of high velocity projectiles on the planned trajectory and forget about it.

Given that there is no shielding technology, the railgun has some advantages over the other options:

  • economics: you are firing some chunk of metal, no fancy systems or advanced technology projectile, so you can have a lot of them on board and the munitions are way more secure than normal munitions
  • the projectiles are small and passive: this make the detection a lot harder than a missile with some active guidance system. As bonus, they also are a lot harder to intercept
  • we can now fire at about 3 Km/s, the velocity can probably increase to some (very) small percent of light's speed. If you can make 0.05% of c you have a very powerful and economic weapon
  • in space you have no aerodynamic drag, so your destructive power is not decreased over distance and the trajectory is basically linear.
  • given the basically hostile environment, you don't really need to blow up the ship, you just need to make a hole in the hull to cause damages. As bonus, if you hit some critical area of the ship, it will probably blow-up anyway.

All the other options have some disadvantage that make them useless while fighting in space:

  • missiles have the problem to be relatively easy to spot and have the same maneuvering problem of a ship.
  • both missiles and torpedoes have the problem to deliver they destructive power: in space both conventional explosives or nuclear weapon are not very effective and must be detonated at contact or at very close range
  • strikecrafts have the same problems (even if smaller) of the capital ships
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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Aug 10 '16 at 13:55
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Realistically, you've looking at missiles and armed drones of some kind, with ballistic, or better yet laser weapons serving as close-range defensive and anti-missile weapons.

Space is big.

We all know this, but I'm not sure we all understand just how big. (not judging by many of the other answers, at least). Space battles will take place while fleets are thousands, if not millions (1 light second) of kilometers apart. The purpose of these battles will be to either destroy an enemy ship, or cripple it, then approach and board it (which would be really dangerous for a variety of reasons).

Kinetic Projectiles Suck In Space

Here's the deal with any sort of kinetic projectiles: you can't possibly accelerate them anywhere near a decent fraction of the speed of light - the amount of energy involved would be tremendous.

This means that these kinetic projectiles are going to take hours to reach their targets (assuming that the engagement happens at something along the lines of a few thousand kilometers, which is considered CQB range in space). Any minute change in target velocity or direction is going to equate to a miss.

To quote Jules from the comment section: *Even at [targets] 1 light second [away] and [travelling at] 1%c, your kinetic weapons will take nearly 2 minutes to reach target

You would be forced to shoot thousands of these things shotgun style, and hope one connects - it's not a good approach to combat.

Add to this the fact that you're travelling across the solar system at the slow speed provided by "conventional engines" and it's going to make for some pretty boring space combat. It's going to take days for two fleets that have detected each other to close in for combat. Ambushes are going to be rare unless you write in some great "stealth" technology, which is the only circumstance under which these sort of weapons might work.

Fighters Are A Terrible Idea

Fighters are also a terrible idea. Humans have very strict limits on the forces they can endure, and you'd be building in a lot more protection and life support for the pilot than weapons, etc. Instead, develop a decent AI to fly armed drones, and let them loose on the enemy fleet.

Why Missiles and Drones are the Way To Go

So your enemies are far away, somewhere. It's going to be days until you close in for combat. Any kinetic projectile you shoot is most likely going to be easily dodged.

So what you need is a means of attack that will successfull reach the enemy, while accounting for any changes in direction or speed - aka missiles and drones (the difference being that drones can carry missiles).

Swarms of missiles and drones can be launched in your enemy's general direction (or predicted flight path) a few days before contact. These can accelerate for a short amount of time, then "glide" toward your enemy generating minimal power/heat so as to remain as undetectable as possible. When the enemy is within fuel range, and/or when the internal programming determines that the missile has the best chance of making it through the enemy's defences, these will power up and strike out at their targets.

To combat these tactics ships might deploy defensive swarms of drones when they estimate that missiles might be encountered. Alternatively, the hull might be peperred with small kinetic weapon or, better yet, laser turrets which will target approaching missiles when they become active and can thus be tracked. Electronic warfare would also play a huge role in all this.

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  • $\begingroup$ Give the railguns flak-rounds. Easy to dodge a slug, hard to dodge a slug that turns into a point-blank shotgun blast. $\endgroup$ – UIDAlexD Aug 8 '16 at 13:50
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    $\begingroup$ when you have 3 weeks warning? $\endgroup$ – Racheet Aug 8 '16 at 15:12
  • $\begingroup$ @Racheet Well at that range your obviously going to opt for missiles. I'm talking about being inside the range of a few light-minutes. $\endgroup$ – UIDAlexD Aug 8 '16 at 16:15
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    $\begingroup$ @DanielJour - a slug fired by a gauss gun will take a long, long time to reach its target, and most likely miss. A missile which waits until its target gets close before engaging, and then maneuvers around defensive countermeasures in order to try and kill its target will win every time. $\endgroup$ – AndreiROM Aug 8 '16 at 20:02
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    $\begingroup$ @UIDAlexD - Even at 1 light second and 1%*c, your kinetic weapons will take nearly 2 minutes to reach target. Any form of randomized maneuvering will make them extremely unlikely to hit. I'd suggest you'd need to close to maybe 10% of that range before such a weapon would be effective, but that puts you well within the range of any missile system, so your chance of being able to close that far is quite slim. $\endgroup$ – Jules Aug 9 '16 at 0:12
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The options you listed need not be mutually exclusive. You could for instance use railgun type launchers to accelerate bombs, missiles, drones and/or fighters (like a carrier launch rail) so they require less fuel (ie, only maneuvering jets) to intercept and track the target. Only fighters would really need fuel for the return trip.

Also you left out some extremely important offensive systems. In future space warfare the deadliest weapons will probably be electronic warfare systems. You don't have to physically damage a spacecraft to win an engagement, you only need to disable, confuse or avoid it. EWS can potentially do that at the longest distance since it only requires a communications channel and a ship subsystem that accepts any form of remote command codes. It's unlikely a ship wouldn't be remotely operable since it would be the fleet admirals' first line of defense against rogue captains and insurrections. Many ship systems would likely be run by AI and attacking/confusing/crashing the AI minds would be a basic first line of attack (it essentially costs you nothing to try). On a more low-tech level you have basic jamming and EMP weapons. In all cases you're not brutishly trying to bash your way through metal to kill meatbags when your enemys' most valuable systems are fragile circuits.

Also in space there's no collateral damage or pollution to worry about (unless you're stealing the ship itself) so presumably neutron bombs, directed nuclear explosions and other radiation weapons are all fair game. Since there's no shielding tech any radiation that penetrates metal is going to cause a world of hurt for the systems and crew aboard. Also since radiation travels faster and further than mechanical/chemical systems these weapons give you the first strike.

And finally nanobots are almost within our technology capabilities today. In 200 years it isn't unfeasible that you could launch canisters filled with swarms of tiny robots that "eat" materials used in circuits. These could really make a mess even without magical replication capabilities. One "bug" in a critical enemy system and it's game over.

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  • $\begingroup$ A friend and myself are working on a game universe and we had the exact same railgun idea as you. Called them Semi Active Guidance rounds - Basically railgun slugs that give the compactness of a regular round (Because they don't need to accelerate up to an initial speed) with the guidance of a missile (Because they can move left/right/up/down onto a collision course.) $\endgroup$ – UIDAlexD Aug 8 '16 at 16:44
  • $\begingroup$ I really like the idea of warships not really having any weapons on board... except for the suite of electronic warfare modules / mechanisms / computers / etc. manned by a small army of nerdy hackers. ;D $\endgroup$ – Shaamaan Aug 9 '16 at 10:15
  • $\begingroup$ "It's unlikely a ship wouldn't be remotely operable since it would be the fleet admirals' first line of defense against rogue captains and insurrections." It seems unlikely to me that, after this exploit is used the first time, military entities would continue to keep the same vulnerabilities. To my knowledge, even nuclear-armed aircraft and submarines in the real world cannot be remotely disabled by their owning nations. $\endgroup$ – Catgut Aug 9 '16 at 16:32
  • $\begingroup$ @Catgut There are plenty of reasons beyond "disabling" a ship that you would want remote control. The most obvious being that you might have fleets of 10's of thousands of ships, drones, smart missiles and high-velocity debris all buzzing around at hundreds of kilometers per second and you'd probably need an AI for fleet coordination and to avoid friendly-fire. You might also want remote control if the crew is killed or where there is no crew in the first place (since it's unlikely combat ships would actually need humans on board). $\endgroup$ – SpliFF Aug 9 '16 at 21:48
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Missiles and torpedoes are both great options.

Lasers could be ok, but only if they make some advances in efficiency. They can also be used for communication, so serve a dual purpose.

The kinetic weapons have huge promise, And while ammo is cheaper than missiles, It is heavy to carry a lot of it. Edit: Also, with no atmosphere in space, projectiles will essentially travel forever, or until they run into something. If you're lucky they have enough velocity to leave the solar system, removing the problem. If not they just become high velocity meteors zipping around to potentially hit someone years down the road.

The nuclear warheads would be good for heavily armored ships, and for their EMP potential, though that cuts both ways, and the warships would likely be hardened.

Fighters could be useful since they are smaller than capitol ships and more maneuverable, and can be used to strike targets from unexpected directions and up close.

One big potential weapon you're missing for close combat is the fusion or fission drives on the ships. If you accelerate toward the enemy, then turn and start firing your engine, you'd have a pretty effective nuclear flame thrower.
In Larry Niven's Known Space series this was used by humanity against the Kzinti to great effect.

Edit: As UIDAlexD pointed out:
The Kzinti lesson is, "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive." or "If their reaction drive is powerful enough to be interesting, then they aren't unarmed."

enter image description here

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    $\begingroup$ The Kizinti lesson. Beautiful. $\endgroup$ – UIDAlexD Aug 8 '16 at 14:05
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    $\begingroup$ If you're going to down vote, at least take a second to say why... $\endgroup$ – AndyD273 Aug 8 '16 at 17:06
  • $\begingroup$ Probably because we're not appeasing the laser god. All hail lasers, anyone who says otherwise as wrong. $\endgroup$ – UIDAlexD Aug 8 '16 at 17:08
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Space is incredibly vast, and you have to deal with issues like no stealth in space, the fact that everything is operating in the same medium (hence there is no advantage for "fighters" vs capital ships) and most especially heat rejection.

Sites like Atomic Rockets and Rocketkunk Manifesto have plenty to say about space warfare and all the other ancillary subjects about living and working in space, so I won't go into a lot of detail. World building Stack Exchange also has a multitude of questions about space warfare, so some of what you are looking for may already be answered.

Based on various readings, I have gradually changed my view of space warfare. Even though massive laserstars packing Free Electron Lasers capable of vaporizing metal and ceramic in milliseconds at a range of 1 light second (almost the distance from the Earth to the Moon) are theoretically possible, the sheer mass of equipment needed to build such a device and the need for massive radiators to keep the equipment functional would seem to argue against giant lasers. Fission and fusion rockets also have issues based on their generally high ISP/low thrust performance.

There is an answer, however. Nuclear bombs can provide compact and reliable energy for weapons of various sorts, and as a bonus, can also power the ship itself.

A project ORION nuclear pulse drive (or a variation based on the implosion of fusion pellets) is the only ship which can provide both high thrust and high ISP. Pulse drive ships give you the ability to build and operate very large ships which can also move relatively quickly both across the solar system and make tactical combat manoeuvres during a confrontation.

enter image description here

This illustration is of a 4000 ton ORION battleship concept developed by the USAF in the 1960's. It is big enough to carry Minuteman III ICBMs as the main battery, several spaceplanes, 5" naval cannon in turrets and Casaba Howitzer nuclear shaped charges.

The nuclear shaped charges is the second direction that we should look at. A nuclear device is a very compact energy storage unit. In space, a nuclear weapon on its own is not very useful, since the energy is emitted in a sphere and the inverse square law has it radiating its energy away without effect unless you are very close. There is no material medium to transmit energy via shock waves or thermal effects as in an earthly explosion. However, nuclear devices can power a multitude of devices.

Nuclear weapons have been used to experimentally drive "shotgun" charges and accelerate clouds of pellets to 70 km/sec, and theoretically can accelerate these pellets to over 100km/sec. Nuclear shaped charges can drive streams of liquid metal at insane velocities, and the Casaba Howitzer was meant to create and accelerate a stream of plasma at up to 10% of the speed of light. A small booster charge, missile or even a railgun could be used to rapidly launch a cloud of these devices at the enemy, and only a very massive amount of shielding would protect you from the impact of nuclear accelerated pellets, metal or plasma.

enter image description here

Conceptual drawing of a Casaba Howitzer by Scott Lowthar

Interestingly enough, the stream of plasma is almost as powerful as the illumination of a Ravening Beam of Death (RBoD) laser weapon (see Atomic Rockets for the calculations), and could be further collimated and accelerated using a magnetic accelerator (for obvious reasons, this would be an off board device flying in formation with the main spacecraft).

enter image description here

To visualize this as a weapon, picture the beam going from right to left rather than left to right

So what we would be looking at are fairly large spacecraft with a belly full of nuclear charges. This allows the ship to make energetic combat manoeuvres and dispense an immense amount of punishment without having to carry large on board generators or heat radiators. Bring on the Space Battleships!

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  • $\begingroup$ Upvoted for mention of Atomic Rockets, that site is the answer to so many "hard science" space questions. $\endgroup$ – Jason K Aug 9 '16 at 17:00
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The deadliest weapons on fission/fusion propelled spacecraft are their propulsion systems. The engines shot out jets of radioactive particles if it's fission or fusion products like helium nuclei if it's fusion.

Easiest if we stick with a fusion plasma exhaust, it has a velocity 12.5% of lightspeed. Faster than kinetic munitions and missiles. While lasers are quicker a plasma jet cam absorb and deflect laser beams. Besides laser beams diverge and lose focus too fast to be effective at range.

Mount fission/fusion engines fore and aft on a spacecraft and it's armed to kill. Pop-guns like machine-cannons can be added for close-contact combat, but why bother?

A side-issue: it seems doubtful if spacecraft with fission/fusion propulsion could reach the outer rim of the solar system in a few weeks. Yes if the acceleration was around 1 g over its trajectory to reach the wormholes. The trouble is the rate of acceleration for fission/fusion spaceships will be around one centimetre per second squared. I am only guesstimating here, but the trip times should be a few months at least.

This is based on Matloff and Mallove's discussion in The Starflight Handbook of the ratio of the mass of power plants in spacecraft to the acceleration they can achieve. With nuclear fusion propulsion, the answer is one centimetre per second squared.

This doesn't necessarily prevent your vessels from having higher accelerations. This is your fictional world, after all.

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  • $\begingroup$ The problem with these is that particles spread out rather very fast at the nozzle, decreasing effective range similar to lasers. Remember energetic particles will push each other. A ship that is built for long range travel should be able to handle space debris at those speeds if they don't fall to a narrow section. $\endgroup$ – Cem Kalyoncu Aug 8 '16 at 17:40
  • $\begingroup$ I've not read the Starflight Handbook, so I'm not sure what variety of fusion propulsion they're discussing, but the figures I've seen for the "Orion" type nuclear drive systems get considerably better acceleration than that, and the ICF variant has a theoretical travel time to the nearest starsystem of only 50 years. See en.wikipedia.org/wiki/Nuclear_pulse_propulsion $\endgroup$ – Perkins Aug 8 '16 at 23:04
  • $\begingroup$ @Perkins Plasma & ion propulsion. Nuclear pulse propulsion has better acceleration performance, but the OP' s propulsion wasn't an NP drive IMHO. I suspect ICF propulsion falls inside the Matloff-Mallove limits, but I'd need more details to be sure. I only suggested travel times to the wormholes was longer than the OP anticipated, but still very feasible. A minor detail overall. $\endgroup$ – a4android Aug 9 '16 at 4:16
  • $\begingroup$ @CemKalyoncu. Good point! Something I neglected to clarify in my answer. If fusion engines are used as weapons their exhaust jets will need to be focused to ensure hitting their targets and doing the maximum damage. I assumed anyone reading it would assume I had assumed a focal mechanism. Wrongly I see. This should clarify this, but plasma fusion jets will not have an unlimited range. Divergence will soon lessen their firepower. I don't understand your comment RE space debris, please tell me more. $\endgroup$ – a4android Aug 9 '16 at 4:23
  • $\begingroup$ Some of the particles from the exhaust will eventually hit your target. If you spacecraft is not well protected, particles at 0.125c will destroy it even if they are few particles. $\endgroup$ – Cem Kalyoncu Aug 9 '16 at 5:41
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I'm thinking along the lines of 'Combat Wasps' from Peter F Hamilton's Night's Dawn Trilogy. Essentially autonomous multi-warhead systems, that break down into various individual warheads - some nukes, some one shot laser pulses, some electronic warfare pods. Such systems constantly try to outmanoeuvre and defeat those launched by the enemy, with the goal of reaching an enemy hull with a single active nuke while preventing enemy warheads from reaching friendly targets.

While most of the tech from this series of books is vastly unattainable, these seems like something we could feasibly implement within the next 150 years - we already have warheads capable of scattering into multiple, independently targeted sub-munitions, which makes this entirely possible within the specified time frame.

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    $\begingroup$ Also electronic warfare would allow a way of overpowering or actually stealing a ship without destroying it, bringing in precious resources. I would expect to see a rapid arms-race around electronic attack/defence with a lot of that happening in software. $\endgroup$ – glenatron Aug 8 '16 at 16:54
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Everyone likes to parrot "Fighters are useless!" Consider the following, though.

Fighter spiel

Carrier-based aircraft came to be because of the need to project firepower over long distances. Battleship guns could reach out a couple dozen miles at most, but carriers and aircraft can deliver explosives-on-target over hundreds of miles. From an engineering standpoint, the advantage is that I'm only sending enough engine and fuel to reach the target and return, instead of sending my entire ship to drop a single bomb.

Just because you're in space doesn't mean that tradeoff goes away. It'll be a lot easier for a 20-ton 'fighter' to close range with the enemy and deliver effective fire-on-target than it will be to slew my 10,000 ton dreadnaught through a hail of oncoming fire. For one, the strikecraft is a smaller target, but for two much more of its mass is dedicated to engines and weapons. A dreadnaught has to carry crew, life support, ammo, enough supplies for an entire deployment, armor, vast amounts of fuel, ect. On the other hand, a strikecraft just needs an engine, a single (optional) pilot wearing a space suit, and a frame to bolt weapons to.

"But humans black out under high-G!" Who said the drone was going to be pulling any more Gs than a manned craft? There's no air to turn against in space, so all that G-Force has to come from engine acceleration. Sure, there's going to be violent evasive action, but how violent does it really need to be? Suppose I'm flying an absolutely monstrous 10 meter tall assault craft. If I fire my downwards thrusters at 5G (Something easily tolerable by a trained pilot) I'll have moved my ship nearly 25 meters in a single second - more than enough room for a would-be killing blow to miss.

Don't get me wrong, there will be no death-star trench runs, but getting in close (A few hundred kilometers AT LEAST) to the enemy with a small, agile craft has its benefits. It gives you a better position to launch your weapons so their defenses have less time to act, it gives you better electronic warfare opportunities, and it also forces them to spend point-defense resources shooting fruitlessly at you instead of your missiles.

Weapons and such

As for weapons, don't glorify lasers too much. The generate absolutely insane amounts of heat, and struggle to bore through even minor armor. While beams of light might be perfectly accurate, the turrets they're mounted in probably won't be, and with electronic warfare that's just gonna get worse. Against an ablative armor design (Or even a ship rolling on its long-axis) lasers haven't got a hope in hell.

Lasers wouldn't be completely useless, however. While they suck at dealing with anything more than a tin can, they can fry any optical targeting systems an enemy might be using. It won't win a fight, but it will give the enemy a nasty jab in the eye and force them to rely on other, more easily jammed sensors like RADAR.

Other weapons work pretty much like you'd expect them to. Regular old bullets are surprisingly good at point defense - even with their comparably low muzzle velocity they're cheap and spammable, have almost no power requirement beyond moving the turret, and ejected shell-casings serve as a kind of heat-sink. This would make for a good wall-of-lead against incoming missiles.

Missiles are great because they're basically a fighter without the return option. While you don't get the engine (Most of the weight of a missile or fighter) back, you can still use them as a long-range silver-bullet. The real issue with missiles isn't so much the weapon itself as the storage space it takes up.

Railguns and Coilguns (With nuclear-tipped slugs, if you want) look great for mid-to-close range combat. The ammunition is cheap, simple, and easy to store in bulk. The power requirements are modest, and the armor penetration is superb - While a laser is trying to bore through the outer hull, a railgun slug will have already punched through the ships reactor and out the other side. You could make harder-to-evade bursting ammo - an explosive charge in the slug could shatter it when near the target, resulting in a cloud of shrapnel that will lack the sheer power, but more than make up for it in the higher chance of intercept.

You might want to watch The Expanse, notably episode 4. It has a really great depiction of realistic space combat.

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  • $\begingroup$ As you say, carriers came to deliver firepower over long distance, but in space you can fire way longer without problems, so you don't really need a fighter to deliver your weapon at some thousand Km. Also, a fighter in space has the problem that every maneuver require fuel so there is a high risk to fall under the tyranny of the rocket equation. And as final point, you need to avoid the AA Guns, which can trivially be a small caliber railgun that fire .50 caliber munitions at mach 10, so at a few hundreds meter, your fighter is dead even before knowing it. $\endgroup$ – Gianluca Aug 8 '16 at 15:49
  • $\begingroup$ Longer range means more potential to evade, and getting a weapons platform closer in means less potential to evade. A thousand KM might sound long-range to us but it's a knife-fight in space. I find it funny how you bring up the rocket equation for fighters, but not for massive capitol ships. What is it about having armor and a crew compliment that makes you exempt from the rocket equation? Finally, I addressed that already. Like I said, it won't be a death-star-trench-run. The closest a fighter will get is a few hundred KM if it doesn't want to die. $\endgroup$ – UIDAlexD Aug 8 '16 at 16:14
  • $\begingroup$ But closer range means less potential to evade for both the ship and the fighter. A thousand Km, for a projectile fired at Mach 10 means a time to target of about 5 minutes (probably a lot less since the fighter is approaching the ship). And I suspect that is way easier to detect a fighter at some thousand Km than a .50 bullet traveling at Mach 10. The rocket equation stand also for the ship, but I never say that the ship will maneuver easily, but the fighter has to maneuver easily to avoid AA guns. So, given a mass for the fighter, the more fuel you add, the less weapon it have. $\endgroup$ – Gianluca Aug 8 '16 at 16:28
  • $\begingroup$ Point of the fighter isn't to engage other fighters, it's to engage ponderous and heavy capital ships. Also you don't have to detect something to evade it - you just have to move randomly enough that it's probably not going to hit you. The figher, being smaller and having higher TWR, can make quicker evasive movements. The capital ships can't. So, while our fighter can juke AA fire all day long, the capital is bound to get hit. $\endgroup$ – UIDAlexD Aug 8 '16 at 16:36
  • $\begingroup$ The "tyranny of the rocket equation" mostly has to do with getting out of the Earth's gravity well. If you're already in space, you're not fighting against 9.8 m/s/s acceleration. Yes, you have to use fuel to move your fuel, but the biggest hurdle by far is in the past. $\endgroup$ – Martin Carney Aug 8 '16 at 16:44
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At your technology levels, it will depend on a single question: How effective are anti-missile defenses?

If and only if ships can achieve something like a 99.9% success rate intercepting missiles before they get close enough to do damage would you see any other type of weapon. (Railguns would be good against stationary targets at any range, but the question is about ship-to-ship).

Here's why:

An invading ship starts out very far away from anything except possibly a defensive station near the wormhole if the wormhole is static. To attack with any medium or short ranged weapons it would need to commit to an approach vector that would clearly signal its intentions and target to any defenders. If the shortest route takes two weeks for example, a feint would add an unacceptable extra few weeks in enemy territory.

So the ideal strategy for an invader would be to only stay long enough to locate its targets, fire a swarm of missiles and retreat. Again, firing some slugs with a big railgun would work for "stationary" targets whose location can be predicted from orbital mechanics and measurements. If one percent of the missiles gets through and cripples a target ship, firing hundreds of missiles would be preferable to risking a big ship and trained crew.

For the defenders, missiles would also be the weapon of choice. They can handle much higher acceleration than manned craft, so can reach the target hours or days earlier, long before any unguided weapon has a chance of hitting warships that constantly change their vector for exactly that reason.

So, what would happen if all ships sport point defense lasers that vaporize all missiles? First off, such a weapon is likely to vaporize drones, fighters and torpedoes as well. In fact, the only weapon that might make it past this defense would be a railgun, as vaporizing the guidance system or thrusters of a missile is much easier than vaporizing a solid metal slug, where even 10% remaining could still cause serious damage due to the high kinetic energy.

With only lasers and railguns left, the ship with the stronger laser and/or stronger anti-laser armour would try to close the distance to get as much energy on the opponent as they can, while the other ship would try to stay far away and score a hit with the railgun by predicting the other ship's movement.

All kinds of subterfuge would likely be employed to get the opponent into the crosshairs, which would count for more than sheer firepower.

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Due to the distances involved any fleet engagement is likely to only occur at or incredibly near to an objective.

You mention wormholes as the primary means of travel between 2 star systems. These would be very well defined locations. By extension, the location that a ship could emerge from one would be well known. Because of this those locations can be heavily defended with any type of weapon system you can imagine: large kinetic weapons, space "mines" designed to explode on command, a ring of lasers, etc..

By the same token if an enemy fleet manages to smash through those defenses then it's a matter of stopping them at their destination. Locating and tracking that fleet will be trivial and you'll have plenty of time to muster defenses before they arrive.

Are they heading towards that mining space station orbiting a moon? The station will likely have a standing picket fleet to ensure the enemy doesn't get close. Are they heading towards a planet to bombard it? The planet will likely be ringed with defenses designed to kill bombs that are in flight...

My point is: these fights will be up close and personal. It will involve not just the ships but relatively static defenses at the target location. There will be no need to chase an enemy fleet around the solar systems - which means the defenders can simply wait them out.

All of this means that the likely real world attack profile will be to insert a large landing force that can take and hold the gates around the wormholes thereby establishing a beach head. Once that is done then the attacker would transfer additional personnel and ships in order to launch attacks on other target sites. Each attack would require closing on the target until you can be reasonably assured that you can land regular troops - or that you can launch enough nuclear type weapons to obliterate the target.

The defenders goal would be to prevent each location from being taken. The combat would favor the defender because it should be apparent where the enemy would need to be in order to launch their attacks and therefore you could prepare for those attacks well in advance.

Again, because the potential locations are known the defender can place weapons at, or very near them ahead of time - easily sidestepping the problem of distance and therefore any of the weapon systems you described are viable.

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I will go item by item. But first, I think the ship to ship engagement would start from very far (1 AU) to very near (<10000km).

  • Missiles: Good for long range launches. It would take sometime for projectiles to hit the other ship so the other ship would have sometime to maneuver. So long range combat should contain missiles instead of torpedos to adjust for the course.
  • Torpedoes: Good for shorter range engagements. Cheaper than missiles so it should be prefered in close combat.
  • Kinetic weapons: Railgun would be a good idea for mid/short range combat. Since the energy is abundant and there is no air friction, cost wise they will be quite effective.
  • Lasers: loose efficiency very fast with distance. Thus I would say they can be used as point defenses against missiles or torpedoes.
  • Fission/Fusion warheads: Similar to missiles but would be more effective but costly.
  • Strikecraft: If you are going for realism, strike craft will not be very useful. Steering a spacecraft, no matter the size, is not very easy unless you have some magic technology. It would require lots of fuel, which also means lots of additional mass. Since they won't have fission generators, they won't be able to use railguns amd lasers. There is no difference in firing missiles from strikecraft than firing it from the main ship. Only difference it would make is firing torpedoes, but that's not an advantage since it is costly to house a strikecraft in the first place.

Finally I think reaching the outer rims of a solar system in several weeks is not very logical. Of course this depends on where you draw the line but earliest would be heliosphere which is around 3 light days. Even at 0.1c it would take around 30 days to reach there.

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  • $\begingroup$ Please note i said "several weeks" and not "one week" which is a huge difference as you say yourself. $\endgroup$ – user431806 Aug 8 '16 at 13:11
  • $\begingroup$ Yes, I noticed but if the fission is the top technology, even 0.1c is not very likely and 30 days is without taking acceleration into account. Also if you draw the line after oort cloud it would take 16 years to get there with that speed. $\endgroup$ – Cem Kalyoncu Aug 8 '16 at 13:26
  • $\begingroup$ Difference between a fighter and a missile is that you get the fighter back. If each fighter/cruise missile grade engine I build costs a billion credits and weighs 2 tons, what makes more sense: Equipping each of a hundred missiles with a billion credit engine, or giving a missile-bus/fighter a couple engines and loading it up with short-range torpedoes? $\endgroup$ – UIDAlexD Aug 8 '16 at 13:41
  • $\begingroup$ Fighter engine would be much, much more expensive than a missile engine. Missile would need to do minimum correction as the target is mostly adrift. Fighter needs mobility, which would make it expensive and laser based weapons would render close combat extremely dangerous. $\endgroup$ – Cem Kalyoncu Aug 8 '16 at 17:26
  • $\begingroup$ @CemKalyoncu The missile still needs enough mobility to reach a target that's preforming evasive maneuvers. Real-life cruise missiles that have similar ranges to jet-aircraft use jet-engines. I'd imagine that a fusion-powered ship would necessitate a fusion-powered cruise missile, at least for very long-range combat. Even then there's still the issue that the missile is mostly engine. A missile has to get to its target to blow it up. A fighter means that a missile can allocate more of itself to the blowing up and not just the getting there. $\endgroup$ – UIDAlexD Aug 8 '16 at 19:49
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Projectiles, explosive and otherwise and lasers are what I see here.
1. I propose that cosmic rays could be used as a weapon. Cosmic rays (energetic particles flying at a significant fraction of light speed) are already a problem for space travel. Anyone hanging around in space might have some routine countermeasures but huge amounts of these rays or exotic frequencies or lack of charge on the particle could overcome countermeasures appropriate for standard cirumstances.

Such a weapon might be called a particle beam. I envision more a particle shotgun.

Benefits 1: Fast particles traversing the innards are bad for living things and for electronics.

2: Fast particles are very small and pretty much impossible to detect until they are right next to you.

3: A neutral particle would be not be blockable with magnetic fields unless you somehow impart a charge to it first.

4: Shrapnel got nothing on atoms. 100 kg of lead atoms (tradition!) covers a lot of area.

  1. Atoms are pretty much indestructable. They can go really fast. I like the idea of a shot thru a wormhole, banked gravitationally by a red giant, thru another wormhole and to the target.

Big drawback for movie scifi: Unsexy.

1: A particle beam wont look cool. It will be invisible.

2: Damage done is not cool. Stuff hit wont explode. Electronics will not work, or not work right.

3: Casualties are not cool. People hit wont explode. They might feel sick and throw up and die a while later, or maybe get cancer. This latter possibility offers some interesting scifi scenery, like first aid that includes cancer treatment.

  1. Antimatter. Antimatter is a spectacular weapon since human made stuff is standard matter and so on contacting antimatter will change to energy with a massive explosion. A minefield of antimatter in space would be difficult to deal with.
    • If a chunk of antimatter slowly traversing empty space is hit by a particle of normal matter, the particle and corresponding mass of antimatter is destroyed. The rest of the antimatter remains, although it would be blown into smaller bits. Each of these dispersing bits retains the power to destroy matter with an energetic explosion. So as an antimatter minefield persists it grows in size and will get more and more granular and harder to sweep.
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  • $\begingroup$ I was wondering: how big an area could a lead atom particle shotgun cover. I did some math. If I messed up an order of magnitude, please call it out. Lead has 207.2 grams/mole. So 482 moles in 100 kg of lead making 2.9 x 10^26 atoms. Spacing atoms at 1 per micrometer that is 1,000,000 per meter. You could cover approx. 1700 square km at that spacing. Hong Kong is 1100 square km but one face of the moon (considered as a flat circle) is 9 million square km. Covering a moon sized area at that particle density will take more than one shot. $\endgroup$ – Willk Jan 11 '17 at 15:01
  • $\begingroup$ Thinking further about countermeasures vs a particle beam like this. One would want robots using clockwork and vacuum tubes: resistant to particles. These would be fun, steampunky robots to write. $\endgroup$ – Willk Jan 11 '17 at 15:08

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