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What theoretically workable weapons (they don't necessarily have to exist, they just have to be possible with a little bit of unobtainium) would be the most effective for ship-to-ship combat in space?

The technology level in my universe is roughly Stargate / Honorverse level. Here's what this means:

  • Energy shields exist, but they aren't Star Trek-level perfect. They work by absorbing all the energy of anything that hits them from the outside, storing it in capacitors. Once the capacitors are full, the shield goes down until the capacitors can be emptied. The capacitors can be used to power the ship's systems, but don't have an especially high capacity. As a result, offensive tactics in my universe center around hitting your opponents with large salvos. Also, it's worth noting that they aren't very effective against missiles.

    • EDIT: While the shields aren't infinitely powerful, they do have quite a bit of durability. After all, they have to protect the ship against interstellar gas and micrometeorites while the ships are moving.
  • Anti-missile countermeasures are effective, but not 100% effective. For purposes of this question, let's set the optimum effectiveness at 98%, with a small decrease in effectiveness as the amount of incoming missiles increases.

  • Power supply isn't a problem. For purposes of this question, they have something along the lines of a ZPM.

  • Most ships have some ablative armor and anti-rad measures. As a result, while missiles do a lot of damage, a single missile / torpedo getting through isn't the end of the world.

EDIT: "With a little bit of unobtainium" means "slightly better material sciences", not "do whatever the heck you want". In other words, answers must at least be theoretically plausible. For example: directed energy weapons and (small) antimatter warheads are okay, but de-mat guns aren't.

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  • $\begingroup$ So, we're selecting weapons that would be feasible with real-world tech today vs. defensive tech from stargate/honorverse? You know that other than missles/torpedoes everything else would either need to be a spinal mount or built onto a honking huge ship due to Newton's 3rd law, because energy weapons are not feasible using today's tech vs. fiction tech... right? $\endgroup$ – JBH Oct 3 '20 at 2:21
  • $\begingroup$ Also, please take a moment to remove the word "best" and any other superlatives. What's "best" is always subjective and opinion-based. You need to ask, "given the following specific conditions, what weapons will meet the following objectives?" Then let the community vote for what they think is "best." $\endgroup$ – JBH Oct 3 '20 at 2:22
  • $\begingroup$ @JBH I did not say "real world tech from today", I said "just have to be possible with better material sciences". In other words, directed energy weapons are okay but not de-mat guns. $\endgroup$ – The Daleks Oct 3 '20 at 14:22
  • $\begingroup$ Rikhter R-23 cannon as used on Salyut-3 en.wikipedia.org/wiki/Salyut_3#On-board_gun $\endgroup$ – user_1818839 Oct 3 '20 at 15:17
  • $\begingroup$ @TheDaleks What does the phrase "currently feasible" mean to you? $\endgroup$ – JBH Oct 3 '20 at 22:23
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So I thought about adding this in a comment but it seems like it needs its own answer so here goes.

Casaba howitzer

Ok, so more info.

So to explain this rather oddly named weapon, first we have to talk about shaped charges. A shaped charge is, very broadly speaking, an explosive that is formed in such a way as to direct the explosion in a particular direction instead of a spherical blast. We use these for mining, demolition, and military applications all the time.

So one day, some one asked the question, what if we did a shaped charge, but on a nuke?

See where I’m going with this?

A Casaba howitzer is a nuclear shaped charge, often called a nuclear spear. Why? Because one exploding would look like a massive white hot spear of nuclear fire. This is a fantastic way to direct the massive power of a nuclear device over a long distance without wasting the majority of its energy. So you put this on a missile, it flies out to the edge of the ship’s missile defense system and detonates, sending a torrent of superheated plasma traveling at an appreciable fraction of light speed directly toward the target. Multiply this by, oh let’s say a couple thousand missiles or so.... it’s not exactly a pretty picture for the target ship in question.

Finally, we can do this today, this is absolutely current technology. So if you’re talking far enough future that we have spaceships and shielding, this will be easy technology for your future societies to produce en masse. So imagine swarms of multiple thousands of Casaba howitzers flying at a ship and detonating all at once. To quote Phil Swift.

Now that’s a lotta damage!

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A single railgun salvo will overwhelm any possible shield.

enter image description here

Weapons like these can fire a 1200kg projectile at just under 3km/s. That's 360MJ of energy.

Impacted into a shield, a single hit delivers ~100kwh of energy. Assuming a projectile length of 1m, impact is spread over about 400 microseconds. That's an instantaneous power transfer into your shield's capacitors of 900 GW - Just under the average power consumption for the entire USA.

I'm assuming your shield capacitors is something like this prototype 10,000 Farad SuperCapacitor, these capacitors need low voltage to function. 3 - 4 volts sort of range. This means the connection between your shield and the capacitor has to be able to sustain 300 giga-Amps for half a second. Even if you put 100,000 of them in series (which'd be a considerable percentage of your ships mass), you're still looking at mega amps.

The conductor size required to connect the shield emitter to the capacitor is just extreme. Even superconductors stop being super conductors once they get beyond about 10,000 amps. Lets assume you can get cable resistance down to 10ohm. But that's not the biggest problem, the problem is capacitors take time to charge.

Over the 400ms impact time, your 100,000 string of capacitors will only absorb 40 kA / 16gw. You'll need 56 banks in parallel (of 100,000 mega capacitors).

This is one 10,000 Farad SuperCapacitor. You'll need 5,600,000 of these:
enter image description here

... for one hit!

Now lets assume you have a massive ship that you can devote 111,765,360kg just for capacitors, (which is the weight of an Egyptian pyramid). You've successfully absorbed one hit!

Now consider that this railgun can fire at 10rpm - there will probably be several of them firing in a salvo. You can even fine tune the speed of the projectile so multiple can be fired from the same gun at different times and impact at the same time.

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  • $\begingroup$ With a 98% success rate on missile interception, I imagine those same countermeasures will be able to hit a kinetic impactor. The question is whether that would do anything $\endgroup$ – Kyyshak Oct 3 '20 at 12:59
  • $\begingroup$ The capacitors are a bit more powerful than your example, but this is still a very good answer. Bravo! $\endgroup$ – The Daleks Oct 3 '20 at 13:04
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Railguns and nukes

I know both have been mentioned and @Ash 's one about the railguns is fairly complete. I think however the missiles shouldn't be iverlooked, so I'll go in debt here.

The missiles can potentially ignore the shields. A nuke can be detonated before the target, generating heat, electronomagnatic waves (including light) and shockwave. Of course, generating this temporary fireball must be closer than you might think with all but the EM. Without a medium to travel through, the shockwave and heat will only move with the material provided by the bomb. This means if the material doesn't pass the shield, you're pretty safe.

However, the EM is dangerous, as the light contains heat that passes through the shields and abother part of the EM is EMP (I know the whole EM range is technically EMP, but it gets the point across). WMP will severely interfere with electronic devices. The bigger the amount of conductive material, the more it can be affected as a charge builds inside. This can obviously be protected against, as even without solar storms our current sattelites require protection from EMP. Protection can still be overwhelmed, which nukes likely do. This way you might even disable ships and leave them open for capture. The light can heat up the surface very rapidly, which can lead to warping of the material as well.

With 2% success a missile will reach a target it might seem not a good option to use nukes. However, in current nuke technology they also use fakes. Especially in ICBMs they put a group of fake nukes with 3 or 4 real ones. Believe it or not, there are all kinds of regulations how many fake nukes can be launched with a real one. Here you might just ignore that. Fire the missile(s), let it break apart in 20-50 fake ones per missile and 3-10 real ones in the mix. Likely nukes have a better chance, as they don't need to get that close. Now just overwhelm the enemies defencive system and detonate a nuke close enough to kill the other ship.

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  • $\begingroup$ Why not combine them and fire the nukes from the railguns. If chilled to the temperature of the cosmic background radiation before launch they should be very hard to hit for missile defences as they do not emit any heat before detonation. Also consider en.m.wikipedia.org/wiki/Nuclear_pumped_laser $\endgroup$ – lijat Oct 3 '20 at 7:46
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    $\begingroup$ First no EMP from nukes in space, only works in a magnetic field. second nukes actually have to be closer than conventional explosives in space. In space explosives damage using either shaped charges or shrapnel. Nukes are not really effective in space, space craft already have to be shielded against radiation and radiant heat, and there is no air to propagate shock. So you have to detonate them up close to have any effect. Nukes actually end up as better defensive tools than offensive in space. $\endgroup$ – John Oct 3 '20 at 12:05
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Kinetic weapons and missiles.

Kinetic energy is just better at delivering energy than any other means while generating less heat on the ship than anything except missiles. Heat is the real killer in space. As a bonus anti-missile defenses are not that effective against dumb kinetic mass. in space you basically have two effective weapons missiles and kinetics (aka mass drivers) lasers don't actually make good weapons. Missiles work because they are the hardest to dodge or counter, you can't predict their path easily. Shrapnel based missiles are surprisingly effective in space, without air shrapnel travels far and fast.

It is harder to hit with kinetics but if you do they are overpoweringly destructive. As a bonus their range is essentially infinite, since a slug will keep traveling in a straight line without loosing energy until it hits something.

RICK ROBINSON'S FIRST LAW OF SPACE COMBAT An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.

Or to put it another way a 2kg lump of mass traveling at 30 miles per second delivers the same destructive energy as a tomahawk missile. At high enough speed (~8o% C) they outperform antimatter weapons. As a bonus several of the problems with hypervelocity weapons just go away in space and the ones you have to solve are ones everything has, AKA heat.

You even have the option of adding rockets to a projectile to make it steerable or with a weak explosive to fragment them just before impact. Both make it nearly impossible to predict and intercept.

Most importantly if your shields still obey the laws of physics they may not actually help against kinetic projectiles, just trade one set of a problems for a completely different and equally bad set of problems.

I suggest the Atomic rockets site for a detailed breakdown of how effective different weapons are in space.

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    $\begingroup$ Getting a 2kg lump to 80% of the speed of light is extremely difficult - quite possibly not realistic even in an advanced tech setting. Any reasonably sane (achievable) acceleration would take a long time to reach a significant fraction of C - hard to imagine in a combat scenario. $\endgroup$ – StephenG Oct 3 '20 at 6:11
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    $\begingroup$ I spent a lot of time designing a setting based around the idea that once a missile (or drone, really) gets close enough to an enemy vessel even the debris from its destruction is a significant threat to the ship. Most of the drones were basically just bins of shrapnel with a big engine. Oh course, that setting had handwavium reactionless drives, but the principle of ‘air and gravity won’t save you now!’ Stands. $\endgroup$ – Joe Bloggs Oct 3 '20 at 6:33
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    $\begingroup$ @JoeBloggs that is one of the reasons missiles work so well, they don't need to hit you just explode nearby, point defense is not great against shrapnel. $\endgroup$ – John Oct 3 '20 at 11:49
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    $\begingroup$ @StephenG but getting a 2kg mass up to 30 miles per second is fairly easy, current railguns might do it if we didn't insist on firing them in an atmosphere. 80% C is difficult but completely possible if you have force fields and human lifetime interstellar travel. likely reserved for larger craft or disposable sentries. But magnetic acceleration is only constrained by how much force your rails can withstand. $\endgroup$ – John Oct 3 '20 at 11:56
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Pencil Beams A paper sponsored by NASA under its Innovative Advanced Concepts Program looked at a combination of a 'cold' coupled laser and particle beam for 'beamed' propulsion. In theory the idea vastly reduces 'spread' by the beam and vastly increases its range so more energy 'hits' the target. The Tough SF blog does a detailed analysis of the device form a weapons perspective and the results are potentially devastating a long range.

Basically the laser beam surrounds and contains the particle beam (hence the 'pencil' analogy, while the particle beam 'attracts' photons in the laser beam preventing them from disbursing as distance increases.

According to the Tough SF the result as a weapon would be a beam fired from a ship near earth being able to hit and damage a target on the opposite side of the solar system! The details of his breakdown are in the Feb 19 chapter of the blog.

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Ramships.

Nice shield you got. How about I climb through it? And when I get over there I'm going to sit in your chair and read your books!

Your shields are great against meteorites and really good against smaller stuff folks are hucking around. But my ship has got a big point in front. Once it is up against your shield I can push it on thru with my engines. It will make sparks, and probably a lot of weird noises you will hear on your side; it stays quiet over here except for us singing. And then once it is thru the shield, a little bit farther through your hull.

Now don't make that face. This is not Ben Hur! I don't want to rip your ship in half! Your books would fall out into space! No, your ship is pretty nice and your books too, so we are going to march thru the point of our ship and come over there. Once you all figure out who you are working for, we will issue the new uniforms, then back the ram ship out and patch that hole up.

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  • Missiles with antimatter warheads should be the most efficient way to deliver destructive energy to the enemy ship. Bonus points if you have "shaped antimatter charges" that deliver most of the energy in the direction of impact, instead of spreading in in all directions. And unless your armor is several orders of magnitute stronger than anything we have today, as single missille hit will be a serious problem. Energy weapons cannot keep up with that amount of energy: Even if your ZPM is literally able to produce as much energy as a shipload of antimatter within the course of a single battle, no weapon could handle this amount of energy without evaporating, even if you have materials at hand that can withstand a million degrees.There is only one way to have energy weapons that are on par with AM warheads:
  • One- shot kill vehicles that utilize an antimatter explosion to power a laser, or otherwise create a directed high-energy beam that is directed at the target. Such a vehicle would be started from the mothership, and once it is at a safe distance, aim itself at the target and go boom ( Similar to Project Excalibur).
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    $\begingroup$ Anti-matter weapons at first glance look like wonderful weapons. The problem is getting all the antimatter to combine with an equal amount of normal matter instantaneously. How does every single atom of antimatter end up in perfect alignment with its opposite number in a missile warhead? It would be like having a pitcher of salt and a pitcher of pepper, smashing the two together and expecting every single grain to end up in perfect alignment! The best you could hope for is an anti-matter 'fizzle' not an anti-matter bomb. You'd get a better result ramming the target at high V with normal matter $\endgroup$ – Mon Oct 6 '20 at 12:22
  • $\begingroup$ @Mon: Interesting Point. I hadn't thought of this. This looks like a tough engineering problem, but not neccessarily an impossible one. You could have ultrathin layers of matter and antimatter interlaced, maybe held apart by some kind of magnetic field or electrostatic repulsion. $\endgroup$ – bluecloud771 Oct 7 '20 at 15:21
  • $\begingroup$ Blue, it would be fiendishly complex, probably impossibly so even a tiny amount of anti-hydrogen the simplest and lightest atom you could get contains 602000000000000000000000 !!! individual atoms. And you would need that many Penning Traps each holding a single atom of anti-matter to make it work. And it would be huge! Making a fusion bomb with a similar yield would be child's play by comparison. You would probably be better off looking at particle beam weapons made from anti particles $\endgroup$ – Mon Oct 8 '20 at 0:40

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