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I want to know what are some general advantages(and disadvantages) of using plasma-based weaponry over kinetics. I know containment is generally the killer, but in my setting that is a non-issue through some kind of self-made magnetic field that contains the plasma, albeit a bit unstable(if someone blows on it, it will pop, although that's a bit hard to do when it is moving several thousand kilometers per second in your general direction). I know it's a bit of a stretch but I'm willing to use it. Energy is also not a problem either, assume there will be sufficient power to use it to the full capabilities. Also, very good magnets are available. I would like to avoid being too hand-wavium, but a bit of s stretch is fine. What would this look like, and how does it compare to just using normal railgun slugs?

EDIT: How the plasma guns work, is that the plasma is fired out of a coilgun. It is contained by a magnetic field generated from inside the plasma(I don't know enough about magnetic fields to say how well that works), without coming into contact with the coils. Upon contact with anything with sufficient energy, it pops, becoming just a wash of quickly dissipating plasma. Until popped, it stays together in a mostly coherent ball of plasma.

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  • $\begingroup$ Please read the tag descriptions when you pick them. Science based and science fiction are conflicting tags. I have taken the liberty of removing the first one. $\endgroup$
    – L.Dutch
    Apr 23 at 4:15
  • $\begingroup$ A couple of quick points. Firstly, because plasma (of all types) are electrically charged they can be disrupted/manipulated by magnetic fields and since in space most manned vessels require magnetic shielding to protect the crews from solar radiation? You may have a problem whihc requires you to have a either a highly energetic weapon or one you fire at very close range. $\endgroup$
    – Mon
    Apr 23 at 7:25
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    $\begingroup$ The second point is that its theoretically possible to hit a space ship with a laser and generate an (astronomically brief) pulse of plasma on its surface. IF that first laser pulse is followed almost instantaneously by a second one? Again in theory the follow up laser pulse MIGHT accelerate the plasma (before it can disperse) back into the hull of the ship at speeds some significant % of the speed of light! If it worked? the damage done could be considerable given plasma has mass! Again there are range limitations but this might be an option. $\endgroup$
    – Mon
    Apr 23 at 7:31
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    $\begingroup$ Could you give us details of how your plasma based weaponry works? $\endgroup$ Apr 23 at 16:52
  • $\begingroup$ If you read the Dune books, they are very, very deficient in explaining how anything works. But they're great books anyway. If you say "fired plasma torpedoes and destroyed the other ship", people are just going to imagine something and go on. In Dune, he often references "communications equipment". By not specifying how that works, this book from the late 60s isn't dated by mentioning wired communication. Gateway, while being a great book, dates itself by mentioning "tapes" a lot. $\endgroup$
    – Almo
    Apr 25 at 20:08

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This is a hard sell

Magnetic fields don't just "exist." There must be a north and south pole. Said another way, there must be a beginning and an end to the field you're trying to use to contain the plasma. One end is your ship.

The other end is the target ship.

The biggest problem is how you get the other ship to act as the other pole of the magnet. You can't use your own ship and try to extend the flux lines because they're curved. Anything that misses the target ship comes right back on you. You could try to set up electromagnetic fields — but that assumes the target ship is a significantly higher or lower electrical potential than your own and all they'd need to do to make the magnetic flux jump away from their ship is electrically charge their hull and adjust the potential until the fields jumped. There's so much distance in space and no matter what you do the plasma will travel so slowly that they have plenty of time to figure that out.

And then you run into the problem that plasma is basically just ionized gas. The energy used to accelerate the ionized gas would be better used directly attacking the enemy ship. And you spent a lot of energy making that plasma in the first place... from a depletable supply of gas. And when the supply is depleted, you're done shooting.

Worse is the problem of velocity in probable space combat. It's fast and at long distances. You need to attach that magnetic field, hold it there, wait for your plasma to transit... all in the seconds or fraction of seconds you have between attack runs.

The more we rely on "science" to explain space combat, the more the only thing that works is missiles

Rail guns, rockets, whatever the slug is and however it's accelerated, you need to get it into the way of your target ship's path and keep it there. Missiles are preferable to rail guns because they can adjust their trajectory mid-flight. Slugs can't. Of course, these are a depletable supply, too... so maybe that's not as big an issue as I thought.

I'd embrace the tag in its fullness.

What most new writers don't seem to understand is that the description of how devastating power is delivered to the enemy is really nothing more than a literary MacGuffin

Unless you're trying to write a technical guide (and to a degree even then), you want to explain the details of space, your ship, and combat as little as possible. You may not believe it, but it's a distraction to the reader. Oh, they'll have fun reading about magnetic flux lines and surges of plasma... but they're not reading your story to get an education, few if any of them are capable of judging the authenticity of your solution, and spending too much time explaining the details gets boring (don't believe me? Go read anything by Fyodor Dostoevsky).

Great science fiction dares to imagine the impossible and to present it with credibility. To that end there are no technical advantages to using plasma over (e.g.) rail guns. All that changes is how they're described to the user. What they do is identical: they cause damage to the enemy ship.

I get it that you're trying to minimize handwaving and maximize realism — but it's a new writer mistake. We can't build a plasma-based energy weapon today, so you're already imagining an impossible future. Good for you! Now think about what super heated gas will do to your enemy ships and go forth and write your story!

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    $\begingroup$ I'd note as a counterpoint that when a piece of technology can be readily understood and is understood by the characters operating it, describing how it functions to the extent that that the characters understand it is a kind of show-don't-tell (not that you should always show-don't-tell, far from it, but sometimes you should), or can set up a future scene. $\endgroup$
    – g s
    Apr 23 at 5:37
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    $\begingroup$ I.E. how the weapon delivers plasma to the target is irrelevant in the scene where Captain Zap is shooting the Grognars in chapter 1. But we explain that it builds up a magnetic containment channel and then the gunnery officer reports "Magnetic containment channel achieved!" before Zap gives the triumphant order to fire the devastating main gun, which helps build the scene. And when Zap goes rogue to rescue the Grognar civilians in chapter 9, we can have him fly through the ion storm with strong magnetic fields (from chapter 6!) to disrupt the admiralty ships' aim and save the day. $\endgroup$
    – g s
    Apr 23 at 5:46
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    $\begingroup$ @Railguns: Get your head out of ship-to-ship combat in 1600 1700. The rail gun is not onboard, its remote, clinging to an asteroid far out, eating it and spewing out death in a pre-encoded pattern. If you know it, you know what volumes will become dead volumes in what time. Everyone else, is mass produced swiss cheese. $\endgroup$
    – Pica
    Apr 23 at 7:01
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    $\begingroup$ @JBH Magnetic fields don't need to terminate on an object. Indeed, they shouldn't terminate at all. (You seem to be imagining a bar magnet and ignoring the magnetic field lines which are inside the magnet.) The two ships therefore don't need to be opposite poles. Magnetic fields and plasma tend to travel together ( en.wikipedia.org/wiki/Alfv%C3%A9n%27s_theorem ), so you might want your plasma to carry an embedded field with it, oriented to help neutralize opposing shields. You could also fire positive and negative charges at the same velocity, to minimize the magnetic pressure. $\endgroup$ Apr 23 at 16:03
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    $\begingroup$ @JBH Magnetic flux lines don't have beginning or end, per Gauss's Law. en.wikipedia.org/wiki/Gauss%27s_law_for_magnetism If your plasma's cold (or resistive) enough, you can have the fluid crossing magnetic field lines, but typically isn't considered plasma at that point. Agree it's a ridiculous amount of energy $\endgroup$ Apr 23 at 21:46
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Classic scifi plasma weapons don't work. A blob of plasma (a plasmoid) has internal pressure due to its temperature and magnetic field, and unless confined by an external magnetic field it will expand rapidly into irrelevance. If you make a sort of plasmoid box to hold it in and then shoot that, then congratulations: you've made a missile, only one that's a good deal more complex and fragile than the regular kind. You may as well just use a nuke or fragmentation warhead or something instead.

In the real world a plasmoid-throwing weapon was proposed (and pops up in a large percentage of the answers here to questions about plasma weapons) in the form of MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation, because acronym technology remains more advanced than energy weapon technology). Whilst this was an enormous contraption, it was made with '90s technology and driven with a '70s capacitor bank, so it is shrinkable to some extent. The main thing is that it had a range of a few thousand kilometers, and struck with approximately the energy of a hand-grenade. That's OK (mostly) for taking out cold-war era ICBMs, but a bit rubbish for anything much bigger or tougher. The excellent Project Rho has more to say on the subject of the impracticality of plasma weapons.

A slightly more interesting plasma weapon that's been actually researched in real life is the Casaba Howitzer, a thing that grew out of the pulse units used for the propulsion system of Project Orion. Again, Project Rho has plenty to say about the Casaba Howitzer. The basic gist of it is that with a bit of careful engineering, it is possible to make a sort of nuclear shaped charge... a reasonable percentage of the energy released by the blast can be channeled towards a target too distant to be struck by the bomb's radiation and fireball (not that there will be much of a fireball in space). In the simplest terms, the radiation case of a nuclear warhead is made open ended instead of sealed (and probably made of something non-fissionable), and at the open end you put a disk of material that is blasted into a jet of plasma by the radiation emitted by the nuclear reactions of the warhead.

The amount of energy that can be focussed is almost certainly not as much as was originally pitched (80%!) but even a small percentage of a nuclear explosion is still quite a lot of energy. The jet of hot, dense plasma travels towards its target at at least a thousand kilometers per second, limiting the amount of time it has to expand into harmlessness, giving you a plasma weapon of sorts albeit a very short ranged one. The effective range of such a weapon is awkward to calculate, but seems likely to be of the order of 100 km or so, maybe 1000 km for larger or well-engineered devices, but extrapolating further is dubious. Because the focussing is only partial, and because the warhead is a one-shot deal anyway, you use these things as missile warheads, or as railgun or coilgun-driven shells.

What would this look like

A very brief bright flash shooting into the distance in the blink of an eye. The brief blinding brightness of a nuclear explosion in a vacuum, combined with the speed of the jet and the limited range means that protected human eyes might not even be able to see the jet of plasma at all... just a flash, and the target going bang (which might look like a second flash very shortly after the first, though dimmer due to distance and having a fraction of the energy of the original nuke blast). Unprotected human eyes will likely be blinded. The double flash should distinguish it from kinetic or laser weapons.

how does it compare to just using normal railgun slugs?

A big slab of the surface of the target will be struck by the jet. As it is intended as a weapon rather than a propulsion system, the kinetic energy of the jet will be much higher than its momentum so the initial impact won't actually "smash" or "push". The particles of the plasma aren't travelling that fast on the grand scheme of things (probably less than 1% of lightspeed) so they won't have a significant attenuation length... all the interesting stuff will happen on the outside.

Within the effective range of the jet, this will basically involve the surface slab being flashed into plasma in an instant, which basically means it violently explodes. This will shove the target to some amount, causing it to be deflected or spun depending on how powerful the attack was an how heavy the target was. Spaced armor can help to some extent, but nuclear blasts are Quite Powerful, and even a small proportion of the bomb's energy delivered to the target is going to produce a large bang which will likely severely damage or destroy the underlying compartments which may themselves go bang depending on what was in them.

Outside of the effective range the heating and explosive effects will be much reduced. Surface material and equipment may still be ablated away. Suitable armor may in fact be immune to out-of-range strikes... the pusher plate of an Orion Drive spacecraft, for example, is designed to withstand that sort of thing. Closer strikes can still damage or destroy a pusher plate, however.

After the initial blast, the affected area will be glowing very hot, and space being what it is, it will take a moment to cool down. Conduction of this heat into the hull might further damage other systems.

Railguns, conversely, produce a hole on the outside of the target, a short damage track where the impacted material is completely destroyed, and a much larger cone-shaped volume of damage oriented along that track as stuff is shoved out of the way by the impact shockwave. There will be a flash and sparks as material is superheated or vaporized, but this effect will be much less than a casaba-howitzer strike.

Very loosely speaking, hypervelocity projectiles may produce a lot more internal damage than visible external damage, and nukes and casaba-howitzers will cause a lot more visible external damage over a much wider area which will potentially glow afterwards. A projectile that penetrates the entire ship will probably cause a big hole on the other side. A casaba-howitzer that penetrates the entire ship has probably just blown it in half.

And to roll back to the main question:

What are advantages of plasma based weaponry in ship-to-ship combat

Regular plasma weapons? none. They are probably worse than all of your other options.

Casaba howitzers?

  • make nukes viable in space.
  • increase effective killing range of projectiles, helping them strike quicker and reduce the time spent close to point-defence systems.
  • the jet travels at thousands of kilometers per second, and so is impractical to deflect, disrupt or evade once created.
  • because they can be fitted to missiles or shells, they can have much longer range than ship-mounted lasers and can orbit around a planet to strike a target on the far side.
  • the warheads need to aim themselves before firing, and so unlike a dumb projectile they can cope with an evading target or poor initial aim
  • unlike a laser pulse or dumb projectile, warheads can self-destruct, rendering them (hopefully) harmless. Being downrange of a railgun battle can sometimes be hazardous, as the projectiles retain their striking power over an effectively unlimited distance.

As a footnote, Matterbeam, the author of ToughSF, has written a lot on the subject of Casaba Howitzers and related nuclear weaponry including nuclear forged fragments and so on. Their work is interesting, but they extrapolate XKCD style (what if we just chucked a few extra zeroes on the end?) and so their examples should be taken with a very large grain of salt, because they have little regard for practicality. Conversely, if you have a softer scifi setting (and your desire for plasma weapons suggests you might) you can just take their figures as-is and run with them, because 10000 km long megatonne fusion lances are awesome.

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Plasma based weaponry isn't really a thing in reality. Plasma weaponry in a lot of media is portrayed like some sort of electric lava, but real plasma is basically somewhere between lightning and fire and exists as a short lived state of matter higher than gas. The closest reality you'd likely find is plasma cutters, which burn compressed gases into a super heated plasma, but only work at short distances and are very fuel dependent.

That sort of weaponry might be useful for some sort of boarding action at point blank range, or perhaps literally cutting an enemy ship in half, but the size of the plasma exhaust required would essentially be the equivalent of just pointing your thrusters at the enemy ship and burning through it with the exhaust (which is also an example of real plasma).

Plasma also doesn't naturally last very long without being continuously fed more fuel, so space being as empty as it is makes that even more difficult to produce. You might be able to get away with some sort of lightning gun in atmosphere by ionizing the air, but space is just too empty.

Bottom line is basically that unless you have very specific circumstances, real plasma weaponry isn't feasible in space.


Edit to add that Lightsabers are kind of the only semi-realistic plasma based weapons in major sci-fi media that I've scene. The Hacksmith guys have done a great job of showing proof of concept even though the real deal is obviously not near as powerful as their inspiration..

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  • $\begingroup$ Plasma is ionised "gas". The lightning IS made of plasma, so is the spark or the discharge in the neon light. Plasma is not short-lived state of matter - most of the universe matter is in state of plasma, Sun for example. $\endgroup$
    – Crowley
    Apr 25 at 12:19
  • $\begingroup$ Real plasma is also not nearly as solid as a lightsaber. Gas has very little mass or cohesion. You couldn't swordfight with the hacksmith's latest replica. $\endgroup$ Apr 30 at 0:44
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My other esteemed fellow World Builders have given many grounded and reasonable answers as to why Plasma doesn't work...

However, in the Rule of Cool, Plasma is Awesome - and therefore I will attempt to give an answer

If we are attacking space targets, then we can presume that they are pressurized vessels.

Plasma balls have an additional destructive effect on target.

Whereas Rail Guns punch a small hole in the outer hull, this is quickly dealt with by sealing off compartments (much the same as how a Warship will have watertight compartments).

When the Plasma Ball hits the target, the hot gasses initially fill the area - causing a massive positive pressure wave. Milliseconds after this, once they have cooled and the vacuum of space takes affect, there is a second, equally violent negative pressure wave.

This is similar to how Torpedo explosions underneath the hull of a ship work - a Structure can withstand a large pressure wave in one direction, but when it is nearly instantly reversed, it's much more devestating.

The result of this is that Plasma weaponary has additional internal effects that can rupture the pressure-vessels breaking the seal and resulting in additional damage.

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Let's not fool ourselves, this isn't a science question. It's a science-fiction question. For reasons that other answers have already addressed. So I'm not going to worry about justifying my hand-waving. Just roll with it.

In direct answer, plasma weapons have a couple of advantages:

  • High energy output - as much as you can load into the plasma at the weapon.
  • Limited range - no debris.

That second one is more important than it sounds.

Let's face it, when you're throwing rocks massive chunks of metal at each other every miss is a hazard to someone, somewhere. Any projectile that's sent down-range with enough power to do serious damage to your target is a kinetic impactor waiting to happen. It could be thousands or even millions of years in transit, and most of them will miss anything actually inhabited, but spraying kinetic impactors around the galaxy is bad form.

Plasma weapons on the other hand will dissipate in short order. Even if you somehow manage to hold them in shape for extended periods the plasma itself will eventually radiate all of its energy and become functionally harmless. Maybe some day the cold remnants will be intercepted and studied, but it's not going to randomly wipe out all life on a planet.


Plasma weapons rely on encapsulating high-temperature plasma and projecting them at a target. If you want something hot enough to actually do damage then magnetic fields aren't going to cut the mustard - not unless you've figured out something about magnetic fields that the rest of us haven't - so we're going to rely on a classic SF mainstay: forcefields.

If you don't want forcefields protecting your ships then don't worry, these fields are short-lived, expensive and directed inwards. Producing large fields to protect your ships would be ruinously expensive. If you want ship shields they can be based on a different, cheaper principle.

Anyway, weapons based on plasma come in two basic forms: projectiles and beams.

Plasma Projectiles

These are your classic glowy bullets seen streaming across the battlefield in pretty much every SF space battle that isn't trying to be realistic. For all intents in purposes they're just the SF version of a tracer round stuffed full of high explosive. They can be massive balls of sunfire or tiny bullets.

Clearly encapsulating a raging ball of plasma isn't easy, and simple magnetic fields aren't going to do the trick. Instead you're going to need a short-lived but very strong forcefield. At the core of every plasma projectile is a field generator that produces two forcefields: one to contain the plasma, and the other to protect the generator itself. The generator itself leaches a tiny bit of the plasma for power and is overdriven hard enough to melt itself after a handful of seconds, collapsing the containment and letting the plasma burst free. Ideally you want the field to collapse at the front first, directing the plasma into the target.

Launchers for this kind of plasma weapon would have a magazine of small projectiles - the field generators - that are directed into a chamber where the high-energy plasma is generated and enacpsulated, then the whole projectile is accelerated with magnetic fields like a coil gun.

Projectiles have a few advantages, but tend to be less powerful than beams. They're quick to fire, self-contained and will burst like flak when they reach the end of their runtime. No worries about spraying kinetic impactors around to ruin someone's day a few thousand years from now in a neighbouring system.

Plasma Beams

Any time you see a beam weapon in SF battles it's probably one of these bad boys. A plasma beam weapon is generally short range but extremely powerful.

These guys use a specialized forcefield generator that effectively extend the barrel of the projector out toward the target, then blasts massive quantities of plasma down that tube. It's more of a "reach out and touch somebody" weapon than the projectiles above. Of course generating a field like that is energy expensive, and maintaining cohesion at a distance is ruinously expensive, so these things are severely limited in range.

On the plus side once you have a nice long tube you can fill it with much stronger plasma than a puny projectile. Nuclear-pumped lasers in your plasma chamber, magnetic acceleration in the launcher itself, etc. All reinforced by field generators to prevent blow-back. And once the initial burst has exited the plasma chamber you can close off the lance tube for added safety.

(Would be a shame if someone sent a high-powered X-ray laser down your plasma tube. But nobody could aim that well. Right?)

A Note on Color

Plasma is generated by applying incredible amounts of energy to a solid pellet until it is energetic enough to strip the electrons off the nuclei. Depending on the particular elements you use in your feed pellets the plasma will have different colors. And of course everybody uses different pellet composition based purely on what's most available... right? I mean, sure, you could go with more expensive pellet materials just to get pretty gold or green plasma, but who'd sacrifice cost for mere aesthetics? No, no, it's all about being able to distinguish your friends in the fight.

OK, I'd totally go with the expensive rounds. Style is important after all.

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  • $\begingroup$ I like your ideas, but I will point out that the chances of a round hitting anything after a battle are minuscule. Only maybe if fired in orbit around a heavily trafficked planet. And probably not even then. $\endgroup$
    – Bubbles
    Apr 24 at 17:03
  • $\begingroup$ @Bubbles A wise and funny man once said: "Space is big. Really big." If your projectiles are fired good and hard they're on a long journey into eternity. Good chance they end up in a black hole or a star... but the chance of hitting a planet a few million years from now is non-zero. Small, but still possible. $\endgroup$
    – Corey
    Apr 25 at 0:16
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Since this is Science-FICTION angle, lets give it a nice spin:

The main difference between using a plasma bolt and a solid projectile slug is that if you hit the enemy ship with a solid kinetic projectile going at the speeds required for interstellar combat...the enemy ship is vaporized. the sheer energy delivered would at the very least blow the enemy ship to smithereens, or more likely, convert the kinetic energy to heat and ash the whole thing.

This, is bad for business. Spaceships are insanely expensive after all. They are significantly more valuable as salvage or booty, than whatever paycheck you get for fighting them.

What you really want to use in space combat, is a plasma bolt: a very tiny, lightweight kinetic rod that creates a small magnetic field around it, which contains ionised plasma. It is basically a pinkie-sized, low kinetic energy crossbow bolt that moves at incredible speeds to make a small hole in the hull of the enemy ship, at which point it stops, and releases the plasma.

A tiny mote of extremely ionised gas, suddenly released inside the enemy ship does two things:

  • It BsoDs all the electronics with a sudden, point-blank EMP explosion, which almost always causes the ship reactor to shut down
  • it flashbangs the crew, making them (at the very least) blind, deaf, give them 2nd degree burns, and kill those who were closest. Usually, it uses up at least half of the free-floating oxygen too, and vents the rest, so the flashbanged humans start to suffocate as well. If they want to survive, the HAVE TO surrender to you immediately, and beg for help.

Basically, a bolt of plasma makes a tiny hole in the ship, then briefly turns into a stupendously loud and flashy thunderbolt, then extinguishes itself.

The enemy ship is inert, the crew is either all dead or incapacitated, and you can safely dock and take over the ship with impunity. Replace the circuit breakers, restart system, patch the hole, and space the enemy crew (unless you want to hold them for ransom or something). Keep the nemy ship or sell it. Congratulations space-corsair, you just earned 10 million solar credits with a single shot!

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  • $\begingroup$ I was under the impression though that a very fast-moving projectile would just make a hole, since it is going so fast it cannot efficiently transfer all the energy into the ship. Why is this not the case? $\endgroup$
    – Bubbles
    Apr 25 at 13:49
  • $\begingroup$ the projectile is fast but low mass. It is basically just a delivery needle for the plasma. Once it penetrates the hull it loses pretty much all of its kinetic energy, and stops (or possibly, crumps or disintegrates into shrapnel). The plasma it used to contain stops a microsecond later due to inertia, and spills into the volume of the ship. It has very little mass, and thus very little kinetic energy, so it cannon breach any further, but it once the magnetic sheath failed, it instantly spreads. Basically, It is a super-fast lightweight dart that delivers a ball lightning. $\endgroup$ Apr 26 at 7:00
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Since there isn't a "hard science" tag on the question (despite some answers pretending that there is), I'll just drop the question of how the plasma projectiles work and instead answer why they're great.

And that answer is that - before plasma became viable - kinetic weapons were obviously supreme. And with that came anti-kinetic armor aka aerogels or foams, which take a lot of kinetic impact energy without requiring too much mass (which would make movement expensive).

So we reached a point where most warships were basically impenetreable clouds of metallic aerogels/foams where you would have to hit exactly the same spot over and over and over again in order to eventually do some damage to the ship and incendiary bullet's didn't work that well due to a lack of "free" oxidizer around.

And that's where plasma weapons came in. The advantage of these foams to provide significant structural strength/volume for very little weight also became their primary weakness since plasma impatcs just melt massive amounts of foam in a single hit (due to the paltry ability to conduct heat within the foam). The fact that plasma bolts spread out is only a benefit here since it means "cleansing" a larger area of foam.

While the damage to classical massive armor (especially with anti-plasma cooling systems) is miniscule, those plates are highly vulnerable to kinetic weaponry.

So the best armed ship is neither one with plasma or kinetic weapons but a cruiser equipped with both in order to hit each armor layer with the most effective ammunition.

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  • $\begingroup$ I wonder, considering how well aerogels on Earth protect against heat transfer (which is really well), how does that affect the impact of plasma on the gels? $\endgroup$
    – Corey
    Apr 26 at 1:23
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    $\begingroup$ @Corey because plasma also has (some) mass and likely no insulating cold air within it (since it's designed for vacuum), thereby liquefying the aerogel better than the only-heat-based tests on earth would suggest. The lack of heat transfer is precisely what makes it weak to heat (eg plasma) because it has no way of dissipating the heat $\endgroup$
    – Hobbamok
    Apr 29 at 9:39
  • $\begingroup$ I thought that the insulating properties of aerogels was more about the loose connectivity of the solid materials. The outside may melt, but internally the heat transfer would be worse even with vacuum-filled voids in the aerogel. I'd love to see that tested in space :D $\endgroup$
    – Corey
    Apr 29 at 15:11
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While this isn't hard-science, I'll simply use this as an excuse to invent science rather than throw out known science!

Any kind if interplanetary civilization that is beyond Earth orbit is going to be very high energy.

The energy you can get from being beyond a planet, let alone required to be traveling between stars, is insanely high compared to what we are used to. It is like comparing someone with a rock attached to a stick to a battleship gun.

Sure, both are kinetic impactors, but they that fact tells you next to nothing.

So we'll start with this high energy civilization. You are going to have mass drivers that shoot stuff at near the speed of light, laser weapons that deposit high fractions of the output of an entire sun on a target, and other weapons that rival the destructive power of a dinosaur killing asteroid.

Similarly, you'll have some kind of defensive technology. Anything made out of conventional chemistry has zero durability in this model - so we'll assume unconventional chemistry, so your ships can take damage. Stealing a page for schlock mercenary, I'll assume that post-trans-uranic materials can be forged, are stable and have extremely exotic properties, including insane durability.

We also probably want faster than light travel, assuming a typical space opera setting. The most plausible way to pull this off without mind-bending time travel effects is to add a universal frame of reference and a cross-dimensional drive system.

In this case, our universe is a thin 3+1 dimensional "brane", and relativity is an internal effect caused by the stretching of the "brane". FTL travel exits that 3+1 dimensional brane and uses a nearby alternative surface with a faster speed of light. You isolate your ship from the different physics of this alternative surface using some kind of technological magic (possibly involving matter from this other brane), cross over, travel, then cross back.

This is insanely exotic physics. We can exploit this to give otherwise impractical results.

I will call the FTL space K-space.

So some weapons in this setting:

  1. Conventional mass drivers use insane amounts of energy to project a chunk of mass (usually metal) to near light speed. This chunk of metal has some limited self-guidance abilities.

  2. Kazar Beams are directed energy beam weapons. They travel at FTL speeds vibrating back and forth between our 3+1 brane and the nearby FTL brane. As they enter our space they exist mostly as a beam of directed coherent light, but small amounts of waste emissions bleed off in all directions, producing a glowing line along the weapon path.

  3. Plasma Weapons also use Q-Space. Unlike Kazar Beams, they carry mass as well as light energy between our 'brane and Q-Space. Careful tuning lets it pick up fresh mass from Q-Space, and the resulting exotic fields provide for a containment field of the primordial plasma. Basically, you shoot a contained region of big-bang conditions at the target.

We then invent defences. How about TPU armor, Q-Shields, and Gravitational Deflectors.

TPU armor is great against Kazar beams. The Q-space field is conducted away from the point of impact, routed around the craft, and emitted at the other side, along with the photons.

Q-Shields form a thin line around the ship. When a mass driver projectile crosses them, they collapse, and the mass driver round is deconstructed and shuttled off into Q-Space.

Gravitational Deflectors are the defence against Plasma weapons; the shape of our 3+1 brane is warped, cutting off the supply of Plasma from Q-Space. The material in our universe rapidly cools and dissipates.

But that is just technobabble.

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I suspect the only way a plasma weapon would be viable in space combat is if the charge inbalance (an electron deficit) it creates interacts badly with ones star-drive. Alas, a larger inbalance, in the other direction (an electron glut), is created by firing the weapon. So on top of everything else, it would be a short duration of action weapon.

One thing that could be useful is that it might act as a cloud weapon, needing very little in the way of targeting. The "cloud" also would not necessarily dissipate too quickly. It thus might act like a minefield.

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Projectile Velocity

Two commonly mentioned sci-fi tropes on this SE are "Space is big" and "There is no stealth in space". When you put these two ideas together, it turns out there is stealth in space, but it's not like stealth on Earth where it's the difference between being detectable from 10 km vs 1000 km. In space, it is more like the difference between being invisible at 100,000 km and 10,000,000 km.

The problem with radars being so effective at these ranges is that even the sneakiest, stealthiest, of warships have a lot of distance to cover when firing at another ship once they can see each other.

A modern military grade railgun has a velocity of 2.5 kps. Now let's be generous and say that you future tech the heck out of it and can get that bad boy firing at a whomping 25kps. The amount of damage such weapon could hit with is immense, but the problem is that even at these speeds, your railgun would take over an hour to even reach the enemy ship. That is enough time for the enemy ship to see you fire your shot, stop for a tea break to discuss the best possible countermeasure, and then just move out of the way or otherwise intercept your attack with a point defense weapon. So even though a railgun will technically have the reach for a space battle, it will be too slow for that reach to be relevant.

Missiles are better, but still not great. Missiles can get up to much higher top speeds, but they need time to accelerate. The faster a missile accelerates, the more crushing forces it experiences. While a railgun can do ultra high accelerations because it fires a solid slug, missiles are mostly made of volatile compounds and sensitive electronics; so, getting a missile to accelerate at higher than about 1kps^2 is an engineering nightmare. Again, I'll be generous with the future tech and say your space folks can make a missile that accelerate at 10kps^2. Even if the missile can sustain this acceleration for the entire flight path to maximum detection range, you are looking at a 2.35 to 23.5 minute flight time. Still a huge amount of time for the enemy to see your missile coming and do something about it.

The thing about plasma is that you can put a lot of energy into a very low mass. Because the mass is so low, you can accelerate it to much higher speeds using the same amount of energy as a larger solid mass. If your plasma guns work like particle accelerators, they could fire a bolt of plasma at about 60% of the speed of light (much faster and its interaction with physical matter starts to behave more like radiation than plasma). With this sort of weapon, a stealthy ship could fire at a range of 100,000km. The speed of light means the enemy ship won't even detect the shot until it is 40,000km away at which point it will only take 0.13 seconds to close the gap and hit the enemy ship. Too little time for the defending ship to make a meaningful evasion or fire a countermeasure. Basilly, simply by being faster, plasma weapons allow you to effectively engage the enemy at ranges that are more useful for space battles. The weapons could in fact be far less powerful/efficient than kinetic weapons but still be worth using if it means being able to slowly rip an enemy appart while he tries to get close enough for other weapons to be effective.

Kinetic weapons would still be very useful for when your ships need to bombard a relatively static target like a space stations or ground bases, or for low orbital battles where you have to fight around the curvature of a planet, but for deep space combat, relativistic weapons are the only way to go.

A better way to describe a "Plasma Bolt"

Despite other answers, there is sort of a way for you to make a stable plasma bolt, and it has to do with Special Relativity. As solid matter approaches the speed of light, it, from the perspective of a 3rd party observer begins to appear more and more like a ray of energy and less and less like mass. From the reference frame of a relativistic projectile, it is still a perfectly solid mass held together by normal electromagnetic forces, but when it impacts a much slower solid mass, it is from the perspective of the guy being hit, an insanely hot bolt of plasma, and everything it touches will instantly be converted to plasma giving you the ballistic profile of a thermal explosion. So basically, all you need your plasma gun to be is a coilgun that fires extremely small slugs very fast, and the term "plasma" technically refers not to the state of the projectile from its own reference frame, so much as it describes how it is experienced by the guy getting hit.

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Plasma weapons, seen in Star Trek, Star Wars, Fallout are all based on handwavium and build from unobtaininum. Let me explain.

Plasma is defined as highly ionized state of matter. Under standard conditions (meaning a human can live in) the ions and electrons attract and recombine almost instantly. She spark in the piezo-igniter is made of plasma and you can clearly see how fast it vanishes.

To achieve stable plasma the matter must be subjected to:

  • Extremely high temperatures and pressures. Like in the stars.
  • High voltages / high current densities. Like lightnings, powerline swithes, discharge lights

This is impossible to achieve in space-combat. Unless you introduce some unobtainium part that allow you to keep the plasma confined in small area.

So let's have umobtainium gas that boosts the magnetic field strange way and has high ionising yield.

Firstly it naturally builds toroidal magnetic field. This strong field traps the charged particles within the field using Faraday force. Also the high ionising yield compensate for recombination of free electrons and ions. The magnetic field is sustained by the electric current in the plasma and the magnetic field forces the current to flow.

This "projectile" is not radiating much (most of the radiation is absorbed and consumed for ionisation) and heat dissipation through conduction or convection is almost nonexistent in space anyways.

One need very high energies to form such a field arrangement and needs very intricate electromagnetic "programming" to even stabilize, but once formed it stabilizes until disrupted by any condensed matter. Then all energy needed to form the "projectile" is dissipated there.

The other trick is, if the forming field is moving throughout the buildup stage, the movement is "memorised" and for the observer it looks like it follows the Newton's laws. Except there's no external force to be applied to it.

So the gun looks like reasonably long tube with intricate coiling inside, so the magnetic field it generated can move (like the magnetic field moves in motors or generators) and small chamber around one end that has gas injectors and fast valve.

There are four stages of the firing procedure.

  1. Megnetic field ramp up with gas injection (unobtainium plus other gases, can be noble gas or excimer) in the sealed chambed. in this stage the projectile is initialised and "programming" starts.
  2. Stabilisation sequence. The "projectile" is self-stabilising against vacuum but still needs external magnetic field to keep it that way. The valve opens and small ammount of gas not confined in the "projectile" escapes.
  3. Acceleration. The stabilisation sequence is moving towards the "muzzle", the apparent torus of the projectile is getting thinner and moves faster.
  4. After the projectile is completely stabilised the magnetic field is not needed anymore and this coincedes with the end of the guiding tube.
  5. Space travel. it looks like electromagnetic vortex full of plasma. 6a. Hit. When some condensed matter interferes with the torus, the structure collapses releasing all the energy it is still keeping in form of EM pulse, pressure wave, radiation and heat. 6b. Miss. because still some energy losses take place there is a threshold for lowest energy to keep the system stable. Below the threshold the system collapses releasing all remaining energy as EM pulse and radiation.

It is up to you how fast the projectile can be accelerated, how long it can last and what ammount of energy it can carry.

Compared to kinetic projectiles this one is harder to detect, it has very little mass since the energy is stored in the EM field, and attempts for deflection destabilise it and it explodes.

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  • $\begingroup$ I would like to point out that while yo said that it would be impractical due to needing to recreate the conditions of a star, that is what a fusion reactor does too. And those are pretty close. $\endgroup$
    – Bubbles
    Apr 26 at 16:56
  • $\begingroup$ So far it is possible to perform the enegetically positive reaction (more energy is produced than consumed to initiate it) for quite a short time. Sun is there for milions of years. For the fusion reactor it is still not as good as it sounds - the energy is just dissipated. Next huge step to do is to turn this energy in something easier to handle. $\endgroup$
    – Crowley
    Apr 26 at 18:02

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