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Basically, I want to decisively put an end to any idea that lasers could be used in my space combat in any large degree. One of the solutions I've thought of is a world having advanced armour (either through a coating or something else) that is resistant enough to lasers (or I guess heat because that is what the damage comes from if I am correct) to the point where they are basically useless in combat or at the least are very niche (like maybe you could still use them for taking out enemy sensors at long range). I was wondering if having this be something people could do would imply some other things they should be able to do scientifically that would have important ramifications on the world and whether or not they would still have to deal with getting rid of waste heat from being attacked by a laser even if the direct damage was countered.

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  • $\begingroup$ Hello @MandaloreTheProud, welcome to Worldbuilding. When you have a moment, please read through our tour and the following two Help Center pages to understand how best to use this site: help center and help center. Thanks! $\endgroup$
    – JBH
    Mar 28, 2023 at 21:49
  • $\begingroup$ How thick do you mind the gold armor on your spaceship being is the tradeoff. $\endgroup$ Mar 28, 2023 at 22:37
  • $\begingroup$ Real life is one thing and is that what you're thinking of, or not? That I myself have no idea what 'unfortunate consequences' there might be matters not. What 'unfortunate consequences' do you see? How can you Ask whether it would still have to deal with heat? How that not be a prerequisite? $\endgroup$ Apr 1, 2023 at 21:37

11 Answers 11

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"I want to decisively put an end to any idea that lasers could be used in my space combat in any large degree"

You could do that going the opposite way. You could say that ablative armor is cheap, can be replaced/replenished by simply landing on any old chunk of space ice or dead comet, melting some volatiles and painting them on a spaceship before letting them re-freeze, and when hit by a laser this "armor" vaporizes locally, creating a cloud that immediately intercepts and disperses most of the energy of the laser hit ("thermal blooming").

The only way a laser can get through this kind of "armor" would be by repeatedly hitting the exact same point, which, given a small rotation by the victim and a negligible bit of impredictability in its manoeuvers, is impossible in practice at any reasonable range.

So, lasers are out because they're mostly harmless.

You still keep them aboard - them and slug-throwers - to deflect space debris and rubble, and maybe repel boarders, but using lasers as anti-ship weapons is a ludicrous idea.

You can have laser heads - missiles with fusion bomb-pumped lasers - but those aren't properly lasers - they're missiles that just need to get near enough.

if we had but power enough, and time

Super-duper fusion reactors come with issues of their own: efficiency. You would need to dump a frightful amount of waste heat, making the attacking ship large, clumsy and fragile. Static bases on ice worlds, capable of dumping heat underground, might equip monstrous pulsed lasers. Ships, not so much.

Pulsed lasers are more feasible in an atmosphere and a gravity field, because both concur to disperse the vaporized material. In vacuum and microgravity, you'd get a cloud of ablated material all around the targeted ship, and the cloud would quickly dissipate most of the incoming energy.

Using missile heads, you can hit from multiple directions and maximize initial kinetic transfer, getting more literal bang for your buck.

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  • $\begingroup$ Would this counter pulsed lasers as well? I remember reading the ToughSF blog and I think it said pulsed lasers could overcome issues of having to stay firing at the one spot for a while. If so, could a pulse laser very quickly break through the ablative armour? $\endgroup$ Mar 28, 2023 at 22:02
  • $\begingroup$ @MandaloreTheProud not really. You need to supply a pulse with so much energy (not power) to ablate a substantial amount of armor. To vaporize ice we need (273-30)+334+100+2230 = 2907 J per gram. If our armor is barely ten cm thick, that means 29070 J per square cm and we need to deliver this in much less than one millisecond to prevent blooming; power is then about 30 MW per square cm (a 10cm x 10cm hit = 3 gigawatts). "Doping" the ice with reflective metal powder and carbon black would increase both blooming and reflection, rapidly making the power requirements truly insane. $\endgroup$
    – LSerni
    Mar 29, 2023 at 14:04
  • $\begingroup$ The problem I'm finding (not saying it's anyone who is answering's fault) is a lot of the answers do seem to involve saying that lasers would bring power output issues, but in the kind of sci-fi world I imagine, it's usually got something like the Expanse's Epstein drive, which as far as I understand produces a mass amount of energy, on top of good fusion reactors. $\endgroup$ Mar 29, 2023 at 22:26
  • $\begingroup$ @MandaloreTheProud power output issues can be solved, but that gives you even larger waste heat issues. Adding to answer. $\endgroup$
    – LSerni
    Mar 30, 2023 at 8:43
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Frame Challenge: Lasers are a no-go because laserboats are flying radiators

Just bring in proper heat management to your universe, and earn the realism points that even The Expanse didn't.

Modern multi-megawatt CO2 lasers barely scratch 15-20% in efficiency (output power / pump power). That means, for every terawatt beam you've got to dump four more terawatts of waste heat. This is besides your power plant's inefficiency; if it's 50% efficient, you're looking at ten TW to dump. And that in turn is before any combat redundancy in radiators, which you do want to have.

The only way to dump heat in vacuum is radiation, as opposed to conduction and convection you're used to in Earth's atmosphere. The only way you can radiate heat is bringing something on your ship red-hot at least.

Radiators on a laserboat have to be huge (or so hot it starts melting) to dump that much heat. And they can't be armored with anything other than wet paper, or they can't radiate. And by "huge" I mean "several times bigger than the rest of the ship".

Basically, a terawatt laserboat is the ultimate glass cannon. Your navy may build and fly one, but it is so easily countered with missile spam cutting up the giant fins that nobody really bothers.

(They can be cool mining or research vessels, though.)

P.S. In case it gets moved to chat: nuke-pumped lasers are hard-countered with nuclear-tipped anti-missiles deliberately inducing a nuclear fizzle, a technique known as nuclear dudding. LIM-49 Spartan and 51T6 Gorgon ABMs are good examples; disabling warheads even when missing them by a kilometre.

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    $\begingroup$ A solid write up. A counter point could be that a laser boat doesn't necessarily have to survive long term. Consider a self-sacrificing laser drone that gets as close to the target as possible, then explosively generates a laser akin to Project Excalibur - wikipedia. Critical ship systems could be armored, but external sensors are intrinsically vulnerable. $\endgroup$
    – abestrange
    Mar 29, 2023 at 16:36
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    $\begingroup$ "The only way to dump heat in vacuum is radiation" -- Well, almost. What about ejectable heat sinks? You'd basically need a Thermos bottle with a high-heat-capacity mass inside, set up to absorb heat from the rest of the spacecraft. Once the temperature in your heat sink chamber is too great, you eject the mass. I'm sure the engineering would be ... challenging, but the principle isn't really that different from today's heat pumps. $\endgroup$
    – Brian
    Mar 29, 2023 at 18:58
  • $\begingroup$ This got me thinking; what if they used several small lazers and focused them on a small point? There are 2 major counters to this: 1. you have now reveled many ship locations of ships capable of high power lazer transmission instead of just 1, and stealth is a key part of space battles. 2. in order to focus on the ship you need proper ranging from a reference ship. $\endgroup$
    – philn
    Mar 29, 2023 at 22:35
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    $\begingroup$ @ymbirtt Yes, under the assumption that the missile can't actually get too close to the enemy ship before being shot down. And/Or the missile could be on a ballistic trajectory so it is cold and thus almost invisible, but that means without steering it's not actually going to hit the enemy ship, just pass within maybe a few hundred km. A laser warhead would do damage in those circumstances where a nuke warhead would not. See also: laser mines. $\endgroup$
    – causative
    Mar 30, 2023 at 11:11
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    $\begingroup$ Warships probably wouldn't use CO2 lasers. Free electron lasers could hypothetically reach 100% efficiency converting electricity to death. What energy isn't converted remains in the electron beam and can be reused with a proper design. But nothing's perfect and waste heat even with FEL (especially overhead systems) would still be quite high. This is probably the best answer as to why lasers are unviable. If your radiators are physical panels (rather than liquid droplet, curie point, dusty plasma, etc.), losing them in battle means losing your main weapon. Radiators are fragile by necessity. $\endgroup$
    – BMF
    Mar 30, 2023 at 16:03
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This blog post from ToughSF is a great read on defending spacecraft from laser warfare, with a specific focus on mirror armor, which I will be mostly basing my answer on.

In short, there's no perfect defense against lasers. Any mirror will only be 99.999% effective (realistically less than that, but still), and in a relatively narrow range of wavelengths, and that 0.001% of beam energy absorbed will heat and degrade the mirror material until it's no longer effective and is promptly blasted away.

However, in a scenario where lasers dominate, armor can be effective in closing the distances between opposing ships, from millions down to several thousand km, forcing them to slug it out with missiles and kinetics. Good for narrative purposes. The catch is that most if not all of the ship's systems are devoted to shrugging off laser fire.


Realistic space lasers are pulsed, rather than continuous fire. Millions of high-energy pulses spaced microseconds apart. When a beam pulse strikes and heats the surface to a high enough temperature, the surface material flashes into a gas and rapidly expands, so fast that it causes mechanical stress in the material helping to weaken it. In the microsecond gap between pulses, the flashed material explodes and clears before the next pulse.

pulse laser graph

Optimal pulse lengths depend on the armor material used by the opponent, as different materials have different mechanical attributes, like ways of cracking and melting.

The best armor material is one that takes the most energy to heat up and the most energy to destroy. High heat capacity and high melting/vaporization energy. It also should have a high tensile strength to fight the mechanical strain of microsecond pulse train lasers. Ideally, it'd also be lightweight and reflective.

Graphite comes close as a candidate, with high heat capacity (0.72kJ/kg/K) and an extreme vaporization energy (59.5MJ/kg at 4000K), but has poor mechanical strength (30MPa). It is also not very reflective.


Hot materials will radiate blackbody radiation. Energy radiated scales with the fourth power of temperature, meaning the hotter something can get the more energy it is able to shrug off. For high-performance armor, the radiation should be comparable to the laser intensity. When blackbody radiation is equal to laser intensity the laser does no damage, merely heating up the armor. This happens at great distances where the beam intensity is lower.

Graphite vaporizes at 4000K and can dissipate up to 14.5MW/m^2. It can withstand the beam of a 10MW laser from a distance of 8500km — no damage is incurred beyond that point. That's already within reasonable missile range.

Active cooling to pull heat away from the armor can reduce that distance even further.


Sloping the armor in the direction of the beam can steepen the angle of incidence, spreading the beam intensity over a greater area, the spot elongating from a circle to an oval. At an angle of 80 degrees, beam intensity on the armor is reduced by 83%. This suggests that sharp cones are great at reducing laser effectiveness. Polygonal shapes such as pyramids with triangular, square, hexagonal or other bases could be more effective than a rounded cone by creating a compound angle (vertical and horizontal sloping) against the laser.

star 1 star 2

Star pyramid. 80 deg vertical slope, 67.5 deg horizontal slope.

Under extreme angles of sloping, Fresnel reflection becomes significant, and more of the beam energy is dissipated. Graphite has a refractive index n = 1.5179 in 450nm light. That index, along with the slope angle, can be used to calculate how much of the laser's energy is reflected away. An extreme compounded slope such as the one produced by the star pyramid above would allow for nearly 70% of the laser energy to bounce off harmlessly.

The graphite octogram star pyramid above would survive the 10MW laser at a distance of 2000km.

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  • $\begingroup$ Yeah I've seen this blogpost and it did give me some early ideas on countering lasers, it's just that it seems it doesn't make them unviable enough for my tastes unless all my ships are going to have their shape entirely designed around the star pyramid concept on top of the armour being built around countering lasers. My problem is that star pyramids don't look that great to me. I guess I could just handwave it away with armour advancements along the lines of graphite making lasers obsolete. $\endgroup$ Mar 29, 2023 at 22:18
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    $\begingroup$ @MandaloreTheProud Truth is, lasers aren't as unviable as they're made out to be. Their energy demands are bound to be a mere fraction of the engine's. Mega- to gigawatt thrust power and all. Heat dissipation and capacitor banks are hardly an issue in that respect. They're made "unviable" by the existence of better weapons like UREBs. Higher efficiency, far less bloom and subsequently far greater range, near-lightspeed, deadly penetrating radiation target side, nearly impossible to defend against except really high-mass armor or "don't be there". $\endgroup$
    – BMF
    Mar 29, 2023 at 22:57
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    $\begingroup$ @MandaloreTheProud It's a good question, kinda wondered that myself. In both the books and show we really only see kinetics and nukes. My guess is that ships can close the distance too quickly. Burning 10 gees is nothing on Epstein. 10 gees for 10 minutes and you've crossed nearly 20,000 km. 20 mins and its over 70,000 km. With a big honkin laser it's reasonable that you're only going to get a full recharge and adequate firing solution (you're aiming at sub-pixels while the other ship maneuvers) every minute or so. Only a few shots before both ships are in missile range, so why bother? $\endgroup$
    – BMF
    Mar 29, 2023 at 23:16
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    $\begingroup$ That's placing some strict limitations on lasers though. A 10 MW laser is child's play on a proper warship. Ranges are more into the 100,000+ km regime, depending on wavelength. But still, The Expanse ships can close those distances pretty damn fast. $\endgroup$
    – BMF
    Mar 29, 2023 at 23:19
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    $\begingroup$ @causative No one said Epstein was realistic. It's what OP is working with though. Have you heard of MagOrion? There are more than a few types (ICF, Z-pinch, electron beam, etc.), but the gist is basically "modern" Orion with higher engine efficiency. Magnetic fields instead of pusher plates, better pulse units, higher burn-up fractions, that sort of thing. Most carry all the high-thrust, high-ISP benefits of mechanical Orion, some drastically improving them. The smaller variants have insane thrust power and accelerations. Hypothetical until built, ofc, but not inconceivable or implausible. $\endgroup$
    – BMF
    Mar 30, 2023 at 15:44
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It might work...

There are advanced insulating materials today that are fantastic at rejecting heat. But lasers aren't just beams of heat. They're beams of light — and that means you need to deal with photons, not just heat.

Reflection

A perfectly mirrored surface would work, but at the energy levels needed for space combat, "perfect" would have to be remarkably close to "perfect." Every photon not reflected is left to wreak havoc with your ship. That previous link states that a very good dielectric mirror can reflect 99.999% of a narrow range of wavelengths, which might not prove useful in combat (build a laser outside the range of wavelengths...). Note, though, that at 99.999% reflection there's still 0.001% of energy dumped into your ship. 0.001% of a terrawatt laser (perhaps the bare minimum for space combat) is still 10 megawatts of energy.

My thanks to @ZizyArcher for catching my math error. He's correct, in terms of space battles one would think that 10MW isn't very much. A ship might encounter that simply passing within a normal distance from a star. That lends a lot of credence to the mirror method.

Disruption

Another solution is something akin to the way flares are used to distract incoming missiles. Your ship squirts out a heavy mist of something oily or dusty that reflects, absorbs, and otherwise disrupts the incoming beam. This can consume most (if not all) of the energy before it hits your ship.

The only problem with this solution is that information cannot travel faster than the speed of light. In other words, if you can detect the fact that a laser has been fired, then you have already been hit by the beam. Thus, this solution would have to be constantly active during combat, which might make it impractical to use.

@BMF (thank you!) brings up a couple of more problems with this solution that are worth noting.

  • If you can see through the dust, the laser can get through it. That means the dust needs to be whomping thick, and that means all your sensors were just thrown to the dusty/oily wind.

  • Lasers, while impractical (see my alternative, below), have one advantage: they can be pulsed. This means the first pulse burns through the disruption, then the next gets through. Or you just keep pulsing (if you have the energy) and eventually you get through. Frankly, most armor will have this weakness. (See this and this from Worldbuilding.se.)

Ablation

Ablative armor, in the case of lasers, is armor that vaporizes from the heat the laser delivers. Basically, armor becomes a consumable that must be replaced after each round of combat. The problem with ablation or any other dissipate-the-heat solution is that you need to account for photons, not just heat. The impact of a photon is a bigger deal than simple thermal resistance. An example is that an emergency blanket (one of those that fit in your pocket and look kinda silvery) will thermally insulate, but when exposed long enough to sunlight, aka "photons," it becomes brittle and eventually cracks.

Absorption

Another possibility is that you build your ship out of the most thermally conductive material you can find, then make sure you have something akin to a futuristic-almost-magical thermoelectric generator that's taking all that heat and converting it into (hopefully) useful energy that can be applied to the imminent destruction of your enemies! This has some cons, not the least of which is that a thermally conductive material is a fuse by any other name. If your opponent beings a big enough laser to the fight, the hull of your ship will vaporize like so much flash paper.

But maybe you should think about making lasers impractical to use.

I'm going to give you an idea that I've been saving for myself for my Great American Novel that, honestly, I'll likely never have time to write. It's not the greatest idea in the world, but I liked it enough to hold onto it for a fair number of years. Hopefully it either works for you or gives someone else inspiration to come up with an idea that will.

Lasers take a LOT of instantaneous power. Power isn't free, and it isn't simply floating around waiting to be used. Power must be generated. That means if you're going to throw a dozen petajoules at your enemy, those joules must either...

(a) be constantly available via an engine or power planet that's constantly generating tons more power than the ship ever needs save at the moment the laser is fired or...

@jpa points out that it's plausible for such a power plant to produce a significant and detectable magnetic field, thereby making the ship more detectable even before it can get a shot off. While shielding an electromagnetic signature is possible (see Faraday Cages) such a solution kinda only works if the sink for the energy goes somewhere kinda enormous (like a planet) when compared to the source field strength and charge involved. Thus, I think what @jpa is pitching is a very good point.

(b) the energy is being stored in batteries waiting to be used. Those batteries can be discharged when not in combat to keep things safe, but during combat those batteries are only discharged immediately after a laser was fired.

@BenVoigt points out that my answer is ignoring the reality that generating a laser isn't a perfect process. The lower the efficiency of power consumption to generate and transmit the laser, the more the ship needs to handle the problem. Enough waste heat and you either can't effectively strike your target or you vaporize yourself in the effort of doing so. A ship that can handle the waste heat lights up the darkness of space like an infrared Christmas tree. Yet another reason why lasers are impractical to begin with, but I digress...

What that all means is that a laser-firing ship is a disastrous explosion waiting to happen! Either the ship is over-powered (from a power plant perspective) or has a bunch of barely stable batteries just waiting to be hit. Once hit, the result is always catastrophic!

I.E., why on earth would anybody use a laser-firing ship? Why would anyone want to serve on one? It's a death sentence. Worse, whatever you do to make a laser-firing ship more safe, also makes the ship less efficient in combat.

In other words, you don't need to make lasers worthless because of advanced armor. They're pretty easy to justify as worthless all by themselves. After all, who other than Slim Pickens wants to sit on a barely contained explosion?

@Zovits points out that today's astronauts gladly sit on a barely contained explosion and the line of applicants is very long, so Slim's not alone. I chuckled with this entirely correct observation, but I suspect that given the choice of not sitting on a barely contained explosion would be taken by all of them — if it existed. Today it doesn't, but in the OP's world it does so long as lasers aren't involved.

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    $\begingroup$ Another problem with throwing dust in front of the ship to scatter/absorb the beam is that if you can see through the dust, the laser can too. Whatever you toss ahead better be opaque, and that typically means solid. Also, there's a trick with lasers to perform "atmospheric hole burning". The first pulse ionizes some meters of gas, wait some microseconds for the gas to expand and rarify, then the next pulse arrives. $\endgroup$
    – BMF
    Mar 28, 2023 at 23:02
  • $\begingroup$ @BMF Those are some excellent points! $\endgroup$
    – JBH
    Mar 28, 2023 at 23:07
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    $\begingroup$ Your TW->GW calculation is wrong, you would have 10 MW which is not that much actually. Besides, you would use pulse laser. On the ship side you would need huge mirrors tuned for that wavelength to have manageable energy density, on the target side receiving focused burst there is no possible defense with currently known materials besides a lot of matter that gets blasted away every pulse. $\endgroup$ Mar 29, 2023 at 10:08
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    $\begingroup$ @zovits Point well taken! $\endgroup$
    – JBH
    Mar 29, 2023 at 16:27
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    $\begingroup$ @ZizyArcher You're right! Thanks for catching that! (duh.) $\endgroup$
    – JBH
    Mar 29, 2023 at 16:28
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Retro reflective shielding

While using a smooth polished reflective surface as shielding is one option, an alternative is to use reflective surface with a cubic pattern that will additionally reflect the light back where it came from. Not good if you want to avoid RADAR/LIDAR but if the reflection is accurate enough then you effectively turn your enemies weapons back onto them. Literally targeting their weapon ports. Though retro reflectors are often cubic prisms where the back surface actually reflects the light so weathering of the outer surface doesn't diminish it's effectiveness. Manufactured diamond could possibly work well in this role (though strong things tend to also be brittle so that could be a physical weakness).

Efficiency works both ways

A reflective surface that is able to reflect 99% of the light that hits it seems perfectly reasonable, but producing LASER light with this level of efficiency and also having a power source with this level of efficiency is likely a much bigger challenge. If you can't produce a LASER weapon and power supply that has comparable efficiency to what is possible in shields you end up dealing with more heat than your opponent.

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  • $\begingroup$ I like this idea: don't just reflect the laser, bounce it back on them. If you build the reflectors out of materials that are transparent to radio frequency you put a scattering layer underneath. As long as your enemies aren't using x-ray lasers you'd be fine :P $\endgroup$
    – Corey
    Mar 29, 2023 at 23:23
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Heat radiation

Heat is probably the worst thing you can have in space. The reason is simple. There are precious few ways to get rid of it. As you're basically going through a vacuum there is too little to take up the heat. You need to radiate it away. This is a slow process. Look at the International Space Station. It actually has a lot of plates to radiate heat away from the station.

Take this to the space battle. To fire a tera watt laser, you also produce tons of heat to fire it. If the opponent can reflect part of the beam you are in danger of receiving more heat than your opposition. If you're not careful, things overheat. From life support to batteries to the organisms inside.

It can be safer to just fire rockets and the like. Things that take (part of the) heat with them. A laser can still be useful, but only in very niche situations.

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Frame challenge: Lasers as a primary armament are difficult, if not impossible, to justify using. Heat management, energy requirements, EMR signature, weapon dispersion with distance, and targeting (both because of target ablation, and material properties of the target) all make it incredibly difficult to do serious damage to even a lightly armored target. Kinetic weapons, while limited on ammunition, are much cheaper and much more space efficient, and can be "rearmed" at any source of material, given an ammunition forge that you feed raw material into. Missiles (which I will refer to as chemical or thermal weapons) pack a much bigger punch for each shot, and tend to end conflicts much faster.

Lasers, while nearly useless as a primary armament, do serve one critical purpose though. When an OpFor vessel is unarmored, or has had its armor stripped from it through combat, a focused pulse laser at close range can cheaply and quickly/precisely cripple or destroy the target, without having to waste ammunition or risk missing the target (or risk damaging something on the target you wish to retrieve intact). They also serve as both CIWS/Anti-missle defenses, and as a last line weapon for when your ammunition reserves deplete, allowing you to still defend yourself on the regroup or retreat.

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  • $\begingroup$ Would a ship with an efficient fusion drive and fusion reactor with efficient heat radiation have to really deal with this? $\endgroup$ Mar 29, 2023 at 23:14
  • $\begingroup$ @MandaloreTheProud efficient radiators and reactors still leaves you with range and target material/ablation issues, which still points to a less effective weapon, pound for pound. The precision and speed of a laser weapon are its real strengths. $\endgroup$
    – GOATNine
    Mar 31, 2023 at 13:37
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The way you make any weapon useless is to make them too costly to use. Cost in battle can include many things, but here's an idea that would make it extremely difficult to justify firing a laser at a space ship: photoelectric conversion.

One of the major issues with space ships is the mass of the generators required to power them. We solve this problem in a variety of ways today, but just about everything we put in space (inside the orbit of Jupiter at least) uses photovoltaic cells to provide at least some of the power requirements. With current material science we are starting to produce photoelectric metamaterials that are significantly more efficient at turning photons into electron flow, with the goal of drastically improving the power output of solar panels.

Since this is a science fiction question, we can take it a whole lot further.

Imagine a material that converts photons across a reasonable range of frequencies to electricity at extremely high efficiency. Armor plates covered in this material would do double duty as solar panels to provide supplementary power, but where they'd really shine (or whatever the exact opposite of that is) is when someone is dumb enough to point a laser at you. All those lovely megawatts of laser power flowing into your power grid would be a real boon in the energy-expensive battle environment. Pump it through to your weapons array and let your enemy have his energy back as kinetic or plasma fire.

About five minutes after that becomes a reality every ship would tear out their primary laser batteries and replace them with literally anything else. Laser point defense would still have a place of course, but nobody's ever going to point a large laser at a black ship ever again. Well, nobody with a brain.

The minor inefficiencies are of course going to produce heat and probably degradation of the material. We can solve the heat issue by using some of the absorbed power to run our heat management systems and use multiple layers of ablative armor panels to prolong the longevity of the protection, laminated with other materials to provide kinetic and plasma protection. Maybe dump all that heat into sodium tanks and fire those at your enemies, like napalm.

Et voila, no more lasers in combat.

Well, not offensively anyway. With this kind of armor on the field we can do something much more fun with lasers: support laser platforms! Big, slow ships built around massive power plants whose role in combat is to stand clear of the fight and pump power into friendly ships by shooting them with lasers. Your ships could then carry much smaller power plants but still pack a massive punch because their power is externally derived. Imagine a corvette-class ship that maneuvers like a frigate but hits like a destroyer... as long as the support platform is sending power.

Or how about swarms of little ships that are individually pretty weak and take a long time to fire their main cannons, but are able to share power with each other. The could focus power down to an individual ship, let it fire a big shot, then move the power to the next ship that's ready and in position to fire. Maybe it blows the firing ship up, but they're a lot cheaper to build than destroyers. (It'd be a real shame if someone sold this stuff to that hive species you've been fighting, wouldn't it.)

If you want to get really silly though (as if we weren't already there), how about dropping a ship into the photosphere of the local sun and using the abundant energy to power magnetic fields that channel solar plasma into tightly controlled beams. For mining purposes, obviously. Definitely not a weapon that could glass a planet in the habitable zone. Absolutely not designed to create coronal mass ejections on demand. What kind of lunatic do you take me for?


And yes, there's a simple solution to this: dirty solar panels don't generate power as efficiently. If you open combat with a volley of paint or mud or something to foul the armor you can hit them with lasers again. That'll probably surprise the heck out of someone the first time you do it.

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  • $\begingroup$ This is a very interesting solution. Also regarding dirtying the solar panels to counter this system, fights would be long enough range to where that would be difficult I would think. And if you decide to deliver the dirt with like a missile or something, then why not just hit the ship with a missile? $\endgroup$ Mar 30, 2023 at 0:42
  • $\begingroup$ Well, refitting the main cannons on your entire fleet is a bit expensive. Mud missiles are relatively cheap to produce. Point defense would just splatter them around unless it was particularly powerful. I read one humorous story where the ship's waste tanks were dumped into an escape pod and fired at an enemy ship, PD lasers just turned it into a flaming ball of... waste. Because even in space primates fling poo 😄 $\endgroup$
    – Corey
    Mar 30, 2023 at 0:57
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Frame Challenge:

I'm going to cite Dune here as a good method of making insert Weaponary unusable.

In Dune - people have personal energy shields, these sheilds when hit by 'directed energy weapons' can potentially cause an explosion equivalent to a Nuclear blast (Atomics in the universe) - or it could simply kill the target and the attacker.

Additionally, the use of Atomics by the great houses is strictly forbidden and should one house use it against another, the other houses would annihilate the aggressor house.

Because of this, a sort of MAD or Mutually Assured Destruction stalemate occurs.

In short:

Anyone who is 'worth' killing is likely to be wearing a Shield and using a laser against a shielded target could result in a Nuclear explosion and a Nuclear explosion would result in everyone getting destroyed: No one uses Lasers for fear of triggering this

So - to answer your question in a different way - you could make it so that the common method of protecting oneself in Space (a Necessity) would cause catastrophic damage to both parties if one of them attempted to use Lasers - therefore no one does.

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    $\begingroup$ causing the enemies shield to explode with the force of a nuclear blast is bad when you are engaged in close combat infantry fighting on a planetary surface, but is very good when your target is in space a long way away. You could destroy the entire enemy armada with a laser pointer $\endgroup$
    – mgh42
    Mar 29, 2023 at 0:12
  • $\begingroup$ @mgh42 - in Dune though, the effect can happen either at the shield, or at the shooter. You might take your own fleet out. $\endgroup$ Mar 29, 2023 at 0:32
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    $\begingroup$ that's easily solvable in space with a swarm of one use drones with laser pointers. The MAD stalemate is the only reason that shields in Dune are remotely viable, without that it's just sending your military out with a huge bomb strapped to them $\endgroup$
    – mgh42
    Mar 29, 2023 at 0:44
  • $\begingroup$ The ship discharging the laser is Far Away, while the nuclear detonation is going to be right against your ship. $\endgroup$
    – RonJohn
    Mar 29, 2023 at 8:16
  • $\begingroup$ In Dune, things happened in a certain order. First, laser weapons were never used because they are pretty useless (see my future answer). Second, shields became standard to provide protection in space combat. Third, lasers were found to cause shields to explode, making shields useless. Fourth, simple lasers may be on ships to account for anyone stupid enough to use shields on their ships, but they aren't used for combat and shields aren't used for combat because of that either. $\endgroup$ Mar 29, 2023 at 21:25
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Thrust by ablation.

There are two types of laser shield (without going into force-field-shields and other things Star Trek); reflective shields and ablative ones.

We've recently had several questions regarding reflective ones, all have answers about how useless they are.

Ablation however, is the heating and evaporation of material from the heat shield. Something like graphite or other material absorbing lots of energy when it evaporates.

In principle it's great, absorbs several shots, cheep and can be easily replaceable by droids after a fight.

The disadvantage is that if you're in a nice tight formation, all with ablative nose-ends facing the enemy - they can hit you off-centre and this will create thrust by plasma-plume, just like they're turning on a rocket-engine forcing your nose over and changing your vector.

It's a bit mean of them, but aimed accurately, they can smash your ships into each-other before you even get into the fight.

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    $\begingroup$ Manoeuvring thrusters could still compensate however though right? Like if a ship has a large array of manoeuvring thrusters along all its vectors, they could just fire to compensate for any added thrust from what you described. Obviously it wouldn't be perfect having to fire them to compensate, but also how long would it take to even get that effect from the armour and how big of an acceleration would this have? $\endgroup$ Mar 28, 2023 at 22:06
  • $\begingroup$ Good question. Depends on the dimensions/weight distribution of your ships (if all the mass is up the rear-end anyway then only a little energy is needed to turn it). My suggestion to defend against this would be - flat front-ends and having all the mass of your ships near the front-end. If they enfilade you - getting at you from the sides/top/bottom too, then they can push you about. Fast-reacting reaction-control thrusters, yeah, you'd need them. @MandaloreTheProud $\endgroup$ Mar 28, 2023 at 22:15
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You can't put an end to using lasers except if you handwave it to a large degree. The thing is that current Earth-based pulsed lasers are already powerful enough to be useful to blast missiles out of the sky, and this is an active area of research to make it actually work in practice. I believe we will get there in a decade or so. You can't even invent "huge explosion mostly stopped all this research blahblah", there are far too many lasers used in far too many settings - unless someone external prohibits/prevents lasers, research will likely keep going on. Yeah, your large lasers might keep exploding because of handwavium, but smaller lasers are known to already work reasonably well and a bunch of them would be good enough to blast a missile out of the sky with great aiming.

So, lasers for point defense against missiles flying long range? You can count on it. I believe it will lead to laser side dominating eventually, making missiles unplausible for long-range space combat.

Now, for ship defenses preventing lasers from attacking same size ships. Side firing beam would have huge mirrors and focus on a much smaller spot on the target ship. Firing side can be optimized for a single wavelength (possibly several or even tunable), receiving side must accept anything as you can't know what the attacker will use.

CW laser: Top side would likely be dielectric mirror tuned for the expected wavelength range that doesn't absorb but lets some light through. Underneath you would have a metallic mirror on a high aspect ratio structure. This greatly increases effective area and lets the structure survive. This passive defense is likely good enough that CW lasers are useless against ships in the same class and possibly one lower ... but a larger ship will be able to smash smaller one, including missiles.

Pulsed laser: Dielectric mirror starts absorbing unhealthy amount and the high aspect ratio is beneficial just for the first shot and gone afterward. The only realistic defense is ablative armor. It doesn't work quite as good against CW with higher average power, but you can use (in)efficiency argument and old passive armor as why ships wouldn't use it much. Here, the moment you see someone, you can deploy anti-laser magnetic particles (chunks of iron) flying around the ship on predictable trajectories way out of the ship, with some brief holes around windows and guns every now and then so you see what is going on and fire at the target. Enemy projectile weapons smash right through your "shield", but a lot of laser gets absorbed vaporizing that iron. With iron being cheap enough you can make this pretty effective for ships in the same class. Again, smaller ships couldn't really survive hits from larger ones... but that's pretty much par for the course with most weapons.

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