So I'm aware that the usual hard sci-fi array of spacecraft weapons generally includes self-guided missiles, rail guns, lasers, etc.

However, in keeping with this spirit of hard science, I've encountered a truly terrible problem- lasers and particle beams are invisible in a vacuum: the lack of pretty colored energy beams tearing through spacecraft truly is a travesty.

So, are there feasible weapons that could a) work effectively as a space weapon and b) produce a visual effect resembling a classic "energy beam" or "bolt"?

  • 4
    $\begingroup$ maybe the smart windscreen is capable of visually showing the trajectories of the beam/pulse in false colour ;D $\endgroup$
    – user6760
    Jan 24, 2021 at 11:44
  • 7
    $\begingroup$ Strictly, it's not true that laser beams are completely invisible in space because space isn't completely empty. Even outside of a system, the interstellar medium still has around one atom of hydrogen per cubic centimeter. So, if you're firing a laser that's powerful enough to be useful as a weapon, then a decent camera or sensor would be able to pick up the beam's path from the sparse scattering of matter that flares up when it gets hit. The laser would probably need to be very powerful to be seen with the naked eye, but a helmet with an AR system could display it to the wearer. $\endgroup$
    – Dragongeek
    Jan 24, 2021 at 12:37
  • $\begingroup$ If the laser is going to hit the ship, there will be no clue before it hits. And reflected/refracted light from the laser will arrive at the same time (or slower for reflections) as the beam itself. You might be able to see shots that missed the ship. $\endgroup$
    – NomadMaker
    Jan 24, 2021 at 20:05
  • $\begingroup$ Lasers themselves would be too fast to really perceive unless it was a large continuous burst. And there wouldn't be any misses bc you can't dodge lasers except at extreme ranges. $\endgroup$
    – Efialtes
    Jan 24, 2021 at 21:35
  • $\begingroup$ @Efialtes To dodge you must know it is coming. So less of a dodge and more like bad leading on the aim. $\endgroup$
    – DKNguyen
    Jan 24, 2021 at 21:46

6 Answers 6



The MARAUDER project as part of the cold war Strategic defense initiative could potentially be what you are looking for.

In short it's a railgun firing microscopic rings of bluish lightning that would most likely look like blue streaks when fired.

It was a coaxial plasma railgun capable of launching tiny toroids of plasma at speeds of 3km/s to 10km/s, though I don't doubt with future tech we could bring it up to around 30km/s.

These toroids are small, only around a couple miligrams of plasma, however you could also scale that up with a bigger cannon.

These plasma projectiles on impact would hit the target with the equivalent impact of 5 pounds of tnt and around 10MJ or energy. It would also bathe the target in all kinds of electronics frying radiation.

This damage in and of itself is underwhelming, however if it were utilized in a rapid fire fashion it could be devastating. However rapid fire increases heat buildup and wear on the weapon. The electronics frying capability would be devastating but only if the craft is not properly hardened against it. However, this could also provide justification for human crews as electronics would cease to function if not heavily shielded. But then again this radiation might also cook the crew inside as well so maybe not a great idea.

In practical terms I am not entirely sure of its utility as a space weapon in comparison with other types.

First of all, it has a relatively low velocity, far above most kinetic weapons, but also far below lasers and particle beams. This would make it harder to hit target beyond 1 light second accurately, but would also force the battles of your universe to take place at sub light second ranges. However it's low velocity could mean that it could have its toroids potentially destabilized by a particle beam or laser "shooting them down".

Another issue that could further limit the range of this type of weapon is that the toroid would be unable to hold itself indefinitely and as it cools down it would dissipate into a high velocity puff of gas with negligible impact. This would have the advantage of making space battles in your universe relatively free of stray ordnance and other hazards posed by the deployment of kinetics.

It also has the issue of having high power consumption which could be a detriment, but that's a universal issue with most energy weapons.

That being said you'll need a nuclear reactor and a huge capacitor bank along with substantial numbers of radiators. This means that your universe would only see these mounted on relatively large purpose built warships.

It also requires tanks of most likely cryogenic propellant to act as ammo, which could be a liability because puncturing them could leave you defenseless if the fuel leaked out. However this could have the added benefit of not requiring separate tanks for your plasma source as you could simply tap off some hydrogen from your main fuel supply.

I am not entirely sure what its utility would be for orbital bombardment or defense but I'm guessing that it wouldn't have the mass or sheer oomph to penetrate the atmosphere. So my gut reaction would be to say it only works in space. However casaba howitzers which are also plasma weapons crossed with particle beams and the bastard stepchild of nuclear pulse units have been said to have some potential in that category so we can always be hopeful.

Overall this weapon does have its advantages and disadvantages, it's a jack of all trades, master of none in regards to space weapons. It lacks the punch of kinetics or the speed of lasers or the simplicity of a missile rack, but it forms a nice middle ground. It is a markedly inferior weapon to the others mentioned so you'd need to come up with a rationale for choosing it over other options. Why would a government in their right mind pick this over a laser? Why would they use a railgun to shoot somewhat damaging balls of lightning when they could fire hypervelocity penetrators that can cleave through armor like a knife through butter? These are questions left for the author to answer.

P.S. If you made it to the end of the article I have a crackpot idea about how to miniaturize this thing and get rid of the massive capacitor bank and nuclear reactor.

You could used an explosively driven compressed flux ferromagnetic generator. In short it is a bomb that explodes around some electrical coils to create a pulse of power in a process that I can't entirely wrap my head around.

This means you can use "shells" that you load into the railgun that detonate and power the machine for each shot.

However even cooler is using metallic hydrogen superexplosives to do it. Assuming your society has the means to manufacture metallic hydrogen in bulk which means you probably have access to much better weaponry, but that's besides the point. These explosives work by forcing metastable metallic hydrogen to heat up to around 1000K to break it back into molecular hydrogen in a violent reaction that is over 50 times more effective than tnt for it's weight. The heating could be accomplished by a thermite derivative triggered by a primer cap of some sort.

So this basically means that not only is the explosion so powerful you only need a small pellet to get the needed power, but not only that, you can use the superheated hydrogen plasma released as your propellant. Meaning in a single self-contained cartridge you can create ball lightning without needing all this fancy hardware. Just a barrel with some rails.

However this has profound implications on you setting as this tech could allow for solid fuel rocket boosters that can achieve nuclear thermal performance levels, tactical thermonuclear weapons packaged into 60mm mortar shells (perfect for orion drives) and a whole host of applications that would promptly make this weapon vastly obsolete. Not to mention the fact that metallic hydrogen is potentially a room temp superconducting material meaning it could perform insane miracles.

So with that I'll say good luck with this weapon idea.

  • 1
    $\begingroup$ I just had a read of the wiki article, I think they were aiming for 3 - 10 thousand km/s because one line mentions 3% lightspeed, I sure wouldn't want to get hit by a 3p.s.l. grain of sand (pretty sure you'd trigger a neutron shower as well from the resulting nuclear fusion on impact) $\endgroup$
    – Samwise
    Jan 24, 2021 at 22:31
  • $\begingroup$ I have perfect environment for such weapon. Thanks for an idea. $\endgroup$
    – Zjerzy
    Jan 24, 2021 at 22:56
  • $\begingroup$ It's funny, what Wikipedia calls devastating you call underwhelming. Well, I suppose everyone's got their own frame of reference... $\endgroup$
    – noughtnaut
    Jan 24, 2021 at 23:47
  • $\begingroup$ Does anybody have any estimates on how quickly the plasma from such weapon would cool off and dissipate in a vacuum? This looks so promising that I just wait for reality to ruin it somewhere in the details. $\endgroup$ Jan 25, 2021 at 1:28
  • $\begingroup$ @Noughtnaut 5lb of tnt is underwhelming in comparison to kinetic weaponry. Anything going over 3km/s packs it's own weight in tnt. That same railgun firing a solid slug of the same size would do much more damage at longer range with greater penetration potential imo, the only thing it wouldn't do is have the same electronics frying potential. $\endgroup$
    – Efialtes
    Jan 25, 2021 at 2:01

Particles could emit blackbody radiation.

When you accelerate your particles, they get hot as a side effect. You are ok with that. You accelerate them very fast and they get so hot that they shine with blackbody radiation according to their temperature.


Black-body radiation has a characteristic, continuous frequency spectrum that depends only on the body's temperature,[10] called the Planck spectrum or Planck's law. As the temperature increases past about 500 degrees Celsius, black bodies start to emit significant amounts of visible light. Viewed in the dark by the human eye, the first faint glow appears as a "ghostly" grey (the visible light is actually red, but low intensity light activates only the eye's grey-level sensors). With rising temperature, the glow becomes visible even when there is some background surrounding light: first as a dull red, then yellow, and eventually a "dazzling bluish-white" as the temperature rises.[14][15] When the body appears white, it is emitting a substantial fraction of its energy as ultraviolet radiation. The Sun, with an effective temperature of approximately 5800 K,[16] is an approximate black body with an emission spectrum peaked in the central, yellow-green part of the visible spectrum, but with significant power in the ultraviolet as well.

Your particles shine and there are enough of them in your beam for this light to be seen. I could imagine that these particles will cool down as they radiate away their heat. The color of the beam will change with distance. The particles are moving with relativistic velocities and so to see the color change you will need a very long beam.


A. C. Clark's novel Earthlight comes immediately on mind. It describes a weapon which quite matches what are you looking for. Jet of molten metal propelled by electromagnetic field. But it could be worth of reading the book for battle description in original. The DARPA project MAHEM is/was based on similar idea, so it should not be completely unrealistic.

  • $\begingroup$ Nice first answer, welcome to the site. $\endgroup$ Jan 25, 2021 at 0:02
  • $\begingroup$ My answer was inspired by a similar project, so not far off there. Cool idea. $\endgroup$
    – Efialtes
    Jan 25, 2021 at 2:08
  • $\begingroup$ Or, scaling it up, you have Casaba Howitzers, which use shaped-charge nuclear explosives to generate the jets of metal. $\endgroup$
    – nick012000
    Jan 25, 2021 at 2:51

monitors add it

The reason it shows up is simple. The monitors and cameras show them, as they can spot the laser frequencies.

Visual confirmation of things becomes less and less viable on high speeds and distances. An ATC doesn't often look out of it's windows, nor do pilots. They mostly fly on instruments.

In a spaceship this is even more so. Windows are a structural weak point and there is a small chance you would implement them in spaceships for anything other than recreation in the future. You'll have strong cameras with good resolution, zoom and frequency ranges for any visual confirmation you want to do, that the computer displays on the monitor for you. And for your purposes it'll display the lasers in all their beauty.

If we go even more realistic we'll probably not fly the ship and fire the weapons as an advanced AI can only understand and react to such amounts of details in the correct way, but that isn't the best for some stories.

  • 1
    $\begingroup$ Let's just hope the graphics cards are available to display the lasers at that time. $\endgroup$
    – Trioxidane
    Jan 24, 2021 at 10:50
  • $\begingroup$ I would think that laser light would be invisible to the camera and monitor just like it is to an eyeball. If there is nothing in the path of the laser to scatter the beam, no light from the laser reaches the viewer regardless of the modality used to view. $\endgroup$
    – Willk
    Jan 24, 2021 at 22:46
  • $\begingroup$ @Willk although that is true, I have no way of fixing that part. $\endgroup$
    – Trioxidane
    Jan 24, 2021 at 23:43
  • $\begingroup$ But then how would the monitors add false color if they could not detect them either? $\endgroup$
    – Willk
    Jan 25, 2021 at 2:16
  • $\begingroup$ @Willk read the comment again? $\endgroup$
    – Trioxidane
    Jan 25, 2021 at 7:19

Casaba Howitzers

Similar to some of the other answers here in terms of visibility mechanism, a casaba howitzer is an offshoot of the Orion nuclear pulse detonation engine technology.

It is a nuclear shaped charge that converts a spherical blast into a roughly 2.5 degree beam with around 90% efficiency. This results in a stream of exceptionally hot plasma and dissociated subatomic particles streaking through space at a significant fraction of the speed of light. It would definitely be both visible from outside its path (due to blackbody radiation) and fast enough to be a practical weapon at space combat distances.

It's also the way you make nukes practical in space since kiloton warheads will provide the same energy density as gigaton warheads, just in a much smaller area. (Which is perfect since most of the area of a spherical charge is wasted, whether in space or in atmosphere)

It's not exactly a ship-mounted weapon since that 10% lossage does expand in a spherical pattern, so you've got to kick the device to a safe distance from your own ship before you set it off. But since most of that 10% will be headed away from you that's not necessarily very far depending on what you have for shielding/armor.

  • $\begingroup$ Stick it on a missile and you can use it as a standoff warhead to get past most point defense. $\endgroup$
    – Efialtes
    Jan 25, 2021 at 19:26
  • $\begingroup$ @Efialtes Yup. I did the math at one point out of curiosity and it definitely solves the "nukes waste too much energy" problem. I forget the exact numbers, but basically focusing it down to that 2.5degree beam roughly makes kilotons hit like gigatons (as long as you don't miss.) $\endgroup$
    – Perkins
    Jul 1, 2021 at 5:37

There is no stealth in space. Projectiles that are hotter than the background show up as hot spots, those that are cooler as cool spots, and there is next to no "cover" on scales much smaller than a globular cluster.

So you don't care if your weapons emit.

A problem with any kind of directed energy weapon is that inverse-square law. Their power goes down with the square of range.

A problem with almost any kind of kinetic or mass-based weapon is that the enemy can see it coming and dodge, and they are slow.

On top of that, you can random-walk, and at non-trivial distances make any kind of aiming a crap-shoot.

A plus side is that most mass based weapons (except, say, black hole bullets) experience time, so they can have sensors themselves and redirect where they are going.

So what you want is a fast weapon (reducing enemy counter-battery and dodge time) that can maneuver (hence mass-based).

So one idea is a microscopic antimatter Bussard ramjet missile. It converts interstellar hydrogen into propulsion using magnetic fields and its own mass. It will glow ridiculously brightly as any interaction with the interstellar medium causes particle annihilation.

As a staged missile, you start off with a conventional matter-antimatter converter launcher that gets the entire thing up to speed (perhaps powered by a laser up its backside). When it runs out of speed, it uses matter-antimatter converting technology to convert its payload missile into an antimatter one and lets it fly away from the "sabot" stage.

Such a weapon can reach a good fraction of c, maneuver as it approaches its target, and if it appears to miss can self-destruct in order to bombard the target with high-energy antimatter dust.

It will also be very bright. Maybe too bright, as it might be visible mainly in gamma rays. But the engine itself might glow in the visible spectrum.

Another idea is black hole munitions. Micro black holes are another total conversion engine you could attach to a missile; they'll put out the energy of a nuclear bomb every second (the shorter their lifetime, the brighter).

Throw some big science words at it; spin a micro black hole up to ring singularity speeds and charge it to permit coupling, and use it to accelerate propellant. Have three such black holes in a metastable orbit, and cause them to shatter as you approach your target, creating massive gravity waves and a directed neutrino pulse.

Going further, your weapons are Alcubierre drives. They form an event horizon round themselves artificially, which in turn generates hawking radiation based on the steepness of the curve (which is bright). The munition literally breaks the speed of light and distorts space as it goes through a target, causing destruction. Of course, this technology also permits communicating with the past via bullets, so "shooting enemy ships" is sort of like using a nuclear bomb as a paperweight.

You could have a gravity-munition that does space warping without the ability to break light speed, and has a similar near-singularity psuedo-Hawking radiation glow.

Another exotic idea is controlled false vacuum collapse. The universe's laws of physics have done something similar to "phase changes" when matter goes from gas to liquid to solid in the past (during the period near the big bang). Some have posited that our current vacuum state is not actually the lowest energy state, but might be metastable; what we call the vacuum is actually a false vacuum.

In that theory, the state of the vacuum can spontaneously collapse into a lower, more stable state (which would correspond to a change in the laws of physics, basically). Such a change could then propagate at the speed of light. Nobody would know it was coming, but it would literally rearrange the everything.

What if there was a lower energy somehow unstable vacuum state that you could only arrange if you carefully encased it in exotic space-time geometry? Like, imagine a glider in the game of Life; it would propagate in one direction, leaving behind normal space, but messing up whatever it hit? The exotic space-time geometry that encases it might decay at a rate of a Planck distance every 10^10 Planck-distances traveled.

In the game of Life, "spaceships" (self perpetuating constructs that move) travel at a fraction of the speed of light in Life (which is 1 square per iteration). Such a complex bit of space-time geometry might also travel at a fraction of the speed of light.

Then, as it tears apart the laws of physics then they snap back, energy could be released, causing a bright glow. We could have it break conservation of energy (perhaps it ends up interacting with Dark Energy, changing the rate of expansion of the universe, in order to fuel itself), or it could just fuel itself using the interstellar medium.

The interstellar medium is 1 proton/cubic centimeter. At the speed of light speeds, a 1 meter radius total conversion puts out 141 078 Watts.

Based off the Stefan–Boltzmann law, the color temperature is 1251 K -- the color of glowing red iron.

  • $\begingroup$ To create your black hole you could use tons of nuclear bomb pumped lasers all focused on on point to create a "kugelblitz" you would need insane energy to do it. $\endgroup$
    – Efialtes
    Jan 26, 2021 at 13:49
  • $\begingroup$ @efia I think it would have to be far more exotic than that. $\endgroup$
    – Yakk
    Jan 26, 2021 at 13:53

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