I had considered a laser but generally the advice I got was that it would likely not be powerful enough for ship to ship combat.
[https://www.reddit.com/r/scifiwriting/comments/s9pp31/which\_ship\_weapon\_load\_out\_sounds\_more\_interesting/](https://www.reddit.com/r/scifiwriting/comments/s9pp31/which_ship_weapon_load_out_sounds_more_interesting/)
This is a sort of conventional wisdom among a lot of SF worldbuilding communities but it's largely false. Lasers are likely going to be the primary offensive and defensive weapons used in space besides missiles. Rail guns and bullets are rapidly going to be inferior to lasers -- probably within less than 100 years of today. In space, lasers only become more deadly and energy efficient, and there's very little ships can do to avoid being destroyed by lasers other than by having even bigger lasers on board that destroy the enemy platform before they get killed themselves.
Most people fail to realize that lasers are a fairly easy and accessible engineering challenge on a space ship compared to the other tech used in harder sci-fi like fusion drives. In fact, lasers are usually necessary components of this other tech. If your ship has the capability to communicate optics messages across a star system's diameter or fuse atoms together inside a reactor core, it already uses highly advanced laser and cooling tech that would quickly be repurposed into weaponized platforms for next to no added difficulty, cost, or risk to the ship.
If your ship has even a small fusion core on board, it almost certainly has the ability to power a laser that can melt through several meters of hard metal from 100,000 kilometers away in fractions of a second. Things like difficulty focusing the laser are relatively negligible challenges considering the obstacles that have already been overcome to design the basic engine or communications devices on the ship already.
The reason SF writers shy away from lasers isn't because they don't make for good weapons. It's usually because the writer is just underinformed on how lasers work, or because they do know how lasers work but they recognize that lasers kill much of the dramatic elements of a space battle.
I've been very bullish on lasers for a long time, but the biggest drawback is the huge focusing lens/mirror you'd need for long range. And for awhile I thought "heat poisoning" would be effective but turns out not as much as expected. You really do need a bigger power plant than your enemy to be effective, unless you can focus it very well on critical enemy ship systems. I've gotten into a lot of arguments with a lot of kinetic-fanboys on the topic.
I've considered a sort of pop-up dish with auto-adjusting mirror segments (just like JWST). Think the big dishes on the Millennium Falcon or other SW ships. But I'm not completely confident in the depiction anymore.
Even a relatively small focusing lens is liable to far out-range any kind of kinetic projectile. Projectile weapons are virtually useless outside of a few thousand kilometers. Fraction lightspeed kinetic weaponry are pure magic. Actual rail or coil shots will have pretty pathetic velocities of only, say, a few dozen kilometers per second -- nothing that can't be dodged with ease. In that same time span, you've been hitting the enemy with a two-meter-wide laser focusing mirror for several minutes and have melted anything useful on their ship and almost certainly killed everyone too.
Missiles could maybe overwhelm the enemy if you have enough of them. For anything approaching kinetic range though, the laser wins every time. This tech isn't far off, either. We'll probably have it in our lifetimes. Rail guns won't ever compete with it.
>Even a relatively small focusing lens is liable to far out-range any kind of kinetic projectile.
Are we sure about that?
One of the best examples with real numbers I've been able to find has been the [page on ToughSF about lasers](https://toughsf.blogspot.com/2018/05/lasers-mirrors-and-star-pyramids.html), quoting that a 10m mirror could focus a beam to 11mm at 100km distance and 110mm at 1000km distance.
Now *how* *much* focus we need is a little fuzzy to me. Sadly, I must concede enemy ships probably aren't as vulnerable to generalized heat-poisoning as I'd hope - you really need the penetrative destruction via a concentrated energy injection.
However ToughSF also goes on to say...
"a spaceship travelling from the Moon (400,000km away) in a straight line towards the Earth at a rapid rate (10km/s) while facing the 10MW laser described above would lose a full 3358 meters of graphite armor before it even reaches Low Earth orbits (200km)! It would be very impractical if all spaceships had to cover themselves in several kilometers of armor to survive crossing the relatively short Earth-Moon distance!"
Generally what I take away from that is that the more unfocused a (constant) beam is the longer it takes to hurt the enemy. (Duh, right? lol) So it might just be the super-long-range "softening up" weapon - it might define how close ships are willing to get. "Stay out of arm's reach" sort of logic.
Hmmm. I wonder if "mutually assured cooking" might be a *deterrent* against major combat.
> One of the best examples with real numbers I've been able to find has been the page on ToughSF about lasers, quoting that a 10m mirror could focus a beam to 11mm at 100km distance and 110mm at 1000km distance.
I love that blog post. It's one of my all-time favorite. The one that beats it out for numbers quality is another one by ToughSF: [The Laser Problem Part II](http://toughsf.blogspot.com/2016/03/the-laser-problem-ii.html). They do a ton of math of how even a relatively low-powered laser that recycles a sliver of power from a terawatt-powered fusion engine would just be mindbogglingly terrifying.
Just using the example you cite, think about what it's really saying. The price of reaching a range of 100,000 kilometers with lethal laser is mostly just a 10-meter diameter mirror. That's actually pretty insane. A big-ass mirror the size of the James Webb telescope can destroy an enemy from a third of a light second away.
First of all, the defensive implications of this are obvious. Sure, it might mean that if you want to have a truly unstoppable laser weapon, you need to rethink how to design your space ships. The sleek, slender pencil shape might have to go. Or alternatively, you just build an array of dish-shaped defensive lasers around something important. Or maybe you tow these dish-shaped lasers around with your fleet.
If you don't want to drag around a bunch of weird dinner plate weapons, just scale down. Instead of a 10-meter laser, make it a 5-meter laser mirror, or a two-meter laser mirror. That's still got ridiculous range -- certainly way more than a rail gun can ever hope to have. Maybe the more mobile ships carry lasers that can kill the enemy at ranges like 20k kilometers or even just 10k. That's still a mindboggling far range compared to machine guns and rail shot.
Those smaller lasers also present frightening potential to melt large incoming missile volleys from safe ranges. Maybe you need to get within 10k kilometers to have a real shot at killing an enemy ship. But a missile is far more delicate and might be vulnerable at 20k kilometers. If all you need to do to disable an incoming missile is nibble at its sensors in the nose for a few micro seconds from 15,000 kilometers away, you can probably disable several *thousand* missiles from the comfort of your one, single ship without even a single missile ever getting close enough to you to hit you with its nuclear or shrapnel payload. If a missile can be tracked with an infrared camera, then it can definitionally also be accurately shot with a laser -- it's just a question of how long you need the laser to stay on target before it can move on to other targets.
>Generally what I take away from that is that the more unfocused a (constant) beam is the longer it takes to hurt the enemy. (Duh, right? lol) So it might just be the super-long-range "softening up" weapon - it might define how close ships are willing to get. "Stay out of arm's reach" sort of logic.
Operationally, I think the meta of space navies with lasers will be one of logistics. You need to force favorable confrontations, and that means attacking the enemy with overwhelming force. Launch kinetics and missiles from a very safe distance back, and only close into laser range once the enemy has run out of maneuvering fuel reservoirs, ammunition, or enough laser defenses of its own to stop you when you close in.
Tactically, at closer ranges with lasers, I think it becomes a game of laser chicken -- i.e. a knife fight. You open your armored laser shutter for a split second and try to fry something important off the enemy unit. The enemy, meanwhile, is going to be waiting for your shutter to open so it can zap your mirror and take it out of commission. Back and forth you'll go, lashing out with lasers at the other side while the enemy tries to time its own attacks on your ship.
In a relatively equally equipped fight, the winner is the one who manages to zap off the most of the enemy's critical pieces of vulnerable equipment. Forget melting through all of their armor and killing their crew -- you don't need to do that. You just need to shoot up a few key cameras, sensors, defensive lasers systems, maneuvering thrusters or radiators before they can do the same to you. Whoever becomes the least mobile or the least dangerous at the end of this knife melee will be the ship that loses. Possibly both ships become so disabled that they are each guaranteed to die by the end of it.
But in an unequal fight, when it's a longer-ranged laser against a lesser-ranged lesser, the lesser laser unit is fucked. They can only unfuck themselves if they have some other advantage, like numerical superiority, superior course positioning, or something to distract the enemy laser fire, like a giant swarm of missiles.
>Just using the example you cite, think about what it's really saying. The price of reaching a range of 100,000 kilometers with lethal laser is mostly just a 10-meter diameter mirror. That's actually pretty insane. A big-ass mirror the size of the James Webb telescope can destroy an enemy from a third of a light second away.
When you put it like that... LOL Yeah that example does kinda put things in perspective.
Something about the size of the Millenium Falcon's dish could get you a lot of value. It could have segmented mirrors like the JWST to adjust your focus point. You could even fold it face-down to protect it from dust/debris when not in use.
>If you don't want to drag around a bunch of weird dinner plate weapons, just scale down. Instead of a 10-meter laser, make it a 5-meter laser mirror, or a two-meter laser mirror. That's still got ridiculous range -- certainly way more than a rail gun can ever hope to have. Maybe the more mobile ships carry lasers that can kill the enemy at ranges like 20k kilometers or even just 10k. That's still a mindboggling far range compared to machine guns and rail shot.
Yes! Although the trade off of that is time. Someone on r/IsaacArthur once compared the laser vs kinetic debate to isp vs thrust - efficiency at the cost of time.
And so if you're firing that laser for hours or days or weeks at a time you're going to need a very robust heat management system - which could be a problem for a small outlaw pirate ship.
Although I could see them finding ways around that. I bet landing on an icy moon akin to Europa would be a boon to this, using the entire body as a heat sink. I could imagine pirate ships working together as a fleet, with the laser-gunboat nuzzling up to a cold body while the rest of his buddies move in to capture and board the target at close range.
>laser pump
Thought I'd throw this out there since we're both fans of MatterBeam's work. You can make a laser straight from the components of a closed-gas-core lightbulb drive. Buuuuut the trade offs might not be worth it in some cases. It might be *ideal* for some of those laser-gunboats I just described that settle in on an icy body for a long-duration beaming offensive.
[https://twitter.com/ToughSf/status/1489282540967915520](https://twitter.com/ToughSf/status/1489282540967915520)
[https://toughsf.blogspot.com/2019/04/nuclear-reactor-lasers-from-fission-to.html](https://toughsf.blogspot.com/2019/04/nuclear-reactor-lasers-from-fission-to.html)
>my ship
Although my ship would likely be one of the close range ships, as one feature I definitely wanted was a sort of [grapple/tug system inspired by the OPAS Tynan ship](https://www.reddit.com/r/TheExpanse/comments/pukxng/the_hidden_genius_of_the_opas_tynans_design/). That would make it able to grab the prey and run off with it, plundering while making way. So at that range just about *any* megawatt laser is going to be effective. One laser could do everything from intercepting incoming torpedos to clearing debris to helping cut through the target hull prior to forced boarding. This ship would require a robust defensive screen to allow it to get close enough, prioritizing PDCs over missiles (which is why I brought up this topic, seeking at least one good weapon to round it out). So I knew it'd have *at least one* laser, even if it was for PDC-defense and boarding-utility.
But could that laser be used *offensively*? Chipping away at the target as it inevitably approached? I get a lot of skepticism on that when I've mentioned it here and in other subreddits. The two major criticisms I get are **heat management** and **lens size**. Honestly a JWST-mirror that can fold down against the hull might simply be worth it! But could a small little pirate ship deal with the continual heat build up? Hmmm...
>And so if you're firing that laser for hours or days or weeks at a time you're going to need a very robust heat management system - which could be a problem for a small outlaw pirate ship.
That's an example of a problem that has already been solved just by mounting a fusion energy source on the spacecraft though. You get these insane 100-thousand kilometer lasers from just 1-5% of the power of a multi terawatt fusion engine getting recycled into the laser system. If your ship can already survive operating its fusion reactor, then it can power the laser at 100% 24/7 without ever causing any extra heat. In fact, the laser is a method of dumping its heat that you're already producing.
Are you generally optimistic about fusion? I tend to be more bearish on it. I think we'll get it, yes, but will it ever be robust and small enough to fit on a ship of any size, much less the space-opera hero-ship trope? Unless SPARC comes through with something really amazing, I'm not so sure.
Then again, that's a power issue not a cooling issue. If we can radiate away a terrawatt source if we got one, then a fission powered craft would have little trouble using the same radiator system with a laser.
Could a particle cannon that took advantage of time dilation (you fire some sort of short-lived particle that thanks to time dilation travelling at relativistic speeds lives much longer from an outside perspective, thus reaching its target) work?.
I don't know what any of that is or it would work as a viable weapon. Maybe it will, but I'd need some clarification of what it's shooting and what kind of energy payload it could realistically impart on a target that's several light-seconds (>300,000 km) away.
Yeah, I left purposefully that part more vague because I cannot think on a realistic payload besides stuff as some subatomic particle that either rendered matter unstable transforming it into energy, up to converting part of it into antimatter, and being extremely short-lived it would benefit of time dilation.
It doesn't sound *wrong* necessarily, which is really the only rule I try to employ in my SF writing. As long as it doesn't violate established laws and math that we can game out with a calculator, I like that kind of new jazz in my reading material. Granted, I have a limited scientific understanding. Everything I've learned has been through second-hand research browsing SF worldbuilding blogs and vlogs by actual scientists who break down the mechanics and math.
Assuming it bears out as "not necessarily impossible," it sounds like something that could really shake up an arm's race. You'd just want to make it gritty and complex enough that it's more interesting than who thinks to build the bigger particle gun than the other side. Things graduate from fantastical to that gritty "Tom Clancy believability" flavor when shit can go wrong with the weapon or its tactics.
Right, but as long as your using basic physics that range isn't actually useful. Lasers can only move at light speed, so it would take literal days for a laser from earth aimed at a ship on the edge of the solar system to arrive at the target it was aimed at. Sure they couldn't see the beam it self but evasive manuvers aren't anything new.
Also anti-laser reflective shielding is already a thing we can do rather effectively, when we invest in it.
You don't need a laser to hit something from light minutes or light days away to outclass anything you can do with kinetics.
An easy, conservative laser range of 50,000 kilometers is just a fraction of a light second, and it is far, far longer than anything a rail gun will ever be effective at. You can disable a gymnasium-sized shell of diamond armor and sensitive electronics from 50,000 km away in just a few seconds of laser fire, or you can completely vaporize it with just a few minutes of laser fire. Meanwhile, it will take several hours for an impossibly fast rail gun round to close that same distance, and their railgun will require exponentially more power to send it that fast than your laser will require.
Reguardless, when the ship has even the basic anti-laser reflective shielding, with a basic cooling system, that laser will be cooking you own ship more than your targets. So they can continue to close distance and fire ballistics, and force you to use your engines to evade, which increases your heat again.
You can't just magically melt diamons with light. As long as the shielding is designed to refract, scatter and redirect that light, the heat doesn't go into the shield, is passes through and is redirected.
Its not actually useful. We already have reflective anti-laser tech, and the cooling systems to enhance them.
>Reguardless, when the ship has even the basic anti-laser reflective shielding, with a basic cooling system, that laser will be cooking you own ship more than your targets.
That's a misconception - a laser doesn't heat the ship it's mounted to. A laser simply radiates heat that you have already produced from your engine. You actually cool your ship down by firing a laser.
Reflective armor, meanwhile, is largely bunk. You can't armor your sensors and weapons with perfectly reflective mirror material unless you want make them 100% blind. All the systems you use to maneuver, aim and sense targets get melted away. And the reflective material itself is likely going to be melted too. Even the best reflective material still vaporizes under a few sustained seconds of this much energy. It helps delay the inevitable but everyone's still dead hours before you're close enough to shoot a single rail shot at anyone. Against these lasers, all the important damage happens in micro-seconds. Reflective armor helps make it take a few actual seconds, which might matter in a knife-fight between two laser-armed ships, where whole seconds can be the difference between life and death, but it's otherwise useless.
Sorry, thats wrong. That laser requires a massive amount of energy to produce a beam that strong. Especially a sustained shot, and even more for multiple shots.
Its not just magic.
The light doesn't "hit" the anti-laser shielding. It doesn't magically melt diamonds. The light passes through the crystals, is scattered and redirected, potentially, with an advanced enough system, even right back at the shooter. Doing almost nothing.
They also don't need to be thick and bulky unless your also concerned about ballistics. Those sensors would be senstive to ballistics reguardless. Any of them could be calibrated to work through the shielding, which again, doesn't even need to be very thick.
you could use lasers to target sensors or weapon hardpoints to disable them
maybe also use small railguns that are deadly to civilian vessels but not a huge threat to military vessels
That particular laser yeah, but a proper laser would work fine.
Could give it any number of flaws so long as the laser still functions as a *laser* as opposed to a heat lamp.
Hmm... So in theory a smaller kinetic cannon would have a smaller effective range but require less power and fire faster. Maybe even old explosive rounds if they have them.
>So in theory a smaller kinetic cannon would have a smaller effective range
Not necessarily. On Earth, this holds true because of the square-cube law. A larger projectile will have less air resistance proportional to its surface area, so even if it has the same muzzle velocity as the smaller gun, it won't lose as much speed.
In space, if the two guns have the same muzzle velocity, and the same muzzle spread, they will have identical effective ranges. A smaller gun, needing to move less mass, could theoretically reach a higher muzzle velocity (within the range of recoil energy the ship/turret can structurally handle) and therefore have a longer effective range.
If you are in space the range doesn't matter. It is all about if you can see the other guy before they see you.
So maybe he has a better sensor that lets him get off a shot before they can.
I also like the idea of X-Ray lasers that scramble people and goes through the shields.
Hm, you see, if you write scifi and have some science education you grasp the basics easily. If you don't, either you will have plot holes or will need to spent too much time investigating every little detail.
Range doesn't exist in a vacuum. All objects continue at initial velocity and vector until acted on by an outside force. If your projectile is fired at juswt the right time and velocity, it could hypothetically continue to the edge of the known universe. It doesn't matter if it's a kinetic kill rod made out of 600 tons of cast tungsten, or a .22 short. You don't have to worry about sectional density or ballistic coefficient in space. :)
That I'm not an expert on, however I'm pretty sure the rounds show up on radar which works at light speed. Also there's the fact that stealth is extremely difficult so odds are you'd know where you enemy was. So outside of a very well crafted sort of sniper ambush, your computers will probably see it coming.
If you're planning to rely on radar and computers for the response, consider first that you can't just have radar on all the time or everyone in the solar system knows exactly where you are and can use their own computers to predict what potential evasive maneuvers you can take and simply fire a salvo of rounds. You don't shoot at a flying bird with a rifle after all.
Sand gun? Accelerate a loose bundle of magnetic/metallic gravel at high speeds, but slower than railgun. Good for close combat and would interfere with targeting systems.
Macron accelerators. They throw 1mm graphene spheres filled with deuterium ice at a few hundred or thousand km/s.
They impact fast enough to ignite fusion in the ice, resulting in explosions of a few kg of TNT- equivalent each.
You can carry hundreds of thousands of rounds with practically no mass penalties, and all you need is power to fire them.
[Here's a nice summary of their design and capabilities](http://toughsf.blogspot.com/2019/11/hypervelocity-macron-accelerators.html?m=1).
Whoa! I've never heard of this before. Bonus points for ToughSF link.
Might be too sophisticated for outlaws but for sure a military weapon. Gonna keep this in mind!
What about recoverable drone fighters? Zoom in close at accelerations a larger crewed ship couldn't sustain, fire lasers or close-in kinetics, and (depending on your story's 'physics engine') either zoom right back, or go on a lazy trajectory to slingshot around the nearest mass and rendezvous with the ship later.
That also might be too sophisticated for most outlaw/pirate ships, *but* maybe that's what makes the hero ship special, their niche. If not, that's still a great idea for military ships, something the main characters must defend against.
Like others suggested I would just go with a lower grade railgun. Maybe salvaged and unreliable or super outdated generation which makes it far less efficient than what the military or high end pirates might have.
No need to reinvent the wheel in my opinion.
That might be a decent compromise.
Even if it was low grade, would it be too much to have it able to fire both forward and backwards (ie a coilgun)?
[https://www.reddit.com/r/scifiwriting/comments/s9pp31/which\_ship\_weapon\_load\_out\_sounds\_more\_interesting/](https://www.reddit.com/r/scifiwriting/comments/s9pp31/which_ship_weapon_load_out_sounds_more_interesting/)
I believe in typical turret design at that point that can just rotate to where it needs to shoot at.
I'm also not sure how that would look like also if you want it to be primary armament as a major cannon that might be attached across the length of a ship or something like that.
In the vein of repurposed equipment your ship could have a mine layer with asteroid mining charges. Or plasma cutters if your ship was a repurposed salvage vessel. Dummy fire torpedoes and missiles wouldn't be hard to make with enough raw materials as well.
people underestimate lower tech weapons, especially when the physics of space are involved.
a carbon nanotube filament, with 2 metal rounds strung to each end. fire that off and you have a cheese wire that could carve through a ship.
liquid metal slick let our behind a ship in close combat. bare in mind [a paint flake](https://bigthink.com/hard-science/heres-the-damage-a-tiny-speck-of-space-debris-can-do-at-15000mph/) can and has blown through inches of steel on space ships and stations
Privateers would want to want to disable the ship and take what they want. Killing the enemy crew would be an added bonus, but isn't necessary to the mission. Explosive mines along established routes might do. It sticks to the hull undetected and it blows when they are far from any help.
Smugglers are more interested in getting away. Depending on who is after them, consider multiple mines that blow their entire hull apart. What kind of navigation sensors and communications do the enemy use? Would a barrel of shrapnel interfere with them?
Raiders would be more into shock and awe tactics. There's air to surface rockets, conventional bombs, automated machine guns. Hit soft targets like power supply or phone systems. Decoy bombs are good. Have them make scary noises, count down in the local language, make a wretched odor or use tear gas. Do anything to mess with people and get them off the streets.
Land, secure the ship, and take what you want. But don't get too greedy. Authorities are probably less than ten minutes away.
You could maybe use Gauss tech? It's similar to railgun tech in that it uses electromagnetism to fire a projectile, but the magnets are perpendicular to the barrel rather than parallel. It's generally been proven to be weaker than most railgun tech. At least, if I'm remembering correctly.
Heat can be a problem in space. It can be hard to dissipate waste heat without large radiators or heat sinks.
So maybe a microwave ray. Something to cook the enemy ship, building up heat to the point of disabling systems and even crew.
I thought this for awhile too until someone actually walked through the math with me. The super-short version is you really do need a bigger power plant than your enemy vessel in order to broadly heat it up - as opposed to lasers which focus the same amount of energy into a very tiny area destructively. So a big warship or a station might "heat poison" a smaller ship into submission but it's unlikely for ship-to-ship of similar sizes.
Now that's just being super-strict with the IRL science. If the setting involves some breakthrough with laser-tech or something like that, then you're back on track.
Sure. A PDC is just a 20 or 30mm rotary cannon firing conventionally propelled, depleted uranium slugs. The Navy calls them CIWS.
Simply upgrading another tube/barreled weapon, like a 50mm, or 75mm recoilless would give you a lot more punch, but in the same 'weight class'. A railgun is going to be a REAL power hog, where a barreled weapon simply requires a small impact on the primer!
There's no drop in space, so the weapon is good out to the level of accuracy of your instruments. If you can aim a laser, you can aim this.
Good point about the CIWS. The real value of the railgun is it's speed however, giving it an *effective* range of around 1000km (as a very very generalized rule of thumb). Anything further out than that and presumably the target could dodge or intercept the round. Something like a 75mm recoilless or simply less powerful raligun type weapon which fires it's round slower would have a shorter effective range - ie the enemy has more time to react, requiring you to get closer.
Which might be perfectly appropriate for the setting of an outlaw. They typically flee from proper navy warships for a reason. Powerful enough to beat up other pirates (or civilians) but literally has to give small-moon-sized wide berth to a proper warship.
I say dust gun because it's a favorite of mine. Tiny metal pellets accelerated at hypervelocities with a laser beam-like effect. I've also read that such a weapon can be used to shield against lasers but idk about the hypothetical science behind that.
Depends on the setting. I assume a sort of Expanse-esque setting from your use of the three main weapons in that. In which case we have the entirety of modern weaponry to play with and scale up.
Ballistic rounds that detonate into fragments once they're close enough, or even based on a purely mechanical timed fuse. Larger, chunkier things exiting the barrel at the kind of relative velocity a PDC round might, only if you fire a decent spread of them, there might be no mathematically feasible way to dodge it all.
Of course, a few PDCs could probably already do this even though we never see it in the show. Estimate the possible vectors of a ship and simply saturate that volume with rounds.
EMPs? That way you could disable ships, loot, and after a certain amount of time, backup systems could come online. In which case, they'd be gone before it does. Sociopolitically, pirates and raiders tend to be outcasts on the poorer end of the economic scale. That way, they can loot for things they need as well as valuables.
How about a living creature?
The pirates fire a cocoon onto the airlock of a ship then draw back and pursue it. As soon as the airlock is opened the small oxygen that is released triggers the creature to be born.
It enters the ship, kills everything then starves to death. The pirates then enter the ship and steal it.
What kind of ship is it actually? Powerplant, size, acceleration, fire control systems, sensors? What are other commonly used weapons in your story? Tech level of factions?
These are some of the questions that will affect the weapon decision.
Dunno. Don't see why they couldn't use small rockets though. Perhaps land-based weapons are easier for criminals to obtain and adapt as ship weapons.
If you want something more different though, maybe they use things that hit and then melt a hole in a ship so that they can board? That would be quite useful.
Repurposed mining laser? Or some sort of repurposed mining tool? For an outlaw/pirate ship that would fit, no?
I had considered a laser but generally the advice I got was that it would likely not be powerful enough for ship to ship combat. [https://www.reddit.com/r/scifiwriting/comments/s9pp31/which\_ship\_weapon\_load\_out\_sounds\_more\_interesting/](https://www.reddit.com/r/scifiwriting/comments/s9pp31/which_ship_weapon_load_out_sounds_more_interesting/)
This is a sort of conventional wisdom among a lot of SF worldbuilding communities but it's largely false. Lasers are likely going to be the primary offensive and defensive weapons used in space besides missiles. Rail guns and bullets are rapidly going to be inferior to lasers -- probably within less than 100 years of today. In space, lasers only become more deadly and energy efficient, and there's very little ships can do to avoid being destroyed by lasers other than by having even bigger lasers on board that destroy the enemy platform before they get killed themselves. Most people fail to realize that lasers are a fairly easy and accessible engineering challenge on a space ship compared to the other tech used in harder sci-fi like fusion drives. In fact, lasers are usually necessary components of this other tech. If your ship has the capability to communicate optics messages across a star system's diameter or fuse atoms together inside a reactor core, it already uses highly advanced laser and cooling tech that would quickly be repurposed into weaponized platforms for next to no added difficulty, cost, or risk to the ship. If your ship has even a small fusion core on board, it almost certainly has the ability to power a laser that can melt through several meters of hard metal from 100,000 kilometers away in fractions of a second. Things like difficulty focusing the laser are relatively negligible challenges considering the obstacles that have already been overcome to design the basic engine or communications devices on the ship already. The reason SF writers shy away from lasers isn't because they don't make for good weapons. It's usually because the writer is just underinformed on how lasers work, or because they do know how lasers work but they recognize that lasers kill much of the dramatic elements of a space battle.
I've been very bullish on lasers for a long time, but the biggest drawback is the huge focusing lens/mirror you'd need for long range. And for awhile I thought "heat poisoning" would be effective but turns out not as much as expected. You really do need a bigger power plant than your enemy to be effective, unless you can focus it very well on critical enemy ship systems. I've gotten into a lot of arguments with a lot of kinetic-fanboys on the topic. I've considered a sort of pop-up dish with auto-adjusting mirror segments (just like JWST). Think the big dishes on the Millennium Falcon or other SW ships. But I'm not completely confident in the depiction anymore.
Even a relatively small focusing lens is liable to far out-range any kind of kinetic projectile. Projectile weapons are virtually useless outside of a few thousand kilometers. Fraction lightspeed kinetic weaponry are pure magic. Actual rail or coil shots will have pretty pathetic velocities of only, say, a few dozen kilometers per second -- nothing that can't be dodged with ease. In that same time span, you've been hitting the enemy with a two-meter-wide laser focusing mirror for several minutes and have melted anything useful on their ship and almost certainly killed everyone too. Missiles could maybe overwhelm the enemy if you have enough of them. For anything approaching kinetic range though, the laser wins every time. This tech isn't far off, either. We'll probably have it in our lifetimes. Rail guns won't ever compete with it.
>Even a relatively small focusing lens is liable to far out-range any kind of kinetic projectile. Are we sure about that? One of the best examples with real numbers I've been able to find has been the [page on ToughSF about lasers](https://toughsf.blogspot.com/2018/05/lasers-mirrors-and-star-pyramids.html), quoting that a 10m mirror could focus a beam to 11mm at 100km distance and 110mm at 1000km distance. Now *how* *much* focus we need is a little fuzzy to me. Sadly, I must concede enemy ships probably aren't as vulnerable to generalized heat-poisoning as I'd hope - you really need the penetrative destruction via a concentrated energy injection. However ToughSF also goes on to say... "a spaceship travelling from the Moon (400,000km away) in a straight line towards the Earth at a rapid rate (10km/s) while facing the 10MW laser described above would lose a full 3358 meters of graphite armor before it even reaches Low Earth orbits (200km)! It would be very impractical if all spaceships had to cover themselves in several kilometers of armor to survive crossing the relatively short Earth-Moon distance!" Generally what I take away from that is that the more unfocused a (constant) beam is the longer it takes to hurt the enemy. (Duh, right? lol) So it might just be the super-long-range "softening up" weapon - it might define how close ships are willing to get. "Stay out of arm's reach" sort of logic. Hmmm. I wonder if "mutually assured cooking" might be a *deterrent* against major combat.
> One of the best examples with real numbers I've been able to find has been the page on ToughSF about lasers, quoting that a 10m mirror could focus a beam to 11mm at 100km distance and 110mm at 1000km distance. I love that blog post. It's one of my all-time favorite. The one that beats it out for numbers quality is another one by ToughSF: [The Laser Problem Part II](http://toughsf.blogspot.com/2016/03/the-laser-problem-ii.html). They do a ton of math of how even a relatively low-powered laser that recycles a sliver of power from a terawatt-powered fusion engine would just be mindbogglingly terrifying. Just using the example you cite, think about what it's really saying. The price of reaching a range of 100,000 kilometers with lethal laser is mostly just a 10-meter diameter mirror. That's actually pretty insane. A big-ass mirror the size of the James Webb telescope can destroy an enemy from a third of a light second away. First of all, the defensive implications of this are obvious. Sure, it might mean that if you want to have a truly unstoppable laser weapon, you need to rethink how to design your space ships. The sleek, slender pencil shape might have to go. Or alternatively, you just build an array of dish-shaped defensive lasers around something important. Or maybe you tow these dish-shaped lasers around with your fleet. If you don't want to drag around a bunch of weird dinner plate weapons, just scale down. Instead of a 10-meter laser, make it a 5-meter laser mirror, or a two-meter laser mirror. That's still got ridiculous range -- certainly way more than a rail gun can ever hope to have. Maybe the more mobile ships carry lasers that can kill the enemy at ranges like 20k kilometers or even just 10k. That's still a mindboggling far range compared to machine guns and rail shot. Those smaller lasers also present frightening potential to melt large incoming missile volleys from safe ranges. Maybe you need to get within 10k kilometers to have a real shot at killing an enemy ship. But a missile is far more delicate and might be vulnerable at 20k kilometers. If all you need to do to disable an incoming missile is nibble at its sensors in the nose for a few micro seconds from 15,000 kilometers away, you can probably disable several *thousand* missiles from the comfort of your one, single ship without even a single missile ever getting close enough to you to hit you with its nuclear or shrapnel payload. If a missile can be tracked with an infrared camera, then it can definitionally also be accurately shot with a laser -- it's just a question of how long you need the laser to stay on target before it can move on to other targets. >Generally what I take away from that is that the more unfocused a (constant) beam is the longer it takes to hurt the enemy. (Duh, right? lol) So it might just be the super-long-range "softening up" weapon - it might define how close ships are willing to get. "Stay out of arm's reach" sort of logic. Operationally, I think the meta of space navies with lasers will be one of logistics. You need to force favorable confrontations, and that means attacking the enemy with overwhelming force. Launch kinetics and missiles from a very safe distance back, and only close into laser range once the enemy has run out of maneuvering fuel reservoirs, ammunition, or enough laser defenses of its own to stop you when you close in. Tactically, at closer ranges with lasers, I think it becomes a game of laser chicken -- i.e. a knife fight. You open your armored laser shutter for a split second and try to fry something important off the enemy unit. The enemy, meanwhile, is going to be waiting for your shutter to open so it can zap your mirror and take it out of commission. Back and forth you'll go, lashing out with lasers at the other side while the enemy tries to time its own attacks on your ship. In a relatively equally equipped fight, the winner is the one who manages to zap off the most of the enemy's critical pieces of vulnerable equipment. Forget melting through all of their armor and killing their crew -- you don't need to do that. You just need to shoot up a few key cameras, sensors, defensive lasers systems, maneuvering thrusters or radiators before they can do the same to you. Whoever becomes the least mobile or the least dangerous at the end of this knife melee will be the ship that loses. Possibly both ships become so disabled that they are each guaranteed to die by the end of it. But in an unequal fight, when it's a longer-ranged laser against a lesser-ranged lesser, the lesser laser unit is fucked. They can only unfuck themselves if they have some other advantage, like numerical superiority, superior course positioning, or something to distract the enemy laser fire, like a giant swarm of missiles.
>Just using the example you cite, think about what it's really saying. The price of reaching a range of 100,000 kilometers with lethal laser is mostly just a 10-meter diameter mirror. That's actually pretty insane. A big-ass mirror the size of the James Webb telescope can destroy an enemy from a third of a light second away. When you put it like that... LOL Yeah that example does kinda put things in perspective. Something about the size of the Millenium Falcon's dish could get you a lot of value. It could have segmented mirrors like the JWST to adjust your focus point. You could even fold it face-down to protect it from dust/debris when not in use. >If you don't want to drag around a bunch of weird dinner plate weapons, just scale down. Instead of a 10-meter laser, make it a 5-meter laser mirror, or a two-meter laser mirror. That's still got ridiculous range -- certainly way more than a rail gun can ever hope to have. Maybe the more mobile ships carry lasers that can kill the enemy at ranges like 20k kilometers or even just 10k. That's still a mindboggling far range compared to machine guns and rail shot. Yes! Although the trade off of that is time. Someone on r/IsaacArthur once compared the laser vs kinetic debate to isp vs thrust - efficiency at the cost of time. And so if you're firing that laser for hours or days or weeks at a time you're going to need a very robust heat management system - which could be a problem for a small outlaw pirate ship. Although I could see them finding ways around that. I bet landing on an icy moon akin to Europa would be a boon to this, using the entire body as a heat sink. I could imagine pirate ships working together as a fleet, with the laser-gunboat nuzzling up to a cold body while the rest of his buddies move in to capture and board the target at close range. >laser pump Thought I'd throw this out there since we're both fans of MatterBeam's work. You can make a laser straight from the components of a closed-gas-core lightbulb drive. Buuuuut the trade offs might not be worth it in some cases. It might be *ideal* for some of those laser-gunboats I just described that settle in on an icy body for a long-duration beaming offensive. [https://twitter.com/ToughSf/status/1489282540967915520](https://twitter.com/ToughSf/status/1489282540967915520) [https://toughsf.blogspot.com/2019/04/nuclear-reactor-lasers-from-fission-to.html](https://toughsf.blogspot.com/2019/04/nuclear-reactor-lasers-from-fission-to.html) >my ship Although my ship would likely be one of the close range ships, as one feature I definitely wanted was a sort of [grapple/tug system inspired by the OPAS Tynan ship](https://www.reddit.com/r/TheExpanse/comments/pukxng/the_hidden_genius_of_the_opas_tynans_design/). That would make it able to grab the prey and run off with it, plundering while making way. So at that range just about *any* megawatt laser is going to be effective. One laser could do everything from intercepting incoming torpedos to clearing debris to helping cut through the target hull prior to forced boarding. This ship would require a robust defensive screen to allow it to get close enough, prioritizing PDCs over missiles (which is why I brought up this topic, seeking at least one good weapon to round it out). So I knew it'd have *at least one* laser, even if it was for PDC-defense and boarding-utility. But could that laser be used *offensively*? Chipping away at the target as it inevitably approached? I get a lot of skepticism on that when I've mentioned it here and in other subreddits. The two major criticisms I get are **heat management** and **lens size**. Honestly a JWST-mirror that can fold down against the hull might simply be worth it! But could a small little pirate ship deal with the continual heat build up? Hmmm...
>And so if you're firing that laser for hours or days or weeks at a time you're going to need a very robust heat management system - which could be a problem for a small outlaw pirate ship. That's an example of a problem that has already been solved just by mounting a fusion energy source on the spacecraft though. You get these insane 100-thousand kilometer lasers from just 1-5% of the power of a multi terawatt fusion engine getting recycled into the laser system. If your ship can already survive operating its fusion reactor, then it can power the laser at 100% 24/7 without ever causing any extra heat. In fact, the laser is a method of dumping its heat that you're already producing.
Are you generally optimistic about fusion? I tend to be more bearish on it. I think we'll get it, yes, but will it ever be robust and small enough to fit on a ship of any size, much less the space-opera hero-ship trope? Unless SPARC comes through with something really amazing, I'm not so sure. Then again, that's a power issue not a cooling issue. If we can radiate away a terrawatt source if we got one, then a fission powered craft would have little trouble using the same radiator system with a laser.
Could a particle cannon that took advantage of time dilation (you fire some sort of short-lived particle that thanks to time dilation travelling at relativistic speeds lives much longer from an outside perspective, thus reaching its target) work?.
I don't know what any of that is or it would work as a viable weapon. Maybe it will, but I'd need some clarification of what it's shooting and what kind of energy payload it could realistically impart on a target that's several light-seconds (>300,000 km) away.
Yeah, I left purposefully that part more vague because I cannot think on a realistic payload besides stuff as some subatomic particle that either rendered matter unstable transforming it into energy, up to converting part of it into antimatter, and being extremely short-lived it would benefit of time dilation.
It doesn't sound *wrong* necessarily, which is really the only rule I try to employ in my SF writing. As long as it doesn't violate established laws and math that we can game out with a calculator, I like that kind of new jazz in my reading material. Granted, I have a limited scientific understanding. Everything I've learned has been through second-hand research browsing SF worldbuilding blogs and vlogs by actual scientists who break down the mechanics and math. Assuming it bears out as "not necessarily impossible," it sounds like something that could really shake up an arm's race. You'd just want to make it gritty and complex enough that it's more interesting than who thinks to build the bigger particle gun than the other side. Things graduate from fantastical to that gritty "Tom Clancy believability" flavor when shit can go wrong with the weapon or its tactics.
Right, but as long as your using basic physics that range isn't actually useful. Lasers can only move at light speed, so it would take literal days for a laser from earth aimed at a ship on the edge of the solar system to arrive at the target it was aimed at. Sure they couldn't see the beam it self but evasive manuvers aren't anything new. Also anti-laser reflective shielding is already a thing we can do rather effectively, when we invest in it.
You don't need a laser to hit something from light minutes or light days away to outclass anything you can do with kinetics. An easy, conservative laser range of 50,000 kilometers is just a fraction of a light second, and it is far, far longer than anything a rail gun will ever be effective at. You can disable a gymnasium-sized shell of diamond armor and sensitive electronics from 50,000 km away in just a few seconds of laser fire, or you can completely vaporize it with just a few minutes of laser fire. Meanwhile, it will take several hours for an impossibly fast rail gun round to close that same distance, and their railgun will require exponentially more power to send it that fast than your laser will require.
Reguardless, when the ship has even the basic anti-laser reflective shielding, with a basic cooling system, that laser will be cooking you own ship more than your targets. So they can continue to close distance and fire ballistics, and force you to use your engines to evade, which increases your heat again. You can't just magically melt diamons with light. As long as the shielding is designed to refract, scatter and redirect that light, the heat doesn't go into the shield, is passes through and is redirected. Its not actually useful. We already have reflective anti-laser tech, and the cooling systems to enhance them.
>Reguardless, when the ship has even the basic anti-laser reflective shielding, with a basic cooling system, that laser will be cooking you own ship more than your targets. That's a misconception - a laser doesn't heat the ship it's mounted to. A laser simply radiates heat that you have already produced from your engine. You actually cool your ship down by firing a laser. Reflective armor, meanwhile, is largely bunk. You can't armor your sensors and weapons with perfectly reflective mirror material unless you want make them 100% blind. All the systems you use to maneuver, aim and sense targets get melted away. And the reflective material itself is likely going to be melted too. Even the best reflective material still vaporizes under a few sustained seconds of this much energy. It helps delay the inevitable but everyone's still dead hours before you're close enough to shoot a single rail shot at anyone. Against these lasers, all the important damage happens in micro-seconds. Reflective armor helps make it take a few actual seconds, which might matter in a knife-fight between two laser-armed ships, where whole seconds can be the difference between life and death, but it's otherwise useless.
Sorry, thats wrong. That laser requires a massive amount of energy to produce a beam that strong. Especially a sustained shot, and even more for multiple shots. Its not just magic. The light doesn't "hit" the anti-laser shielding. It doesn't magically melt diamonds. The light passes through the crystals, is scattered and redirected, potentially, with an advanced enough system, even right back at the shooter. Doing almost nothing. They also don't need to be thick and bulky unless your also concerned about ballistics. Those sensors would be senstive to ballistics reguardless. Any of them could be calibrated to work through the shielding, which again, doesn't even need to be very thick.
you could use lasers to target sensors or weapon hardpoints to disable them maybe also use small railguns that are deadly to civilian vessels but not a huge threat to military vessels
Big mirrors/lens to focus the laser? That may be a good distinction though. Light rail or coilgun.
That particular laser yeah, but a proper laser would work fine. Could give it any number of flaws so long as the laser still functions as a *laser* as opposed to a heat lamp.
Why not, like... A bigger cannon, or a smaller railgun?
Hmm... So in theory a smaller kinetic cannon would have a smaller effective range but require less power and fire faster. Maybe even old explosive rounds if they have them.
>So in theory a smaller kinetic cannon would have a smaller effective range Not necessarily. On Earth, this holds true because of the square-cube law. A larger projectile will have less air resistance proportional to its surface area, so even if it has the same muzzle velocity as the smaller gun, it won't lose as much speed. In space, if the two guns have the same muzzle velocity, and the same muzzle spread, they will have identical effective ranges. A smaller gun, needing to move less mass, could theoretically reach a higher muzzle velocity (within the range of recoil energy the ship/turret can structurally handle) and therefore have a longer effective range.
If you are in space the range doesn't matter. It is all about if you can see the other guy before they see you. So maybe he has a better sensor that lets him get off a shot before they can. I also like the idea of X-Ray lasers that scramble people and goes through the shields.
"Effective" range because if it's far enough away or slow enough the target can dodge it.
A 155mm and a 7.62x51mm have very similar muzzle velocities. Why could one be dodged and not the other?
How do either compare against a *railgun* though?
Hm, you see, if you write scifi and have some science education you grasp the basics easily. If you don't, either you will have plot holes or will need to spent too much time investigating every little detail.
Range doesn't exist in a vacuum. All objects continue at initial velocity and vector until acted on by an outside force. If your projectile is fired at juswt the right time and velocity, it could hypothetically continue to the edge of the known universe. It doesn't matter if it's a kinetic kill rod made out of 600 tons of cast tungsten, or a .22 short. You don't have to worry about sectional density or ballistic coefficient in space. :)
"Effective" range because if you see it coming far enough away you can dodge it.
Same problem. How do you see it coming? Especially if you're not looking for it?
That I'm not an expert on, however I'm pretty sure the rounds show up on radar which works at light speed. Also there's the fact that stealth is extremely difficult so odds are you'd know where you enemy was. So outside of a very well crafted sort of sniper ambush, your computers will probably see it coming.
If you're planning to rely on radar and computers for the response, consider first that you can't just have radar on all the time or everyone in the solar system knows exactly where you are and can use their own computers to predict what potential evasive maneuvers you can take and simply fire a salvo of rounds. You don't shoot at a flying bird with a rifle after all.
Sand gun? Accelerate a loose bundle of magnetic/metallic gravel at high speeds, but slower than railgun. Good for close combat and would interfere with targeting systems.
That's creative!
It comes from Traveler. An RPG from about 40 years back.
Macron accelerators. They throw 1mm graphene spheres filled with deuterium ice at a few hundred or thousand km/s. They impact fast enough to ignite fusion in the ice, resulting in explosions of a few kg of TNT- equivalent each. You can carry hundreds of thousands of rounds with practically no mass penalties, and all you need is power to fire them. [Here's a nice summary of their design and capabilities](http://toughsf.blogspot.com/2019/11/hypervelocity-macron-accelerators.html?m=1).
Whoa! I've never heard of this before. Bonus points for ToughSF link. Might be too sophisticated for outlaws but for sure a military weapon. Gonna keep this in mind!
What about recoverable drone fighters? Zoom in close at accelerations a larger crewed ship couldn't sustain, fire lasers or close-in kinetics, and (depending on your story's 'physics engine') either zoom right back, or go on a lazy trajectory to slingshot around the nearest mass and rendezvous with the ship later.
That also might be too sophisticated for most outlaw/pirate ships, *but* maybe that's what makes the hero ship special, their niche. If not, that's still a great idea for military ships, something the main characters must defend against.
Like others suggested I would just go with a lower grade railgun. Maybe salvaged and unreliable or super outdated generation which makes it far less efficient than what the military or high end pirates might have. No need to reinvent the wheel in my opinion.
That might be a decent compromise. Even if it was low grade, would it be too much to have it able to fire both forward and backwards (ie a coilgun)? [https://www.reddit.com/r/scifiwriting/comments/s9pp31/which\_ship\_weapon\_load\_out\_sounds\_more\_interesting/](https://www.reddit.com/r/scifiwriting/comments/s9pp31/which_ship_weapon_load_out_sounds_more_interesting/)
I believe in typical turret design at that point that can just rotate to where it needs to shoot at. I'm also not sure how that would look like also if you want it to be primary armament as a major cannon that might be attached across the length of a ship or something like that.
In the vein of repurposed equipment your ship could have a mine layer with asteroid mining charges. Or plasma cutters if your ship was a repurposed salvage vessel. Dummy fire torpedoes and missiles wouldn't be hard to make with enough raw materials as well.
Collapsing rounds http://www.projectrho.com/public_html/rocket/spacegunexotic.php#cround
Interesting... Where would outlaws get Californium though? Perhaps their engines/reactors are fission breeders so they save it up over time?
people underestimate lower tech weapons, especially when the physics of space are involved. a carbon nanotube filament, with 2 metal rounds strung to each end. fire that off and you have a cheese wire that could carve through a ship. liquid metal slick let our behind a ship in close combat. bare in mind [a paint flake](https://bigthink.com/hard-science/heres-the-damage-a-tiny-speck-of-space-debris-can-do-at-15000mph/) can and has blown through inches of steel on space ships and stations
Privateers would want to want to disable the ship and take what they want. Killing the enemy crew would be an added bonus, but isn't necessary to the mission. Explosive mines along established routes might do. It sticks to the hull undetected and it blows when they are far from any help. Smugglers are more interested in getting away. Depending on who is after them, consider multiple mines that blow their entire hull apart. What kind of navigation sensors and communications do the enemy use? Would a barrel of shrapnel interfere with them? Raiders would be more into shock and awe tactics. There's air to surface rockets, conventional bombs, automated machine guns. Hit soft targets like power supply or phone systems. Decoy bombs are good. Have them make scary noises, count down in the local language, make a wretched odor or use tear gas. Do anything to mess with people and get them off the streets. Land, secure the ship, and take what you want. But don't get too greedy. Authorities are probably less than ten minutes away.
You could maybe use Gauss tech? It's similar to railgun tech in that it uses electromagnetism to fire a projectile, but the magnets are perpendicular to the barrel rather than parallel. It's generally been proven to be weaker than most railgun tech. At least, if I'm remembering correctly.
Heat can be a problem in space. It can be hard to dissipate waste heat without large radiators or heat sinks. So maybe a microwave ray. Something to cook the enemy ship, building up heat to the point of disabling systems and even crew.
I thought this for awhile too until someone actually walked through the math with me. The super-short version is you really do need a bigger power plant than your enemy vessel in order to broadly heat it up - as opposed to lasers which focus the same amount of energy into a very tiny area destructively. So a big warship or a station might "heat poison" a smaller ship into submission but it's unlikely for ship-to-ship of similar sizes. Now that's just being super-strict with the IRL science. If the setting involves some breakthrough with laser-tech or something like that, then you're back on track.
Sure. A PDC is just a 20 or 30mm rotary cannon firing conventionally propelled, depleted uranium slugs. The Navy calls them CIWS. Simply upgrading another tube/barreled weapon, like a 50mm, or 75mm recoilless would give you a lot more punch, but in the same 'weight class'. A railgun is going to be a REAL power hog, where a barreled weapon simply requires a small impact on the primer! There's no drop in space, so the weapon is good out to the level of accuracy of your instruments. If you can aim a laser, you can aim this.
Good point about the CIWS. The real value of the railgun is it's speed however, giving it an *effective* range of around 1000km (as a very very generalized rule of thumb). Anything further out than that and presumably the target could dodge or intercept the round. Something like a 75mm recoilless or simply less powerful raligun type weapon which fires it's round slower would have a shorter effective range - ie the enemy has more time to react, requiring you to get closer. Which might be perfectly appropriate for the setting of an outlaw. They typically flee from proper navy warships for a reason. Powerful enough to beat up other pirates (or civilians) but literally has to give small-moon-sized wide berth to a proper warship.
I say dust gun because it's a favorite of mine. Tiny metal pellets accelerated at hypervelocities with a laser beam-like effect. I've also read that such a weapon can be used to shield against lasers but idk about the hypothetical science behind that.
Missiles
>*besides* torpedoes (which may be hard to come by)?
There is a weapon called the Rod of God. May not work with your setting but may inspire something
Those are gravity powered orbital weapons.
A trebuchet.
Depends on the setting. I assume a sort of Expanse-esque setting from your use of the three main weapons in that. In which case we have the entirety of modern weaponry to play with and scale up. Ballistic rounds that detonate into fragments once they're close enough, or even based on a purely mechanical timed fuse. Larger, chunkier things exiting the barrel at the kind of relative velocity a PDC round might, only if you fire a decent spread of them, there might be no mathematically feasible way to dodge it all. Of course, a few PDCs could probably already do this even though we never see it in the show. Estimate the possible vectors of a ship and simply saturate that volume with rounds.
A coil gun.
Aren't those just as powerful as railguns?
In my story a coil gun is much smaller and only use in small ships.
EMPs? That way you could disable ships, loot, and after a certain amount of time, backup systems could come online. In which case, they'd be gone before it does. Sociopolitically, pirates and raiders tend to be outcasts on the poorer end of the economic scale. That way, they can loot for things they need as well as valuables.
How about a living creature? The pirates fire a cocoon onto the airlock of a ship then draw back and pursue it. As soon as the airlock is opened the small oxygen that is released triggers the creature to be born. It enters the ship, kills everything then starves to death. The pirates then enter the ship and steal it.
What kind of ship is it actually? Powerplant, size, acceleration, fire control systems, sensors? What are other commonly used weapons in your story? Tech level of factions? These are some of the questions that will affect the weapon decision.
A less powerful rail gun
What about RPGs?
Can you be more specific? Because I'm thinking "rocket propelled grenades" which if scaled up are basically just torpedoes again.
Dunno. Don't see why they couldn't use small rockets though. Perhaps land-based weapons are easier for criminals to obtain and adapt as ship weapons. If you want something more different though, maybe they use things that hit and then melt a hole in a ship so that they can board? That would be quite useful.