What kind of realistic ranged weapons would be effective in spaceship combat?

So my indomitable army of bunnies have developed space travel and built their first space ship for the exploration of the great universe. However they have a problem!

After some consultation with the great god, google, they have come to the conclusion that laser and plasma weaponry are most likely not feasible. Leaving them with magnetic-based weaponry and missiles(assume that they don't have an innumerable amount nuclear missiles).

However, it seems to me that firing missiles in space might not be an effective weapon against other spaceships. They would be probably unable to maneuver well enough to hit a fast moving spaceship and any civilization that are advanced enough to built advanced spaceships would have good Anti-Ballistic missiles and Close-in weapon systems.

A magnetic-based weaponry is feasible, you can have the space ship's engine power a railgun and fire off kinetic projectiles at high speeds to hit enemy ships. However, I'm worried about the potential recoil from a rail gun knocking the spaceship(I don't think anybody wants to get knocked out of their precise orbit around the planet when they are engaging enemies) around and I think spaceships can also avoid the railgun projectile, provided some distance and anticipation of the projectile(a book said that some ship system could detect the massive buildup of energy needed to fire the railgun and they dodged it)

Nukes as asked in this question seem to be highly effective but I would assume that most ships won't carry a ridiculous amount of nukes to use in minor skirmishes(can you imagine if a accident involving a spaceship with a few hundred nukes on it happened when it came in for a landing on the planet?)

Do we have any effective ranged weaponry for use in space combat which are feasible and able to be uniformly supplied for all ships?

I can't imagine going into space, only to use scaled up rifles in space combat. Someone correct me if my assumption of railguns and magnetic-based weaponry are wrong and that they are in fact the most effective weapons for space combat.

• ITT: EvE online – user23110 Sep 19 '16 at 14:31
• Long range weapons are going to need some sort of self guidance, and really the only feasible thing is going to be missiles (current missile tech already check off all the need-to-dos). They can be countered in a variety of ways, but they will still be the first strike option. As range starts to shorten you need less and less self guidance until direct fire kinetic weapons become optimum. The question about what your going to use more of revolves around how effective your anti-missile-systems are. – Marky Sep 19 '16 at 14:51
• In a vacuum, anything you can out-maneuver, you can probably just out-run. – chepner Sep 19 '16 at 16:41
• One of the big questions here is: what kind of travel method do these ships use? Is FTL travel (wormholes, hyperspace, flicker-jumping, etc) during combat going to be a Thing or are fights going to take place at relativistic or even sub-relativistic speeds? How far apart are ships going to be? All of these details affect the answer to your question. – Draco18s Sep 19 '16 at 18:58
• they have come to the conclusion that laser and plasma weaponry are most likely not feasible Why? If you want something better, tell us exactly why those 2 are not feasible in your opinion. – Mast Sep 20 '16 at 13:51

For something that's relatively small,

Pulse laser ablation

Basically, a laser with a high enough energy, focused on a small enough spot, will instantly turn any surface into a gas. This gas, in a vacuum, will immediately disperse, exposing a hole that was drilled by the package of photons.
However, the real damage comes when the laser excites the surface into a plasma, which has the potential to damage its surroundings. As the laser repeatedly hits a target, the material heats up, making each successive hit more damaging than the last, making the laser a weapon that will win a war of attrition.

As things get bigger, the way that a laser 'turret' tracks its target get more funky, thus a space station could effectively use

Missiles

No tracking required, super long range, the missiles actively seek a target to destroy as opposed to a turret. With a sufficient launching system, missiles could have an infinite range. Though, they could be 'intercepted' by those pesky lasers. This could be solved by launching a higher number of lower damaging missiles, effectively overwhelming any sort of defense. There is a slight problem with missiles, things could outrun them. you don't see this often, but speedy spaceships could be built with light offensive systems for the sole purpose of outrunning missiles. after burning for a few minutes, the missile will run out of fuel and become a projectile, at which point, the ships would move out of the way.

however, to eliminate the problem of heat signature tracking, there would probably be another ranged weapon:

Bombs

Bombs are easy to use, just give them a push in the general direction that they should detonate in, and watch it sail off majestically. The problem with countering bombs, is that they have no heat signature to lock on to. They'd be invisible to an non-optical tracking system. Bombs would be effective at eliminating things like hordes of smaller adversaries, and in some cases, a single larger one.

• How to avoid targets overrunning your missiles: instead of explosive payload, mount ablative lasers on the missiles. They keep firing at the rear/engine of the target while matching Vector and Acceleration to their best ability. Laser guided missiles with lasers FTW. @Jammin4CO – Mindwin Sep 19 '16 at 17:53
• @Mindwin better yet, have the missile launch LAsERs (Light Assault and Engagement Rangers) which then fire ablative lasers at the target. That way, the LAsERs speed will temporarily match the target, and You can land more shots! then you have LASER guided missiles firing LAsERs that fire LASERS. – user23110 Sep 19 '16 at 17:59
• Outrun a missile? The bigger the target, the more unlikely it becomes. It costs loads of energy to compete with the acceleration of a small missile. And once you outran a missile, the next one will be fired already adapted to your new trajectory, so it costs again loads of energy to change it fast enough to outrun the new missile. And if the missiles were designed by me, they would sometimes shut down their engines, looking like being out of fuel, but actually waiting that the target changes its path to something convenient (trying to outrun the next missile) to suddenly accelerate again… – Holger Sep 19 '16 at 18:33
• Outrunning missiles doesn't make much sense (in general; in specific cases, maybe). I'm assuming there is some other purpose to this ship, beyond outrunning missiles (transporting cargo, perhaps, or squishy sacks of meat that can't handle many Gs?), if not, why waste resources on something that will soon be ignored? Trivially: make a copy of your speedy ship, but strip out the cargo or passengers and everything needed to support them. Now you have a missile that is lighter, faster, has greater endurance, and is more disposable than your ship. A purpose-built missile could be even better. – 8bittree Sep 19 '16 at 19:33
• That F/A-18 vs LGM-30 Minuteman ICBM comparison basically demonstrates exactly what I'm talking about. About 1250 miles at up to Mach 1.8 for the F/A-18, vs about 8100 miles at up to Mach 23 for the LGM-30. And that's for something designed to hit mile-wide stationary targets. – 8bittree Sep 19 '16 at 19:57

Relativistic bag of sand.

At the speeds spaceships fly, anything can cause great damage, especially if it flies very fast. Just take a look at how much damage a small fleck of paint can do to current day spacecraft.

A bunch of sand fired at a significant fraction of light speed will be close to impossible to detect in time, and impossible to defend against with point defenses even if detected. By giving it some spread, you can even compensate small errors in accuracy. Imagine it like a huge space shotgun. Even if the enemy spaceship somehow survives a hit, it will be stripped of sensors, weapons and engines.

It would be a very potent weapon especially at the few light-seconds range (Earth - Moon distance), but very dangerous even at much longer ranges, where the target must be constantly moving in random patterns to avoid it. Within the few light-seconds range, not even that would save the target, as its mass would prevent it from moving enough to avoid getting hit.

• It might be interesting to calculate the energy required to accelerate a bag of sand to a suitable speed and how hard it would push your ship back. My guess is that if we took our best rocket technology today and did that then even with our best engines/thrusters compensating for the thrust you'd be shooting out of the solar system backwards and unable to stop for a few generations. – Bill K Sep 19 '16 at 18:59
• At any reasonable speed, your chaff countermeasures are a weapon in their own right! – Graham Sep 19 '16 at 21:58
• @BillK why you just not calculate it en.wikipedia.org/wiki/Momentum#Conservation bag of sand let say 50kg, momentum is kinda 50*c = X * v, let say v=1m/s, then X = 1.5e10 kg. Also to solve problem shoot 2 bags, one for enemy one is recoil bag. – MolbOrg Sep 19 '16 at 22:39
• Yeah, I was visualizing that, a ship that always shoots a copy of everything out both sides :) Kind of wasteful though--it means you need to carry around 2x ammo and expend 2x the energy to accelerate it. Perhaps the best solution is to land your ship on an asteroid and start breaking it down/shooting pieces of it at the enemy. Hmm, this is actually a really good answer--it's not so much what you shoot as where you get it and how you cancel the inertia of shooting it, an external body solves both problems.. – Bill K Sep 19 '16 at 22:46
• You don't really need to shoot anything on the other side, you just need an equal and opposing force. Use a small thruster controlled by the weapons system. – Drunken Code Monkey Sep 20 '16 at 3:24

Bullets (Unless the Ships are Armored - Not Stated in Question)

Note: OP states that ships don't want to get moved out of their orbits during battle, so I'm not assuming a particularly high-velocity fight.

Basic, standard bullets would be pretty devastating to any ship in space and easy to carry/fire. No energy buildup, no drain on your power, and as long as you could hide a muzzle flash your enemy wouldn't even know you were firing on them until the holes started showing up in their hull. You could also have many, many turrets able to target different ship trajectories or areas of the ship.

Sure, they won't blow up the enemy with a great fireball, but how many holes to the great void of space do you think a ship could have before you consider it a big problem? It's not exactly equipped for warfare, but just a few shots could probably wreak major havoc on something like the ISS.

Bullets also have a few advantages over larger weapons - you can carry a LOT of them and they're so small that tracking them seems infeasible. That creates a situation where maneuvering is very difficult for your enemies (where to go?) and ensures they also won't be prematurely blown up by antimissile systems. Plus explosions from larger ordinance in space would create a lot of random debris that could come back to haunt you.

Since there's not a lot to get in their way in space, despite some considerable distances they won't be slowing down either.

Then ensure YOUR ship is full of anti-missile systems of course...

• Very good choice. You can accelerate bullets quickly to a much higher speed and you can fire a spread to compensate for maneuverability--a ship moving only has a small area of possible positions it can be in when your bullets get to it (assuming the ships aren't too far apart)--all you have to do is keep firing a spread that covers the entire area and compensate immediately for course changes. Notice, however, that the fact that you have to fire thrusters to compensate for the mass you are ejecting limits YOUR maneuverability. – Bill K Sep 19 '16 at 18:51
• And if you're using bullets, might as well accelerate them electromagnetically (rail- or coil-gun) because you don't need to carry any propellant mass, no propellant to explode, and you're not limited by the speed-of-sound in your propellent deflagration, so can achieve speeds faster than any traditional artillery piece. – Nick T Sep 19 '16 at 23:47
• I like this idea, because the two big problems with bullets on Earth are air resistance and gravity. Without them, you wouldn't even need rifling -- erratic tumbling wouldn't alter the course, thanks to a lack of air to push on -- and you could use much less energy, since you don't need a bullet to continue traveling faster than sound after several hundred meters through air. – Nic Hartley Sep 20 '16 at 5:36
• A space shuttle moved at up to 26.000 km/h (7,2km/s), while the fastest ballistic chemical-propelled projectile is 8,5km/s. (Source: en.wikipedia.org/wiki/Muzzle_velocity). While i do agree that the idea of spraying bullets at something is generally good, chemically propelled bullets become utterly useless in space, where everything is so fast and so far away from each other. Railguns reach up to 35km/s. Much better, but at an estimated combat distance of.. 100.000km and above (basically 1/4 distance earth/moon and still orbital combat) still useless (the projectile travels 45 minutes) – Andreas Heese Sep 20 '16 at 6:23
• It's going to be really annoying getting hit by one of your stray bullets a hundred thousand years from now. – William Robertson Sep 20 '16 at 15:52

Having your spaceship adjust for recoil is almost trivially easy. If the guns are small enough, then a short burst of thruster applied in the opposite direction will cancel it out. IF the railgun is very large, or even the main weapon, then it is probably best to build it into a spinal mount (i.e the rest of the ship is built around it). The mass of the ship absorbs most of the recoil force, and a blip of main engine power cancels out the rest. This is probably the most plausible solution, since hypervelocity railguns or coilguns need to be very long to generate the velocities required for space combat.

Have Sting space railgun concept to scale with Space Shuttle. Illustration by Scott Lowther

Moving to alternatives, the use of a laser allows you to build very lightweight missiles without needing a lot of rocket fuel. The laser can be focused on the back of the missile to ablate ice, plastic or other lightweight materials which then expand and provide thrust to the missile. Laser launched missiles can be much smaller and cheaper (no expensive rocket booster stage), and the ship itself can be much safer since there is no need to store rocket propellant or solid rocket fuel aboard for missiles. As well, since the laser plasma can be heated to an almost arbitrary degree, such a missile will have a higher ISP than a conventional rocket, so can be smaller for the same amount of deltaV. Adding a homing systems and a small terminal engine to account for evasive action by the target is optional, even a box of kitty litter moving at orbital velocity can have a huge amount of energy (often energy released by high speed impacts is calculated in "Ricks":

In fact, there is Rick Robinson’s First Law of Space Combat, which states that, “An object impacting 3 km/sec delivers kinetic energy equal to its mass in TNT”. Put it another way: put one kilogram of anything in your gun, fire it at a target, have it impact at 3 kilometers a second, viola! You’ve got yourself the equivalent of 1 kilo of TNT going off. (If you need a visual of how much TNT this is, one stick is about 200 grams, so 5 sticks of TNT.) )

Finally, nuclear weapons are very compact sources of energy, and can be used for all kinds of exciting effects. The Conventional Weapons page at Atomic Rockets has the details, but the short version is this:

Nuclear explosions can be used to drive "shotgun" charges of pellets at speeds of up to 100 km/s.

Nuclear shaped charges can drive streams of liquid metal at speeds of nearly 3% of the speed of light.

Casaba Howitzers, a special form of nuclear shaped charge, can accelerate a star hot spindle of plasma at @ 10% of the speed of light, and deliver energy comparable to a super high energy laser (Ravening Beam of Death or RBoD) on target without all the heavy and expensive laser machinery.

So there are lots of interesting options for space combat even if you only want to limit things to kinetics.

Some ideas:

• Why no missiles? They can be like small ships, with a full drive, ECM, anti-counter-missile-lasers and so on. Well, i guess technically that would be drones already...
• Ballistic weapons are IMHO completely useless. If you need to cover distances of several lightseconds, dodging all these projectiles should be a breeze for any sufficiently agile ship. You might try flooding space with projectiles so they can't dodge, but we are talking about a LOT of open space here, and GIGANTIC area of space to cover...let's say combat takes place at 1/100c and you are one lightsecond away of your target... then the area where your target might be is roughly 27,000,000km³....and while your projectile travels all the way, the enemy gets the information about it with light speed, so they can easily calculate how to dodge it.
• What about mines? They could have a small but very powerful drive, be dormant and painted with something that absorbs almost all light, making them impossible to detect. Together with a medium-sized nuke, they'd obliterate anything coming too close.
• Depending on how your rabbits managed to solve problems with micro-meteorites, firing a AA shell in the path of a spaceship might prove useful. If the ship is sufficiently fast, hitting a cloud of metal scraps will shred the ship. Again, you face the problem of not knowing where the enemy ship will be, and your projectile being slow, but it might make the "flood space with stuff you don't want to hit" thing easier.
• Generally speaking, i think your projectiles need their own drive and maneuverability to make up for the other ship changing course. So i really think missiles are the way to go.
• Laser weapons, for whatever reason google said they have not to function, move at the speed of light, making them MUCH harder to dodge and the possible timeframe you need to predict MUCH shorter. So they should hit much more often, give them a try, maybe? :)
• If fighting an enemy in a stationary orbit... go to your handy asteroid belt, gather 2,000 smaller asteroids, tow them, accelerate to 1/10c or above, fire them at stationary target in a small cluster. If you are 100% sure the target won't move, just use a single one, to make them harder to detect. Can also be used to annihilate space stations, moons, planets.... even from outside their solar system, if you can wait long enough. (the thought that 1.000 years ago someone fired an asteroid at earth from alpha centauri or any other neighbouring star system is quite eery... our world is so fragile)
• what about building a giant microwave death ray? Just point it at the enemy ship long enough. If close to the sun, it might have problems dissipating heat already, if you add additional heat... uh oh.
• You have no time to dodge a laser, even if it is fired from lightyears away, because you can't see it coming until it hits you. – Devsman Sep 19 '16 at 19:06
• @Devsman turn it around: you can't aim a laser at anything because you only know where the ship was, let alone is or will be. – Nick T Sep 19 '16 at 23:49
• One thing about dodging ballistic weapons: It would require lots of fuel, which could make ballistic weapons quite effective. – Michael Sep 20 '16 at 5:21
• @NickT This is very true, although at smaller distances (my saying lightyears was as an intentionally impractically large figure) the difficulty of aiming is reduced while the impossibility of dodging is constant. – Devsman Sep 20 '16 at 12:33
• @Devsman: Actually, you can dodge a laser. Maybe not from a surprise attack, but once a battle has started, i KNOw the other guy will shoot at me, and chances are i will know how long his lasers take between shots. So i can keep my course constant, and around the time that i think he is firing, i quickly change course. To make it better, i also randomly change my course a bit earlier and later. Even if the laser only takes 1/10 of a second to travel to me, if i am changing my course during that time, he probably won't hit me, assuming i move at relevant speeds. All about distance, though. – Andreas Heese Sep 20 '16 at 12:36

Space is big.

If you are low-tech, travel anywhere takes a long long time. You use chemical rockets. Getting to orbit is the hard part. You can move around the solar system, but you only get to go places, you don't get to come back: you don't have the fuel to go and stop, then go again. Your ships are tiny, fragile, and no living beings are on them past orbit around your planet.

At the next tier, you are using solar sails and high velocity ion propulsion. We are at the cusp of this tier -- we have sent ion drive unmanned satallites to do some grand tours of the solar system. Unlike our previous probes, these can stop off at a planet, enter orbit, explore using sensors, then fly off somewhere else.

Going beyond that you are using either something exotic (reactionless drives), or something brutal (orion based nuclear drives).

The next stage I can describe is that of a K1 civilization, where you can do things like build launcher lasers to send a small probe to do a flyby of a nearby star.

As a large K2 project, you could take an asteroid (like ceres) and laser-launch it up to speed to colonize another star, with flight time in 1000s of years. The asteroid would use exotic physics to break somehow, as coming to a stop without the laser-launcher is going to be difficult.

At any of these stages, the kinetic energy of the ship itself is going to be absurd. Orbital velocity around a planet, all by itself, makes a pebble orbitting in a significantly different orbit go faster than any bullet we have fired in war.

It just gets worse as our ability to travel goes up.

Basically, space ships are so ridiculously fragile compared to their speed, there is no practical armor unless you invent force shields. Any weapon (pebbles, sand, etc) that contacts will be very very destructive, exploding into plasma.

While you may think that storing nuclear weapons would somehow add danger, the KE of an interstellar ship with any decent speed is going to make a few dozen nuclear weapons irrelevant. At 0.03 C (1000 of years to nearest star) a 100 kg dumb rock is E15.5 J, or a megatonne of TNT.

So a weapon will consist of a mass moving in different orbit/track. If any amount hits, the target is destroyed (chemical bonds aren't strong enough). Dodging consist of seeing the weapon and moving out of its way. Weapons track by thrusting efficiently (like a ship does). Delta-V scales, so weapons are limited by how small you can make the engine technology more than anything else (small engines mean more things to dodge). If the attacked ship has a better engine, it can "out run" (sideways) the defending weapons/dodge them. Static defences are hard, due to square law (there are lots of ways to approach a target, and space is empty).

With science fiction, you'll end up wanting to think about the possibility of crazy propulsion technology and even energy shields. Because given current science, interstellar war isn't ships going pew pew.

In short, interstellar travel of biological beings involves entire-civilization efforts of K2 level civilizations (capable of consuming an entire star's energy output). Interstellar travel of post-biological civilizations could be done slightly easiser, but it mostly consists of sending replicators to the target system and building a new civilization. The weapons of a K2 civilization might involve stellar manipulation to generate controlled solar flares, which are then lazed to launch relativistic smart missiles at a hostile star.

Or maybe poisoning their star to make it somehow go nova.

• it is possible to defend against relativistic projectiles, by placing foil shield, let say at distance 10-20 light seconds against 10-100kg projectiles(i guess). (depends on projectile, their mass, just for illustrating idea). Collision with foil will produce cone of plasma, and distance will determine percentage which will hit the target. Also plasma could be affected with magnetic fields, even at relativistic speeds - so combination of those 2 might get pretty descent defense system. – MolbOrg Sep 19 '16 at 22:51
• @MolbOrg Math time! 1 cm cross section iron bar weighing 100 kg. Foil shield at 10 light seconds. Fe innermost electrons binding energy is 14k electron volts. So to turn 100 kg of iron to (perfect) plasma, you need 2E12 joules. The foil it runs into needs to be about 45 mg. The surface area of a 10 light second sphere is 1E20 m^2. At 45 mg/cm^2 that is 5E19 kg. This is only 1/10000th of Earth's mass. And you can probably make this work without completely ionizing the iron. But still, this is far from easy – Yakk Sep 20 '16 at 1:58
• lol, nice, u have potential. it was principle of defense, most peoples see funny devastating results which projectile may cause, and very few(I saw one actually) look in to which result might cause small matter to that projectile, many see it as ultimate weapon(which is not), and that is the point. For most passive projectile ppl think about, principle will work, there are ways to counteract that defense - usual shield vs sword. Although point in not in to making plasma, but dispersing projectile in first place. If you do not see enemy, and he see u so well, it is probably game over. – MolbOrg Sep 20 '16 at 5:06
• But if you do see or might guess which direction this projectile might come from, we talking about way much less shield mass. Example it not perfect, and was not intended to be, and much depends on details including details about projectiles, with 0.9999999c projectiles it might not work so well(just guessing). But even if we talking about shell, if it is something like earth to defend, it worth to spend hundreds times of earth mass, if it is needed, sources of matter are available in our system. – MolbOrg Sep 20 '16 at 5:06
• Easy solution for ship defense, quite the challenge - destroy source of projectiles, cover by moon/planet/star, divide ship in to 1t chunks scatter them, stretch ship and maneuver vital components(peoples), surround ship with chunks creating covered zones(line of sight) and maneuver vital components randomly from zone to zone. Defense only never wins, so destruction of source is primary goal, detecting direction of source is first step, amount of sources. – MolbOrg Sep 20 '16 at 5:07

Drone Ships
You can have some semi-autonomous drone ships that themselves carry the ballistic weapons that are sufficient to damage another ship. This neatly gets around the problem of recoil bumping you out of orbit.

Pump enough of these out and some of them have to get through the other ships defences. You might also like to arm them with some flares to help stop and anti-drone fire.

• I forgot about that, RC drones sound fun though they are not strictly ranged weaponry(what are they even categorized as? Autonomous weaponry?) – Skye Sep 19 '16 at 13:32
• Well, there's a range from the mothership to the drones, and the ballistic range from the drone to the enemy. I guess. – Snow Sep 19 '16 at 13:34
• The problem with drones is you still have to carry the delta-v they use to maneuver in the first place; unless the drone body itself takes an ultra-small amount of mass, this starts to greatly cut into the the amount of ordinance you can bring with you;ten pounds of fuel and ten pounds of drones carrying ten pounds of weapons is inherently less destructive then ten pounds of fuel and twenty pounds of weapons – Marky Sep 19 '16 at 14:46
• This is the question that Worldbuilding has always needed! – Caleb Woodman Sep 19 '16 at 15:22

OK so I have been biding my time and waiting for this question for a long time, so this answer might be long.

The first manner of business is to decide what the target looks like. Solar panels? Living crew? Reserve fuel? Every weapon needs a target, or it cannot be efficient.

With a living crew, the best tactic is multiple hull breaches. In space, bullets fly as fast as they were fired indefinitely. Depleted Uranium slugs are used commonly today for taking down tanks. A well trained gun turret like on modern combat helicopters might do the trick on it's own.

Laser ablation of a hull or primary target area is feasible, but I believe targeting and usefulness would be improved if the entire mechanism was a self-contained drone with it's own nuclear battery, allowing for closer shots, multiple reloads, and flanking.

A railgun is a fun idea, but it needs a spot to hit. That's millions of dollars of aiming equipment to make sure it hits the target, and the magnetic and kinetic backlash on the owner ship would mean a no crew environment.

A nuclear bomb is absolutely overkill, and radiation storms would result on the planet below if one were fired. Instead, an anti-aircraft flak cloud gun would be a safer option. These weapons go a given distance, then detonate into a large burst area of shrapnel, like a fragmentary grenade. A bonus is that the shell can start very small, thus hard to counter.

Another spacefaring weapon is a nano drone strike. Release a few dozen drones, each has a jet, guiding system, fuel, and a single bullet. Only one needs to succeed to make a hull breach, and they can get as tactical as they need.

What about no crew, though? Well, and EMP, or Electro-Magnetic Pulse, can shut down electricity in the entire ship, unless it's fully insulated, and all you need is a battery on a spike, overloading the system and frying the systems. Dead in orbit.

A missile may be a good option, but it needs to be small. I suggest firing it long before the jet system activates, so that it seems like a non-primary target until too late to stop. The kinetic force of even a 5 Kilo bomb (like dynamite) has enough yield to cripple every ship humanity has ever made.

Now, space is usually way too big for a mine, but a fight in orbit may allow a payload of small bombs to be carpet-spread over the predicted area, disguised as trash or dead satellites. They might also be leveraged in a fight involving a chase.

If you want to use a missile with bigger ordnance, just send some cheap decoys with it, and they won't know what to hit. The decoys may have a small payload just in case for maximum grief factor.

In space, anything you can't counter is your demise.

I think the easiest way to create a devastating space weapon with no extraordinary technology is to make the ship itself the projectile. Shape the ship's hull into a cutting arrow point:

and heavily armor the thing with materials capable of withstanding the impact. Just build up velocity and ram the opposing ships. Your fleet of small fighters will tear the opposing armada to shreds without firing a shot. Complementary weaponry could be basic fragmentation anti-vehicular mines dropping behind, as the whole combat strategy hinges on piercing right through enemy lines, and mines could be dropped inside the larger enemy ships. Maybe a gatling-type laser array in the tip, to soften the impact point on armored targets.

Or you could design remotely guided missiles / drones in a similar fashion, and fill them up with high explosives.

• Your crew thanks you when they will hit their heads over the windows of your ship XD – GameDeveloper Sep 20 '16 at 9:09

(Wow, this has attracted a lot of answers.)

I'd recommend something like the combat wasp system in Peter F Hamilton's Night's Dawn trilogy; there's a nice description of the basics right at the start of the Neutronium Alchemist (the first book) and there are good descriptions of battles using this system throughout the trilogy.

Basically it boils down to dogfights-by-proxy. If beam weapons are relatively ineffective at a distance and/or difficult to aim, you need to get close to your opponent and/or use warheads or collision to inflict serious damage. Manned ships are typically large and hence difficult to manoeuvre, and contain squishy components that don't tolerate rapid directional changes and high acceleration particularly well. You also want automatic systems in charge of the individual 'wasps' given the speed at which decisions and manoeuvring need to be made.

So combat gets dominated by small unmanned space-capable vehicles ('combat wasps', in the series) that are as light and hence manoeuverable as possible. Each ship carries a payload of them and they use a range of payloads ('submunitions' in the books, I think) ranging from nothing (damage is purely kinetic), beam weapons, explosives, nuclear warheads and antimatter. Ships carry as many wasps as they can and vary strategies in terms of release rate and payload diversity. There a couple of ship-based countermeasures like chaff for use as a last resort, but basically that's it.

It's a nice system since:

• it works fairly well from a physics point of view (and fairly hard-sf, apart from antimatter);
• it's an easy concept for readers to grasp;
• it's a plausible explanation for dramatic space battles with lots of explosions.

Humans get to make high-level strategic decisions and preprogram tactics.

It's worth remembering that targets at the bottom of a gravity well are generally highly vulnerable to any sort of spaceborne attack simply because of added kinetic energy.

Alternatively, you could go for something like the system in Ken MacLeod's Fall Revolution series (particularly the Cassini Division); assume that beam weapons are difficult to avoid but can't realistically cause physical damage, and fight battles as long-distance infowars that use lasers etc purely for hacking attempts.

Space, in general, is a place lacking most material substances that are abundant on the planet's surface. So, having a space weapon that is not easily rechargeable in open space looks like a very opportunistic idea. Space travel may take ages (even while traveling at the speed of light), and having a gun with no ammo most of this way is really dumb.

So, in most possible cases, spaceship must be able to produce / refill ammo in open space.

The most available type of energy in given circumstances is solar energy, so weapon using that kind of energy (like EMP cannons and lasers) could be reloaded on the way, therefore more realistically used in a place with a tiny percent of matter, but full of light.

Reloading rocket launcher in open space indeed is possible, if a spaceship is really huge (either to hold a significant amount of rockets or able to manufacture it on the fly).

Space shrapnel usage sounds more realistically - its source could be a random asteroid passing by.

Smart drones, cutting enemy's armor in close combat, also seem to solve the problem of recharging, if their dodge percent and return rates are consistently high.

It's worth noting, that more than 2/3 of matter in universe is antimatter (due to current scientific knowledge), so statistically that kind of matter is to be used in open space more widely, than traditional kind of matter.

P.S. Speaking of open space, it seems that proper camouflage combined with a speed burst is the most effective way of combat.

P.P.S. With proper armor and something like energy shield the ship itself can be like bullet.

• Antimatter is not dark matter, which I think you're confusing. – Bobson Sep 19 '16 at 20:32
• more than 2/3 of matter in universe is antimatter - wow, unexpected – MolbOrg Sep 19 '16 at 22:32
• "the ship itself can be like [a] bullet." True - but people who want to survive combat action usually consider it a bad idea to ride inside kinetic munitions. – brichins Sep 20 '16 at 18:43

About railgun, due to the fact you know the railgun characteristics, it's possible to calculate the intensity and direction of recoil. Consequently, you can compensate the recoil with your engine.

Moreover, you can also shield the railgun in order to hide the massive buildup of energy emitted when firing, thus making dodging more difficult.

I think we need to look at mixing two ideas in order to build a viable low-tech weapons system:

First, lets look at missiles. You're wrong about evading them--the missile has the advantage here as it's much cheaper to move a missile than a ship. You'll burn up the target's fuel trying to evade your missiles, eventually evasion isn't going to work. However, a countermissile is going to be a lot smaller than a missile, given roughly comparable ships I would expect the countermissiles to win. (Lets look at the closest equivalent we have: Anti-ship missiles vs SAMs. The anti-ship missiles are a lot bigger and more expensive and the only way to get them through good defenses is to swarm the defenses with more rounds than can be shot down.) Lacking the ability to saturate defenses in some means (note that this depends on tracking range. If missiles can only be detected at short range you might be able to get them through based on a lack of reaction time) they're pretty useless.

Various ballistic projectiles have been suggested but that's going to need some awfully accurate gunnery. If you could aim them adequately they would be very nasty as they're much smaller and lighter than a countermissile, simply keep firing and you'll get through when their magazine runs dry. The accuracy of shooting is a serious issue, though.

Also, nukes have been suggested--there is no blast wave in space, you have to get close enough for a thermal or radiation kill. That's pretty darn close.

Thus I suggest two variations on a theme: Fragmentation rounds.

Version A: This is based on a missile. It does not attempt to hit it's target, though, a miss distance of a km or two is fine. Thus it doesn't need to use it's engine much if at all on approach, it's going to be much harder to find. Put a stealthy coating on it and it's going to be still harder to find. In time I expect the defenders to pick it up and shoot it down--but too late. The thing is it's simply trying to get close. Its warhead fires and a whole bunch of high speed fragments are heading for the target. Since they are fired from nearby the accurate gunnery problem is avoided. Being little fragments they're very hard to shoot down. It also has a salvage-fuse mode, when it detects an incoming interceptor (thermal source with a zero bearing rate and parallax detectable to a pair of cameras) it fires anyway, albeit with a lower chance of a hit.

Version B is a shorter-range version of the same thing, it's fired from a big gun or like system rather than carried on a missile.

The upgraded versions use a nuke to propel the fragments.

Let's look at an idea weapon for space and see how close we can come with the tech we know of now. The perfect space-weapon has to be accurate, devastating and should not have downsides for the party firing it.

Lasers and plasma weapons are out as per the original request. So what does that leave us with? Kinetic weapons and Missiles if we exclude sci-fi tech. Kinetic weapons are (generally) too slow and have the downside of pushing back on the ship, costing heaps of fuel to compensate for ones that are large enough to cause damage. So missiles are the way to go. However, explosive warheads as we know them now aren't terribly effective. There's no air to propagate the shockwave (no matter what star-wars tries to tell you) so we can't really use those.

I'd suggest a missile as delivery device with a kinetic-kill weapon as payload. Build a missile that's capable of adjusting course and getting to within ~5km of the target. That's half of your weapon: thrusters, engines, rudamentary AI for targetting, etc. The second half is stolen directly from the A-10 thunderbolt: GUNS. A spinal-mounted weapon that's essentially better version of the old Metal Storm concept. Barrels pre-loaded with ammo, electronic-firing mechanism or, if possible, rail or coil-based firing mechanism. Once the missile gets close enough, the weapon kicks in and barfs a massive load of bullets in the general direction of the target. Ideally, we can get our projectiles to go at a significant fraction of the speed of light, but a couple thousand km/s is good enough at that distance.
The advantage of a weapon like this is that you don't have to consider recoil in any way. It's fine if firing destroys the weapon platform (missile) as that just creates more shrapnel flying towards the enemy.

Alternatively, mount a single railgun on the spine of the missile and have it fire a chunk of depleted uranium or tungsten when it's close enough. Requires a bit more aiming but it's likely equally spectacular.

Time to go with the Battle Star Galactica answer. Watch their space combat scenes.

First there is a "flack shield". A bunch of projectiles that generate a huge amount of space junk and effectively reduces incoming damage by blowing it up. This "flack shield" basically renders missiles useless.

Then there is the fighter wings. So your flack shield is all explody, so the enemy tries to fly smaller craft "below" the flack shield where they can shoot missiles and make a mess of things. The answer to that, is your own fighters to defend that area. They shoot bullets, and some small missiles, but their target is smaller craft.

Then you need bombers. Let's say you get your small ships under the flak shield, Now you can focus on doing some real damage. But your going to need bigger bombs and heavier missiles.

To be honest, I always thought that they had a good model for space combat. It's "simple" and mirrors common "today" navy warfare, and doesn't rely on a suspension of belief (other then where did they get the material to make so many bullets). Your main big ship is a sitting duck and it's up to the little ships to try and defend it. In fact, this is basically true today.

• It's "flak" by the way. – Caleb Woodman Sep 21 '16 at 19:47

The rockets we use today are simply a way to eject matter out the back of the ship at the quickest possible rate, pushing the ship in the opposite direction. Anything you shoot out of one end has to be matched by something you shoot out the other (I believe mass x speed must be equal from both ends if you don't want to move, but it might be more complex than that--still the concept holds). The faster you shoot and the more matter you shoot, the stronger the push.

So anything you shoot (with a cannon/railgun) at the other ship costs double if you want to hold your orbit.

Whatever you use should either be self motivated (a light drone full of fuel that acts both as thrust and payload, perhaps) or extremely light (bullets/pellets) or slow.

Self motivated drone: The drone can be self-correcting to a degree, but every bit of velocity it gains between you and your target decreases it's maneuverability and increases your target's chance of evading. If it accelerates the entire way to your target and your target dodges, The drone would have to fire the same amount of time just to cancel it's acceleration. Then it would have to start accelerating back to the target (assuming you and the target were originally not moving relative to each other). Basically if you miss you're done.

Slow stealth drone: This would lead me to say that the best bet might be a stealthy and extremely light drone. Fire it slowly towards where the enemy will probably be then it needs to just float dead until it is near your enemy. At that point it should light up, quickly orient itself at the enemy and fire full engines.

This would minimize the time the enemy has to dodge, and since you don't need it to get there quickly you won't have to compensate much (assuming your ship launches it) or at all, but the enemy detecting your drone would completely nullify/waste the attack, all it would have to do is not be where the drone expects it to be when the drone gets there)

A spread of bearings would be better if detection is possible--but that requires closer range--the further you are away the bigger the spread would have to be to guarantee a hit (and the more bearings, the number of bearings is probably geometrically related to the distance and linearly related to the targets thrust capability, but my physics is way to out of date to do more than guess about that).

Neutron Canon

Fast moving neutrons are easy enough to create, can be accelerated to high speeds, and in sufficient density, will be able to degrade ships and cause damage. Gamma Rays might be good to. Since both are uncharged, EM force fields will be ineffective against them.

• reference to neutrons acceleration could improve this answer – MolbOrg Sep 22 '16 at 0:19

RPG (with modifications: is the most effective weapon). Of course a regular RPG has no maneuver capabilities, instead I would use attack drones each one capable of deploying short-range RPG missiles so that missiles themselves do not need maneuver capabilities.

The rational for it is: carrying stuff on space is expensive, so the ammunition has to weight as few as possible: If the bullet itself includes just few fuel and the explosive without stuff for being able to turn in space (additional thrusters) it will have the minimum possible weight.

The metal concave part of the RPG would be some metal like Gallium that melts at low temperature and is able to weaken enemy ship's hull. The use of drones allows to place shots BEHIND enemy ships, effectively helping to avoid receive hits by fragments of explosion. Also drones could be sacrificed to shield 1 hit.

The ship could also be equipped with magnetic bombs that grip on enemy ship and wait the ship is turned at a proper angle before detonation.

A effective strategy would become to "board" enemy ship, that way both ships have to stop using explosives and start to use alternative strategies (using explosives too nearby is dangerous in space.)

NOTE: RPGs works by detonating small quantity of explosives in order to project a quantity of molten metal into a "ball" that pierce most armored surfaces. The shape of the metal is concave, the explosion just melt it and project it to the focal point of the concave shape.

Gallium is a real threat to aircrafts and metal structures, few drops of gallium can weaken a wide spot of surface that then would just break under internal pressure of the ship.

• While Gallium would likely react with the hull of an enemy vessel, the reaction is not particularly fast, and (given the probably thickness of the hull) very possibly wouldn't penetrate enough to cause the instant (or at least rapid) catastrophic damage needed during a firefight. See this Chemistry.SO answer about gallium's reactivity (especially the links in the comments). Melting a hole through their hull over a couple hours or days would be a great way to avenge your own death though. – brichins Sep 20 '16 at 18:58
• ONce you got it by gallium you have to surrender (if you destroy enemy ship, your ship is anyway going to break in few hours), also I think very hot Gallium react much faster (maybe still requires minutes, but not hours). So well placed shot is anyway a heavy damage. – GameDeveloper Sep 21 '16 at 16:19
• It's hard to keep anything warm in the vacuum of space - even an insulated molten gallium round has to rupture to do anything. Agreed that it would cause major damage, though likely just to a (sealable) section of the ship. I don't think the reaction is fast enough to affect the outcome of a shootout; though over a long fight it'd be a great way to weaken the hull for your next wave. But unless you find a gallium asteroid field to mine, it's just not cost effective. Why bother refining gallium when there are so many cheaper options with a quicker result? For cloak-and-dagger sabotage though... – brichins Sep 21 '16 at 20:46

protected by Serban TanasaSep 19 '16 at 21:37

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