# Physically plausible explanation for missile based space combat?

#### GTOM

If a FEL has a 60% efficiency, and the reflective armor (aluminium golden ceramite whatever layers) have 80% efficiency, its an overall 12% efficiency.
If a nuclear thermo thruster has a 80% efficiency, and a mass ratio of 3, then it has an overall efficiency 26%, that twice the laser efficiency...

If the reflectivity can hold on till the attack drone covers the laser range i dont think its more than few hundred or thousand kilometers.

#### GTOM

While it is classified stuff, so one can only guess, but on other threads, they wrote, this didnt bring too good results, they couldnt achieve too much directivity... a nuclear explosion destroy any material that could shape the explosion, x-rays and gamma rays cant be reflected easily, they wont be coherent to focus them with lenses neither. Also big focusing stuff can be damaged from a bigger distance.
So while this sounds good theoretically, but WWII German mega cannons also sounded good theoretically.

(IMHO if those tests were so successful they would have announced, we have this, so you really shouldnt mess with us.)

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#### Khashishi

If missiles are maneuverable enough, they couldn't be shot down until they are close enough to the target that the blast wave or shrapnel would cause damage anyways. Space missiles will move very fast, so the explosion will continue to move in the direction the missile was traveling and could still destroy the target.

If the missile steers around semi-randomly, then there's no way for a laser to know where to aim.

#### GTOM

If the missile steers around semi-randomly, then there's no way for a laser to know where to aim.
But the laser arrives almost instantly, well focusing the beam to a single location is more troublesome, the first countermeasure against it is spinning.

#### novaprime

Fire them electromagnetically with a rail gun style system. The missile wouldn't be hot, no friction or exploding gases to eat them. The missile passively scans for the target emitting nothing trackable. When the missile decides it's close enough to the target it activates its own stored fuel and accelerates to a much higher velocity for a short burn. Think it it as throwing a bullet before it self ignites. If it misses it just stays dark.

The idea that it's silent and undetectable till it's too close to dodge. After all if the missile isn't seen to can't be targeted by lasers. If you want the missile could start using whatever radar equivalent you want on final approach. And since you said most your fights are going to be in the asteroid belt, there's plenty of junk to clutter up attempt to find the missiles.

-Oh and railguns are real, the military already has several experimental models that work. They're just not practical at the moment.

#### GTOM

Fire them electromagnetically with a rail gun style system. The missile wouldn't be hot, no friction or exploding gases to eat them. The missile passively scans for the target emitting nothing trackable. When the missile decides it's close enough to the target it activates its own stored fuel and accelerates to a much higher velocity for a short burn. Think it it as throwing a bullet before it self ignites. If it misses it just stays dark.

The idea that it's silent and undetectable till it's too close to dodge. After all if the missile isn't seen to can't be targeted by lasers. If you want the missile could start using whatever radar equivalent you want on final approach. And since you said most your fights are going to be in the asteroid belt, there's plenty of junk to clutter up attempt to find the missiles.

-Oh and railguns are real, the military already has several experimental models that work. They're just not practical at the moment.
But wont the electromagnetic flux heat up the projectile, or the gun itself, that heats the missile?
(Otherwise i think, they will use active radars as well against cold projectiles.)

#### Ryan_m_b

Staff Emeritus
Presumably the action of a rail gun firing would be noticeable and the missile would be hot as it leaves the tube (might not be any air resistance but the magnetic force is going to add heat). Given that it seems like it would be trivial to have your tactical awareness software plot the speed and course of the missile. Even if it cooled to the background temperature of space and was perfectly radar invisible your computer would know where it is. If you've got laser weaponry accurate to within thousands of kilometres you could destroy it long before it became an issue.

#### newjerseyrunner

If I were living in the not too distant future, where missions to mars / moon / asteroid belt are common, but no starships yet, I'd build my weapons entirely in space, maybe a single launch to send up some advanced computers that can't be produced on site. It would also be very simple in design, if I had automated drones producing them, I'd want them pumped out quickly, that way if half of them get destroyed on their way to the target, many still hit and they'll be so destructive, I'd win anyway.

Think about NORAD. Right now, it's impenetrable. It was designed so that the Soviet Union could pummel it with nuclear weapons and it would stay standing. The energy of the bomb is reflected off of the mountain. It's literally in the heart of a mountain, no nuke or antimatter bomb could affect it.

A million tons of steel hitting the mountain a hundred thousand miles an hour is a different story. My war machine would orbit the earth very high, maybe even orbit the moon. The guidance system, controls... everything would be deep inside millions of pounds of iron that's been harvested from asteroids. Containing a powerful, liquid hydrogen and oxygen rocket, using water also gathered from space. Your lasers wouldn't be able to cut through that, even the atmosphere couldn't destroy it. It's so heavy that by the time it's detected and can be shot at, even the most powerful weapons would only shove it a little off course, and it's shell would protect the guidance system, allowing it to correct pretty much up until it enters the atmosphere and can't navigate anymore. Once it's hit the atmosphere, it'll obliterate anything it hits.

KE = mv^2, double the speed, quadruple the yield.

#### Ryan_m_b

Staff Emeritus
In most space warfare fiction the combatants are quite distant. If that's the case then conventional weapons seem rather useless. Unguided kinetic weapons can be easily tracked and dodged, guided weapons shot when they're in range, beam weapons might not be able to be tracked but minor random course changes would make it extremely unlikely to be hit at range.

The issue then is that combatants would have to get close to fight. Let's say they have beamed weapons: the closer they are the more real time their information is and the likelier your laser will hit the target. But that works both ways, getting closer means your enemy is more likely to hit you.

Enter the combat drone. It's basically a laser weapon with guidance systems. You launch a bunch of these towards your enemy (could launch them quite fast then have them use their propulsion as needed) and along the way they make minor course changes to avoid fire from the defender. The closer they are the more often they figher at the target. You might loose a few but with enough you should hit your target without exposing your own ship.

Of course the best defence against this would be to launch your own drones back. Battles in this case would comprise of ships staying well outside each other's effective weapon range sending waves of drones at each other. Where those drones clash you hope your weapons and software is good enough to ensure you've still got a large enough force heading towards the target.

A notable limitation is that space is vast. If your fictional technology verges on the hard science those drones aren't going to be carrying enough fuel to go long distances fast (more fuel might help but increases weight so slows acceleration). So there's a window of engagement where it makes sense to launch drones, closer than that you open yourself up to fire and further away your drones will take to long to get there and the enemy could just run away.

#### GTOM

You wouldn't care about coherence, intensity and data transmission rate limit the range.

Neglecting small prefactors, the angular spread of a laser beam is at least (wavelength)/(telescope radius). At a distance of d, the laser beam has a width of d times the angle, so the fraction of light hitting the receiver is $$\left(\frac{(receiver~radius) \cdot (telescope~radius)}{distance \cdot wavelength}\right)^2$$
I have tryed to do the math.
Had the following results so far :
so assume 10 MW reactor for 100 ton ship (yeah i know not diamond hard... that applies to the rest as well, but i want to have it something common with reality)
25 km/s exhaust velocity. (e^2 mass ratio for 25km/s for rocket with deceleration)

Calculate with base mass for simplicity : 0,032 kg / s mass ejected from rocket.
800 pushing power 0,008 m/s2 acceleration.

Reach full speed during 40 mil km (so constant speed up and down till Mars when it is closest to Earth) during a month, so two-three month from Earth to Mars.

Laser power only MJ/sec.
10m focusing mirror (while a 100m mirror sounds good, but keep it cool after multiple shots...)

At a 1000 km able to focus at 3cm with 300nm UV-B laser.

10% efficiency versus (SF) titan-mirrorium armor.

Around 2000 C for melting titan armor.
1MJ/10/2000 mol titan, 100g.

So a 3cm spot 3cm thick, it is more than 100g

So to kill the striker craft with a single shot distance smaller than 1000km needed.

30km closing speed for fighter (25+5 save 5 for return in case of intercepting a not so well defended convoy)
during that, laser could burn 3kg titan, and even if striker craft shatters, shrapnels still quite dangerous.

(Assumed 1 arcmin spread. With 30m rocket cross-section, 1/100 of mass would hit, and it is enough...)

If mothership would like to support landed troops with laser, with atmospheric swallow, and 100m mirror, and much bigger output... I think it still needs to be closer than 100.000 km to efficiently attack armored targets, so get into a range, where it can be attacked even from surface launched missiles.

#### Artribution

Thermonuclear missiles, when detonated, flood local space with such extreme levels of heat, light, EM waves and particle radiation that sensors are effectively jammed, rendering an enemy blind and helpless. A swarm detonation of such weapons around an enemy formation can maintain the sensor-blinding effect continuously, putting even a large fleet out of action. Humans have a term for the sensor-jamming effect: nuclear blackout.

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#### GTOM

Thermonuclear missiles, when detonated, flood local space with such extreme levels of heat, light, EM waves and particle radiation that sensors are effectively jammed, rendering an enemy blind and helpless. A swarm detonation of such weapons around an enemy formation can maintain the sensor-blinding effect continuously, putting even a large fleet out of action. Humans have a term for the sensor-jamming effect: nuclear blackout.
I still dont like the idea that every goon would throw nukes in space. I think a good kW laser jammer could do the sensor black out thing, or at least reduce targeting accuracy.

According to it, skirt jamming (jam with not exactly same frequency) could require 60dB jamming/signal or more. That is a million times more than the signal.
So at a distance of 10.000km if reflected or emitted signals are scattered well (inverse squre law) it could be able to do the trick. If lots of probes emitted, use the lidars shaded from enemy jammers to find them.

Probably striker craft should be UFO shaped? (spin, and a sharp edge at the middle, to scatter the beams more)

#### Artribution

Well, in this scenario, I don't have any idea how the enemy's scanning devices work. But a nuclear blast (or many nuclear blasts) is generally good because the intensity and wide range of emissions interferes with almost everything, from masking a spacecraft's heat signature to interfering with radar waves and magnetics. On top of that, it destroys unshielded electronics. And blackout is a known effect in nuclear strategy, so it's good if you want something non-speculative.

Another thing worth mentioning is that nuclear warheads can be improved by sheathing them in different materials that add to their effects. For example, they could be made to scatter radar-absorbing particles over a wide radius for improved jamming efficiency, and such particles could linger for some time.

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#### Ryan_m_b

Staff Emeritus
If you're close enough to deploy nukes and shine jamming lasers on their sensors you're close enough to kill them, or be killed by them. It's difficult to have these sorts of discussions without a setting to discuss it in, complete with available technology.

#### GTOM

If you're close enough to deploy nukes and shine jamming lasers on their sensors you're close enough to kill them, or be killed by them. It's difficult to have these sorts of discussions without a setting to discuss it in, complete with available technology.
I think i gave much info with my calculations, but i gladly give more, what would you like to know?
At this point, while i dont know too much about sensors or astronomy, i dont clearly see why the jamming range has to be so close to kill range, they dont have to exactly focus on the sensors.
With a distance of thousands of kms, and inverse square to the signals, i would think it is like blind someone with a reflector, who has a night-vision google. Burn the skin require much bigger power.

#### Artribution

If you're close enough to deploy nukes and shine jamming lasers on their sensors you're close enough to kill them, or be killed by them. It's difficult to have these sorts of discussions without a setting to discuss it in, complete with available technology.
Nukes (call them fusion disintegrators if you want to be all sci-fi) can be launched from as far away as another planet. The final stage could be very small and very hard to track without an engine burning, and the stage before that could actually serve as a useful decoy. I agree we can't really come to a decision without some understanding of the technologies available, but we can speculate about physically plausible explanations.

#### GTOM

The final stage could be very small and very hard to track without an engine burning, and the stage before that could actually serve as a useful decoy. I agree we can't really come to a decision without some understanding of the technologies available, but we can speculate about physically plausible explanations.
Interesting idea, that stage as a decoy, yes launch range is near unlimited vs stationary target.

So, summarize things.

Basic setup : prolonged war for the asteroid mines, with multiple parties, (privateers included) I would say at at least hundred years have passed since they started to colonize other celestials.

Technology available : everything that exists now + fusion rockets (i gave details about them in calculations post) i think it would be illogical not to have at least a MJ output laser with so much power on board, some new alloys (the titan-mirrorium armor i talked about) hibernation (manned spacecraft not much more expensive than unmanned, general distrust in decision making AIs due to one party's cutting edge in robotics, hacking) drone fighters, neural interfaces (human factor still worth mentioning in drone operating) advanced high-thrust low specific impulse drives for striker craft (I can think about nuclear-thermo)

Most likely war situations are attacking cargo convoys (with frigates and privateers) and overtake mines (that is cover based combat)
I think even cargo ships should have lidars against a meteor (even if a hit is an unlikely event) and shielded electronics vs cosmic rays.
Restrictions : orbital bombardment of settlements is war crime (while Earth's gov is pretty corrupt, they wont overlook that one - that would mean even politicans couldnt be safe) I barely see any reason why would employing nukes were a different category.

#### Artribution

I don't see why using nukes in space would necessarily be considered a war crime. We're talking about combat between military spacecraft. Would anyone care if they blew each other up with nuclear missiles instead of photon torpedoes? It's the same result either way: a big flash of light ensues, and the offending spacecraft disappears.

Also, thermonuclear devices have all kinds of applications for asteroid mining.

And your story reminds me of a highly underrated classic.

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#### GTOM

I don't see why using nukes in space would necessarily be considered a war crime. We're talking about combat between military spacecraft. Why would anyone care if they blew each other up with nuclear missiles instead of photon torpedoes? It's the same result either way: a big flash of light ensues, and the offending spacecraft disappears.

Also, thermonuclear devices have all kinds of applications for asteroid mining.

And your story reminds me of a highly underrated classic.
Thanks for the link, sounds interesting. :) (Although now i dont really have time for gaming.)
Use nuclear bombs for mining? Isnt it a problem, that the sorroundings will be contaminated by really nasty isotopes? Otherwise in my setting in majority of cases mining corps war against eash other too (i would describe it space feudalism)

Still, lets have a megaton explosion at the distance of 10.000 km. So energy released is on the order of 10^15 J. Apply inverse square law, 10^7m, 10^14 on square, so energy density on ship will be around 10J/m2.
If a 20 KJ jamming laser focus on whole ship with 30m diameter density will be around 30J/m2. And it can be operated in continous mode. (The point would be turn off everything but the crudest sensors not much more sensitive than human eye, to cause targeting problems).

Even if the nuke is total black, and even have liquid helium vs IR detection, if the enemy has any guess about attack direction, they can send some small probes forward, and detect the shadow of the nuke.

#### Artribution

But:
1. A laser will only jam a target's light and heat sensors. Sensors that work on other principles would be unaffected.
2. If the jammed target is part of a larger formation (a fleet of manned spacecraft or just one spacecraft with a surrounding network of drones) the jamming laser and its source will be visible to them.
3. If the jammed target is in contact with the other nearby spacecraft (or drones) as part of a tactical computer network, it's possible even the 'jammed' spacecraft could ignore the jamming by using another spacecraft's sensors.
4. A laser would have more limited range than a swarm of missiles and (unlike a missile) firing a laser requires getting close enough to expose your own spacecraft to risk.
5. A missile can evade, unlike a laser.
6. A missile can go around asteroids and dwarf planets, unlike a laser.
7. A missile swarm can shut down their engines and act as an orbiting minefield.
8. Missiles have a continuous mode, too—we call it launch all the missiles.
9. Near-future technologies might very well allow a small missile to be practically invisible (active camouflage) and transparent to radar/EM/laser detection (plasma stealth). Those are both areas of active research.
10. If jamming lasers are so much better, is there any reason a missile can't carry a short-range laser of its own, along with other ECM?

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#### Ryan_m_b

Staff Emeritus
A missile cannot evade a laser point defence at close range. It can randomly change course and junk but the closer it gets the smaller the envelop of possible locations it could be in, thus more chance that a laser shot into that envelop will hit it. At 10,000km a laser burst only takes 30 milliseconds to cross the distance.

As for stealth space is huge so hiding round planets or moons will rarely be available. Not to mention the enemy will see you coming on the way out. And there is no stealth in space. You might be able to hide yourself to visual and radar but you can't hide your heat signature. Even running cold won't help. If you fire a missile it will be hot as it leaves, the enemy could see it and their computer automatically plot it's course. If it did turn off its engine and cool down its last known position and speed will make it easy to shoot down.

Regarding jamming if you need to precisely hit their sensors then they can evade you by dodging, random course corrections and rolls. That means you have to food an area which just energetically doesn't make much sense on the scales involved in space. If you're close enough that the light takes fractions of a second to find its target you're close enough for them to just shoot you.

#### GTOM

But:
1. A laser will only jam a target's light and heat sensors. Sensors that work on other principles would be unaffected.
2. If the jammed target is part of a larger formation (a fleet of manned spacecraft or just one spacecraft with a surrounding network of drones) the jamming laser and its source will be visible to them.
3. If the jammed target is in contact with the other nearby spacecraft (or drones) as part of a tactical computer network, it's possible even the 'jammed' spacecraft could ignore the jamming by using another spacecraft's sensors.
4. A laser would have more limited range than a swarm of missiles and (unlike a missile) firing a laser requires getting close enough to expose your own spacecraft to risk.
5. A missile can evade, unlike a laser.
6. A missile can go around asteroids and dwarf planets, unlike a laser.
7. A missile swarm can shut down their engines and act as an orbiting minefield.
8. Missiles have a continuous mode, too—we call it launch all the missiles.
9. Near-future technologies might very well allow a small missile to be practically invisible (active camouflage) and transparent to radar/EM/laser detection (plasma stealth). Those are both areas of active research.
10. If jamming lasers are so much better, is there any reason a missile can't carry a short-range laser of its own, along with other ECM?
2-3 yes to give enough energy to all observers in the area, sure dont make it easier. :(
4. Well, i have no problem with the expose your own spacecraft thing, but it is more fun to read about missiles burst, closing in etc.
5. ?? Why should a beam evade? (FTL senses is outside the limit of human science for my setting)
6. Yes an important part in asteroid mine capturing (well, the limit between a really smart missile and a drone fighter is blurred)
7. That minefield part vs cargo ships sound interesting.
8. They should definitally try to overwhelm defences in squadrons or swarms.
10. No such reason, although the entire launcher ship can have much more power output.

If you're close enough that the light takes fractions of a second to find its target you're close enough for them to just shoot you.
I calculated earlier that 10m focusing mirror, 1000km distance, UV-B laser, MJ output still not enough for instant kill if i apply the (more or less futuristic) heat resistant broadband mirror armor.

#### Artribution

A missile cannot evade a laser point defence at close range. It can randomly change course and junk but the closer it gets the smaller the envelop of possible locations it could be in, thus more chance that a laser shot into that envelop will hit it. At 10,000km a laser burst only takes 30 milliseconds to cross the distance.
If the laser beam is meters in radius and the missile is traveling at hundreds of relative meters/second, it could be very hard to hit. And a hit might not be enough—it might need some sustained contact to burn through. And if it's not just one missile but a salvo of missiles, you might be in trouble.

Also, once the first salvo detonates (even if still quite far from the target), the light/heat/EM/particle interference generated will make salvo 2 that much harder to hit.

As for stealth space is huge so hiding round planets or moons will rarely be available.
It seems that this story takes place in the asteroid belt. What I meant by "go around asteroids" was that if you're orbiting Ceres and you want to destroy something orbiting on the far side, you can't fire a laser because it won't have enough range and it can't go around the planetoid, but a missile can. And, depending on the orbit, the engine burn required to line up an orbital intercept can be done while the target is still on the far side and unable to detect your heat signature. You can just coast from there. (At least this works in Kerbal.)

And there is no stealth in space. You might be able to hide yourself to visual and radar but you can't hide your heat signature. Even running cold won't help. If you fire a missile it will be hot as it leaves, the enemy could see it and their computer automatically plot it's course.
If they have line of sight, yes, but they might not. Or they might be very far away, potentially orbiting another planetoid. Missile range is quite far.

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Why should a beam evade? (FTL senses is outside the limit of human science for my setting)
I mean the laser weapon itself can't evade very well, because it has a giant beam of light coming out of it.

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"Physically plausible explanation for missile based space combat?"

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