Physically plausible explanation for missile based space combat?

[GTOM]

I think that burst behind celestial part could work in orbital combat. To build up enough speed to intercept fusion ship on route, a huge way is required to boost.
If the missile is coming directly for ship, that makes hit not so hard, but to focus on a small area, that requires exact distance too.
The laser beam can't detected directly in space if your sensors arent hit by it, although the lascannon will still produce quite a heat sign.
However, from 100.000km with parameters i calculated, it takes quite a time to drill through armor.

 

[Ryan_m_b]

A beamed weapon doesn't have to instantly kill, it just has to be shone on the target enough to heat damage the reflective armour and destroy it once this is done. Space is big and it takes a long time to physically move through it, even at 10Gs constant thrust it takes 41 minute to cross a light second. Within that range you can pretty easily aim a laser and be sure of it hitting. Even if it takes a solid ten minutes of shining a laser (with corrections as the missile moves and attempts to dodge) you're safe. Plus sustaining high acceleration for a long time is going to take a lot of fuel and a powerful engine. At that point your missiles become small nuclear spaceships.

It's worth noting as well that there are other forms of beam weapon that couldn't be so easily reflected, for example: particle beams, FELs and X-Ray lasers. In regards to the idea of swarming missiles sure: if you can deploy in such numerical strength then you'll win. But working with the assumptions I mentioned in the previous paragraph an attacker would need to launch 5 missiles at the defender to be sure of a win, and that's if they have only one point defence laser. If they have 10 you need to launch 41.

Edit: It would probably be useful to try and design a missile using technology appropriate for your setting. Work out the ISP and mass flow so you can figure out how much fuel its going to need to accelerate constantly and how much energy that will take. I may have a go later if I have more time than I do this evening, off the top of my head though I'd put money on any "missile" capable of doing this as becoming very large. At that point why not mount a beam weapon to it and make it a drone?

 

[GTOM]

A beamed weapon doesn't have to instantly kill, it just has to be shone on the target enough to heat damage the reflective armour and destroy it once this is done. Space is big and it takes a long time to physically move through it, even at 10Gs constant thrust it takes 41 minute to cross a light second. Within that range you can pretty easily aim a laser and be sure of it hitting. Even if it takes a solid ten minutes of shining a laser (with corrections as the missile moves and attempts to dodge) you're safe. Plus sustaining high acceleration for a long time is going to take a lot of fuel and a powerful engine. At that point your missiles become small nuclear spaceships.

It's worth noting as well that there are other forms of beam weapon that couldn't be so easily reflected, particle beams for instance. In regards to the idea of swarming missiles sure: if you can deploy in such numerical strength then you'll win. But working with the assumptions I mentioned in the previous paragraph an attacker would need to launch 5 missiles at the defender to be sure of a win, and that's if they have only one point defence laser. If they have 10 you need to launch 41.

As far as i know, particle beams scatter more than lasers (at this point i plan to introduce plasma point range defence as a breakthrough in the later half of story, but will be countered by magnetic field warheads that scatter the beam)
With the 30km/s closing speed i assumed, it is near three hours... More than a ton of titan with my previous calculations...

Hmm, although attack warship can have a ton of armor, it only have to mask the heat and light signs of attack missiles/drones by provide enough background clutter.

 

[Ryan_m_b]

Particle beams can be neutral, magnets won't affect them and they won't be repulsive so scatter won't be much of an issue (certainly not in vacuum). The U.S. Navy has a project for FEL point defence on their ships IRL. So if you're willing to speculate that there's no show stoppers were not aware of it would seem they are plausible as a long range space weapon.

As for hiding the ships I'm not convinced. You'd have to put out a fantastic amount of energy in order to "over expose" all their sensors. Bear in mind we have technology that allows cameras to filter out the light of the sun, unless you have more than that focused on the enemy ship they're going to see you.

30kmps is very slow. It would be within the effective range of a beam weapon for quite a lot of time.

 

[GTOM]

Particle beams can be neutral, magnets won't affect them and they won't be repulsive so scatter won't be much of an issue (certainly not in vacuum). The U.S. Navy has a project for FEL point defence on their ships IRL. So if you're willing to speculate that there's no show stoppers were not aware of it would seem they are plausible as a long range space weapon.

As for hiding the ships I'm not convinced. You'd have to put out a fantastic amount of energy in order to "over expose" all their sensors. Bear in mind we have technology that allows cameras to filter out the light of the sun, unless you have more than that focused on the enemy ship they're going to see you.

30kmps is very slow. It would be within the effective range of a beam weapon for quite a lot of time.

Neutral particle beams? I thought they need to be charged in order to accelerate them, two opposite charged beams can be used, but it will be still a plasma weapon. Is there some new development?

I thought at first 100 km/s but i would need at least a GW reactor, then explain why lasers could only produce a MJ / sec?

That fantastic amount of energy wouldn't be still much less than do serious damage to armor? Well, that sun filter camera is surely interesting, any link about it, how much decibel of light intensity it can handle?

Well i found that Sun is magnitude -27 6.31×10^10 compared to magnitude 0.
With 10.000km and some kW-s of light and thermal radiation, that scatter everywhere (10^14 distance squared), and few kWs laser hits all the ship it would be 10^14 more laser power than signal power.

 

[Ryan_m_b]

Read the link I posted above about modern research in particle beams. I don't understand the technology exactly but it seems like it's possible now to create a beam emitter that charges the atoms, accelerates them, then adds/subtracts an electron just as they leave creating a very fast stream of neutral particles.

As for a sun filter if you google it I'm sure you'll find plenty of examples. Its a pretty common piece of kit for photographers wanting to take pictures of solar eclipses and the like. God knows what the best possible filter could do in the world, or what could be developed by a military if needed.

Jamming sensors suffered from the same problem as beam weapons: the further away you are the more powerful a laser you need to guarantee a hit (by spreading the beam over a wider area). That quickly becomes impractical. If you're close enough that you can flood their sensors and keep doing so as they dodge and roll you're close enough to hit them with something more powerful, and be hit by the same.

 

[GTOM]

Read the link I posted above about modern research in particle beams. I don't understand the technology exactly but it seems like it's possible now to create a beam emitter that charges the atoms, accelerates them, then adds/subtracts an electron just as they leave creating a very fast stream of neutral particles.

As for a sun filter if you google it I'm sure you'll find plenty of examples. Its a pretty common piece of kit for photographers wanting to take pictures of solar eclipses and the like. God knows what the best possible filter could do in the world, or what could be developed by a military if needed.

Jamming sensors suffered from the same problem as beam weapons: the further away you are the more powerful a laser you need to guarantee a hit (by spreading the beam over a wider area). That quickly becomes impractical. If you're close enough that you can flood their sensors and keep doing so as they dodge and roll you're close enough to hit them with something more powerful, and be hit by the same.

ok, i see you edited last post, i read it.
Otherwise the good thing about particle beams, that the fusion ships rocket is also kind of particle accelerator, so technology might be bit similar...
Still, without big focusing mirrors i can hardly imagine them to be focused as much as lasers. According to link, that applies to present day xaser as well.

http://www.mreclipse.com/SEphoto/SEphoto.html
These filters typically attenuate the Sun’s visible and infrared energy by a factor of 100,000.

 

[Ryan_m_b]

I'd be inclined to think that isn't an insurmountable problem. Particle accelerators crash streams of particles together at a whisker under the speed of light and the military seems to think that hitting an object miles away shouldn't be much of a problem. If you're setting has nuclear fusion propulsion spacecraft it doesn't seem unlikely that a technique for focusing particle beams over a light second would be in use.

 

[Artribution]

It's worth noting as well that there are other forms of beam weapon that couldn't be so easily reflected, for example: particle beams, FELs and X-Ray lasers. In regards to the idea of swarming missiles sure: if you can deploy in such numerical strength then you'll win. But working with the assumptions I mentioned in the previous paragraph an attacker would need to launch 5 missiles at the defender to be sure of a win, and that's if they have only one point defence laser. If they have 10 you need to launch 41.

Considering we already have MIRV missiles that separate into 14 independently targeted re-entry vehicles each, is that really an obstacle? Just launch 10 of those and you've got a 140-missile Itano circus.

A beamed weapon doesn't have to instantly kill, it just has to be shone on the target enough to heat damage the reflective armour and destroy it once this is done. Space is big and it takes a long time to physically move through it, even at 10Gs constant thrust it takes 41 minute to cross a light second. Within that range you can pretty easily aim a laser and be sure of it hitting. Even if it takes a solid ten minutes of shining a laser (with corrections as the missile moves and attempts to dodge) you're safe. Plus sustaining high acceleration for a long time is going to take a lot of fuel and a powerful engine. At that point your missiles become small nuclear spaceships.

How do you know you can even detect them? They could (reasonably enough with near-future tech) be practically invisible to radar and visible light and if their orbit is aligned to intersect with yours, they don't even need to burn their engines.

 

[Ryan_m_b]

Again it depends on your missile. If you can carry enough to overwhelm an enemy then fine, but if you're of equal resources then you don't have that option. In terms of being detected anything hotter than the background of space can be detected with IR sensors, the hotter the easier. With an interferometer array you could be continually scanning your system and identity all objects of this sort. After its launched it doesn't matter if it goes cold and relies on radar/invisible stealth because it would be child's play for a computer to extrapolate current position based in previous speed and heading.

Even pointing your exhaust away doesn't help. The heat from the reaction (especially if you require a powerplant for the engine) will be enough to make your ship hundreds of degrees hotter than the background.

 

[Artribution]

An Ohio-class submarine has 24 ICBM tubes, each of which can launch a Trident missile that splits into 12 separate, independently targeted missiles, for a total of 288 missiles in one barrage. If it were launching old Peacekeeper missiles from the 1960s, there would be 336 missiles per barrage. Just seems like a point-defense laser might have some trouble coping is all.

And those are ICBMs. If we were just talking about tactical nuclear warheads, it could be an entire new definition of spam.

Yeah, it's expensive, all those missiles, but victory is the only thing that counts. If you don't win, your entire spacecraft is a waste of money.

And if you launch from the other side of the planetoid (I'm guessing most space combat happens in orbit), the enemy wouldn't have any chance of detecting their engine heat. After the initial burn, they could just coast the rest of the way to intercept.

 

[GTOM]

In case of convoy attack, fight happens in deep space. Otherwise, most likely they fight around an asteroid.

 

[Ryan_m_b]

Gain it depends on how good your point defence is. If you can deliver multi-mega joule particle beam shots then it's a question how how rapid is your rate of fire (for orbital distances the chance of missing is likely to be nil). As a quick exercise:

Let's say missiles and target have a closing speed of 50kmps and they're detected 1000km out. That's 20 seconds before being hit. If there are 500 missiles incoming then the rate of fire to guarantee safety is 25 shots per second. Now it comes down to how many beam emitters you have and how rapidly they can fire. If you have many...it starts seeming reasonable within the confines of the setting.

As for where battles occur I don't see why it would be primarily in orbit. If you're attacking a planet then you have to travel from somewhere else. Given that's the case battle would likely start once the chances of hitting someone with a long range weapon within a reasonable time converge. I expect the shooting would start at distances of light seconds, if you had beam technology good enough. Even if not the attacker in this scenario would be better off firing a whole bunch of beam drones ahead of them to engage the enemy.

In an effort to jump ahead (we seem to be circling a bit) I'd like to pose this question: why would a barrage of missiles be better than a barrage of beam-drones? The latter seem the obvious choice to me (assuming equivalently effective tech) because as the two barrages close the drones begin to fire, picking off the missiles. For a missile to kill a drone it has to be very close, likely much closer than the effective range of a beam weapon.

 

[GTOM]

My problem with beam drones, that they don't have the power source and waste heat treatment of the ship.
(Although the ship could give them power with lasers.)
If one attacks an asteroid, he will come with superior firepower, cover in this situation could help the defenders.
I rather care about total power output than number of lasers.
In case of particle waepons also appropriate, i wonder, what if the defender had a really strong magnetic field, to bring back the metallic particles and reattach it to the hull?

 

[Ryan_m_b]

Likely a drone would have to be fairly large to carry a power source and radiators. Still even if they were 10 tonnes a squadron of 10 would mass just 20% of the ISS. The advantage to beam drones is that they could fire at distance whilst approaching the enemy allowing you to keep your craft further away. Missiles might be good if you fire enough at close distance but if you have to fire from long range they'll be picked off.

I don't know what you mean by a magnetic field to draw in metal. If the attacked was shooting metal at you then maybe (but it would have to be insanely powerful to deflect anything) but that won't help against a neutral beam of non metal particles.

In your setting I presume the asteroids are habitats? If so a beamed weapon would be quite appropriate. You could fit quite a large reactor and radiators on an asteroid. Having a continual gigawatt weapon would seem possible in that situation.

 

[Artribution]

I'd like to pose this question: why would a barrage of missiles be better than a barrage of beam-drones? The latter seem the obvious choice to me (assuming equivalently effective tech) because as the two barrages close the drones begin to fire, picking off the missiles. For a missile to kill a drone it has to be very close, likely much closer than the effective range of a beam weapon.

Beam drones seem a bit more high-tech. They need more power, more accurate targeting, more efficient propulsion/fuel (missiles aren't supposed to return when their assignment is completed), etc.

Against a larger spacecraft , they could partly make up for the lower energy of their individual beams by focus-firing, though.

And your prediction rests on the assumption that the missiles' stealth and ECM is ineffective.

 

[GTOM]

I thought about use the magnetic field to reattach the metallic particles torn from the armor by the beam. Or make them super hard to evaporate.
(So a kind of energy shield...)

Yes it is a problem, that planetary defence has quite an amount of resources, it is hard to overwhelm.

I also give a fairly low chance to that stealth thing, if they really try to discover them with both active and sensitive IR sensors (and they can really detect very small intensity of IR radiation), i focus on other solutions.

I think on the equip the fighters with lasers thing, after all, they don't need all the power output of ship, just produce a big pulse to produce a beam capable to damage sensors, focusing equipment etc.

 

[Ryan_m_b]

Stealth just doesn't work in space, for reasons discussed (you can find long essays/articles on this online that go over this issue). Drones would require more mass and technology, they'd essentially have to be small unmanned nuclear space craft. But even if you carry less of them it's a question of how much more effective they are. IIRC project NERVA consisted of a small nuclear reactor capable of in excess of a hundred megawatts of power. If you take just 10% you have a potential ten megawatt beamed weapon.

 

[Ryan_m_b]

Interesting article relevant to beam weapon accuracy:

http://m.iopscience.iop.org/article...sessionid=CAFE9D2D2646BBEAF09F5A871E47EE34.c1

It reports an X-Ray free election laser with an accuracy of 1 nanoradian. Over a light second such a beam would only spread to a couple of feet in diameter if starting from a small point.

 

[Artribution]

I'm just not convinced of the "no stealth in space" claims. It seems not to account for likely developments in technology. Plasma stealth and infrared invisibility are both current areas of active research and new systems are being worked on all the time.

 

[GTOM]

I'm just not convinced of the "no stealth in space" claims. It seems not to account for likely developments in technology. Plasma stealth and infrared invisibility are both current areas of active research and new systems are being worked on all the time.

If thrusters operate it would require Mass Effect magitech to make it IR invisible. Also there is a finite limit of containing waste heat, plus heat comes from swallowing beams of active sensors.
Maybe in orbital combat, but i would exclude it in deep space.

 

[Artribution]

Thrusters don't necessarily have to operate at all after the initial launch. It depends what you're trying to do.

And besides, stealth can take other forms besides just rendering something undetectable. Stealth also encompasses decoys, sensor ghosts, ECM, etc.

 

[GTOM]

Thrusters don't necessarily have to operate at all after the initial launch. It depends what you're trying to do.

And besides, stealth can take other forms besides just rendering something undetectable. Stealth also encompasses decoys, sensor ghosts, ECM, etc.

ECM, well that is my original idea of jamming is easier than burn through armor with beam weapons, no matter how sensors are hardened. but focus X-ray this punctual...
Maybe i should really forget the epic space battle thing in this setting, and save it for FTL setting...
Laser drone fighters still rather unepic, no dodging shrapnels, no missiles closing in etc...

 

[Ryan_m_b]

I've read books that take the drone approach that do have some pretty epic space battles. The nights dawn trilogy I'd highly recommend if you're interested in that (a fantastic trilogy overall as well). It is an FTL setting so the battles do tend to be closer. The tension comes from when enemy drones burst through your own (through luck or greater numbers) so now they're careering towards the ship intent on destroying it.

 

[Artribution]

Also, the earlier estimates for missile barrage (336 independent missiles, etc.) are based on Trident missiles, the MIRVs of which are all 100-kiloton warheads (Hiroshima was 16 kilotons). If you're firing smaller, 1-kiloton tactical nuclear weapons, you wouldn't be talking about hundreds of missiles, but several thousands per barrage. I think even a network of advanced beam drones could have difficulty stopping that.

 

[GTOM]

Also, the earlier estimates for missile barrage (336 independent missiles, etc.) are based on Trident missiles, the MIRVs of which are all 100-kiloton warheads (Hiroshima was 16 kilotons). If you're firing smaller, 1-kiloton tactical nuclear weapons, you wouldn't be talking about hundreds of missiles, but thousands or tens of thousands per barrage. I think even a network of advanced beam drones could have difficulty stopping that.

If the goal is to take out the ship, with only 25km/s closing speed, one don't need any nuclear warhead. The blind sensors part is the though thing, but directed radiation is more efficient.
Ok, i will read Night's dawn, and digest ideas, thanks.
(I have already wrote a part with captain is sweating as fighter approaches and try to take it out with laser... but i sure haven't calculated with nanorad xaser...
Plan B would be stick to the idea, that no advanced high-sensitivity sensor unharmed if that x burst focused on entire ship, and continue that semi stealth with only sensors robust and sensitive as an axe from a light second...)

 

[Ryan_m_b]

Again it all depends on how far away the attackers are and how many shots off the defenders can get. The type of missiles you're talking about use chemical rocket propulsion and tend to be quite small. So thrust time is in the low minutes at best. Even if we generously assume 10gs for 10 minutes that's a top speed of 60kmps. It would take 5000 seconds to cross a light second distance. Even if you had a thousand the enemy would only have to fire once every five seconds to be safe.

The limits to missiles thrust time are very important. Small missiles means less sophisticated propulsion and less fuel so a lot less delta V. Longer range missiles are going to resemble small space ships, which brings us back to the laser drone idea.

 

[GTOM]

Otherwise the good thing about that xaser, that if they have such stuff, i could pretty much rule out using lasers against infantry, atmosphere swallows and scatters them so much (at least Earth's i don't know what is the transparency of Mars atmosphere) that it is a waste to use it, even if reactor don't run out of power, i don't think such a high energy application don't need regular, expensive maintenance.

 

[Ryan_m_b]

This might help you work it out:
http://web-docs.gsi.de/~stoe_exp/web_programs/x_ray_absorption/index.php

I'm not sure how much the atmosphere absorbs X-Ray's, if you can generate powerful focused ones I don't think it would stop it much. Using the link and assuming a 10 MJ X-Ray and 10km of air (given that the vast majority of atmospheric mass is within the first 10km) it seems like virtually all of it would hit the target.

Then again if you're in the situation of needing boots on the ground you probably care about not destroying all the infrastructure. If the fighting is inside (or underground in burried habitats) orbital support is useless.

 

[GTOM]

This might help you work it out:
http://web-docs.gsi.de/~stoe_exp/web_programs/x_ray_absorption/index.php

I'm not sure how much the atmosphere absorbs X-Ray's, if you can generate powerful focused ones I don't think it would stop it much. Using the link and assuming a 10 MJ X-Ray and 10km of air (given that the vast majority of atmospheric mass is within the first 10km) it seems like virtually all of it would hit the target.

Then again if you're in the situation of needing boots on the ground you probably care about not destroying all the infrastructure. If the fighting is inside (or underground in burried habitats) orbital support is useless.

It said 100% swallow with 100km air. Otherwise x-ray is ionizing radiation cause cancer, it is pretty sure a war crime to use it against a settlement.

 

[Ryan_m_b]

Oh yeah so it is, there was an error when I first used it. I thought the length was in meters. Yeah doesn't seem like an XFEL is much use in firing through atmosphere. For that sort of thing kinetic bombardment would be more effective.

At least it works both ways, a ground based XFEL wouldn't be able to shoot an orbiting ship.

 

[GTOM]

Ok, thank you really much, whatever solution i will take from the two i have mentioned earlier, i surely have to rewrite things.

 

[Artribution]

The limits to missiles thrust time are very important. Small missiles means less sophisticated propulsion and less fuel so a lot less delta V.

In long-range missiles (ICBMs), most of the thrust is supplied by the main rocket before the MIRVs separate, so the propulsion can actually be quite sophisticated and with high delta V.

The type of missiles you're talking about use chemical rocket propulsion and tend to be quite small. So thrust time is in the low minutes at best. Even if we generously assume 10gs for 10 minutes that's a top speed of 60kmps. It would take 5000 seconds to cross a light second distance. Even if you had a thousand the enemy would only have to fire once every five seconds to be safe.

Does a missile always use chemical rockets, and does it have to be small? Do we have to assume that every time a drone fires, it's a hit, and it hits a real MIRV and not a decoy or sensor ghost, and it's an instant burn-through and a kill?

Also, you could program the missiles to detonate when critically damaged, so that their emissions would help obscure the rest from targeting scanners.

Also, the missiles might actually be passing through a region of space not occupied by laser drones. I mean, that's possible, right? The laser drones could be elsewhere, maybe intercepting other missiles?

Maybe i should really forget the epic space battle thing in this setting, and save it for FTL setting...
Laser drone fighters still rather unepic, no dodging shrapnels, no missiles closing in etc...

If you don't want super-effective laser drones, can't you just write that they don't exist because no one's made them yet? They are kinda high-tech.

Closing argument:

 

[Ryan_m_b]

It's late here so just a few quick comments:

1) If the missiles are using more than chemical rockets (e.g a nuclear thermal drive) then they automatically become a lot bigger as they need a nuclear reactor, heat radiators etc. Suddenly you're talking about a small spaceship rather than a small missile. That knocks down the number a ship can carry by quite a bit.

1.5) You mentioned MIRVs, using that system might give you lots of missiles but it means that in the boost phase the defender can knock out 12 missiles in one shot. So even if you gave your first stage a nuclear rocket you've traded slow speed for low number of targets.

1.75) Even if you could make nuclear rockets small enough that every missile could be one the enemy could do the same but swap the warhead out for an X-Ray laser. Powered by the on-board reactor they'd be able to each shoot one enemy missile and destroy the entire threat.

2) I don't see how a decoy could work. With a reasonably good sensor and software you could work out the mass of a ship by the exhaust velocity, mass flow and the overall acceleration of the ship. To be exactly the same as a real missile a decoy would need to mass the same. Unless uranium was rare I don't see the point.

3) I don't know what a sensor ghost is (googling it brings up something from Star Trek and crackpot ghost detectors) but I don't see how any sort of ECM could make it look like a missile existed a light second away when it doesn't.

4) As for being an instant kill we're assuming a high level of accuracy based on the nanoradian XFEL linked above. Speculating that this space age civilisation could produce one capable of mega joule emission (seems reasonable given that this is a world where fusion propulsion technology exists) that's equivalent to a tank shell. It's hard to see a missile surviving that.

5) I don't see how a drone could be elsewhere to the extent it wasn't useful. Given that beam weapons effective to up to a light second are compatible with GTOMs setting you'd have to really screw up as a tactician to not have one around to act on point defence.

6) Even ignoring drones a 1-light second MJ X-Ray laser would be a potent point defence. If you could fire once every few seconds you could pick off thousands of missiles crossing a light second distance at a few tens of kmps

 

[Artribution]

1.75) Even if you could make nuclear rockets small enough that every missile could be one the enemy could do the same but swap the warhead out for an X-Ray laser. Powered by the on-board reactor they'd be able to each shoot one enemy missile and destroy the entire threat.

This is how small actual MIRVs are:

Those are W87 warheads - 475-kiloton city-destroyers, well beyond our needs.

If the missiles are using more than chemical rockets (e.g a nuclear thermal drive) then they automatically become a lot bigger as they need a nuclear reactor, heat radiators etc. Suddenly you're talking about a small spaceship massing a few tonnes rather than a small missile. That knocks down the number a ship can carry by quite a bit.

I don't know what the tonnage of interplanetary spacecraft in this story is like, but actual ICBMs weigh a lot more than that already.

2) I don't see how a decoy could work. With a reasonably good sensor and software you could work out the mass of a ship by the exhaust velocity, mass flow and the overall acceleration of the ship. To be exactly the same as a real missile a decoy would need to mass the same. Unless uranium was rare I don't see the point.

3) I don't know what a sensor ghost is (googling it brings up something from Star Trek and crackpot ghost detectors) but I don't see how any sort of ECM could make it look like a missile existed a light second away when it doesn't.

Well, using plasma to absorb and distort EM profile, varying electric and magnetic fields, just plain old-fashioned invisibility via active camouflage, clouds of chaff like real ICBMs use... It just seems that there are various possible ways of messing with sensors, and then you can just detonate some of the swarm to mask the rest in radiation, heat and light, or have them detonate automatically when damaged.

Also, I've mentioned this before, but after MIRV separation, there might not be any exhaust velocity or acceleration to measure in order to work out mass; assuming you can actually see and measure the exhaust in the first place, you would really only be measuring the mass of the discarded boost stage.

1.5) You mentioned MIRVs, using that system might give you lots of missiles but it means that in the boost phase the defender can knock out 12 missiles in one shot. So even if you gave your first stage a nuclear rocket you've traded slow speed for low number of targets.

If they're close enough to blast your missiles with lasers as they launch, doesn't that imply you're close enough to blast them back and possibly jam them?

 

[GTOM]

Ok i decided the following: at first laser fighters. If they maintain 1g acceleration they arent trivial to hit precisely from a lightsec. Maybe they arent really good against a battleship with much bigger armor and firepower ( although if they can get into right angle to attack radiators ) but good against a convoy.

Then with help of alien metal missiles will be introduced as new fearful weapon. They will be lidar invisible able to contain heat for hours in inertial phase while modify their position with thethers ( connect a squadron with cables ) and near unkillable with lasers.

 

[Ryan_m_b]

This is how small actual MIRVs are:

Those are W87 warheads - 475-kiloton city-destroyers, well beyond our needs.

I don't know what the tonnage of interplanetary spacecraft in this story is like, but actual ICBMs weigh a lot more than that already.

But on top of that you need to add a nuclear reactor, radiators and reaction mass. That requires each MIRV to be more akin in mass to Project Pluto or a Saturn C-5N.

I can't find much information on how much those would have massed (pictures of NERVA and PLUTO look a fair size bigger than those warheads) but we can use the rocket equation to figure out how good such an engine would be. A bit of googling suggests an exhaust velocity of 9kmps. Mass ratio for different delta Vs:

10kmps - 3.03
20kmps - 9.22
50kmps - 256.67
100kmps - 66910.49

So if you have a nuclear thermal MIRV massing X tonnes it will need that ratio of fuel above for those speeds. Not going anywhere fast it doesn't seem, unless GTOM is allowing really small fusion drives in his setting. Even if you could accelerate one up to 100kmps it would take 50 minutes to cross a light second.

Well, using plasma to absorb and distort EM profile, varying electric and magnetic fields, just plain old-fashioned invisibility via active camouflage, clouds of chaff like real ICBMs use... It just seems that there are various possible ways of messing with sensors, and then you can just detonate some of the swarm to mask the rest in radiation, heat and light, or have them detonate automatically when damaged.

All of those are going to make your missiles shine like beacons in infra red. If a bomb detonates and over-exposes a sensor then presumably it's going to be back to working fine a second later when the explosion is over.

Also, I've mentioned this before, but after MIRV separation, there might not be any exhaust velocity or acceleration to measure in order to work out mass; assuming you can actually see and measure the exhaust in the first place, you would really only be measuring the mass of the discarded boost stage.

As I've mentioned before even if you shut down everything and run very cold your previous speed and heading is likely to be known (unless we're assuming that military space ships won't have simple technology like IR sensors and a tracking computer). So even if you were completely invisible you'd be as easy to shoot as a fish in a barrel.

If they're close enough to blast your missiles with lasers as they launch, doesn't that imply you're close enough to blast them back and possibly jam them?

That was part of my point but even if they weren't close enough unless they have very good engines they're going to crawl across interplanetary space. I'm not sure why the defender (presumably with a fusion drive as GTOM has indicated) wouldn't just out maneuver them and pick them off from a distance with beam weapons.

 

[Ryan_m_b]

Ok i decided the following: at first laser fighters. If they maintain 1g acceleration they arent trivial to hit precisely from a lightsec. Maybe they arent really good against a battleship with much bigger armor and firepower ( although if they can get into right angle to attack radiators ) but good against a convoy.

Depends how many there are. If you assume a squadron of ten each capable of putting out a MJ beam then every salvo from them is the equivalent of 5-10 tank shells. Even with a slow rate of fire it seems like it could add up to a lot of damage, especially if they hit thrusters to limit the battleships ability to dodge.

Then with help of alien metal missiles will be introduced as new fearful weapon. They will be lidar invisible able to contain heat for hours in inertial phase while modify their position with thethers ( connect a squadron with cables ) and near unkillable with lasers.

Well fair enough. It's your story if you want to take it down that route. The Polity novels had a similar technology, an alien race could produce this exotic metal armour that would absorb massive amounts of energy and re-radiate it out into space. Don't think such a thing is physically plausible based on what we know now but it is SF after all.

 

[Artribution]

I can't find much information on how much those would have massed (pictures of NERVA and PLUTO look a fair size bigger than those warheads) but we can use the rocket equation to figure out how good such an engine would be. A bit of googling suggests an exhaust velocity of 9kmps. Mass ratio for different delta Vs:

10kmps - 3.03
20kmps - 9.22
50kmps - 256.67
100kmps - 66910.49

So if you have a nuclear thermal MIRV massing X tonnes it will need that ratio of fuel above for those speeds. Not going anywhere fast it doesn't seem, unless GTOM is allowing really small fusion drives in his setting. Even if you could accelerate one up to 100kmps it would take 50 minutes to cross a light second.

I wonder if smaller rocket-propelled missiles could actually be launched from a railgun for higher acceleration and to save on fuel and mass. But we're kind of talking in circles here—speed only matters if you don't think stealth or countermeasures could protect them.

If a bomb detonates and over-exposes a sensor then presumably it's going to be back to working fine a second later when the explosion is over.

Can we be sure of that? Thermonuclear weapons can be very versatile. The blast characteristics and emissions can be modified in all sorts of ways. They can be "enhanced radiation weapons" like neutron bombs, throwing out specific kinds of emissions and particles. They can be nuclear shaped charges, which (instead of a spherical blast) direct a jet or cone-shaped blast in a desired direction. If designed for it, they could even channel their blasts into a tight beam like a kind of x-ray or gamma-ray laser. I don't even think it would be very difficult to design a missile with an outer casing that could adjust itself in-flight to alter the shape and emission profile of its blast.

As I've mentioned before even if you shut down everything and run very cold your previous speed and heading is likely to be known (unless we're assuming that military space ships won't have simple technology like IR sensors and a tracking computer). So even if you were completely invisible you'd be as easy to shoot as a fish in a barrel.

If your missile launch is observed by an enemy capable of attacking it with lasers, then you're also close enough to attack or jam that enemy with your own lasers, and therefore, you can't assume the enemy would be aware of the speed and heading of your missiles. Also, once the MIRVs separate from the launch stage, that data is no longer applicable. The MIRVs could have rockets of their own, or just RCS thrusters. And if they're only eight inches long (tactical nuclear warheads are) and traveling at relatively high velocity, and making random minor course adjustments, hitting them with a laser at a distance of a light-second would seem to pose a challenge even for an advanced computer, and that's all assuming that none of their stealth and countermeasures work at all.

 

[Ryan_m_b]

I wonder if smaller rocket-propelled missiles could actually be launched from a railgun for higher acceleration and to save on fuel and mass. But we're kind of talking in circles here—speed only matters if you don't think stealth or countermeasures could protect them.

Quite.

Can we be sure of that? Thermonuclear weapons can be very versatile. The blast characteristics and emissions can be modified in all sorts of ways. They can be "enhanced radiation weapons" like neutron bombs, throwing out specific kinds of emissions and particles. They can be nuclear shaped charges, which (instead of a spherical blast) direct a jet or cone-shaped blast in a desired direction. If designed for it, they could even channel their blasts into a tight beam like a kind of x-ray or gamma-ray laser. I don't even think it would be very difficult to design a missile with an outer casing that could adjust itself in-flight to alter the shape and emission profile of its blast.

Unless you're pretty close to the enemy I don't see how any of that matters.

If your missile launch is observed by an enemy capable of attacking it with lasers, then you're also close enough to attack or jam that enemy with your own lasers, and therefore, you can't assume the enemy would be aware of the speed and heading of your missiles. Also, once the MIRVs separate from the launch stage, that data is no longer applicable. The MIRVs could have rockets of their own, or just RCS thrusters. And if they're only eight inches long (tactical nuclear warheads are) and traveling at relatively high velocity, and making random minor course adjustments, hitting them with a laser at a distance of a light-second would seem to pose a challenge even for an advanced computer, and that's all assuming that none of their stealth and countermeasures work at all.

An enemy could be extremely far away and observe your missiles. There's no line of sight in space, detection depends on the size of your sensors and the wavelength being observed. Not only that but sensors across a ship and between different ships can act as interferometers forming extremely capable long range sensors. If we're positing a world where space combat is a part of life then you can bet that sensors will constantly be scanning the whole sky, tracking as many ships in the system as possible and looking for things like a MIRV launch.

MIRVs separating presumably requires some form of power, that means there's a source of heat on the missile that can be detected. If their making random course corrections there's also a source of power and an exhaust emission. You mention traveling fast but unless they're traveling extremely fast crossing a distance like a light second is going to take on the order of hours. Plenty of time to shoot down with long range beam weapons or simply fly away if you're in a ship.

 

[GTOM]

If their making random course corrections there's also a source of power and an exhaust emission. You mention traveling fast but unless they're traveling extremely fast crossing a distance like a light second is going to take on the order of hours. Plenty of time to shoot down with long range beam weapons or simply fly away if you're in a ship.

I proposed tether propulsion for the first part, if there are 100m long nanotube cables, the missiles can be (almost) anywhere in a 100m circle. (Connect them and rotate them around each other, pull the cables, or let them loose)
But i don't deny, with deep space conditions, on similar tech level, detection is the easier thing.
(For my other, FTL setting, the alienware missiles will have another upgrade, if they are destroyed, they emit a strong directed X-pulse, so they hit back. i think i name the magitech material pulsarium. )
Although i don't rule out some stealth attack part in orbit (launch magitech drone from landing cargo shuttle in order to hack PDF satellite).
Or people rebel on liberated in Red Army style planet when third partys fleet comes. When occupy force fleet turn sensors toward coming fleet, attack them in the back with missiles (boost them on other side of planet, and contain their heat with some liquid helium for a time)

 

[Ryan_m_b]

I proposed tether propulsion for the first part, if there are 100m long nanotube cables, the missiles can be (almost) anywhere in a 100m circle. (Connect them and rotate them around each other, pull the cables, or let them loose)

Assuming they weren't observed deploying the enemy could just shoot in the middle of that 100m and sever the tether, sending either ship/missile flying off. To reconnect/correct the course they'd have to power up.

But i don't deny, with deep space conditions, on similar tech level, detection is the easier thing.

It is the most different aspect of space compared to other forms of human experience, line of site is essentially infinite which changes a lot of strategy and tactics.

(For my other, FTL setting, the alienware missiles will have another upgrade, if they are destroyed, they emit a strong directed X-pulse, so they hit back. i think i name the magitech material pulsarium. )

http://www.alienware.co.uk/?ST=alienware&dgc=ST&cid=41141&lid=1069630&acd=239715600820560&ven1=s51xsHpOB&ven2=e have moved onto missiles in your setting eh? Guess gaming isn't that lucrative in the future

Although i don't rule out some stealth attack part in orbit (launch magitech drone from landing cargo shuttle in order to hack PDF satellite).
Or people rebel on liberated in Red Army style planet when third partys fleet comes. When occupy force fleet turn sensors toward coming fleet, attack them in the back with missiles (boost them on other side of planet, and contain their heat with some liquid helium for a time)

Stealth in orbit may be possible, I'm not hugely convinced that heat dumps would last very long (moving heat around takes energy which costs heat so you're constantly expending increasing amounts of energy to contain an increasing amount of heat).

Still a big thing that we've not touched on is subterfuge. You might be able to sneak weapons close to a fleet, for example: hiding a nuke aboard a trading ship that travels nearby then sabotages its own systems and sends out an SOS.

 

[GTOM]

Assuming they weren't observed deploying the enemy could just shoot in the middle of that 100m and sever the tether, sending either ship/missile flying off. To reconnect/correct the course they'd have to power up.

Other setups are also possible, like connect three, and they don't even know the radius of the circle.

It is the most different aspect of space compared to other forms of human experience, line of site is essentially infinite which changes a lot of strategy and tactics.

I have compared it to chess, you can see whole board.

Stealth in orbit may be possible, I'm not hugely convinced that heat dumps would last very long (moving heat around takes energy which costs heat so you're constantly expending increasing amounts of energy to contain an increasing amount of heat).

Yes, doing it for long time surely isn't realistic.

Still a big thing that we've not touched on is subterfuge. You might be able to sneak weapons close to a fleet, for example: hiding a nuke aboard a trading ship that travels nearby then sabotages its own systems and sends out an SOS.

Yes, such things will be really important in my story.

 

[Artribution]

Unless you're pretty close to the enemy I don't see how any of that matters.

Found a description of what some shaped-charge applications could look like:

Back in the 1960's, rocket scientist came up with the infamous "Orion Drive." This was basically a firecracker under a tin can. Except the tin can is a spacecraft , and the firecracker is a nuclear warhead.

Anyway, they realized that about 90% of the nuclear energy of an unmodified nuclear device would be wasted. The blast is radiated isotropically, only a small amount actually hits the pusher-plate and does useful work. So they tried to figure out how to channel all the blast in the desired direction. A nuclear shaped charge.

Remember that in the vacuum of space, most of the energy of a nuclear warhead is in the form of x-rays. The nuclear device is encased in a radiation case of x-ray opaque material (uranium) with a hole in the top. This forces the x-rays to exit only from the hole. Whereupon they run full tilt into a large mass of beryllium oxide (channel filler).

The beryllium transforms the nuclear fury of x-rays into a nuclear fury of heat. Perched on top of the beryllium is the propellant: a thick plate of tungsten. The nuclear fury of heat turns the tungsten plate into a star-core-hot spindle-shaped-plume of ionized tungsten plasma. The x-ray opaque material and the beryllium oxide also vaporize a few microseconds later, but that's OK, their job is done.

The tungsten plasma jet hits square on the Orion drive pusher plate, said plate is designed to be large enough to catch all of the plasma. With the reference design of nuclear pulse unit, the plume is confined to a cone of about 22.5 degrees. About 85% of the nuclear device's energy is directed into the desired direction, which I think you'd agree is a vast improvement over 10%.

About this time the representatives of the military (who were funding this project) noticed that if you could make the plume a little faster and with a narrower cone, it would no longer be a propulsion system component. It would be a nuclear directed energy weapon. Thus was born project Casaba-Howitzer.

Details are scarce since the project is still classified after all these years. Tungsten has an atomic number (Z) of 74. When the tungsten plate is vaporized, the resulting plasma jet has a relatively low velocity and diverges at a wide angle (22.5 degrees). Now, if you replace the tungsten with a material with a low Z, the plasma jet will instead have a high velocity at a narrow angle ("high velocity" meaning "a recognizable fraction of the speed of light"). The jet angle also grows narrower as the thickness of the plate is reduced. This is undesirable for a propulsion system component (because it will destroy the pusher plate), but just perfect for a weapon (because it will destroy the enemy ship).

The report below suggests that the practical minimum half angle the jet can be focused to is 5.7° (0.1 radians).

They would also be perfect as an anti-ballistic missile defence. One hit by a Casaba Howitzer and a Soviet ICBM would be instantly vaporized. Which is why project Casaba-Howitzer's name came up a few times in the 1983 Strategic Defense Initiative.

Casaba Howitzers fired from orbit at ground targets on Terra would be inefficient, which is not the same as "does no damage." A nuclear warhead fired at a ground target would do far more damage, but the Casaba Howitzer bolt is instantaneous, non-interceptable, and would still do massive damage to an aircraft carrier.

Scott Lowther has done some research into a 1960's design for an Orion-drive battleship. It was to be armed with naval gun turrets, minuteman missiles with city-killing 20 megatons warheads, and Casaba-Howitzer weapons. It appears that the Casaba-Howitzer charges would be from subkiloton to several kilotons in yield, be launched on pancake booster rockets until they were far enough from the battleship to prevent damage (several hundred yards), whereupon they would explode and skewer the hapless target with a spear of nuclear flame. The battleship would probably carry a stockpile of Casaba-Howitzer weapons in the low hundreds.

Mr. Lowther estimates that each Casaba-Howitzer round would have a yield "up to a few kilotons" and could deliver close to 50% of that energy in the spear of nuclear flame. Three kilotons is 1.256 × 10¹³ joules, 50% of that is 6.276 × 10¹² joules per bolt.

This is thirty-five times as powerful as a GBU-43/B Massive Ordnance Air Blast bomb, the second most powerful non-nuclear weapon ever designed. Per bolt.

Get a copy of the report for more details, including a reconstruction of a Casaba-Howitzer charge.

What is the mass and volume of a Casaba-Howitzer charge? Apparently this also is still classified. An Orion Drive nuclear pulse unit would be about 1,150 kg, have a blast yield of about 29 kilotons, and be a cylinder with a radius of 0.4 meters and a height of 0.87 meters. The volume would therefore be about 0.4 cubic meters. As previously mentioned a Casaba-Howitzer charge would have a yield ranging from sub-kiloton to a few kilotons, so presumably it would be smaller and of lower mass than a pulse unit.

http://www.projectrho.com/public_html/rocket/spacegunconvent.php​

There are some other applications there, very interesting reading.

MIRVs separating presumably requires some form of power, that means there's a source of heat on the missile that can be detected. If their making random course corrections there's also a source of power and an exhaust emission.

Yeah, there'd be an exhaust emission, but you're saying your sensors could detect and accurately measure the tiny plume of expellant gas from a 25-centimeter MIRV's RCS thrusters from a light-second away? Seems incredible. Even if you could scan the entire sky with that much accuracy, and you fired your laser as soon as you measured it, by the time your laser reached the position you plotted, the MIRV could simply have made another random minor adjustment, and this is assuming you have a rapid-fire laser that could keep up the firing rate. And the missile could use other launch systems (railgun etc.) that wouldn't produce any exhaust capable of being tracked.

edit: fixed some numbers given above

 

[GTOM]

Found a description of what some shaped-charge applications could look like:

http://www.projectrho.com/public_html/rocket/spacegunconvent.php​

There are some other applications there, very interesting reading.

I am skeptical about that, on other threads, they mentioned, they could achieve some directivity, but not much.
Anyway we are at the point, that the missile itself should spit directed beams, than i like more the laser fighter thing, it can't expend that much energy, but more able to focus on radiators, hot lasercannons.

Otherwise, i had the following thoughts : yes, the ship propulsion require much more power than the cannon, but an entire 50 ton propulsion system takes that heat.
In case of a laser, the surface of the mirror, or the focusing lenses has to take pretty much heat (if i remember correctly that xaser focuses with a Be prism)
Hannibal's method of cracking rocks in the Alps was heat them up, then cool them rapidly.
So, present day high power lasers has pretty low rate of fire, hours, i guess it can be helped, but in the future probably their rate of fire will be still low. That at least gives more time to beam rockets to get close enough to do serious damage.

Maybe big battleships should have some bomb-pulsed system, that has enermous power in order to counter PDF cannons, but has a really low rate of fire, so a big battleship isn't really good against squadrons of smaller ships, it needs escort.

Yeah, there'd be an exhaust emission, but you're saying your sensors could detect and accurately measure the tiny plume of expellant gas from a 25-centimeter MIRV's RCS thrusters from a light-second away? Seems incredible. Even if you could scan the entire sky with that much accuracy, and you fired your laser as soon as you measured it, by the time your laser reached the position you plotted, the MIRV could simply have made another random minor adjustment, and this is assuming you have a rapid-fire laser that could keep up the firing rate. And the missile could use other launch systems (railgun etc.) that wouldn't produce any exhaust capable of being tracked.

edit: fixed some numbers given above

I have read about the sensitivity of James Webb's IR cam. If tenth of it is true, they shouldn't have any problem detecting a speeding rocket from light seconds.

 

[GTOM]

I had another idea (for the later, operatic setting)
Send swarms of micromissiles about a cm cross section. Even with a nrad spread, from a long distance, much of the energy is wasted.
They form a hive mind for flare rejection and things like that.
(It is rare to employ such things against fighters for cost reasons, but they rather throwing EMP bombs to confuse them in terminal phase, so they can be dodged.)

Well it shouldn't be the only instance of using some kind of micro or nano weapons, although cost issues can prevent make a ground war entirely with theese stuff.

 

[GTOM]

It's worth noting as well that there are other forms of beam weapon that couldn't be so easily reflected, for example: particle beams, FELs and X-Ray lasers. In regards to the idea of swarming missiles sure: if you can deploy in such numerical strength then you'll win. But working with the assumptions I mentioned in the previous paragraph an attacker would need to launch 5 missiles at the defender to be sure of a win, and that's if they have only one point defence laser. If they have 10 you need to launch 41.

About the X-FEL thing :

"Rigorous derivation from Maxwell's equations gives the divisor of 2 and the proportionality constant. In an X-ray FEL the typical undulator wavelength of 1 cm is transformed to X-ray wavelengths on the order of 1 nm by {\displaystyle \gamma }https://wikimedia.org/api/rest_v1/media/math/render/svg/a223c880b0ce3da8f64ee33c4f0010beee400b1a ≈ 2000, i.e. the electrons have to travel with the speed of 0.9999998c."

Doesnt that mean, that the process is very inefficient due to the big relativistic mass?

 

[Noisy Rhysling]

One reason for using missiles would be "because you can". A mixed weapon arsenal gives you more options than just one system. Missiles could be used as a threat to herd the enemy toward a specific location. They could also be used to lay mines, those would be waiting for the enemy to come at you from a specific direction. Send the missiles out to an intermediate location and redirect them when you're sure of the enemy's course. They would also require less power from the ship's systems, especially if they're "fire-and-forget" types. Missiles could be fired at more than one enemy, or more enemies than can be covered by the lasers. They would also be useful against non-ship targets, such as surface installations. Our terrestrial warships carry a mixed bag of systems to enable them to counter more threats.

 

[Noisy Rhysling]

Oh, and one way to give the reader information without preaching would be to have senior officers instructing midshipmen. Q&A sessions about their studies, or hands-on training sessions. (My wife would call this "Hogwarts in space.")

 

[GTOM]

One reason for using missiles would be "because you can". A mixed weapon arsenal gives you more options than just one system. Missiles could be used as a threat to herd the enemy toward a specific location. They could also be used to lay mines, those would be waiting for the enemy to come at you from a specific direction. Send the missiles out to an intermediate location and redirect them when you're sure of the enemy's course. They would also require less power from the ship's systems, especially if they're "fire-and-forget" types. Missiles could be fired at more than one enemy, or more enemies than can be covered by the lasers. They would also be useful against non-ship targets, such as surface installations. Our terrestrial warships carry a mixed bag of systems to enable them to counter more threats.

Good ideas. Although most combat will be in the asteroid belt, they can solve bombardment by moving things to the opposite side (unless attack from two opposite direction a bit GO like style), dig deep the reactor.
I think missiles can be most useful, when there is a fuel producing asteroid, they can build masses of missiles very cheap, and enemy ships has to come close to capture the place. (Usually no big ones come close until fast agile fighters sorrounded and scanned the entire place.)
Information handle is a good question, i usually narrate that, and try to avoid too big infoblocks.