Space Warfare - How would the ships be built/designed?

[GeneralVeers]

Tater, you've asked me the same question about twenty times now.

What was that saying about doing the same thing over and over, and expecting a different result??? Uhhhh.....nuts. Can't remember.

I don't have to prove anything. The basic proof-of-concept has already been done in the real world, during operational testing of the YAL-1 airborne laser and other weapons platforms.

[tater]

BTW, it is indeed a theoretical discussion, so you need to do some math to justify a position. When the suggestion is made that a powerful laser would burn through, you argue that we need to characterize the laser better vs the real life targeting laser. True enough. The same is true of the sand defense. You need to characterize it such that it works.

Even with just the targeting laser, to be effective as a defense, the sand must equal the properties of the thickness of sandstorm that defeats the targeting laser. That's a given, right? If a low power laser penetrates XX meters into a roaring sandstorm (we'd have to define the penetration as "retains 30% of transmitted power" or something, obviously), then we need to shield a craft with XX meters of an identical mix of aerosols/gases (including density).

We should all agree that this is true, right, I've just moved your sandstorm---and just the part the beam interacts with---to space.

Now all we need to do is find the density of that volume of sandstorm, then figure out how wide we can make a cloud of that depth/density along the side of the ship between us and the target. Is that 50kg? If not, then traveller sandcasters are toast for targeting lasers (much less HELs). If it is possible with just 50kg, then they might have some efficacy vs HELs, and the calculation becomes substantially more complex. If the needed mass is more than 50kg, but not ridiculously high, then they might be effective in RL (worth the mass), but the traveller canon is clearly nonsense.

- - - Updated - - -

Tater, you've asked me the same question about twenty times now.

What was that saying about doing the same thing over and over, and expecting a different result??? Uhhhh.....nuts. Can't remember.

I don't have to prove anything. The basic proof-of-concept has already been done in the real world, during operational testing of the YAL-1 airborne laser and other weapons platforms.

They were not fired in space, and you have not provided evidence that sand stopped that laser in a handful of meters, which is how much path length you have to work with. We're not talking about multi-km deep clouds, we're talking about at most a few 10s of meters.

ABL was designed with the idea that max range would be 400km. We are talking abut substantially more powerful lasers (or way better focused), 400km is not worth it for a deep space weapon.

Edited September 15, 2015 by tater

[Rune]

I'm hardly an expert on lasers (my knowledge is admittedly limited to designating lasers and whatever I read on Winchell's Atomic Rocket's site), but I suspect that we'd find that, in the future, weaponized lasers are inferior to other, more thermally efficient weapons because heat management will be the primary limiting factor in warship capability. Plus I don't believe a ship-based laser battery could dramatically overheat a warship designed for space superiority/dominance: the volley of hyper-velocity tungsten annular blast warhead shells fired from the lased vessel's mass drivers would tear the lasing vessel in half well before the heat became an issue.

Now, in terms of hull integrity, those lasers could possibly burn their way through and do some damage in the meantime, but I suspect lasers that burn holes and lasers that just heat ships up to overload their cooling systems will likely be two different kinds of lasers: one fired from ships, the other fired from ground or large "stationary" orbital installations.

Personally, I suspect lasers would be restricted to point defence and sensor blinding/EW duties, though I could see atypical wavelength lasers being used to irradiate crew members, or disable electronic systems like some experimental lasers do now. I might even go a step further and speculate that future armour systems will be what dictate which weapons systems end up being the best primary armament.

Scoundrel, +1 on the sandcaster comments. This ones about lasers, tough... I'm hardly an expert in lasers either, but I think the basic physics of the thing are heavily tilted against kinetics here.

It's all a question of range, really... let's examine it a bit further, and let it be the last time I do this, at lest in this thread... let's suppose two otherwise identical hypothetical warships, one equipped with a 1MW 10km/s railgun (that's one 100kg round every second, and you will notice I am being generous with the muzzle velocity by about a factor of two or three), compared to a 1MW laser weapon, like the ones the US Navy wants on their next-gen ships (a bit of a power jump, but 100kW systems are already existing prototypes based on commercial-grade lasers):

First, the size of each weapon system. This are all wild guesses here, of course, but the railgun prototype of the US Navy is apparently already in the MW order of magnitude, and it is going to be fitted on ships. On the other hand, ~10kW laser systems are going to be installed on Humvees (actually, the new one whose name I can't remember right now, but similar size), including power systems. The 100kW laser system on the Ponce is also more like a CIWS in size than the artillery-looking railgun that doesn't include reloading or power systems on the pic, and the laser trailer from Boeing is also supposedly in this power class, and includes cooling and power systems. Let's say the 1MW hypothetical laser is slightly larger than the 1MW hypothetical railgun.

Then, as you note, we must compare efficiency, because laser are notoriously inefficient. They don't really have to, since some diode solid-state lasers get upwards of 80% efficiency in the lab, but all real-life examples have been nowhere near that, and I don't really know about the fiber lasers that this weapon systems use, so thus I happily concede that a laser will be an extremely inefficient thing, depositing more ehat in the warship than in the target. However. Railguns are also notoriously inefficient, creating a lot of heat through friction with the rails, as well as the high-power pulsed nature of their operation that makes for inefficient transmission of power. All in all, still the railgun is probably getting the upper hand here, so I will allow that the laserstar has to have much larger radiators, probably up to twice the size of the other ship (let's remember the power to use the weapon is coming form somewhere, and that somewhere will be lucky to be 50% efficient, so the railgun battleship also needs some serious radiators), with the corresponding increase in mass.

So, that works out to a mass advantage to the railgun battleship. Right? Well, let's spend it in ablative armor, and we have that laserstar by the balls, don't we? We will just close to where we can hit it, and fill it with holes.

But. "Close to where we can hit it" isn't going to be as easy. Remember, we said the ships are otherwise identical, so they can accelerate at the same rate, or a very similar one, so none has a decisive movement advantage. The only advantage is that one is armored, and the other one isn't, or not as much, or that one has a slight wattage advantage on weapons output, it's quite irrelevant. So space being what it is, they will only do battle if they want to, and they will close at the rate any one of them chooses. We might get into complicated space tactics here, but let us fix a closing rate "on the order of km/s". Could be snail pace (favours the "sharpshooter"), could be fast interplanetary trajectory (favours the "tank"). It doesn't really matter much. Because see, the laserstar has an effective range a few orders of magnitude higher than the railgun battleship.

It's really easy to work out. If the railgun is moving at 10km/s towards a 1km cross-section target that can accelerate at a measly 1m/s, for ten seconds, it will miss, 100% of the time, at ~1,100kms (actually, a bit less). So we can call that it's effective range. The 1MW laser system, with a reasonable visible-light wavelenght and a 1m primary mirror in its turrets, can have an effective range way higher than that (I don't want to go there, but the railguns is going to have to be spine-mounted on account of mass and momentum transfer, while the spine-mounted laser can easy have several turrets)... and you won't be able to fire at it anyway. Why? Well, the spot size at 1000kms for such a laser is on the order of 1m^2 (I did the math for reasons, a while ago it's short of right considering I did it for another kind of lasers). That's 1MW of power in a spot of one square meter, which turns out to be 0.1kw/cm^2... not really too .... right? That may be able to ablate, but it'll sure take its sweet time if it tries to go through armor. What's there to worry about! We have armor!

However, turn that spot into a sensor, and the thing will be blinded faster than you can say "photodiode". Even synthetic aperture radars will be happily burned away at that range, even if they can't be seriously fouled up by ECM, at such power levels. And you know, at 10,000kms, that is the same megawatt, but over ten square meters. Definitely not going to touch your fuel tanks or radiators, but you are already blind across the electromagnetic spectrum, so who cares? The ship is effectively dead in the water if it can't target it's fancy railgun or know which direction to run. And even at 100,000kms the 100m beam spot will be already something than optical sensors built to spot warships against space just won't be able to handle. Once the target is blind, the laserstar can then slowly match velocities and close in, staying outside the range of the railgun (and as off-axis form the railgun as it can, in case the enemy has some unopened sensor port in reserve), while it slowly melts away the radiator system to neuter the blind, armored hulk.

Once you are ready to board the overheating hull to rescue the enemy survivors, we expect our laserstar captain to jokingly congratulate the enemy on his choice of weaponry. The losing side would then proceed to develop their own flavour of laserstars, but with fancy 10m optics which turns them just as effective at ten times the range, meaning the next battle will be decided at 100,000kms. And thus a new arms race ensues, over who can blind who the farthest, until the lasers start to miss due to light-lag at much more advanced tech levels.

Rune. Paraphrasing: "in the race between sword and shield, the shield usually is usually unhappy at the end". So better get the longest sword possible.

[Kibble]

Spacecraft built and flown to disable other spacecraft will most likely be disposable. They are supposed to get to the target fast, before the target can complete its objective (make an orbital insertion burn, disable one of your probes, or whatevs) which means hyperbolic trajectories. A probe would have to be big (expensive) to have the delta v to return for re-use. Not to mention large heat radiator panels, large solar panels, and a tough laser mirror are much more massive (expensive) and complex (expensive and unreliable) than a bottle of helium to dump, a simple hypergolic fuel cell, and a cheap one-use reflector.

[shynung]

Spacecraft built and flown to disable other spacecraft will most likely be disposable. They are supposed to get to the target fast, before the target can complete its objective (make an orbital insertion burn, disable one of your probes, or whatevs) which means hyperbolic trajectories. A probe would have to be big (expensive) to have the delta v to return for re-use. Not to mention large heat radiator panels, large solar panels, and a tough laser mirror are much more massive (expensive) and complex (expensive and unreliable) than a bottle of helium to dump, a simple hypergolic fuel cell, and a cheap one-use reflector.

I smell missile warheads.

[Rune]

Spacecraft built and flown to disable other spacecraft will most likely be disposable. They are supposed to get to the target fast, before the target can complete its objective (make an orbital insertion burn, disable one of your probes, or whatevs) which means hyperbolic trajectories. A probe would have to be big (expensive) to have the delta v to return for re-use. Not to mention large heat radiator panels, large solar panels, and a tough laser mirror are much more massive (expensive) and complex (expensive and unreliable) than a bottle of helium to dump, a simple hypergolic fuel cell, and a cheap one-use reflector.

Well I used manned ships for flavour, but that is really in the "identical ships" part of the scenario. Might be drone-scaled, might be huge battleships, that really depends on the size of the payload (in this case, the weapon). Though obviously decent optics will reach farther than disposable ones. And if you want to move your laser cannons far, you are going to need nuclear rockets. And if you have several GWs of reactor to move your multi-ton MW-class laser, might as well give it the turbine and radiator system to have an infinite magazine.

Rune. I'd be interested to hear how small an effective laser drone can be, though.

[Kibble]

Rune. I'd be interested to hear how small an effective laser drone can be, though.

Probably only a little heavier than small space telescopes that already exist, like WIRE or Astro-F.

A reusable laserstar satellite would probably be in the 20 tonne range, with enormous solar panels to power the laser rather than a fuel cell. The solar panels would also be used to power an electric rocket engine. Launched on a hyperbolic intercept like the disposable probe, but spends a few months ion-ing back home (to be mated with another expendable rocket stage for its next mission).

EDIT: One advantage of the reusable probe, is that it could engage multiple targets on a single orbit, like if an entire constellation of enemy satellites is inbound.

Edited September 15, 2015 by Kibble

[Scoundrel]

Scoundrel, +1 on the sandcaster comments. This ones about lasers, [though]... I'm hardly an expert in lasers either, but I think the basic physics of the thing are heavily tilted against kinetics here.

Oh I completely agree with you about the lasers being useful, and certainly for blinding. In fact I am of the opinion that, PD aside, lasers will be used exclusively for blinding enemies because that will require far, far less power than it would to burn through hulls.

See, IMHO, kinetic weapons will still have a place because they won't need to lob 100kg projectiles 10km/s at a million kilometres distance with the absurd hope to outrange a laser. Your blinded hulk (I liked your description btw +1 for that ), unable to anticipate the trajectories of say a half dozen 25-50kg tungsten annular blah blah blah warheads at 5km/s that bracket the target (and fired from a nice safe range of, say, 1000km), will dice that hulk into so many pieces that it will likely be called "the ginsu maneuver!" If it turns out the hulk is armoured like a tank, then a direct hit from said railgun will likely be as effective as any laser, especially if its armour is geared towards ablating heat rather than deflecting heavy pointy metal thingies spat out at ridiculous speeds.

Now, that's not to say your laser star of death - or, as I like to call them, "death stars" - couldn't then just pop the radiators and take their time finishing the vessel off. I simply believe that space combat will revolve around ships orbiting different bodies, sniping at each other where possible during their tiny orbital windows, with everyone trying to blind everyone else until someone who isn't blind can rush in and bring their boomstick to bear and start dishing out some real damage. It is nothing more than my personal opinion that a kinetic weapon is a more likely choice as coup de grâce armament due to its flexibility regarding armoured/protected targets; as well as being an excellent system for delivering area denial ordnance for that initial volley at orbital installations while avoiding generating excessive amounts of heat.

That said, I'm not entrenched in any particular position (aside from the sand thing). If it turns out lasers are the only way to go, then I'm cool with that. I'm just as happy with pyew pyew pyew as I am with dakka dakka dakka!

[Rune]

EDIT: One advantage of the reusable probe, is that it could engage multiple targets in a single orbit, like if an entire constellation of enemy satellites is inbound.

Exactly. If you use one-off lasers, you have to make the cheaper than missiles or be overwhelmed.

Oh I completely agree with you about the lasers being useful, and certainly for blinding. In fact I am of the opinion that, PD aside, lasers will be used exclusively for blinding enemies because that will require far, far less power than it would to burn through hulls.

See, IMHO, kinetic weapons will still have a place because they won't need to lob 100kg projectiles 10km/s at a million kilometres distance with the absurd hope to outrange a laser. Your blinded hulk (I liked your description btw +1 for that ), unable to anticipate the trajectories of say a half dozen 25-50kg tungsten annular blah blah blah warheads at 5km/s that bracket the target (and fired from a nice safe range of, say, 1000km), will dice that hulk into so many pieces that it will likely be called "the ginsu maneuver!" If it turns out the hulk is armoured like a tank, then a direct hit from said railgun will likely be as effective as any laser, especially if its armour is geared towards ablating heat rather than deflecting heavy pointy metal thingies spat out at ridiculous speeds.

Now, that's not to say your laser star of death - or, as I like to call them, "death stars" - couldn't then just pop the radiators and take their time finishing the vessel off. I simply believe that space combat will revolve around ships orbiting different bodies, sniping at each other where possible during their tiny orbital windows, with everyone trying to blind everyone else until someone who isn't blind can rush in and bring their boomstick to bear and start dishing out some real damage. It is nothing more than my personal opinion that a kinetic weapon is a more likely choice as coup de grâce armament due to its flexibility regarding armoured/protected targets; as well as being an excellent system for delivering area denial ordnance for that initial volley at orbital installations while avoiding generating excessive amounts of heat.

That said, I'm not entrenched in any particular position (aside from the sand thing). If it turns out lasers are the only way to go, then I'm cool with that. I'm just as happy with pyew pyew pyew as I am with dakka dakka dakka!

Oh, secondary armament! Well then my friend we have no major differences of opinion, I'm afraid, so the discussion will soon come to a conclusion between us. Railguns are awesome siege weapons, able to bombard anything stationary (planets, big space colonies, asteroid mines and the like) form even more stupendous distances. Of course they could be used to finish off already defeated opponents. Though I will point out, at the same wattage, it you let the beam weapon really tighten the focal point to "I don't care what your hull is made of, now it's plasma" distances, the effects wouldn't be that dissimilar.

Rune. I did oversize the railgun quite a bit, I know. But mostly because the current one tops out at about 2.5km/s, which is a lot less energy, to fire 10kg rounds using 32MJ of electric juice (25MW apparently works out to 10 shots/minute if I can believe the wiki).

Edited September 15, 2015 by Rune

[baggers]

Rune. I did oversize the railgun quite a bit, I know. But mostly because the current one tops out at about 2.5km/s, which is a lot less energy, to fire 10kg rounds using 32MJ of electric juice (25MW apparently works out to 10 shots/minute).

Railguns have about 30% energy transformations effiency. (electric to cinetic) Look pretty good to me. A laser weapon is more 10%. So, for a limited energy source, a railgun will probably be more efficient?

Even for a big warship, having 3 time the punch for the main armament for the same energy source is a big advantage!

Laser could still be used as secondary armament ^^

Edited September 15, 2015 by baggers

[GeneralVeers]

Here's a question I don't think I've seen yet: how much recoil would one of these railguns produce? In space, that could be a problem......or an advantage. If you're fleeing a pursuing bogey, every time you fire at it you're giving yourself a boost in the right direction. Whereas the pursuer's railgun would slow them down.

If anyone here has played Star Control II? Because mentioning technology from games has just worked out so well in this thread, and NOT caused ANY problems at all! There was a ship in Star Control II whose main cannon was so big, every time it was fired the ship went flying backwards. Fun stuff.

BTW, it is indeed a theoretical discussion, so you need to do some math to justify a position.

No, I do not. Precisely because it's a theoretical discussion. The math would be based on theoreticals and best-guesses (as your numbers are), and could therefore be completely wrong. The only way to be sure is to perform operational testing on a real spacecraft. Which leads to a rather perplexing problem I think you can figure out yourself.

The answer was always "no", and it remains "no" now. But, if you ask forty-seven more times, I'll give in and change my answer to "no".

[tater]

You are wrong, as I have demonstrated that a sandstorm != 50kg of sand nearby your ship. Fail to demonstrate your claim that they are the same, and we can just consider you wrong. You will not discuss anything at all, in fact. You could at least admit that creating a bubble of "= sandstorm" conditions is what is required for the actual tests and the spacecraft to be nearly identical cases, right?

It is implausible enough, that the positive claim needs to be justified, not the claim that it is implausible.

Best guess of course can be wrong, but not even bothering to make a best guess calculation is akin to belief in magic without proof (something I'll admit a majority of people on earth do all the time).

Edited September 16, 2015 by tater

[GeneralVeers]

You are wrong, as I have demonstrated that a sandstorm != 50kg of sand nearby your ship.

No you haven't. You merely assumed it, and you picked the necessary numbers out of thin air. How far into a sandstorm would a military-grade laser penetrate before dissipating? You have no idea.

There are other examples, but I don't need them. The point is already made. Magic numbers and handwaving don't cut the mustard with me.

Wow! Look at that, I finally managed to write a post that was fewer than 200 lines. Next I'm going to see flying pigs outside my.........errrr, never mind.

[Scoundrel]

Oh, secondary armament! Well then my friend we have no major differences of opinion, I'm afraid, so the discussion will soon come to a conclusion between us.

That, I'm afraid, is what happens when reasonable people come to reasonable conclusions. Though, that said, I do see a possibility for lasers to be used as primary armament.

Though I will point out, at the same wattage, it you let the beam weapon really tighten the focal point to "I don't care what your hull is made of, now it's plasma" distances, the effects wouldn't be that dissimilar.

I'm not so sure. Some exotic anti-laser armours (boron/graphene composite) would require many MJ of lasing to burn through a single not-particularly-thick layer (this is a guess based on a post in Atomic Rockets - I've low-balled it to be conservative) whereas it would be brittle enough that an astronaut with gooey space glue on one glove and a hammer in the other could easily compromise a 1m section with a few good whacks. He'd be stuck to the ship, but it wouldn't take much to break it.

Heck, maybe they could defeat it with a cloud of high velocity sand particles.

Anyways, I suspect that architects would recognize the vulnerabilities of the vessels and the combat environs they'd be operating in, but be incapable of prioritizing threats properly, making it possible that there would be some warships that ended up with a compromise design that could reasonably allow lasers to maintain superior efficiency over kinetic weapons both as a blinding system as well as a kill system. Though it does make me wonder if there's a point to having a noticeable gap between armour layers...

[tater]

No you haven't. You merely assumed it, and you picked the necessary numbers out of thin air. How far into a sandstorm would a military-grade laser penetrate before dissipating? You have no idea.

I didn't pick the numbers out of thin air, I picked an average sand particle size range for the low atmosphere suspended in sandstorms (it's a gradient, lower = bigger). You don't know, either, yet you claim it is just as effective.

Here is a simple enough boundary value for you. If we take the 50kg of sand, and place it in a tightest packing layer just off the hull, that is the BEST the 50kg can do while covering the whole ship. Grain touching grain, the beam MUST interact with the most possible particles. Is 50kg of silica armor 100% effective, yes or no? Shall we calculate how thick this must be, not even worrying about packing issues?

Assume the ship is a sphere. The surface area of the side facing the laser is 2513m^2 for a 20m radius. That's 19.9 grams per square meter. we're talking about a silicate FOIL on the hull. 20m too big? Half it. Now you have 40 grams per m^2 of silica armor. For a 100 dton sphere (~6.8m radius) you get around 169g/m62 to play with! That results in a quartz "foil" about 0.06 mm thick on the hull. 50kg of sand might be best applied as a paint.

There are other examples, but I don't need them. The point is already made. Magic numbers and handwaving don't cut the mustard with me.

Wow! Look at that, I finally managed to write a post that was fewer than 200 lines. Next I'm going to see flying pigs outside my.........errrr, never mind.

You do need them. By all means, post ANY example with actual numbers, please. Anything at all, then show how to make 50kg of sand match those initial conditions. The question is not, and has not been whether any amount of dust/sand in the air can stop a directed energy weapon, that is a given. The question is can 50kg do it for a traveller starship in certain size ranges with 100% effectiveness and be realistic enough for a player who is not a low-grade moron to suspend disbelief.

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As a reality check, 1mm thick carbon fiber sheet is about 1400 grams per square meter, and carbon is good armor vs lasers, actually.

Edited September 16, 2015 by tater

[GeneralVeers]

You do need them. By all means, post ANY example with actual numbers, please.

No. Not needed. Real-world happenings prove the general concept is sound. My mind is made up.

Though it does make me wonder if there's a point to having a noticeable gap between armour layers...

Modern tank armor already uses this concept. Having a layer of rubber or other flexible material under a ceramic armor tile causes the tile to shift when struck by a kinetic penetrator or HEAT round. The movement helps foil the effort by the ordnance to penetrate the armor.

Edited September 16, 2015 by WedgeAntilles

[Rune]

Railguns have about 30% energy transformations effiency. (electric to cinetic) Look pretty good to me. A laser weapon is more 10%. So, for a limited energy source, a railgun will probably be more efficient?

Even for a big warship, having 3 time the punch for the main armament for the same energy source is a big advantage!

Laser could still be used as secondary armament ^^

Facepalm. You totally missed my whole point. If your weapon can effectively disable a target at ten times the range, who cares how efficient it is! Your enemy is dead in the water without a targeting system for his efficient railgun before he can fire it once!

But I'd be interested to know where did you get your efficiency numbers. 10% is for what kind of lasers? I have found it very hard to get numbers on fiber-optic lasers like the ones in the current generation of 100kW-class designs. And I surely don't get 30% from the numbers in the wiki for the Navy railgun, more like slightly under 10%.

I'm not so sure. Some exotic anti-laser armours (boron/graphene composite) would require many MJ of lasing to burn through a single not-particularly-thick layer (this is a guess based on a post in Atomic Rockets - I've low-balled it to be conservative) whereas it would be brittle enough that an astronaut with gooey space glue on one glove and a hammer in the other could easily compromise a 1m section with a few good whacks. He'd be stuck to the ship, but it wouldn't take much to break it.

Heck, maybe they could defeat it with a cloud of high velocity sand particles.

Anyways, I suspect that architects would recognize the vulnerabilities of the vessels and the combat environs they'd be operating in, but be incapable of prioritizing threats properly, making it possible that there would be some warships that ended up with a compromise design that could reasonably allow lasers to maintain superior efficiency over kinetic weapons both as a blinding system as well as a kill system. Though it does make me wonder if there's a point to having a noticeable gap between armour layers...

Considering the nature of hypervelocity impacts, kinetic armoring will be done with whipple shields, much more effective per unit of mass, and already used for MMOD mitigation. In whipple armor, you recognize that your armor is going to turn to plasma at the point of contact with the projectile... but the projectile is going to turn into plasma too, so you try to get that point to be far enough from the next layer. This way, the energy is spread over a wider surface, and invested in vaporizing a larger area of that second layer, and so on and so forth. Nothing says you you can't do it with sheets of really thin carbon-carbon cloth over a frame, with some tungsten thrown in for good measure to create a composite multi-layer blanket made of micron to mm thick sheets.

Rune. This are spaceships after all. You don't have the mass budget to build them like tanks.

[baggers]

Facepalm. You totally missed my whole point. If your weapon can effectively disable a target at ten times the range, who cares how efficient it is! Your enemy is dead in the water without a targeting system for his efficient railgun before he can fire it once!

Sorry, I assumed guided projectiles for railguns.

Note that it's the actual railgun design for navy: capable of firing sub-orbital guided projectiles via railguns. Next stage is orbital, and interplanetary guided projectile fired via railguns.

In that scenario, I think "regular" ships and submarines will play a full role in interplanetary warfares as railgun mobile and stealth platforms. They certainly have many advantages.

But I'd be interested to know where did you get your efficiency numbers. 10% is for what kind of lasers? I have found it very hard to get numbers on fiber-optic lasers like the ones in the current generation of 100kW-class designs. And I surely don't get 30% from the numbers in the wiki for the Navy railgun, more like slightly under 10%.

30% was from an scientific study about electromagnetic gun used for orbital launch. I can't find it at the moment. The actual navy is more 15%, right:

-> 25 MW for 32 MJ @10 shots/min. -> 1500 MJ, compared to 32 MJ x 10 = 320 MJ so 15% efficiency.

10% for laser, ehr... found that on random internet forums about lasers ^^. Wiki say 20% maximum for carbon-dioxyde laser, and they are the more efficient at the moment.

Lets assume a small advantage for railguns effiency, especially at extreme ranges. Note a railgun can shoot behind a planet, using gravity assist for projectiles ^^

[Rune]

Sorry, I assumed guided projectiles for railguns.

Note that it's the actual railgun design for navy: capable of firing sub-orbital guided projectiles via railguns. Next stage is orbital, and interplanetary guided projectile fired via railguns.

In that scenario, I think "regular" ships and submarines will play a full role in interplanetary warfares as railgun mobile and stealth platforms. They certainly have many advantages.

30% was from an scientific study about electromagnetic gun used for orbital launch. I can't find it at the moment. The actual navy is more 15%, right:

-> 25 MW for 32 MJ @10 shots/min. -> 1500 MJ, compared to 32 MJ x 10 = 320 MJ so 15% efficiency.

10% for laser, ehr... found that on random internet forums about lasers ^^. Wiki say 20% maximum for carbon-dioxyde laser, and they are the more efficient at the moment.

Lets assume a small advantage for railguns effiency, especially at extreme ranges. Note a railgun can shoot behind a planet, using gravity assist for projectiles ^^

You know? I think I'm just going to quote myself:

Scoundrel, +1 on the sandcaster comments. This ones about lasers, tough... I'm hardly an expert in lasers either, but I think the basic physics of the thing are heavily tilted against kinetics here.

It's all a question of range, really... let's examine it a bit further, and let it be the last time I do this, at lest in this thread... let's suppose two otherwise identical hypothetical warships, one equipped with a 1MW 10km/s railgun (that's one 100kg round every second, and you will notice I am being generous with the muzzle velocity by about a factor of two or three), compared to a 1MW laser weapon, like the ones the US Navy wants on their next-gen ships (a bit of a power jump, but 100kW systems are already existing prototypes based on commercial-grade lasers):

First, the size of each weapon system. This are all wild guesses here, of course, but the railgun prototype of the US Navy is apparently already in the MW order of magnitude, and it is going to be fitted on ships. On the other hand, ~10kW laser systems are going to be installed on Humvees (actually, the new one whose name I can't remember right now, but similar size), including power systems. The 100kW laser system on the Ponce is also more like a CIWS in size than the artillery-looking railgun that doesn't include reloading or power systems on the pic, and the laser trailer from Boeing is also supposedly in this power class, and includes cooling and power systems. Let's say the 1MW hypothetical laser is slightly larger than the 1MW hypothetical railgun.

Then, as you note, we must compare efficiency, because laser are notoriously inefficient. They don't really have to, since some diode solid-state lasers get upwards of 80% efficiency in the lab, but all real-life examples have been nowhere near that, and I don't really know about the fiber lasers that this weapon systems use, so thus I happily concede that a laser will be an extremely inefficient thing, depositing more ehat in the warship than in the target. However. Railguns are also notoriously inefficient, creating a lot of heat through friction with the rails, as well as the high-power pulsed nature of their operation that makes for inefficient transmission of power. All in all, still the railgun is probably getting the upper hand here, so I will allow that the laserstar has to have much larger radiators, probably up to twice the size of the other ship (let's remember the power to use the weapon is coming form somewhere, and that somewhere will be lucky to be 50% efficient, so the railgun battleship also needs some serious radiators), with the corresponding increase in mass.

So, that works out to a mass advantage to the railgun battleship. Right? Well, let's spend it in ablative armor, and we have that laserstar by the balls, don't we? We will just close to where we can hit it, and fill it with holes.

But. "Close to where we can hit it" isn't going to be as easy. Remember, we said the ships are otherwise identical, so they can accelerate at the same rate, or a very similar one, so none has a decisive movement advantage. The only advantage is that one is armored, and the other one isn't, or not as much, or that one has a slight wattage advantage on weapons output, it's quite irrelevant. So space being what it is, they will only do battle if they want to, and they will close at the rate any one of them chooses. We might get into complicated space tactics here, but let us fix a closing rate "on the order of km/s". Could be snail pace (favours the "sharpshooter"), could be fast interplanetary trajectory (favours the "tank"). It doesn't really matter much. Because see, the laserstar has an effective range a few orders of magnitude higher than the railgun battleship.

It's really easy to work out. If the railgun is moving at 10km/s towards a 1km cross-section target that can accelerate at a measly 1m/s, for ten seconds, it will miss, 100% of the time, at ~1,100kms (actually, a bit less). So we can call that it's effective range. The 1MW laser system, with a reasonable visible-light wavelenght and a 1m primary mirror in its turrets, can have an effective range way higher than that (I don't want to go there, but the railguns is going to have to be spine-mounted on account of mass and momentum transfer, while the spine-mounted laser can easy have several turrets)... and you won't be able to fire at it anyway. Why? Well, the spot size at 1000kms for such a laser is on the order of 1m^2 (I did the math for reasons, a while ago it's short of right considering I did it for another kind of lasers). That's 1MW of power in a spot of one square meter, which turns out to be 0.1kw/cm^2... not really too hot, right? That may be able to ablate, but it'll sure take its sweet time if it tries to go through armor. What's there to worry about! We have armor! We can just hold on until we get close enough for our railgun to connect.

However, turn that spot into a sensor, and the thing will be blinded faster than you can say "photodiode". Even synthetic aperture radars will be happily burned away at that range, even if they can't be seriously fouled up by ECM, at such power levels. And you know, at 10,000kms, that is the same megawatt, but over ten square meters. Definitely not going to touch your fuel tanks or radiators, but you are already blind across the electromagnetic spectrum, so who cares? The ship is effectively dead in the water if it can't target it's fancy railgun or know which direction to run. And even at 100,000kms the 100m beam spot will be already something than optical sensors built to spot warships against space just won't be able to handle. Once the target is blind, the laserstar can then slowly match velocities and close in, staying outside the range of the railgun (and as off-axis form the railgun as it can, in case the enemy has some unopened sensor port in reserve), while it slowly melts away the radiator system to neuter the blind, armored hulk.

Once you are ready to board the overheating hull to rescue the enemy survivors, we expect our laserstar captain to jokingly congratulate the enemy on his choice of weaponry. The losing side would then proceed to develop their own flavour of laserstars, but with fancy 10m optics which turns them just as effective at ten times the range, meaning the next battle will be decided at 100,000kms. And thus a new arms race ensues, over who can blind who the farthest, until the lasers start to miss due to light-lag at much more advanced tech levels.

Rune. Paraphrasing: "in the race between sword and shield, the shield is usually unhappy at the end". So better get the longest sword possible.

As to guided railgun shots, those use lifting surfaces to perform terminal guidance in the RL concept, so you know, I don't know how good that would work for you in space... If they used rocket engines, they would be missiles. And never mind they still need a targeting system, if they are missiles they can be exploded with pathetically weak lasers.

Rune. Firing a railgun to a moving target behind a planet is an absurdly bad idea, BTW. Think about the orbital dynamics a minute, you who I assume plays KSP...

Edited September 16, 2015 by Rune

[Darnok]

Rune. Firing a railgun to a moving target behind a planet is an absurdly bad idea, BTW. Think about the orbital dynamics a minute, you who I assume plays KSP...

Why it is bad idea? It is great idea! Imagine you have two railguns on your ship. one is aiming to hit target in shortest orbit (in close range fight straight line) and other one target enemy ship side, because with curved orbits you can hit your enemy almost from behind

[Rune]

Why it is bad idea? It is great idea! Imagine you have two railguns on your ship. one is aiming to hit target in shortest orbit (in close range fight straight line) and other one target enemy ship side, because with curved orbits you can hit your enemy almost from behind

'K, example scenario, you are in low Earth orbit, orbiting stably on the other side of an enemy you want to destroy because they are invading Earth or something. I'm going to handwave your total sensor superiority so you can actually know that, of course, but let's go with that. Now, your orbital velocity is on the order of 7.5km/s. Your target's is pretty much the same, only since it's on the other side of its orbit, its vector is pointing 180º offset or thereabouts. How do you fire your single 2.5-10km/s shot so that is connects with the target, exactly?

Options:

Fire prograde: your shot either goes into a higher orbit or escapes the Earth-Moon system. On extreme rare occurrences of high-powered railguns, you make a new crater on the Moon. It would cross your orbit, with higher orbital period than yours. How does that help?

Fire retrograde: let's hope there isn't anybody living where you just dropped your payload, because it hits with more velocity than you fired it with. You are supposed to be defending those people, not bombarding them.

Fire north: you get a slightly inclined orbit with a higher apoapsis. On extreme railgun cases, you actually put the round on interplanetary trajectories, but those are unlikely since they are very far away form the 2.5km/s the Navy has tested. The only orbit your target intersects is actually yours. If you casually hit a multiple of your orbital period, watch out in the coming orbits, you might have to slightly side step your own missile.

Fire south: pretty much the same.

Fire down: if you are in a low enough orbit, the round hits the atmosphere before coming back up and it's slowed by the atmosphere. If not, you just shifted the period of it's orbit and made it intersect yours at two points, increasing it's eccentricity and orbital period. Interesting things may happen, see below.

Fire up: your shot starts to lose velocity and gain height, reaching a much higher apoapsis. If the enemy warship is in just the right position, roughly in your same orbit, and you have just the right amount of speed in your rails, and accuracy (without fins, remember), you might just have a chance to actually make it intersect with the target's orbit when he is actually going to whiz by that location on a future time. Great, right? Except as soon as the enemy sees the red-hot round going over the horizon, you would imagine they would fire up the RCS system to sidestep a few cm/s. The round doesn't miss the target until tens of minutes or hours have gone by, but in the meantime simple ballistics and knowledge of the enemy's weapons gives the target a fairly good idea of where your ship was located when it fired that shot. Great, you just revealed to the enemy you exist and have sensor advantage over them, they are likely running like hell form there, because without sensor advantage everybody is toast eventually.

So yeah, feel free to enlighten me on the orbital mechanics of your shot.

Rune. And please don't bring guided missiles into the equation, because that is another argument, even if easily debunked.

Edited September 16, 2015 by Rune

[Darnok]

'K, example scenario, you are in low Earth orbit, orbiting stably on the other side of an enemy...

I am talking about scenario where ships are less than 90º from each other.

So shooting simple projectile in straight line would be possible. yes projectile would change into fireball revealing your position if you would aim in atmosphere, but its apoapsis would be closer to the Moon than the Earth (I would have to wait few days for those bullets to come back?) and I didn't said I would fire single projectile and wait it hits target it would be firestorm.

Projectiles should be made out of something that can melt under high temperature, so you wouldn't bomb people on Earth.

First I would shoot projectiles that would make longer orbit and hit your side or almost from back, so you wouldn't detect them in atmo

As for guided missiles, I know they are different thing... but you could send object that can only increase its velocity and when fuel is depleted it explodes changing into small projectile storm, it could be build in way that it also explodes when it is heated by lasers.

Edited September 16, 2015 by Darnok

[Kibble]

Isn't a "guided projectile" just a "spacecraft"? And a railgun is just an alternate way of putting it on an intercept than a cheap, regular rocket stage!

[Rakaydos]

I'm more interested in using railguns to deploy disposable sensor platforms designed to have stealth in space at tactical ranges and durations (Active cooling, cold gas RCS, ect) that can get clear of the enemy's laserblind and have their own sensors, tramsmitting back to the mothership.

Alternate versions can mount weapon systems- if they can remained undetected long enough to get into effective Casabla Howitzer range, game over. These arnt Missiles, but they're Torpedos, at least.

[GeneralVeers]

Isn't a "guided projectile" just a "spacecraft"? And a railgun is just an alternate way of putting it on an intercept than a cheap, regular rocket stage!

Have the best of both worlds. Launch your guided missiles using a railgun.