Homemade coil gun

[Sky Captain]

So even if you made one that shoots 7.62x51 bullet at 1000 m/s it would still be perfectly legal to carry around?

[CaptainChewbacca]

I think at 1000 m/s you'd get some sort of compression/ignition of the air, which might count as an explosion. If not, then yes, under federal law it would be legal to carry around.

Of course, as soon as you point it at someone...

[dragon]

Considering the speed of sound at sea lever is approx 340m/s so you are talking an object 2.9 times to the speed of sound. I'm thinking the authorities might have a problem with that.

[General Zod]

I think at 1000 m/s you'd get some sort of compression/ignition of the air, which might count as an explosion. If not, then yes, under federal law it would be legal to carry around.

Of course, as soon as you point it at someone...

Ever see Youtube videos of the Navy testing their own railguns? The air's heated up so much that you do see a significant amount of flame from the barrel.

[Steel]

I think at 1000 m/s you'd get some sort of compression/ignition of the air, which might count as an explosion. If not, then yes, under federal law it would be legal to carry around.

Of course, as soon as you point it at someone...

Ever see Youtube videos of the Navy testing their own railguns? The air's heated up so much that you do see a significant amount of flame from the barrel.

I think thats actually about half the rails you're seeing there. One of the reasons they're not going to see service any time soon.

[Chaotic Neutral]

Couldn't they make a version that fires the projectiles much slower, and give it an explosive inside? The railgun wouldn't melt, and the hit would still hurt.

[Starglider]

Couldn't they make a version that fires the projectiles much slower, and give it an explosive inside? The railgun wouldn't melt, and the hit would still hurt.

If you're making a low-velocity grenade launcher, why not just use compressed gas? Vastly simpler, cheaper and more reliable.

[General Zod]

Couldn't they make a version that fires the projectiles much slower, and give it an explosive inside? The railgun wouldn't melt, and the hit would still hurt.

That defeats the whole point of a railgun. Which is to have highly destructive projectiles you can lob at high velocities without having to worry about storing dangerous explosives that could endanger your ship if it gets hit.

[starslayer]

I think at 1000 m/s you'd get some sort of compression/ignition of the air, which might count as an explosion. If not, then yes, under federal law it would be legal to carry around.

No, you don't. Modern tank guns have muzzle velocities much higher than this (an Abrams' gun has a muzzle velocity of ~1500 m/s), and this kind of thing doesn't happen to their projectiles. With rail guns, that large muzzle flame is the plasma that used to be the rails, like Steel said, not the air being heated by the passing of the projectile.

[Sarevok]

Ah but we are talking about coilguns here. There is no rail erosion problem to deal with. So giant plasma plume as the gun destroys itself after a single shot is unlikely.

[Sea Skimmer]

High power coilguns replace the rail erosion problem with a switch erosion problem and a fair number of other hardware problems waiting to be solved. The massive current you need to make the thing work at a militarily useful power have to be shunted from one coil to another very rapidly. This is not easily done without being destructive to the contact points as you end up requiring gigawatt scale energy pulses. This shunting also limits the effectiveness of the magnetic field, since its not being kept at peak power every last millisecond which forces power requirements up even higher.

If you get up into ICBM velocities then projectiles will start turning the air into plasma, but that's 6,000 meters per second

[adam_grif]

Semi-related question:

As ABM systems improve drastically, could we see the development of railgun munitions with nuclear payloads as a way to deliver fast, "cold" (so it's much more difficult to intercept) strategic weapons?

[Sea Skimmer]

Semi-related question:

As ABM systems improve drastically, could we see the development of railgun munitions with nuclear payloads as a way to deliver fast, "cold" (so it's much more difficult to intercept) strategic weapons?

I doubt a nuclear warhead would like being subject to that much intensive magnetism. But even if it didn't mind, any artillery cannon railgun or not with enough velocity to compete with ICBMs would be the size of the Iraqi Babylon Gun, real expensive and fixed in point of aim. At best you could make bunker complexes like the German V-3 aimed at various targets around the world. This would generally suck, because each gun can only shoot in one direction while a group of missile silos can be freely retargeted. I mean, you could put the giant gun on a giant armored turntable if you wanted but that turntable is certain to cost more then building a bunch of extra gun barrels into hillsides.

The main issue is ABM exploits the low maneuverability of the missile RV. A shell makes that even worse. What you want is a long range weapon that can not only go fast, but make turns and attack from more then one altitude or trajectory. You can get that out of hypersonics, or suborbital glider craft like the X-20 Dynasoar, a concept now returning full bore for conventional weapons projects like HTV-2. Artillery and rockets certainly have some great value for combating battlefield ABM though.

Stealth is basically hopeless in near earth space because no matter how cold you get the warhead the background of space is still going to be colder. A half degree difference is enough to be spotted. Radar stealth might help knock some distance off detection ranges, but knocking even 1,000 miles off a 3,000 mile range UHF early warning radar... well this isn't that helpful.

[adam_grif]

But even if it didn't mind, any artillery cannon railgun or not with enough velocity to compete with ICBMs would be the size of the Iraqi Babylon Gun, real expensive and fixed in point of aim.

The eventual aim of the Navy's railgun project is to get the projectile to hit 5.8 kips, which is halfway to escape velocity. I hardly think you need a Babylon gun to get twice that speed if that's theoretically achievable on a cruiser mount or something like that.

Of course, that's if we're trying to replace the functionality of an ICBM. I was thinking more along the lines of MRBM niche, where the 6-7 km/s makes time to target on the order of a couple of minutes. Mounted on a submarine or something like that.

[Starglider]

Of course, that's if we're trying to replace the functionality of an ICBM. I was thinking more along the lines of MRBM niche, where the 6-7 km/s makes time to target on the order of a couple of minutes. Mounted on a submarine or something like that.

Aside from the crazy ablation and drag issues of trying to do 7 km/s through the lower atmosphere, a 35 metre accelerator (the biggest you could conceivably put on a submarine) would have to impose an average acceleration of 71000 g. Nuclear weapons can be hardened to hundreds of g of acceleration and thousands of g of instantaneous shock (as in the Sprint interceptor), but I really doubt you can build one that will survive a 70,000 g launch. Even shell guidance electronics can't (for the new DDG-1000 class);

The gun. Ah yes, the gun. It fires shells, 155mm ones. Guided shells whose electronics can withstand 40,000G. The acceleration in the gun barrel is 100,000G. Ooops.

[Chaotic Neutral]

Isn't the solution for massive acceleration just a longer barrel and less acceleration?

[Sea Skimmer]

Isn't the solution for massive acceleration just a longer barrel and less acceleration?

Yes, which is why you are going to end up with a very long gun that must be bolted into a very strong framework to hold it straight.. and this is almost certainly going to end up as a fixed installation or else only mobile by rail and most likely only then in pieces if we assume projectiles with very high resistance can be built. The fact that this is an EM gun makes everything worse because the barrel will be far heavier then a conventional gun barrel.

Note that the 35 meter barrel suggested above, would still be longer then the barrel of the German 80cm Gustav gun or the smaller caliber but longer ranged K12E and Paris gun's.

[adam_grif]

As long as you don't mind not having the gun mounted on a turret and being stuck with only 20-25 degree angling left and right, you can just have the railgun being largely internal sticking out at the front/top of the Sub. I'm not sure how that would work out for taking up internal volume and would result in a funny shaped interior (to say the least), but if the length of the sub is 170 meters like an Ohio class sub, you should easily to go 3-3.5x the length of Starglider's 35 meter proposal. Even at only 2x length that puts the average acceleration at under the 40,000, and at 3x length it puts it at ~22,700 G's.


For a stationary installation that wants to whip it up to 15 kips (a number I just pulled out of my ass), with an acceleration of 500 G's (another number from my ass, to satisfy the "hundreds of G's" requirement from SG) the round would have to accelerate over 30 seconds and the barrel length would need to be 225 kilometers.



Something isn't right here. Are you sure that "hundreds of G's" is all that nukes can take? Or is that just what they were built to tolerate since they all used rockets anyway that never had to go much higher?

[Sea Skimmer]

As long as you don't mind not having the gun mounted on a turret and being stuck with only 20-25 degree angling left and right, you can just have the railgun being largely internal sticking out at the front/top of the Sub.

I'd love to see a drawing of how you imagine you'll have a traversing only partially internal gun on a submarine that doesn't create a massive amount of flow noise. You'd need some huge curved slot and some elaborate exposed equipment to traverse the thing or something.

The whole point of a submarine is stealth, which makes regularly firing long range ballistic shells a dubious operational concept from the onset when nukes are involved. The only realistic way of mounting a gun on a modern submarine would be to make it vertical and able to lock down under a hatch in the recoiled position. That means the hull diameter is your limit. Anything else is going to make too much noise and have too many moving parts to be sane.

I'm not sure how that would work out for taking up internal volume and would result in a funny shaped interior (to say the least), but if the length of the sub is 170 meters like an Ohio class sub, you should easily to go 3-3.5x the length of Starglider's 35 meter proposal. Even at only 2x length that puts the average acceleration at under the 40,000, and at 3x length it puts it at ~22,700 G's.

Great so this idea will cost six billion dollars in ordered to build an Ohio sized hull to mount a single gun it has to surface to fire. You do also realize right that a submarine sits LOW in the water which means WAVES break across the deck on the surface right? I don’t know how you intend to exploit a significant portion of the ships length to hold a barrel while it’s also somehow elevated above this. Do you expect the length of the submarine splits open to elevate the gun or something?

The whole idea of a moving turret on a submarine with a 105 meter gun barrel is preposterous to say the least. Its certainly not going to beat out an Ohio class armed with missiles for strategic attack, all the more so since those missiles need not always be Trident. You could pack three or four IRBMs into the same silo and with far less effort then designing and building such a freakish submarine for example. Enemy ABM defense requirements are now quadrupled and yet you still retain enough missile range to strike any point on land. The downside would be you only have 3-4 nuclear warheads instead of 8 but this doesn't matter so much now when aresnals have been heavily cut back.

For a stationary installation that wants to whip it up to 15 kips (a number I just pulled out of my ass), with an acceleration of 500 G's (another number from my ass, to satisfy the "hundreds of G's" requirement from SG) the round would have to accelerate over 30 seconds and the barrel length would need to be 225 kilometers.

11.2km/s will already take you not to orbit but totally out of earth’s gravity so you are not likely to need to go higher then that.

Something isn't right here. Are you sure that "hundreds of G's" is all that nukes can take? Or is that just what they were built to tolerate since they all used rockets anyway that never had to go much higher?

A far more relevant criteria is the shock of the impact when a nuclear bomb actually hits the ground for a ground burst. Existing designs can take the high hundred of gravities doing that, this is what limits the performance of the B-61-11. Higher shock tolerance designs are possible, but even an order of magnitude increase only gives you 10,000 G resistance. That’d make a big difference for an gravity bomb striking dirt, it still leaves the gun in a tough spot.

Shock hardening also simply requires volume. You’ve got plenty of volume in a free fall gravity bomb, a lot of a nuclear bomb is just empty space for ballistic shaping, but an artillery shell can’t be so forgiving. Unless this 105 meter long gun is also supposed to be of a massive caliber?

[Sarevok]

Assuming guided shells is not the very intense magnetic field generated by the rail or coil gun also going to interfere with the electronics ?

[Sea Skimmer]

Yeah it would, though a GPS guidance system is simple enough that the circuitry could be highly ruggedized, and you don’t need any conventional explosive fusing or PAL equipment. It’s the fusing I would have the greatest concern about. Induce a current in that and the nuke blows itself apart. The USN still hasn’t solved shielding its aircraft against EM catapult emissions, this is not a hopeful sign considering that for that application the magnetic field is under a steel deck rather then wrapped around and actually flowing across a projectile.

Personally I wouldn’t be surprised if high power EM guns simply never work to any worthwhile degree, but I think the last ten years of technology alone has also shown very plainly that we do not know the limits of what we can do with inventing new materials an manufacturing processes so who knows. Luckily electro thermal cannon provide a huge alternative field of research, and for a fixed installation a conventionally propelled space launch cannon is within sanity, if maybe not much practical reason.

[adam_grif]

I'd love to see a drawing of how you imagine you'll have a traversing only partially internal gun on a submarine that doesn't create a massive amount of flow noise. You'd need some huge curved slot and some elaborate exposed equipment to traverse the thing or something.

Are you imagining that I'm saying that this will be swimming around with the gun sticking several meters out of the top of the submarine?



Red is the hull (it's an entirely rectangular submarine obviously), black is the gun and green is the approximate traversal range of the gun. If this internal gun that angles up a bit to protrude when you're firing it (there would be some sort of door at the top, obviously) is still somehow a problem for Stealth or "too complex to be sane", then it can simply be entirely fixed, with the submarine rotating to change the facing and varied velocity to hit closer targets. Variable velocity is one of the advantages of EM guns after all.

I don't understand why you think this is somehow insanely complex or stealth defeating or something though. Obviously it has to open hatches and aim up to fire out of the water, but it's not like an SSBN firing it's missiles is stealthy anyway.

You do also realize right that a submarine sits LOW in the water which means WAVES break across the deck on the surface right?

Is this significant enough an issue to prevent it's operation?

If so, is there some reason why a sub couldn't be designed to not sit low in the water, perhaps with a specialized section housing the gun that is the same height as the sail? If it already has an irregular structure like that I can't imagine it would destroy stealth or something.

Shock hardening also simply requires volume. You’ve got plenty of volume in a free fall gravity bomb, a lot of a nuclear bomb is just empty space for ballistic shaping, but an artillery shell can’t be so forgiving. Unless this 105 meter long gun is also supposed to be of a massive caliber?

I'm a little lost here. Are you saying that shock hardening is equivelant to the acceleration it can take, or are you saying that the railgun warheads would be useless because they can't groundburst?

Why don't the bomb designers just have a faux-groundburst setting that triggers detonation slightly above ground?

[Sea Skimmer]

Are you imagining that I'm saying that this will be swimming around with the gun sticking several meters out of the top of the submarine?

You have to do that, or else the entire barrel has to move forward enough to rise above the waves, so yeah that what seems to be required.

[img]http://www.mario-kart.net/gamespy/image ... ca.PNG[img]

So yeah... that's going to suck hard. You don't have enough elevation for proper range and your taking up a massive amount of absurdly expensive space and the barrel is totally exposed to the effects of the ocean.

Red is the hull (it's an entirely rectangular submarine obviously), black is the gun and green is the approximate traversal range of the gun. If this internal gun that angles up a bit to protrude when you're firing it (there would be some sort of door at the top, obviously) is still somehow a problem for Stealth or "too complex to be sane", then it can simply be entirely fixed, with the submarine rotating to change the facing and varied velocity to hit closer targets. Variable velocity is one of the advantages of EM guns after all.

Your going to need velocity like mad when you can't elevate to the required angles for optimal ballistics. This mounting will not work. You need 55 degrees minimal which means the whole gun has to move if you install it anything like this. In reality though more like 80 degrees might be optimal for such a high velocity with a guided shell. See Advanced Gun System and Vertical Gun System before it.

I don't understand why you think this is somehow insanely complex or stealth defeating or something though. Obviously it has to open hatches and aim up to fire out of the water, but it's not like an SSBN firing it's missiles is stealthy anyway.

You don't understand because you don't understand ballistics or a couple other factors at work. An SSBN firing missiles can salvo them all off rapidly, and at least its not cruising on the freaking surface to do it.

Is this significant enough an issue to prevent it's operation?

You get water down the barrel and the gun will explode when you fire it. Never mind the fact that you now need a railgun made internally of metals which are proof against saltwater immersion. In anything but a flat glassy calm sea a submarine on the surface looks something like this.
http://www.veteran.com/files/images/US- ... review.jpg

Your railgun firing out of the top of the deck is not going to function in conditions like this, and you've already completely exposed the boat by surfacing. To be realistic you need a weapon which you can fire from periscope depth and extend the barrel enough to rise above wave action. This is why a vertical gun is really the only thing that has a chance. It can then use almost all of its barrel length to gain elevation, and need only move up and down which is fairly simple compared to traversing or elevating. It would also fire equally well in every direction, removing the tactical limitation of needing to point the sub at a specific target.

If so, is there some reason why a sub couldn't be designed to not sit low in the water, perhaps with a specialized section housing the gun that is the same height as the sail? If it already has an irregular structure like that I can't imagine it would destroy stealth or something.

Submarines sit low in the water because they are fucking submarines. Even if you designed the submarine with excessive ballast tank capacity so it would sit higher with more free board, which would slow down surfacing and diving and make the sub much more expensive in the process, you'd still have the problem of the basic hull shape easily allowing waves to wash over the deck. Placing a gun inside the sail could work, but not if you insist on this ridiculous a mounting method for a 100 meter barrel.

Not that it matters at all though because we already know this would be stupidly expensive and yet fails to offer a very convincing solution to ABM in the first place. Its just a money spending exercise of technology.

I'm a little lost here. Are you saying that shock hardening is equivelant to the acceleration it can take, or are you saying that the railgun warheads would be useless because they can't groundburst?

The point was that nuke design right now is NOT based on the soft acceleration of rocket launch or free fall bomb released, its based on the far more demanding acceleration of impact. You design shock hardening to count a specific level of acceleration for a specific period of time (some shock hardening relies on crushing foam ect... so time matters). The more effective shock hardening you want the more volume and weight it will consume. So that forces up the projectile size rapidly. In a bomb that isn't critical, but it is critical in a shell.

Why don't the bomb designers just have a faux-groundburst setting that triggers detonation slightly above ground?

Because then it wouldn't be a ground burst now would it? Actually contacting the earth or burrowing just a few feet makes a tremendous difference on how effectively the blast is transmitted into the ground. That makes a huge difference in how deep of a bunker the nuke can take out and how big a crater it blasts. So much so that at 3ft a 300kt nuke could already be as effective as a 5.6 megaton nuke that went off on the surface. So the point is, designers already did all the easy shock hardening. Anything else you are going to pay for big time and you need a radical increase to make this work at all.

[Sky Captain]

During cold war US built nukes that fitted inside 280 mm artilery shell and worked after being fired from cannon so it is possible to design nuke that can survive high acceleration. Obviously railgun of similar length would produce more rapid acceleration so it would recquire even more acceleration hardening, but I suppose with modern technology it would be possible to build more durable nuclear artillery shells than it was possible in 1955.

Anyway I think main point of railguns is to be able to fire artillery shells at distances that currently are possible to reach only with missiles and do it cheaper than missile or air attack of similar effectivness would cost. If you need to build multi billion dollar platform just to be able to move your railgun around then it kinda defeats the whole purpose of it being cheaper than already existing missile systems.

[LaCroix]

Sorry if I interrupt, but isn't firing a high-energy magnetic device inside a floating steel tube a way of asking for trouble?

-Hull compression due magnetic field
I think the boat might handle this fine, but with such a massive field, it might as well be damaged by the short but huge impulse.

-Hull/component magnetizing
Just imagine the tin mugs sticking to the hull everywhere - compass go haywire - the everything used on the boat and the hull itself must be made of non-magnetic material.
And we know that exposure to strong magnetic fields is not easy on humans as well, especially if long-term.