World's Most Powerful Rail Gun Delivered to Navy

[Tsyroc]

I figured I'd put this in Science instead of News because the technical information makes up more of the article than the "news" portion does.

World's Most Powerful Rail Gun Delivered to Navy

For true sci-fi fans, any mention of a real-world rail gun will draw an instant, slightly audible gasp. Instead of relying on chemical propellants -- such as gunpowder -- a rail gun uses magnetic "rails" to launch a solid, nonexplosive projectile at incredible speed. Theoretically, rail guns would be able to precisely strike targets at extreme ranges, and would negate the risks associated with carrying around tons of explosive ammo. More to the point, they're cool-sounding, just like lasers.

Which is why the news that BAE Systems has delivered a functional, 32-megajoule Electro-Magnetic Laboratory Rail Gun (32-MJ LRG) to the U.S. Naval Surface Warfare Center in Dahlgren, Va., is exciting. Installation of the laboratory launcher is currently under way, and according to BAE, this is the first step toward the Navy's goal of developing a tactical 64-megajoule ship-mounted weapon.

The lab version doesn't look particularly menacing -- more like a long, belt-fed airport screening device than like a futuristic cannon -- but the system will fire rounds at up to Mach 8, drawing on tremendous amounts of electricity to generate the current for each test shot. That, of course, is the problem with rail guns: Like lasers, they're out of step with modern-day generators and capacitors. Eight and 9-megajoule rail guns have been fired before, but providing 3 million amps of power per shot has been a limitation. At 32 megajoules, this new system appears to be the most powerful rail gun ever built, and the x is installing additional capacitors at the Dahlgren facility to support it. The planned 64-megajoule weapon, if it's ever built, could require even more power -- a staggering 6 million amps.

According to Dr. Amir Chaboki, the program manager for Electro-Magnetic Rail Guns at BAE Systems, "The power is available. The challenge is how you use it." The Navy’s electrically propelled DDG 100 Destroyer, Chaboki says, is a prime candidate for the final 64-megajoule system. Around 72 megawatts (MW) of the vessel's power can be used for propulsion. But during combat, the destroyer's speed could be brought down, freeing up energy for a rail gun. Chaboki calculates that firing the 64-megajoule weapon six times per minute would require 16 MW of power, which would be supplied by either onboard capacitors or pulsed alternators. The more daunting challenge is the force of the rail gun itself: A few shots can dislodge the conducting rails -- or even damage the barrel of the gun.

While the 32-MJ LRG should start firing soon, it could take another 13 years for a 64-megajoule system to be built and deployed on a ship. The Marines, in particular, are interested in the potential for rail guns to deliver supporting fire from up to 220 miles away -- around 10 times further than standard ship-mounted cannons -- with rounds landing more quickly and with less advance warning than a volley of Tomahawk cruise missiles.

Effective rail guns will require a major breakthrough in materials between now and 2020, to keep the guns themselves from being shredded by each high-velocity barrage. Which means that for now, rail guns are precisely like lasers in one crucial way: They're Holy Grails, irresistible precisely because they're out of reach

I thought the last bit was pretty good. Keep dreaming people

[Kodiak]

Now I'm even more depressed that I accepted a job in semiconductor before I heard back from BAE. I'd be interested to know how large the entire 64 MJ system would be. I hadn't thought they'd even got this close to practical application of railgun technology, but I'm glad the article still acknowledges that they're a long way off from being useful.

[Einhander Sn0m4n]

Oh yummy. What's the calibre and bore shape? I'm assuming roughly circular and 155mm, probly also 50-70 calibres long, too.

I'm actually more interested in the projectile/armature designs, myself.

[Darth Wong]

The wear on the rails is a serious problem with no projected solution. I find it hard to believe that railguns could ever become viable in this role, although I suppose I shouldn't say it's impossible. Better men than me have gotten burned for saying that sort of thing in the past, but it does seem rather implausible.

[Darth Wong]

Now I'm even more depressed that I accepted a job in semiconductor before I heard back from BAE.

There are some people out there who work on really "cool" things, but the harsh reality for most of us is that we end up working on boring shit. I met an engineer once who spent 20 years doing nothing but designing wiring harnesses for the doors in cars. At the end of the day, you just want to pay the damned bills.

[Einhander Sn0m4n]

The wear on the rails is a serious problem with no projected solution. I find it hard to believe that railguns could ever become viable in this role, although I suppose I shouldn't say it's impossible. Better men than me have gotten burned for saying that sort of thing in the past, but it does seem rather implausible.

I hear rumors that they're working on solving it.

[wjs7744]

I met an engineer once who spent 20 years doing nothing but designing wiring harnesses for the doors in cars.

Twenty years? You'd think he would have gotten it right by then. (All hail my tremendous ignorance of engineering)

[Gullible Jones]

Hmmm... Forgive my ignorance, but why not use a coilgun? Are they less efficient?

[wjs7744]

Hmmm... Forgive my ignorance, but why not use a coilgun? Are they less efficient?

I'm far from an expert, but I understand that they use an electric current to drive the projectile, while a railgun uses current induced by the movement of the projectile itself. That would mean that there is some positive feedback in the railgun, not to mention that it isn't limited by how fast you can switch the electromagnets off and on again like a coilgun.

Now one of the more scientifically minded members will post there own explanation and make me look like a fool. Just you watch.

[Kodiak]

Now I'm even more depressed that I accepted a job in semiconductor before I heard back from BAE.

There are some people out there who work on really "cool" things, but the harsh reality for most of us is that we end up working on boring shit. I met an engineer once who spent 20 years doing nothing but designing wiring harnesses for the doors in cars. At the end of the day, you just want to pay the damned bills.

Yeah, I was faced with the choice of "Boring Job" vs. "Having my first child be born without insurance". It wasn't much of a choice, really.

[Darth Wong]

I met an engineer once who spent 20 years doing nothing but designing wiring harnesses for the doors in cars.

Twenty years? You'd think he would have gotten it right by then. (All hail my tremendous ignorance of engineering)

Every time they design a new model of car, the routing pathways are different, so you need to design new harnesses. Obviously.

[Ariphaos]

Hmmm... Forgive my ignorance, but why not use a coilgun? Are they less efficient?

A coilgun is limited by magnetic saturation - that is, in ferromagnetic materials, there is a point at which you cannot accelerate them any faster.

I'm missing something in the basic math for figuring out just how fast it is, however, so I couldn't tell you how fast it was. I am not sure, for instance, if

There is also the issue that, in order to achieve optimum efficiency, individual coils cannot be spaced evenly along a barrel, and need some pretty attractive timing. A railgun, on the other hand, is a technically simple device in comparison.

[Darth Wong]

And the faster the projectile travels down a coilgun's mechanism, the more precise the timing needs to be. With a railgun, increased speed is basically a function of how much power you can deliver and how much erosion you can tolerate without shredding the mechanism.

[Ariphaos]

Ghetto edit: I'm honestly not sure if it's even possible to have such a thing as an effective personal coilgun, since there is an acceleration limit, there is a minimum length of barrel required to achieve a certain speed.

[Gullible Jones]

Out of curiousity, what about using superconducting coils (for a large gun)? Would the cooling systems be excessively bulky and/or otherwise unfeasible for naval use?

(Re personal coilguns... Thanks for the tip. Looks like the background of my SF-universe-in-progress is going to need a bit of editing. )

[Hawkwings]

Superconducting coils have the same problem: timing. It doesn't matter how good the conductivity is if you can't control it.

[Sea Skimmer]

I find it hard to believe that timing could be a long term obstacle to developing a coilgun. Even back in WW2 the Germans were able to build cannon which had multiple firing chambers spread along the length of its barrel. Each chamber fired in succession precisely as the shell passed to build up to an unprecedented 1,500m/s velocity. The timing system worked, but the barrel had a tendency to burst because propellant gas would leak past the shell and prematurely ignite firing chambers. This concept was standardized for Hitles V-3 super cannon farm.

PObvisouly the timing demands here are much greater, but just look at GPS Surveying. Using nothing but normal GPS timing data corrected by ground stations, it can obtain accuracy within five millimeters in calculating your position on the earth’s surface. If that’s what you can do with an air transmission of data, then a big hardwired actively cooled gun barrel should be a whole lot easier

Barrel erosion has no real solution, and the jobs we want railguns for mostly involve high volumes of fire. It’s too bad we don’t have battleships to shoot them at, then a barrel life of as little as 100 rounds would become acceptable.

[Surlethe]

Would it be possible to use some sort of maglev to reduce friction, or would that dick with the firing mechanism?

[Pu-239]

Well, you still need to have a (large) current flowing through the projectile (it works since the motion induced is at right angles to the electric field going around the rails and the direction of current (perpendicular to the projectile across the rails) so no.

Perhaps you can use induction to transfer current through the projectile w/o contact? Have a transformer in the projectile to pick up AC from a series of coils on a third rail while current is flowing through the other two rails w/ their direction synchronized to the AC. Probably won't work due to the huge currents required might not be suitable for this purpose (windings in transformer and coils would probably fry, since they must be much thinner than the rails). Superconductors maybe? Although possibly you'd have coils blowing themselves apart too due to the same mechanism that would otherwise propel projectile- how do they transmit and supply power to the rails? Just really really thick wires to the capacitor/compulsator bank placed safely apart?

[nickolay1]

Yes, because the projectile needs to conduct current.

[nickolay1]

Perhaps you can use induction to transfer current through the projectile w/o contact? Have a transformer in the projectile to pick up AC from a series of coils on a third rail while current is flowing through the other two rails w/ their direction synchronized to the AC. Probably won't work due to the huge currents required might not be suitable for this purpose (windings in transformer and coils would probably fry, since they must be much thinner than the rails). Superconductors maybe? Although possibly you'd have coils blowing themselves apart too due to the same mechanism that would otherwise propel projectile- how do they transmit and supply power to the rails? Just really really thick wires to the capacitor/compulsator bank placed safely apart?

This would not work because such a transformer would have to be immense. Furthermore, a railgun requires a DC pulse.

[Pu-239]

Perhaps you can use induction to transfer current through the projectile w/o contact? Have a transformer in the projectile to pick up AC from a series of coils on a third rail while current is flowing through the other two rails w/ their direction synchronized to the AC. Probably won't work due to the huge currents required might not be suitable for this purpose (windings in transformer and coils would probably fry, since they must be much thinner than the rails). Superconductors maybe? Although possibly you'd have coils blowing themselves apart too due to the same mechanism that would otherwise propel projectile- how do they transmit and supply power to the rails? Just really really thick wires to the capacitor/compulsator bank placed safely apart?

This would not work because such a transformer would have to be immense. Furthermore, a railgun requires a DC pulse.

Hrm, forgot about it being a pulse- well, if it's a pulse, since the current is changing that dispenses w/ the need for AC right? Of course, that doesn't do anything about transformer size...

[sketerpot]

Attention, "Popular Mechanics":

Amps are a unit of current! Watts measure power! Joules measure energy! They are not the same thing!

[Stravo]

Is there a way to create a swappable magnetic coil system sort of like replacing the barrel of a burned out machine gun in WW2. After you fire a certain amount of shots you swap out the damaged coils and insert the new coils. It might take some time but I'm willing to bet that US Navy ships won't be worrying too much about return fire while this is happening and any surface ships engaged by such a weapon won't last long enough for the barrel swap system to be much of a hindrance in combat.

[Beowulf]

The problem with railguns isn't that the coils get damaged, it's that the rails the projectiles ride along get severely eroded away. Also, these rails are fairly large pieces of metal. Swapping them isn't going to be easy while the ship is underway.