Navy's New Railgun

[BigGrib]

http://www.foxnews.com/story/0,2933,327205,00.html

Check this out, the Navy's New Railgun

[OuchProgramme]

Woah...dang.

That's pretty intense.
Looks awfully big though

[jimmy101]

A few inaccuracies and/or misleading statements.

fired the electromagnetic railgun at what they said was a record power level: 10 megajoules

That is input energy and not output energy. If the railgun has the same kind of efficiencies as typical coilgun, figure the muzzle energy is about 1% of the input energy, 100KJ.

I wonder what the muzzle energy is of a 16" naval gun? Does it approach a megajoule?

Because the railgun uses electricity and not gunpowder to fire projectiles, it eliminates the possibility of explosions on ships.

Eliminates? Not really. Guess what a capacitor bank holding megajoules of energy does when it fails? It explodes.

Pretty cool, but my gut feeling is the chances of actually replacing "the standard 5-inch gun on its ships" is pretty slim.

[DYI]

Eliminates? Not really. Guess what a capacitor bank holding megajoules of energy does when it fails? It explodes.

Yeah, thats what I was thinking of. But cap banks don't explode when they get hit by an explosive round fired at the ship, they explode due to internal failure.

And I believe that high velocity railguns/coilguns achieve much higher efficiencies, over 25% in some cases. This may only be coilguns though. And 16" naval guns DEFINITELY have muzzle energies over 1MJ, but I don't know about the 5" guns. I could see the railguns being used as naval weapons, simply for their longer effective range and less explosive munitions being stored on the ship, but I can also see reliability issues killing them.

[clide]

A few inaccuracies and/or misleading statements.

fired the electromagnetic railgun at what they said was a record power level: 10 megajoules

That is input energy and not output energy. If the railgun has the same kind of efficiencies as typical coilgun, figure the muzzle energy is about 1% of the input energy, 100KJ.

That would make the sentence that followed just plain wrong then?

The previous railgun power-use record was about 9 megajoules of muzzle energy.

[Skywalker]

I think they get better efficiency, maybe 50%? Don't quote me on it, though.

[jackssmirkingrevenge]

I wonder what the muzzle energy is of a 16" naval gun? Does it approach a megajoule?

According to this data (from an excellent site), we're talking of over 1,200 kg at around 760 metres per second, so 350,000,000 joules more or less

Imagine being hit by 25 million airgun pellets, all at the same time

[Ragnarok]

@Jimmy:101: Actually, a good rail gun is about 30 to 50% efficent if it's got a high enough injection velocity. At those speeds, it's going to be doing pretty well.

And a decent amateur coilgun is closer to 5% efficent - some high grade laboratory coilguns can do 20% efficiency or more.

1% efficiency is what ghetto coilguns are likely to get.

[jackssmirkingrevenge]

Have a look here for some details of the US Navy development.

[Hotwired]

Can't imagine a railgun replacing the good old deck cannon any time in the forseeable future.

In the demonstration Thursday, engineers fired the electromagnetic railgun at what they said was a record power level: 10 megajoules.

The previous railgun power-use record was about 9 megajoules of muzzle energy.

So it is talking muzzle energy when it says 10MJ.

I wonder if they're still having to replace the rails after each shot.

[jackssmirkingrevenge]

there's a more detailed article about the equipment in question here.

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.

[Hotwired]

To hell with the cost, the semi-destruction of the gun after each shot and to hell with the weight!

We've got a cool-sounding weapon and you dont

[Ragnarok]

I dug up some more info on this.

A staggering muzzle velocity of 2520 m/s (8267 fps) which although a lot, is somewhat short of the railgun velocity record of 16 km/s (52,500 fps).
The actual muzzle energy was quite a bit higher than just 10 MJ - 10.64 MJ (7,850,000 ft-lbs) with a 3.35 kg (7.4 lbs) projectile.

Possibly most amazing, the currents developed in the rails are around 3 million amps. And here's a pretty photo.

The efficiency of the final goal of a 64 MJ prototype (which will need 6 million amps) is expected to be around 40%, so I'd say the current version must be getting around that.

What I want to know is what did they use as a backstop? Certainly you couldn't stop anything like that with, say, for example, a garden shed.

[Hotwired]

Over here in the UK theres a testing range which is literally just pointing the guns out to sea.

Locals got a bit miffed that DU rounds were creating doubled headed fish or something though.

Mind you, enough reinforced concrete and a big enough hillside will stop any KE round

[Pilgrimman]

My absolute favorite weapons are railguns. When I work for DARPA (I hope ) I want to work on one! Have you guys seen the old railgun test video from the Navy? Just google it, it should come up. It's pretty sweet, too! I hope someone produces a viable plasma rail version with plasma armatures so that the rails never have to be replaced!