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Allen McDuffee writes the US Navy's latest weapon is an electromagnetic railgun launcher that can hurl a 23-pound projectile at speeds exceeding Mach 7 with a range of 100 miles turning a destroyer into super-long-range machine gun able to fire up to a dozen relatively inexpensive projectiles every minute. The Navy says the cost differential $25,000 for a railgun projectile versus $500,000 to $1.5 million for a missile will make potential enemies think twice about the economic viability of engaging U.S. forces. "[It] will give our adversaries a huge moment of pause to go: 'Do I even want to go engage a naval ship?'" says Rear Admiral Matt Klunder. "Because you are going to lose. You could throw anything at us, frankly, and the fact that we now can shoot a number of these rounds at a very affordable cost, it's my opinion that they don't win."
Engineers already have tested this futuristic weapon on land, and the Navy plans to begin sea trials aboard a Joint High Speed Vessel Millinocket in 2016. Railguns use electromagnetic energy known as the Lorenz Force to launch a projectile between two conductive rails. The high-power electric pulse generates a magnetic field to fire the projectile with very little recoil, officials say. Weapons like the electromagnetic rail gun could help U.S. forces retain their edge and give them an asymmetric advantage over rivals, making it too expensive to use missiles to attack U.S. warships because of the cheap way to defeat them. "Your magazine never runs out, you just keep shooting, and that's compelling."
(Score: 0) by Anonymous Coward on Friday April 11 2014, @05:36PM
I've only taken a year of physics so I'm not expert but I wonder how it reduces recoil.
"The high-power electric pulse generates a magnetic field to fire the projectile with very little recoil"
Unless the thing is producing forward motion in flight against the air/wind being pushed backwards the conservation of momentum would say that the ship would have to be pushed in the opposite direction with equal momentum that the object is being pushed forward. Is the advantage that the ammunition is less massive and so the recoil isn't as strong? Or is there electromagnetic propulsion against the air in flight or something (not sure if that makes sense)? Also, as others have noted, Wikipedia seems to indicate that the power supplies necessary are big and expensive.
http://en.wikipedia.org/wiki/Railgun [wikipedia.org]
(Score: 2) by frojack on Friday April 11 2014, @07:10PM
Big and expensive is what the navy does well. So no worries there.
The projectile weighs 22 pounds. Yes, it will induce recoil, but that is a tiny projectile, compared to what the Navy is used to firing from large bore guns.
It is progressively accelerated down the barrel (rails), and as such the recoil is time-dispersed compared to a chemically fired gun where force is much more instantaneously applied.
(Traditional guns propellants are progressive burning solids (to be distinguished from explosives), and add SOME momentum (by ever expanding gas) as the projectile moves down the barrel, but the highest pressure is achieved within a couple liner feet of the breech within 12 milliseconds. [dtic.mil] Force on the projectile decreases as the projectile moved down the barrel. )
Rails are timed to add relatively constant, or even increasing force as the projectile moved down the rail. This spreads the recoil out over a small amount of time. The weapon structure needs no recoil management for the sizes being deployed in this General Atomics test.
When the larger BAE rail gun (the next phase of the program) comes on line, it has built in Recoil handlers.
No, you are mistaken. I've always had this sig.
(Score: 3, Interesting) by Foobar Bazbot on Friday April 11 2014, @09:58PM
The characterization of railguns as "low recoil" arises from a comparison based on equal projectile kinetic energy. The validity of this comparison is just a bit dubious; there's no end of argument over whether momentum, energy, or something else is the correct metric for characterizing guns. IMO, the answer for simple kinetic impactors (no explosives, no expand-on-impact hollowpoint/softpoint designs, etc.) against simple homogeneous targets is generally momentum for projectile velocities << the speed of sound in the target, energy for projectile velocities >> the speed of sound in the target, and something in the middle for velocities on the order of the speed of sound in the target. Considering the speed of sound in water (about 1500m/s, or M~=4 in air) as representing the target, conventional guns range from much slower to slightly faster, and railguns are much faster. Naval guns are on the upper end for conventional guns, so at least energy isn't very wrong...
Anyway, taking as given that equal kinetic energy is the correct baseline, kinetic energy scales as m*v^2, so twice the velocity = 1/4 the mass. Momentum scales as m*v, so twice the velocity means 1/4*2 = 1/2 the momentum, thus 1/2 the recoil. So a (very) high velocity gun has a (very very) very light projectile, and thus has "(very) little recoil", QED.
Practically, there's no real competition to conventional guns at the velocities they're suited to; as you say. the powerplant and high-current capacitor bank (or flywheel+homopolar generator, or other ultra-low-impedance energy storage) required are just silly compared to storing that energy in chemical form as gunpowder. But any pressure gun is theoretically limited to a projectile Mach number of 1 w/r/t the propellant (practically, the velocity must be substantially lower) -- due to the high temperature of combustion gases, this is much greater than the speed of sound in air, but still presents a practical limit of around 2km/s for conventional guns (with crazy stuff like HARP going as far as 3.6km/s). Light-gas guns can improve on this by using propellant gases chosen for high speed of sound, but magnetic guns avoid the limitation altogether. We'd love a 7km/s conventional gun, but since that's not an option, we deal with the downsides of magnetic guns.
Now to quibble over the implicit assumption that projectile mass and velocity are the only recoil-related parameters: At the same momentum, magnetic guns do have a slight recoil advantage over non-muzzle-braked pressure guns (both light-gas guns and conventional guns*) in that they only expel the projectile**, while conventional guns also expel a comparable mass of propellant gas (and frequently unburnt particles) at comparable velocity. Muzzle brakes (which aren't generally used on naval guns) redirect some fraction of this gas backward; as momentum is a vector quantity, this subtracts from the recoil, and if the fraction is great enough, actually reverses the magnetic guns' advantage. But this difference is hardly enough to make magnetic guns attractive at comparable velocities -- as I said, we presently only put up with them because they're one of the only options for hyper-velocity.
*with some exceptions, such as pistols firing intrinsically-silenced ammo [world.guns.ru]
**and the armature, if that's not part of the projectile. Even if it is, some part of the armature is typically converted to plasma, and leaves at ludicrous velocity, but it's ordinarily a small mass.
(Score: 2) by Foobar Bazbot on Friday April 11 2014, @10:18PM
of course. we'd love a "7km/s" gun of whatever sort, too, but I got the 5.5 km/s (planned for the final version) with Mach 7 (for the current prototype). Oops.