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Navy Debuts New Railgun That Launches Shells at Mach 7
Jeremiah Cornelius writes: "The U.S. Navy's new railgun technology, developed by General Atomics, uses the Lorentz force in a type of linear, electric motor to hurl a 23-pound projectile at speeds exceeding Mach 7 — in excess of 5,000 mph. The weapon has a range of 100 miles and doesn't require explosive warheads. 'The electromagnetic railgun represents an incredible new offensive capability for the U.S. Navy,' says Rear Adm. Bryant Fuller, the Navy's chief engineer. 'This capability will allow us to effectively counter a wide range of threats at a relatively low cost, while keeping our ships and sailors safer by removing the need to carry as many high-explosive weapons.' Sea trials begin aboard an experimental Navy catamaran, the USNS Millinocket, in 2016."
...Can someone who is explain where the big fiery explosion out of the railgun is coming from, if this thing is electromagnetically driven?
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Actually, do we know that there's any burning going on at all? I believe the light from a fire is not directly emitted by the chemical reaction, it's a result of the combustion gasses glowing from the heat. In which case just heating even an inert gas sufficiently will cause it to glow similarly. And the immense high-speed compression from a mach-7 projectile traveling down a confined tube should generate plenty of heat.
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Perhaps one of the big benefits of a naval railgun is that it's so difficult to defend against. Old-fashioned anti-ship missiles can be disabled or destroyed by the defending ship's close-in defenses. This is because the incoming missile is filled with sensitive electronics, guidance systems, explosives, fuel, turbojet engines, stabilizing fins, etc, and is very likely to be damaged or destroyed if hit by a 20mm round from the defending ship's CIWS missile defenses.
However, how do you shoot down a hunk of metal traveling at mach 7 toward your ship? It wouldn't make any difference if you hit it with a 20mm round from the goalkeeper or phalanx. The projectile would just keep flying toward the ship and strike it anyways. Besides, how would you even hit something which is so small and traveling at mach 7.
It doesn't seem there would be any good defense against this.
I suspect it's compression rather than friction doing most of the heating. Much like an orbital reentry vehicle - the gas within the shockwave starts to glow long before it contacts the vehicle itself.
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Energy is not the issue – it is the rate of fire. Diesel engines power the supper capacitors, they discharge to fire the gun, and then fill them up again. I have read that this cycle might be measured in minutes instead of seconds. How big of an issue that it will be is a big question.
That depends on how many capacitor banks you've got, yes? Or possibly the sustained power output of the generators, though that's perhaps more of an issue for sustained firing. (Naval ships are pretty big; you can fit a lot of capacitors and generators in there.)
What I'm impressed at is that they can fire the railgun multiple times instead of needing to strip it down and rebuild it each time. That was always the problem with the early railguns; they'd be fine firing once but after that would be so burned up from the currents that they'd be unable to take a second shot on any reasonable timescale. They were cool, but not practical weapons. I'm guessing that that must've been solved, and the result is that pure kinetic weaponry starts to make sense again for ship-level encounters.
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Tolerances causes more cost than you think, and documentation around military contract is generally at least half the cost of anything. It's not the contractors taking the piss (what, are you in OZ or UK?), but the government being stupid in supporting the military industrial complex.
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I found it interesting to describe by calculating kinetic energy. A stabbing ~ 185 joules. A gunshot of 45 caliber ACP round ~ 702 joules. A 1 ton vehicle going 100mph ~ 1 megajoule. A giant truck about to hit a series of tubes ~ 30 Megajoules. The kinetic energy of this railgun as it leaves the muzzle ~ 30.9 Megajoules.
Smaller diameter projectiles have more drag per unit mass and slow down faster due to air resistance. It's called their ballistic coefficient.
The practice for howitzer-like weapons like railguns is to fire their projectiles in a high arc to get them out of thick atmosphere as fast as possible to reduce air friction. They still won't hit their target at anything like their muzzle velocity even after they recover some kinetic energy on the way back down to target from the top of their parabolic arc.
The ballistically efficient shells from the late-model 15" US Naval rifles had a muzzle velocity of about 3500 feet/second and a flight time to target at maximum range (25 miles or so) of a couple of minutes. Their velocity at impact was half that of their muzzle velocity. I don't see these railgun projectiles achieving anything like that performance as drag increases roughly as the square of velocity and their ballistic coefficient will be a lot less.