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World's Most Powerful Rail Gun Delivered to US Navy
An anonymous reader writes "The world's most powerful functional rail gun capable of accelerating projectiles up to Mach 8 has been delivered to the Navy. The new rail gun is a 32-megajoule Electro-Magnetic Laboratory Rail Gun. The Navy eventually hopes to have 64-megajoule ship mounted rail guns. '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.'"
I'm vaguely remembering a conversation I had when I was in the Navy, but from what I remember, the USS Enterprise was over engineered to have 8 reactors when they knew only 4-6 were really necessary because they had some thoughts of mounting energy weapons. since the Enterprise was drawn up in the late 50's I'm not sure whether to doubt it or not.
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Mach 8 is about 9800KPH. Escape velocity from the Earth's surface is 40,320KPH. This gun is already firing at over 24% of escape velocity. A 64Mj gun would be almost 50%; a 132Mj gun would shoot projectiles right into orbit.
I wonder whether coming generations of this gun could shoot unmanned exploration vehicles or satellites out into space. The Pentagon will probably try to use it just to shoot down spacecraft, but instead we could use their budgets to increase space industry and exploration.
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I wonder how many times this thing can be fired. They need to get 32 megajoules of energy out of the gun, and without the metal that this power passes through melting. That's not an easy thing to do.
Railguns today tend to melt after each shot, leaving one to replace the rails (the biggest, conducting the part of the gun, the bit in contact with the "bullet").
I wonder what the efficiency is. 32 megajoules come in, how many leave in the bullet. (Generally they only get about 2%-5% efficiency).
An alternative, easier and safer, is a coil gun. Here's a nice index of coilguns : World's coilgun arsenal. But like their railgun brothers, they're not very efficient. The very best of them have the bullet speed of a mini handgun, but they're trivial to make, and rely only on batteries and metal.
The Enterprise was the prototype. Plus, Nimtz carriers only have 2 reactors. So it wouldn't surprise me if they overengineered her power supply for the intent purpose of mounting experimental weapons.
:P)
That being said, the Nimtz reactors are a bit more advanced than the Enterprise (lessons learned and all that), so that has a lot to do with the reduction in the number of reactors.
Everything beyond that is classified. I could tell you, but then I'd have to shoot you. (Assuming that I already knew and therefore had been shot.
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I had a physics teacher who used to work at Los Alamos who did some consulting for the military on the side. In the late 80's/early 90's, they had him evaluate the results of some rail-gun tests. They were shooting a small ball projectile at tanks. The projectile left a perfectly round smooth bored hole all the way through the tank, wherever it was fired. The military wanted to know if they could use this to disable things (fire through the engine block) without destroying other things (people, electronics, paperwork, whatever) inside.
In evaluating it, they found that the internal air temperature flashed to something really high (like an oven) in the microsecond the ball travelled through, and that the vaporized steel from the first surface of the tank would kill everyone in the compartment.
It brings home what kind of speeds we're talking about here.
I'm waiting until they start listing the speeds of rail guns in terms of [decimal]c. Full of relativistic goodness. Of course, if they're only at Mach 8, they've got a way to go. The X-15 was near mach 7 and the scramjet tests have hit mach 10, and I'm sure those were more massive than the rail gun's projectiles.
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Some of the features:
Navy Fact File
As I recall, the original list of superweapons was much more impressive. It just got pared back a smidge when Congress balked at the price tag.
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As I recall, the ship had eight reactors because that's how many it took to keep the thing moving. They were expensive and Congress wanted the Navy to go back to fuel oil. As I recall, the JFK was conventional. When the Nimitz class came about, the reactor technology had progressed to the point where they could get away with two and the operational costs came down enough that Congress relented. What the Navy really likes about nuclear is that it gives the carriers so much operational flexibility. A modern carrier has fourteen days of combat stores onboard. The reactors also produce the steam to fire the catapults, a very energy-intensive process. I also heard something about some nuke carriers carrying bunker fuel to help keep the destroyers topped off but that seems a bit silly since there are already fleet oilers to perform that task.
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I sat next to one of the directors of the Navy's rail gun program, during a flight to Boston, and I had one of the most interesting talks with him. The projectiles fired experience about 30,000 g's of acceleration, compared with 12,000 g's for a conventional gun. The major problem is that about 20% of the g's are experienced laterally because the projectile bounce when it is traveling down the rails. The projectiles do not contain explosives, because the kinetic energy is enough to do some pretty good damage. The materials problem with the rails was solved a while ago, and they need to survive for about 1000 shots to be comparable to today's guns. They also don't store the energy for very long before firing, because of losses and safety.
I suspect that's an urban legend. (Lots of 'em floating around the Navy.) I've never seen anything, anywhere, indicating that the Navy was looking at energy weapons in that time frame.
At any rate, the reactor plant of the Enterprise was originally sized on the need to launch full (Vigilante) sized aircraft while steaming at maximum speed. Plus some additional capacity for operational reserve, in case one or more reactors were down, plus a fudge factor for future growth and to cover against concerns about reactor performance. There was also a general concern in the Navy at the time over the profliferation of electronic systems and their increasing demands for power.
Since the reactors ended up performing reliably and more-or-less to spec, and big aircraft didn't become common in the fleet - Enterprise ended up considerably overpowered, much more so than follow on CVN's. The follow on CVN's carry fewer reactors partly because of this, and partly because the individual reactors are so much more powerful and specifically designed for carriers. (The A2W reactor used by Enterprise is actually a slightly uprated C1W reactor - originally intended to be used in pairs for cruisers.)
In fact, Enterprise ended up with so much excess steam capacity - that (IIRC) half the steam recievers (a sort of capacitor to hold steam for the catapults) she was built with have subsequently been removed. Off-and-on there has been discussion of mothballing a pair of her reactors in place.