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Navy Gets 8-Megajoule Rail Gun Working
prototypo writes "The Free Lance-Star newspaper is reporting that the Navy Surface Warfare Center in Dahlgren, Virginia has successfully demonstrated an 8-megajoule electromagnetic rail gun. A 32-megajoule version is due to be tested in June. A 64-megajoule version is anticipated to extend the range of naval gunfire (currently about 15 nautical miles for a 5-inch naval gun) to more than 200 nautical miles by 2020. The projectiles are small, but go so fast that have enough kinetic punch to replace a Tomahawk missile at a fraction of the cost. In the final version, they will apex at 95 miles altitude, well into space. These systems were initially part of Reagan's SDI program ("Star Wars"). An interesting tidbit in the article is that the rail gun is only expected to fire ten times or less per day, presumably because of the amount of electricity needed. I guess we now need a warp core to power them."
That's called a mass driver. Using em to catapult vehicles into space.
Ask someone who knows: Gerald Bull
I have *never* understood how railguns work. Here is an explanation, although it still leaves me frowning and making funny shapes with my fingers all stretched out.
One presumes there are sonic booms associated with this. Anyone know if they're louder or quieter than the explosions associated with heavy ship artillery?
Nostalgia's not what it used to be.
Has anyone else found out about these guys?
It's an old site but it's still just as awesome. I almost considered trying this out myself but I'm not exactly sure if such a thing is legal.
Did you read the original post? It says it can go up some 90 miles before coming back down. If thats not an arc, I dont know what is.
I'm almost positive the main issue is not electricity generation but rail friction. The best rail guns I'd heard of until today needed completely overhauling after each test firing because the rails themselves are damaged so badly as the projectile passes. Coil guns are better in this respect, as the projectile doesn't have to touch the coils...
qntm.org
Travelling that fast....how much wind effect would there actually be?
Well, wind is only one factor. Moisture density (clouds) could come into play as well. You're talking 200 miles, where only a very slight variation on forces acting on a small mass, (3.2Kg) could be enough to miss by a city block. At least the Tomahawk has guidance systems. Hitting the chinese embassy in Beograd was an intelligence failure, not guidance.
A feeling of having made the same mistake before: Deja Foobar
a 60 degree rise in a quarter ton of cooling water
A cubic foot of seawater weighs approximately 64 pounds. A quarter ton, or 500 pounds, means this thing would raise less than 8 cubic feet of seawater by those 60 degrees. (A cubic foot of fresh water is 62 pounds, so the difference is negligible) That's a miniscule amount of global warming that this thing will add to the ocean each time it fires. And with entire oceans to heat up I doubt the Navy is too concerned about that environmental impact.
Excellent point. Here's a quick reference from the Wiki article:
Full-scale models have been built and fired, including a very successful 90 mm bore, 9 MJ (6.6 million foot-pounds) kinetic energy gun developed by DARPA, but they all suffer from extreme rail damage and need to be serviced after every shot. Rail and insulator ablation issues still need to be addressed before railguns can start to replace conventional weapons.
Just because something gets launched to higher than the arbitrary height we have assigned to "the edge of space" does not mean that it will stay up there. The object has to also be travelling at orbital velocity. At LEO of about 200km, orbital velocity is around 7800m/s, aka ~17,500mph.
Not to say that this gun cannot fire projectiles into orbit, just to say that firing something into space and having it stay there is much harder than just firing something into space.
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You are correct, sir! (*DING*)
Unless something has changed in the last year or so, the railguns will fire Extended Range Guided Munitions - a type of GPS-guided "smart" shell.
On another subject, it seems I was right when I suspected that these ships would be unable to maintain a high rate of fire. I never expected it to be this bad, though. Seems our DD(X) class is going to need a fleet of tanker escorts shoud a real war break out.
*grumbles something about failure to improve nuclear generators for destroyer use*
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100kW is around 134 hp. There are motorcycles capable of generating more power than that, and a single cylinder of a ship's diesel makes more than that, too.
boldly going forward, 'cause we can't find reverse
Good thing they are surrounded by PLENTY of water......
TIME is the Aether...
You can't have a spiral orbit unless you're under power. A projectile will travel a ballistic path -- an ellipse. Elliptical paths have the curious property that if you travel along them far enough you'll end up back where you started. So if you fire horizontally your spacecraft will have part of it's orbit in the atmosphere (which doesn't work so well) and it will come back and hit your rail gun from behind (provided it doesn't hit a mountain). If you fire at some angle above horizontal your projectile's orbit will intersect the ground at some point.
This should explain the concept that we're talking about.
The basic idea is that, if you want to change the altitude of an orbiting object at a certain point, you need to give it a push ON THE OTHER SIDE of the planet the object is orbiting (you want a lower altitude over china, you need to decrease speed over america).
If you change the velocity the bullet exits the muzzle of the cannon (or the railgun or whatever), you are making the bullet go higher/lower at the other side, and then hitting the cannon faster/slower when it returns. That is, unless it reaches escape velocity (it'll never return) or hits the planet. To circularize the orbit (basically to make the bullet go higher over the cannon), you need to give it a push when it's on the other side of the planet, that's what the rocket is for.
GPG 0x1B479C78
"Electric" does not mean "electronic." EMPs will affect ICs, but if I were to build the same thing with a crapload of vacuum tubes, it would survive a blast without a problem. It is the delicate nature of ICs that lead them to be affected. I have a nice old VW Bug that would survive an EMP without a problem. The radio might have a problem (though it is all transistor, no tubes and no ICs, and I haven't really paid much attention to how well transistors survive an EMP because it isn't really relevant), but everything else will work fine, including the headlights and electric ignition. If the EMP was strong enough, it could cause the starter and alternator to fail, but at those levels, the car would likely have to be close enough to the blast that the mechanical pieces would be affected (the EMP is the least of your worries if the vehicle is vaporized).
Given the most simplistic versions of this, it could be an all-mechanical firing mechanism (some guy in a room throwing a huge switch). I expect that it could be integrated into the ships systems with ICs, but they would be hardened, and if it is done the "military way" then there will be a manual way of doing it in an emergency. A diesel engine that charges a flywheel and supplies power to this thing would be completely unaffected by an EMP. But I wouldn't want to be the guy that flips the switch on this.
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"Unlike a Tomahawk, it's unlikely you can install a GPS receiver in the "bullet" because of the high launch g-forces, so using terminal guidance is probably out."
n er/2006/04thursday/dandrea_inp_track.ppt
The projectile that is fired DOES use GPS guidance. Look at slide 3 from this presentation from the Office of Naval Research.
http://www.onr.navy.mil/about/conferences/rd_part
Current US Navy destroyers have some 70 MW installed for propulsion, and electric generators for 7.5 MW.
The next generation of destroyers will have a turbine-electric powerplant, with the entire 80 MW available as electric power.
And regardless of current specs, if the USN adopts rail guns, they'll find a place to park another generator, if need be. 2.5 MW generators aren't that large.
Just don't rely on the fuel to provide any structural integrity, as it is not really solid like a fireworks rocket. The SRBs used to launch the space shuttle are a good example of this. They have a void in the center of the rocket running through their entire length. This is because the fuel burns at the surface, and this configuration enlarges the surface by a large factor, providing considerably more power. So rather than burning from the end of the rocket, the fuel burns from the inside out.
The kinetic energy of the recoil will be precisely equal to the kinetic energy of the projectile.
With that said, the Navy has had decades of experience in dealing with guns that make your whole battleship slew sideways when fired. There are ways to absorb and/or re-direct the recoil.
Clear, Dark Skies
I saw an episode of Future Weapons where they had a company developing a gps guided artillery round fired from a tank. Their biggest hurdle was getting the electronics to survive. These things only go 1/10th of the distance that this rail gun is talking about so I would think it's a pretty big hurdle.
www.joshferguson.org
According to this presentation
http://www.launchloop.com/isdc2002energy.pdf
32 megajoules of energy are found in 1/4 gallon of gasoline, or the sunlight falling on a square meter of Denver, Co on a sunny day. If correct, the energy requirements of these guns are far less than what the original poster has presumed them to be....
I'm just pointing out that the military can solve many limitations by throwing money at them, and no one in the government is embracing plans to limit military spending at this time.
You need to read more about the DOD budget process inside the Pentagon and the White House. It isn't so much that they are proposing spending less, as there are a LOT of fights over exactly where to devote the spending, and which service gets how much, and how it is portioned out. How much goes to maintenance, how much to new equipment purchases, how much to soldiers, sailors, marines, and airmen. How much to R&D like this?
Very high cost equipment does indeed get canceled, simply because it costs too much. Usually measured as "too much over budget" but it is related to cost. Cost does matter.
The Navy has this as a very real problem over the next 10 years. The next generation aircraft carrier is projected to cost $10 billion. The Navy currently spends $10 billion per year building ships and submarines. A ship must be fully appropriated in the year that construction is begun. The year they start building the next-gen aircraft carrier, does the Navy simply not build any submarines, which they want to build 2 per year for a cost of $2.2 billion each? How about DDG-51 class destroyers, at a cost of $1.4 billion each? Or DD(X) (now renamed to DDG-1000) class destroyers, at a cost of about $3 billion each? Amphibious assault ships, like the LPD-17, which I don't know a cost for, probably north of $1 billion? Or LCS ships, for the low cost of about $400 million each?
What doesn't get built the year they start the next aircraft carrier?
The Air Force has the same problem, with F-22 aircraft that cost $200 million each... they aren't buying 600 of them like they planned 10 years ago. Instead they are getting... 190 I think. Ditto with the F-35 (JSF), which they are not buying 4,000 of, or whatever the original purchase number was, because they are also fairly pricey.
Just because the military works with large budgets, doesn't mean that the cost of equipment doesn't matter. It matters very much.
And they really do care about limiting costs, because it really does affect how many they can buy.
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Actually, Aegis guided missle destroyers (DDG) are used for fleet air defense and ballistic missile defence. http://en.wikipedia.org/wiki/Arleigh_Burke_class_d estroyer, http://en.wikipedia.org/wiki/Aegis_Ballistic_Missi le_Defense_System
Stay hopeful that the Crystalline Amoeba poops your car out soon
The army has successfully tested self guided howitzer shells. The electronics have withstood 16,000Gs. I think they can make electronics that can withstand a railgun.
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You can have very strong mangetic fields without them leaking all over the place - you just need to give them a preferential path to flow though. You'd have to assume they've covered that base - after all it would improve their efficiency to be using high permeability cores rather than free air.
You are correct. In fact, 8,000 joules is about the capacity of a standard AA rechargable battery.
.22 short handgun (330m/s), in a 10cm muzzle, you'd need to do it in about 0.0003s (0.1m/(330m/s)==0.0003s). As a result, you'd need about 20 joules:
8,000j = 2,222 V*mAh
2,222 V*mAh/1.2V = 1851.85 mAh
As a result, using an array of eight paralell AA rechargables and a capacitor array, one could probably build a railpistol, capable of 4-8 shots per charge (depending on the failure characteristics of the batteries, and the wear-and-tear on the caps). That is, given they've solved the rail damage issue.
Mind you, the max discharge rate on Lithium is 1.5A, and on NiMH is 6.4A, so you end up waiting 2-4 minutes between shots
1851.85 mAh/(8*6.4A)=130.21s
You can, of course, decrease this time by switching from a large-pistol to a rifle form factor, thus affording enough room for a larger batter/capacitor array, and a shorter recharge time.
For the coveted one-shot-per-second in quake, you'd need:
1851.85 mAh/(1s*6.4A)=1041 batteries
This is rediculous, of course. You get a lot more flexibility if you move from NiMH to Alkaline (with their higher discharge rates). Also, you don't need supersonic speed from a handgun.
Example: To launch a 0.22" short bullet (1.8g) to the same velocity as a standard
((0.00018 kg)*(0.1 m)*(330m/s))/(0.0003s)=19.8 j
19.8j = 5.5 v*mAh
5.5v*mAh/1.2v = 4.58 mAh
4.58 mAh/(1s*6.4A)=2.57 batteries
4.58 mAh/(8*6.4A)=0.33s
So, you could get the power of a saturday night special, with a 3 shots-per-second limit in a four-or-so pound package and a lot more technology. That's, of course, assuming ideal energy transfer and no friction (heh, yeah right).
Which, of course, is why this is only used for BFG tech; the extra weight is a lot smaller and a lot more efficient on a Volkswagon launcher.
And if anyone links to the Gauss pistol kit, I'll be very cross. A gauss gun is not a railgun. They operate using different configurations, and require different electromagnetic engineering techniques. And gauss guns are more complicated.
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Railguns might have more linear acceleration, but guns don't just go bang. The projectile accelerates throughout the whole trip through the barrel.
No, it's not. Any unpowered bit of mass will travel in an ellipse, or a parabola if the ground gets in the way. Yes, you have to use the right equation. No, "orbital paths" are not something different than the "natural ellipse" that objects travel in close to the ground. All the unpowered objects in the solar system travel in ellipses. If your projectile has too much energy it will not be in Earth orbit anymore, but orbit the sun instead, still in an ellipse.
You can say that the ability of an object to orbit is determined by the energy only if you want, but an object that has part of that orbit that intersects the ground won't orbit for very long. That's what happens if you fire an unpowered projectile from the surface. It's orbit MUST intersect the firing point, barring some sort of acceleration in flight.
None of what you describe admits a spiral as an allowed orbit.
It's pretty common to see Naval vessels powered by an on-board nuclear reactor. Although I don't think the US Navy is currently running anything nuclear powered that isn't a submarine or aircraft carrier, they have in the past. Russia currently runs nuclear powered cruisers (such as the Kirov class) and icebreakers.
8MJ is 8MW for one second. My university has a 36MW power plant, on site. The D2G reactor, which was used on nuclear destroyers in the US Navy, has a power output in excess of 150MW.
Somehow, I don't see generating power as a huge problem. Even a 64MJ launcher operating at 1% efficiency would only require 42 seconds of power from the D2G.