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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.
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.
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
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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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.
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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
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.
You mispelled centuries.
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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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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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.