Glad to see the rail gun making its practicle appearence.
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Given the amount of space they save by not having to store as much ammunition per unit of destructive capabilities, they probably make back that energy cost in how much less power it takes to push the ship.
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Dakka usually has to do with the the number of rounds flying so I'm not sure how this qualifies.
Well, right now, they're working to speed up the fire rate to achieve 10 rounds/minute. So they're pursuing "more dakka" for the railgun. Is it a step down from the fire rate of their current guns? Probably, but I think even an ork could understand once he saw the boom.
_________________ "Aaaah! Emotions are weird!" - Amdee "... Mirrorshades prevent the forces of normalcy from realizing that one is crazed and possibly dangerous. They are the symbol of the sun-staring visionary, the biker, the rocker, the policeman, and similar outlaws." - Bruce Sterling, preface to Mirrorshades
Joined: Thu Sep 03, 2009 9:59 am Posts: 15740 Location: Combat Information Center
3.3 billion is not terribly expensive for a cruiser at today's prices - which the Zumwalt class really is, given its design mass of 14,564 tons. Given that the limit for heavy cruisers was 10,000 tons under the post WWI naval treaties, destroyers have been creeping up into cruiser weight and capability for a very long time.
As for generating 32 MJ, pretty much any ship out there can generate that much energy, seeing as that's less than the energy content of 1 kilogram (or, in other words, less than a third of a gallon) of gasoline. The Aegis radar puts out 6 Megawatts of power, or in other words, 6 megajoules per second, so it would only take a little over 5 seconds to generate enough power for the shot, and the ship can generate that power while steaming at full speed in combat conditions (which is obviously when it would need to steam at full speed and run the radar at full power.) The 2 A4W reactors on a Nimitz-class carrier are rated at 550Mw; a carrier has two and a single one would be vastly more than needed to fire this gun, even if a ship had two of them. It's basic requirement of energy per shot is quite practical.
The problem most likely has to do with storing all that energy and then releasing it in the very short time the projectile is in the barrel of the gun. That's the part that probably doesn't exist yet. Generating 32MJ is trivial; releasing it in the sudden fashion a railgun needs might not be.
It sounds from this though, like they've at least partly solved the barrel erosion problem. In previous tests it was eroding so badly that it looked like a barrel might be good for 2-3 shots. Now they're talking about how to make it stand up to "repeated" shots, so that means they've most likely gotten the problem at least partly under control. That's critical, because that was the biggest issue the gun was facing.
Also, in case anyone is wondering, the reason the projectile looks so funny is the armature at the rear, and the front flat section to make the projectile not fly so far or bury itself so deep in something it can't be recovered. The real projo probably will have a detaching armature and a more traditional nose.
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OK, I finally watched this. Cool stuff. But, what's with the freakin' fireball? I mean, it was cool and all, but, if this is just electricity or magnetic energy, and not explosives, why is there fire? Just the amount of friction on the barrel? Still seems like a lot of flame.
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Seriously if this thing is going to be ready to fire that is going to be more dangerous than storing modern ammunition. Holy hell.
Might as well just get the ship up to 88mph.
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Whoa, whoa, wait - what does this mean for space combat? What would the velocity be on this thing in space? There are rail guns in Eve, I always loved those. Huh.
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But the rate of deceleration would be far less. Range would be ridiculous.
Theoretically, with a longer barrel, you could get more velocity out of the projectile. But, that would require exponentially(? I think?) more power. I don't think its a linear relationship where more power = the same amount of more velocity.
But someone who's better at physics and stuff would have to say.
I think what he's referring to is that sound doesn't propagate in space, so "mach" doesn't have much meaning. You have the right of it, in that I think you mean whatever velocity mach 5 corresponds to (i.e. 5 times the speed of sound at sea level).
One thing must be cleared up regarding usage in space - deceleration does not exist. That word entered the common parlance because most people don't understand "accelerating in the opposite direction." This clip from Mass Effect 2 rather accurately describes what is going on:
Basically, the only things acting on a bullet fired from a rail gun out in space would the gravitational fields of very large rocks, and even larger thermonuclear reactors. Maybe it hits something. Maybe it gets sucked into orbit around a very large floating thing. That last one is probably unlikely. Five times the speed of sound is actually pretty slow out in space. I don't think it's moving fast enough to orbit anything. I'm not exactly hip to the relevant astronomical numbers, and I'm too lazy to do the math to predict what's going to happen, but it's not catastrophic. Rocks crash together out there all the time that are hauling *** way faster than this bullet is moving.
Regarding linearity between power and velocity, strictly speaking we can show a linear relationship between the barrel length and the velocity of the bullet. Doing so also ignores a number of things such as friction, air resistance, eddy currents within the bullet, and so forth - things that for certain bullet speeds might be largely negligible. Observe the following graph:
There are three distinct regions of that graph where there appears to be a linear relationship between voltage and current. That's your eyes fooling you. The entire graph is nonlinear, but there are three areas where it is very close to linearity. That's the region we'll use to design something because we can make accurate predictions with simple mathematics.
Now, it's probably not barrel length that they're overly concerned with linearizing, but likely electrical current and magnetic flux.
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Joined: Thu Sep 03, 2009 9:59 am Posts: 15740 Location: Combat Information Center
Barrel length is limited by the need to put the gun on a ship. The weight and length of the barrel affects traverse, elevation, and possiblity susceptibility to damage in rough seas. The ability to make it go faster by making the barrel longer therefore has an upper practical limit regardless of its theoretical limit. I don't know what that barrel length is, but I imagine the prototype's barrel is fairly similar to what they expect to be feasible.
As for whether it could orbit anything in space, mach 5 is around a mile per second, or 1.6 kilometers per second roughly. Escape veolcity for Earth at the earth's surface is 11.2 KPS. At the moon, earth orbit escape is only 1.4 KPS, so whether it could orbit would probably depend a lot on the altitude of the orbit.
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Joined: Thu Sep 03, 2009 9:59 am Posts: 15740 Location: Combat Information Center
Aethien wrote:
OK, I finally watched this. Cool stuff. But, what's with the freakin' fireball? I mean, it was cool and all, but, if this is just electricity or magnetic energy, and not explosives, why is there fire? Just the amount of friction on the barrel? Still seems like a lot of flame.
It's also some of the aluminum of the projectile and probably some of the barrel too, vaporizing. A lot less of the barrel now, hopefully.
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Joined: Thu Sep 03, 2009 9:59 am Posts: 15740 Location: Combat Information Center
In space, the range of this thing wouldn't be all that much greater than on earth. Yes, the projectile might keep flying indefinitely, but the problem is aiming it. If you're fighting at ranges similar to those on earth, or even, say, 10x longer it's not that big of a problem, but with a projectile going only at mach 5, you're looking at about 1 second of flight time per mile or so. Once you get over about a hundred miles, there's more and more time for any slight maneuver on the part of the target that wasn't predicted to cause a miss.
At 1000 meters, 1 mil of error (1/6400th of a circle) is right around 1 meter of error. This isn't exact; it's a factor used int he field for artillery calculations under fire, but it's good enough to get the idea. Therefore, at 100 kilometers, or about 60 miles, 1 mil of error, or a maneuver by the target causing 1 mil of error, means you're off by 60 meters. That's 180 feet. If you were firing at a WWII battleship sized target, that would be more than enough error to miss along the ship's vertical axis (yes, I know there's no vertical in space, I mean the vertical of a real water battleship and a spacecraft of the same rough 3 dimensions.). Horizontally, it's not enough to guarantee a miss, but more than 1 mil means you're rapidly accumulating error in terms of actual distance off target at the target range. As the range increases, error does too.
Increasing the speed of the projectile would help a lot. If the projectile is travelling at mach 50 instead of mach 5, that means at 60 miles there's only 6 seconds for a new maneuver to start. It doesn't help with any errors that have crept into the firing solution, but it does make it harder to dodge.
If we got up into fighting at really long ranges, like more than 1 light second, the amount of time information takes to reach the firing platform would become a problem too. At, say, 900,000 km it would take 3 seconds for a radar pulse to return, adding 3 more seconds to the time in which some maneuver could spoil your aim. That's to say nothing of how absurdly fine your adjustments to your gun would need to be; 1 mil of error at 900,000 km would mean a miss by 900 km.
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Joined: Thu Sep 03, 2009 9:11 am Posts: 9449 Location: Your Dreams
It seems to me that even the vacuum in the weapon barrel would allow for significantly greater accelleration in space than inside an atmosphere.
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I'm more of an Earth Science guy.