Approved Directorate Report on Railguns

[Ayzek]

Report

Railguns are a technology that has been researched into since WWII, when the Germans stumbled across it 1 and attempted to develop it into an anti-aircraft system. This didn’t get very far, as the energy needed to power one was outrageous for the time (needing approximately enough energy to light half of Chicago)1. This has changed now, needless to say. The GE LM2500 engine produced 25MW when it was first produced, while its modern counterpart can reach up to 30MW (28.6 MW “when combined with an electric generator) 2. Of course, most ships have more than one engine. The Arleigh Burke class destroyer can produce up to 79MW of power with 4 LM2500 engines 3, while the Zulwalt gets 78MW with two MT30s 4—which can produce anywhere between 25 and 40 MW 5; they’re rated for 36MW on the Queen Elizabeth class aircraft carrier 6 and the Freedom class littoral combat ship 7. The Ford class supercarrier, with its two A1B nuclear reactors 8 produces 240-300 MW each 9, or approximately 2-3 times the A4W reactor of the Nimitz 10, which are quoted at 104MW 10 and 140MW 11. Efficiency Now, here is where it can get a little confusing…a “32MJ railgun” is a railgun that reaches a muzzle velocity of 32MJ (at least I think, based on how the Office of Naval Research (ONR) specifies the muzzle energy is 32MJ). This is done via science. However, a railgun requires much more power to actually reach that muzzle eneregy—because science isn’t actually your friend and has a habit of burning energy while doing things (thanks, resistance). How much power your railgun needs to reach its muzzle velocity depends on its efficiency. IEEE claims a railgun of up to 8MJ have proven an efficiency of 47%, and estimates it might be able to rise to 66% because science (evolves). Some random guy on some sort of discussion site (I don’t actually read the pages I visit, kids; not when I’m already drowned in a crapton of words) suggests an efficiency of 33% for a 10MW gun, based on some test at some point in time 14. I honestly can’t find more accurate measurements and, honestly, I don’t think I care much. For our purposes, our railguns will have an average efficiency of 60% at 36MJ and 40% at 64MJ. Why these values? Because I actually kind of want to use railguns (also kind of based on PopularMechanic’s figures). For all I know, these are hilariously generous. Lemme know if you find anything better, cause I’ll probably be eager to adopt it. What does this mean? Well, firstly I’d like to clarify that with “average efficiency” of “our railguns”, I mean our railguns must have an efficiency no greater than +3% of the number I gave. Eg., a particular 64MJ railgun can have an efficiency of, at best, 43%. This means the best 64MJ railgun would need 148MJ of power. And that’s for one railgun. Power Luckily, MegaJoules and MegaWatts are different things (though not entirely separate). A joule is a unit of energy, while a watt is one joule per second. So, a 160 MJ railgun would require about 10 seconds of charge time if it were being fed 16MW (crazy, isn’t it?). Of course, it’s not so simple; you need capacitors to store that insane amount of power (watts are power, kids) in order to release it all at once—if you fed it power constantly, your gun would fire constantly: 16MJ versus 160MJ. Your shots would be weaker (and your slug fired weaker). Nonetheless, a 64MJ railgun could be fired 6 times per minute with 16W according to PopularMechanics. How many you could have operating concurrently would depend on the ship (more specifically, it’s powerplant) and how dead in the water you want it to be while you’re charging your lasers railguns. So how much power does it take to run a ship? I have no goddamn idea! You could honestly (in theory) reroute all powers to weapons; your ship would keep moving for a bit—it’d lose speed, of course, bit momentum says it’d keep moving a bit after its propellers stop moving. How long? I don’t know. And I don’t care to find out. Rate of Fire Regardless, you need 16W to fire a 64MJ railgun at a rate of 6 rounds per minute with an efficiency of 40%. Here’s a pretty formula for you, if you wanna change it up a bit: R=(J/E)*P Rate of Fire = Joule/Efficiency*Power So the number of railguns you can power simultaneously is: G=Pd/Pc Number of Guns = Dedicated power/consumed power If you were dedicating 64 MW to your 64MJ railguns, you could operate four of ‘em simultaneously (at 16W each). So yeah. Kinetic Energy, Range, and Velocity Now, how much boom does this railgun make, and how much is that really? Well, this is where science does you a solid. 64MJ—assuming no energy loss, a railgun that fires with an energy of 64 megajoules would hit with a kinetic energy of…64 megajoules. But, alas, energy loss is a thing. An unpowered object moving through the atmosphere loses energy to air resistance—the farther your target, the less energy your round hits with. This is because the velocity of the round decreased. I’d give you a formula, but I honestly don’t feel like struggling with the math at the moment, so…tough. Still, PopularMechanic Claims of a range of 220mi or 354 km. We’ll be using that one. Kinetic energy can be up to 64MJ, though, as stated, it’ll probably be lower. Let’s pretend that at a particular range it’s 39MJ. This is about 9.3kg of TNT, according to Atomic Rockets/Projectrho13. This isn’t a particularly big boom. If you’ll check out the source (search for “railgun”), you’ll note it’s a bit less than twice an anti-tank mine, about 6.5 120mm tank KE rounds, 1/13 a 16 inch shell with 54kg HE charge, or 1/49 a Tomahawk missile. It’s probably enough to blow a reasonably nice hole in a ship though. Definitely do some serious damage to an aircraft or missile though…and probably a building too—maybe even a reinforced one. After all, this is pure KE: kinetic energy. Just straight up ripping holes in things. Unless you choose to fill it with explosives. But I think something said that was a bad idea for some sort of reason. Rail Material Anyway, the largest challenge railguns (in real life, anyway) face is the material used for the rails. Most in depth source says that railguns have serious trouble with long-term operation, because, believe it or not, the current running through the is outrageous(ly large) (6 million amps, thanks Popular Mechanics), which heats up the rails to ridiculous levels. Metal does melt, guys. Not only this, but the involved technology involved itself wants to break the gun. The current running through the rails (and projectile) produces an electromagnetic force that pushes out, attempting to push the rails away from one another. This, unfortunately, isn’t something that can be easily overcome (to an ideal extent) with present-day technology. Current railguns get a few dozen shots before they break. Some sources claim a few hundred, though they haven’t confirmed if it’s at “full power” (eg, the 160MJ input energy). This report is an edited/updated version of one written by DeSchaine on CaprecianContinents: here.

Summary

Conclusion So. What happens? The following: 64 MJ is the pinnacle of current Sioran railgun technology. Any higher and it’s inefficient both power-wise and longevity-wise (though not necessarily prohibited). Muzzle velocity is: (2KE/m)^(1/2) or the square root of two times the energy divided by the mass of the round. This is about mach 7 if the projectile is 22kg. Your projectile can be whatever mass you want it to be—the total energy doesn’t really change. The range might though. I’m not too sure. I think a lighter round would fly farther. But science probably still fucks you over (cause that’s a thing science does), so the best range with the best default projectile’ll be 354 km. These values are largely nonnegotiable, unless you can wow me with mathstuff that takes into account air resistance and the curvature of the planet (in addition to angle, energy, gravity, mass, and velocity, I mean). Lifespan for a set of rails is 120 shots at 6rpm. It can change by this formula: 120*ln(6)/ln(rpm), with a cap at 600 (at 1rpm). This formula isn’t based on any sort of science. I just felt like it. (I did consider one based on rate of fire and cool down, but lazy.) Railguns are expensive. The material, the capacitors, the powerplants. Possibly especially the power plants. I mean, you need 16MW to fire one 64MJ railgun at 6 rpm. The capacitors for this might even be large, meaning you can’t just stuff an endless amount of railguns on board. Assuming a one-to-one ratio, you could possibly stuff the same number of guns as a conventionally-armed ship. Rather than the space being used for ammunition, it’s now being used for the capacitors to fire the gun. I suppose it’s possible to have capacitors that are connected to a number of guns, with the capacitors feeding them in succession. That’d help with keeping the gun cool—lasting longer. But, yes: a standard warship (read: a destroyer/cruiser) could operate 1-2 railgun systems (16-32MJ) without draining too much power from other functions. If it’d reroute all power to the guns, it could operate 4-6 (depending on the ship), but it’d be losing speed at it does. This is, of course, assuming the ship doesn’t have extra powerplants dedicating to firing its las0rs railguns. Even then though, one modern non-nuclear powerplant could at best power 2 railguns. A whole powerplant (engine): two railgun. Cool-as-all-hell all-gun barrages are largely out of the question. Unless you only have those 2 railguns, anyway. In-game Development A country must have a GDP of at least 2 trillion to be permitted to have independently developed railgun systems. If your country is not above this floor, you may either purchase such systems from an in-game ally or have developed them with their assistance. Explicitly role playing their development is not required, though encouraged if you're doing it primarily because others already have them.

References

1 http://english.pravda.ru/science/tech/24...railgun-1/ 2 http://en.wikipedia.org/wiki/General_Electric_LM2500 3 http://en.wikipedia.org/wiki/Arleigh_Bur..._destroyer 4 http://en.wikipedia.org/wiki/Zumwalt-class_destroyer 5 http://en.wikipedia.org/wiki/Rolls-Royce_MT30 6 http://en.wikipedia.org/wiki/Queen_Eliza...ft_carrier 7 http://en.wikipedia.org/wiki/Freedom_cla...ombat_ship 8 http://en.wikipedia.org/wiki/Gerald_R._F...ft_carrier 9 http://www.world-nuclear.org/info/Non-Po...red-Ships/ 10 http://en.wikipedia.org/wiki/A1B_reactor 11 http://en.wikipedia.org/wiki/A4W_reactor 12 http://www.onr.navy.mil/Media-Center/Fac...ilgun.aspx 13 http://ieeexplore.ieee.org/xpl/login.jsp...2F00364679 14 http://www.dailytech.com/article.aspx?ne...2#comments 15 http://www.popularmechanics.com/military/a2289/4231461/ 16 http://www.projectrho.com/public_html/ro...Boom_Table

[CONCENTRAL]

Esteemed technologist, railguns are surely a powerful technology in the hands of robber-baron democracies. For freedom and meritocracy-loving defenders, what defense exists at the source? Are the power systems hardened against EMP? Are the rails themselves vulnerable to damage via additional current delivery? If a set of rails fails, how explosively does it do so? We are delighted to learn the hypothetical answers to these hypothetical questions outside of the realm of real warfare.

[Ayzek]

The power systems are likely as hardened against EMP as the rest of the ship. So if the ship was designed to resist EMP, it's not likely it'd be taken out. The rails are designed to take a whoolllleeee lot of current, so I'm skeptical you could break them with an EMP attack. They're not even a complete circuit unless they have the projectile in there. EMP breaks things by overwhelming the tiny-ass circuits found in modern electronics, after all. The rails could be a path into the ship...but it could be designed to not.

This is a curious and convenient read on EMP.

The rails do melt over time (from the sheer current surging them through), which'd make them less efficient and slow down the projectile. If the melting's really bad, they might fail to fire properly, but since railguns deliver damage via kinetic energy and the projectiles don't have kinetic energy until after going through the launch, I doubt it'd explode.

A railgun's greatest advantage is it's range, and the fact that it can't really be defended against. (Though, maybe one could hit a railgun slug with another railgun slug? LOL.) Railguns actually seem to be pretty weak:



Hitting another ship with it would make a nice hole (and take out systems and people), but you'd likely need quite a few more to actually sink it. Unless you get a luck shot and hit it such that it starts taking on water. Or hit ammunition and it blows up.