# What would be the advantages of Magnetic Accelerator Cannons **URL:** \ **Category:** Factual Questions\ **Created:** [September 20, 2007, 12:34am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814 "2007-09-20T00:34:41Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [September 20, 2007, 10:29am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/21 "2007-09-20T10:29:53Z")
[QUOTE=Der Trihs] Lasers dissipate, especially in atmosphere [/QUOTE] I believe we have been able to compensate for that now. Also with a powerful enough laser you could ionize the air which should help prevent this. ---
**Author:** ![essell](https://avatars.discourse-cdn.com/v4/letter/e/34f0e0/32.png) [@essell](https://boards.straightdope.com/u/essell)\ **Post date:** [September 20, 2007, 11:05am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/22 "2007-09-20T11:05:14Z")
[MOO2]Personally, I drop Mass Drivers for Graviton Beams as soon as I can.[/MOO2] I always thought the point of Magnetic Accelerator was the near-light velocity made aiming easier and / or made combat at extreme distances possible. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [September 20, 2007, 12:44pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/23 "2007-09-20T12:44:51Z")
[QUOTE=Snarky\_Kong] The entire point of railguns is that they go really really fast. [/QUOTE] For the Navy it is. Something that you could carry around to go hunting with no. The hand guns in the books use little beads for hand held guns, so think of the recoil of sending a bb out the barrel. You’ld have more recoil than a typical bb gun, but less than a 9mm pistol. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [September 20, 2007, 12:49pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/24 "2007-09-20T12:49:52Z")
[QUOTE=kanicbird] I believe we have been able to compensate for that now. Also with a powerful enough laser you could ionize the air which should help prevent this. [/QUOTE] They can send an electric charge through the ionized air too. It’s a design for some tasers already. You might as well try to fry somebody two ways at once. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [September 20, 2007, 1:03pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/25 "2007-09-20T13:03:12Z")
From a physics perspective, I’d think recoil issues would be less for a rail gun: first, you’re not accelerating all the propellant gases, and second, the acceleration would be slightly more gradual, so a smaller peak force. ---
**Author:** ![muldoonthief](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muldoonthief/32/3188_2.png) [@muldoonthief](https://boards.straightdope.com/u/muldoonthief)\ **Post date:** [September 20, 2007, 1:04pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/26 "2007-09-20T13:04:26Z")
FWIW, conventional firearms have a muzzle velocity which is limited by the speed of sound in the combusting gases (which is usually much higher than the speed of sound in air at STP). Railguns have no such restriction, but the engineering of a reusable hyper-velocity railgun is hard. > [@beowulff](#): > > Along the same lines, I saw a video recently of a new anti-tank missile. I has no explosive, it just uses it’s enormous kinetic energy to destroy the tank. The missile travels at something greater than Mach 4. . [KE penetrators](http://en.wikipedia.org/wiki/Kinetic_energy_penetrator) have been used as anti-tank weapons (by tanks), for decades. They have a muzzle velocity around Mach 4-5. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [September 20, 2007, 3:31pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/27 "2007-09-20T15:31:20Z")
[QUOTE=Harmonious Discord] **\> The entire point of railguns is that they go really really fast.** For the Navy it is. Something that you could carry around to go hunting with no. [/QUOTE] I think the point still stands, the advantage of railguns is that it _can_ be made to go really really fast. For a hand-held weapon, it means you can use a much smaller projectile (bullet) and still do the same amount of damage to the target. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 20, 2007, 3:57pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/28 "2007-09-20T15:57:37Z")
> [@](#): > > Sorry, no. It wouldn’t matter how you’re propelling the mass, the recoil would still be the same…dang, where’s that formula…anyway, for every action, there’s an equal & opposite reaction. Not true, actually. The destructive capability of a projectile depends mostly on its energy, while the recoil depends on momentum. Kinetic energy scales with the square of the velocity, but momentum is directly proportional to the velocity. So if you have a given amount of destruction you want to do (i.e., a given energy), and you make a gun that can get the projectile twice as fast as the old kind of gun, then the projectile will only need to be 1/4 the mass. 1/4 the mass times twice the velocity would mean that the new gun would only have half the momentum (recoil) of the old gun. ---
**Author:** ![psiekier](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/psiekier/32/116_2.png) [@psiekier](https://boards.straightdope.com/u/psiekier)\ **Post date:** [September 20, 2007, 4:32pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/29 "2007-09-20T16:32:59Z")
[QUOTE=Whack-a-Mole] A naval ship would be able to have sufficient space and power generation capacity to mount one (the capacitor for these things is rather large so it limits what can actually carry one around). [/QUOTE] Anybody who remembers the classic _Battletech_ game after they introduced the rules for the ancient Star League technology and later the return of the Clans (who had spent the intervening time away from the civil war perfecting the old technology) should remember the Gauss Rifle, which was essential a magnetic accelerator. In fact, similar weapons were featured in FASA’s other big game, _Renegade Legion_, where they were referred to as Mass Driver Cannons (MDC’s for short). Besides giving it tremendous range and potential for destruction, _Battletech_ twisted the normal ballistic rules with the Gauss Rifle. First, as **H3Knuckles** mentioned in the OP, the ammunition has no propellant or explosive, consisting of solid nickel-ferrous slugs. Even a direct hit on the ammunition store would not cause it to detonate. On the other hand, a critical hit on an unprotected part of the weapon itself would cause the capacitor to loose its fury on the carrying vehicle, resulting in a spectacular and probably crippling explosion. Finally, since the vehicles carrying such weapons were powered by fairly compact fusion reactors, there would not be any problems with supplying the kind of power you would need until you ran out of either targets or ammunition. If they could get around the wear-and-tear on the barrel, I could certainly see something like this mounted on a ship with a 21st-century fission reactor, or even a shore installation… … but minus the 30-foot tall walking war machines, I’d kinda have to wonder what you’d be shooting at. ---
**Author:** ![Sofaspud](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sofaspud](https://boards.straightdope.com/u/Sofaspud)\ **Post date:** [September 20, 2007, 9:47pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/30 "2007-09-20T21:47:10Z")
Re: the recoil: for a true railgun (rather than, say, a coilgun), some of the recoil force is directed outwards – perpendicular to the line of motion of the projectile. Also, they are essentially arc-welding themselves with every shot (not quite, but close enough). Friction in a true railgun is much higher than in a coilgun, and (I would surmise) much higher than in a conventional explosive-powered projectile gun, as well. Anyway, they won’t have as much back-directed recoil as a comparable weapon, but there will still be recoil; the amount of which depends on the mass of the projectile and the speed to which it is accelerated. The formula’s been hinted at above. 🙂 Aside: What most people think of when the term railgun is used is actually a coilgun. In a coilgun, there is no electrical connection between the accelerating coils and the projectile; in a railgun, it won’t move withOUT an electrical connection between the parallel rails and the projectile. The advantage of coilguns over railguns is that they do not suffer from the brutal wear and tear on the ‘barrel’; the downside is, they cannot propel objects nearly as fast. Lotsa good stuff on the 'net about these things, but for starters check out [Wikipedia: Railgun](http://en.wikipedia.org/wiki/Railgun). A Google search will pull up lots more detailed examples, as well. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [September 20, 2007, 9:56pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/31 "2007-09-20T21:56:39Z")
[QUOTE=Sofaspud] Re: the recoil: for a true railgun (rather than, say, a coilgun), some of the recoil force is directed outwards – perpendicular to the line of motion of the projectile. [/QUOTE] How could this possibly reduce backwards recoil momentum at all, other than transferring it to the air as in recoilless rifles? ---
**Author:** ![Sofaspud](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sofaspud](https://boards.straightdope.com/u/Sofaspud)\ **Post date:** [September 20, 2007, 10:05pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/32 "2007-09-20T22:05:40Z")
[QUOTE=Ludovic] How could this possibly reduce backwards recoil momentum at all, other than transferring it to the air as in recoilless rifles? [/QUOTE] I’m not sure I understand your question, honestly. Or perhaps I misunderstand the word perpendicular… What I mean is, the propulsive force of a railgun is caused by an electrical current passing from one rail, through the projectile, and through the second rail. This sets up a strong magnetic flux, which ‘pushes’ the projectile down the rails and hopefully into the target. The projectile ‘pushes’ back based on the usual laws of physics. Part of this force is not directed backwards, however; it is directed outwards, pushing against the inside edge of the rails. If they are not sufficiently braced, they’ll tend to fly apart long before useful velocity is achieved, breaking the circuit and causing the projectile to simply sit there. In a gas (explosive) powered weapon, recoilless rifles excepted, the pressure in the chamber has one direction to go - out the barrel, pushing the projectile in front, and pushing equally hard in the opposite direction. Since the railgun uses a traveling magnetic field rather than a pressure chamber, the force is ‘pushing’ outward rather than directly backward. Think of it this way: the recoil force is still there, but the vector is changed. Does that make sense now? ---
**Author:** ![ambushed](https://avatars.discourse-cdn.com/v4/letter/a/3bc359/32.png) [@ambushed](https://boards.straightdope.com/u/ambushed)\ **Post date:** [September 21, 2007, 1:55am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/33 "2007-09-21T01:55:55Z")
[QUOTE=LiveOnAPlane] Sorry, no. It wouldn’t matter how you’re propelling the mass, the recoil would still be the same…dang, where’s that formula…anyway, for every action, there’s an equal & opposite reaction. Doesn’t matter if you’re throwing it, firing it from a spear gun, firing it from a conventional rifle, or using compressed air. Recoil is still gonna be there, undimished. [/QUOTE] [QUOTE=H3Knuckles] Wouldn’t that be impossible? I mean, the old “for action there is an equal yet opposite reaction” thing? It would seem that if you project a mass away, you would have to have recoil. I would think that if nothing else, than at least the air pushed past the round as it travels down the barrel pressing the barrel itself backwards. [/quote] Yeah, I know a little physics, thanks. That’s why I wrote: > [@ambushed](#): > > I’m pretty sure that the rail guns in the science fiction I’ve read, \*\*the authors have claimed them to have no or little recoil. \*\* Ya’ know, _science fiction_, and all that, in which physically impossible technologies, like FTL drives, impenetrable “force fields”, and zero inertia space drives are commonplace? You know, like _fiction_? ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [September 21, 2007, 2:22am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/34 "2007-09-21T02:22:33Z")
Railguns can operate in a vacuum. (That’s somebody’s cue to explain how a gun _could_ be engineered with a built-in occident or whatever. Go to it! 😃 ) Also, quote from Jim: “Rail Gun: goes back at least to around 1970 and the late Dr. Gerard K. O’Neil’s “High Frontier” proposal. He proposed using it to shoot metal ore off the Moon into Earth orbit for use in building BIG orbital space colonies (the size of mythical Babylon 5 of Sci-Fi fame, or even larger), so the idea undoubtedly goes back even further than that.” [http://blog.wired.com/gadgets/2007/01/us\_navy\_invents.html](http://blog.wired.com/gadgets/2007/01/us_navy_invents.html) ---
**Author:** ![Otara](https://avatars.discourse-cdn.com/v4/letter/o/a88e4f/32.png) [@Otara](https://boards.straightdope.com/u/Otara)\ **Post date:** [September 21, 2007, 2:27am UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/35 "2007-09-21T02:27:57Z")
The reason recoil will be significantly less according to a link I found, is because the propellant isnt being ejected from the barrel as well. So the only recoil created is from the round, rather than the plume of propellant adding on to it, because the propellants ejected mass is also part of the recoil equation. So you wont eliminate recoil, but will get a benefit by eliminating propellant as part of the overall mass being accelerated. Eg if you have 1kg of mass and 5kg of propellant, you’ve managed to reduce the total mass being accelerated by 5kg. Otara ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [September 21, 2007, 1:43pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/36 "2007-09-21T13:43:52Z")
[QUOTE=Measure for Measure] Railguns can operate in a vacuum. (That’s somebody’s cue to explain how a gun _could_ be engineered with a built-in occident or whatever. Go to it! 😃 ) [/QUOTE] Why wouldn’t a gunpowder gun work in a vacuum (besides purely mechanical issues like loss of lubricant or vacuum welding)? Despite what _Firefly_ says, real propellant doesn’t need external oxygen to ignite. **Sofaspud** – Perhaps I’m misunderstanding you. It doesn’t matter what kind of sideways forces there are in a given projectile thrower – zero, more, less, or a force spinning the barrel. The force on the projectile has to equal the recoil force directly backwards on the thrower. So the fact that a railgun exerts a sideways force on the rail has no relation to how much recoil backwards it has. Plus, of course, a gunpowder gun has pretty significant sideways forces. The expanding propellant gases push on all sides: the projectile, the rear of the barrel, and the sides of the barrel. It’s just that if the barrel’s strong enough, the forces on the sides of the barrel cancel each other out. And if the barrel’s not strong enough, well, then you don’t want to be there, of course. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [September 21, 2007, 2:28pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/37 "2007-09-21T14:28:06Z")
[QUOTE=Der Trihs] … And it’s much easier to mount rockets on a solid object to change a projectile’s trajectory, than it is to do the same for a laser beam. [/QUOTE] IMO, that’s the biggest drawback for a laser weapon - line of sight. You would normally want a cannon situated in a defendable and difficult to reach location. The ability to use rockets or gravity to change trajectory helps to bend the payload around your protective barrier (buildings, mountains, curvature of the earth) ---
**Author:** ![Sofaspud](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sofaspud](https://boards.straightdope.com/u/Sofaspud)\ **Post date:** [September 21, 2007, 4:48pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/38 "2007-09-21T16:48:34Z")
[QUOTE=Quercus] Why wouldn’t a gunpowder gun work in a vacuum (besides purely mechanical issues like loss of lubricant or vacuum welding)? Despite what _Firefly_ says, real propellant doesn’t need external oxygen to ignite. [/quote] I have no cite, but I can’t see a reason why it wouldn’t. Gunpowder, IIRC, contains its own oxygen source, right? > [@Quercus](#): > > **Sofaspud** – Perhaps I’m misunderstanding you. It doesn’t matter what kind of sideways forces there are in a given projectile thrower – zero, more, less, or a force spinning the barrel. The force on the projectile has to equal the recoil force directly backwards on the thrower. So the fact that a railgun exerts a sideways force on the rail has no relation to how much recoil backwards it has. > > Plus, of course, a gunpowder gun has pretty significant sideways forces. The expanding propellant gases push on all sides: the projectile, the rear of the barrel, and the sides of the barrel. It’s just that if the barrel’s strong enough, the forces on the sides of the barrel cancel each other out. And if the barrel’s not strong enough, well, then you don’t want to be there, of course. I’ve been reviewing my sources on railgun tech, and it turns out I was mistaken. **Otara** nailed it: > [@Otara](#): > > The reason recoil will be significantly less according to a link I found, is because the propellant isnt being ejected from the barrel as well. What I appear to have been doing is misremembering how the Lorentz force worked, and conflating that with the way the magnetic flux traveling along the rails worked, and coming up with the (incorrect) premise that the recoil vector would be altered. So, to clarify: recoil is felt in line with the rails, directly backwards, opposite the vector of the projectile being accelerated. The Lorentz force isn’t applicable for recoil calculations, so we’ll ignore it. And the sideways force that I _thought_ was the redirected recoil force, is actually the force generated by the magnetic flux itself. It’s very powerful and requires that the rails be braced against it, and it does exert itself perpendicularly to the vector of the projectile, but it’s not caused by the projectile and is not part of the recoil. Essentially, it’s like holding the same pole of two magnets near each other; that’s the force that’s trying to spread the rails. (And, while partially inaccurate, this gives me the highly amusing mental image of the railgun projectile being squeezed out like a zit between two magnetic ‘fingers’. Heh.) ---
**Author:** ![Capt\_B.Phart](https://avatars.discourse-cdn.com/v4/letter/c/9fc29f/32.png) [@Capt\_B.Phart](https://boards.straightdope.com/u/Capt_B.Phart)\ **Post date:** [September 21, 2007, 7:32pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/39 "2007-09-21T19:32:49Z")
[QUOTE=Sofaspud] I have no cite, but I can’t see a reason why it wouldn’t. Gunpowder, IIRC, contains its own oxygen source, right? [/QUOTE] > [@](#): > > Firing a gun in space isn’t as loony an idea as it first seems. The very high muzzle velocity means that shells fired in almost any direction will hit the atmosphere and burn up. Those fired upwards may reach as far as 1500 km higher into space but will then fall back into the atmosphere as well. The only safety concern would be shells fired straight off to either side in a horizontal direction, within 5 or 10 degrees of level. Guided by unearthly implications of Newton’s Laws, some of them could zoom away, then reverse course and fly directly back at the originator within 45 minutes. > > Take the machine gun aboard Salyut-3. The gun was a version of the Nudelmann cannons used on Mig fighters and other Soviet jets since the 1960s, modified to operate in a vacuum that interfered with mechanical lubrication and other functions. It weighed about 40 kg, was 2 meters long, and fired 200 gram projectiles at rate of 900 rounds per minute and a velocity of 780 m/se. It was mounted at one end of the two-man space station, pointing along the station’s long axis. The cosmonauts aimed it by turning the entire station and tracking the target in a viewfinder at the control panel. Each cartridge contained an explosive mix that needed no ambient air to ignite. [From here](http://www.jamesoberg.com/06122001pearlharbor_pol.html) ---
**Author:** ![Capt\_B.Phart](https://avatars.discourse-cdn.com/v4/letter/c/9fc29f/32.png) [@Capt\_B.Phart](https://boards.straightdope.com/u/Capt_B.Phart)\ **Post date:** [September 21, 2007, 8:52pm UTC](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814/40 "2007-09-21T20:52:07Z")
Strikes me that rail/coil guns are a technology that’s proving to be a real bastard to translate into anything practical The idea’s been around since at least [1845](http://www.spectrum.ieee.org/jul07/5296/time) but (a bit like fusion power) actual breakthroughs seem a perpetually [just around the corner](http://www.spectrum.ieee.org/jul07/5296) My WAG is that [ram accelerators](http://findarticles.com/p/articles/mi_m1511/is_n3_v15/ai_15238900) will be made into practical weapons and/or micro-sat launchers long before electric propulsion gets anywhere. Although lacking the SF “Gee-Whizz” of rail/coil guns, [conventional guns](http://www.astronautix.com/lvs/7inrpgun.htm) (even without using a light gas intermediary) seem capable of being used as [launch platforms](http://www.astronautix.com/lvs/martlet4.htm), with [political and financial problems](http://www.astronautix.com/articles/abroject.htm) being harder to overcome than the technological (though the speed of sound in the propellant gas sets an upper limit on speed, as others have pointed out) As to recoil, I guess that’s the reason the reason the apparatus in **Snarky\_Kong’s** vid is mounted on wheels. Although it’s true that in normal gun the propellant gas adds to the recoil, a [muzzle brake](http://en.wikipedia.org/wiki/Muzzle_brake) can offset that. [Previous page](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814.md?page=1) [Next page](https://boards.straightdope.com/t/what-would-be-the-advantages-of-magnetic-accelerator-cannons/419814.md?page=3)