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USN Rail guns in test

According to a news brief from a Janes newsletter, the move into the realm of what was once science fiction weaponry continues apace:

US Navy receives EM railgun prototype.
The US Navy (USN) has taken delivery and started testing a prototype electromagnetic (EM) railgun from BAE Systems as the service continues to develop a surface ship gun that can fire a projectile 50-100 n miles (93-185 km) without using propellants. General Atomics is due to deliver its competing prototype to the USN’s Office of Naval Research (ONR) in April

The future is here.

25 comments to USN Rail guns in test

  • 'Nuke' Gray

    I have always wondered if a rail gun would have an effect on the ground on which it was embedded. If you push projectiles eastward, the land is pushed westward. Sure hope they don’t build it on a faultline!

  • revver

    …really, railguns. *sigh*

    Oh well, it will come in handy when the U.S. liquidates itself to payoff its debt. Taiwan better invest in anti-railgun bunkers.

  • jsallison

    Guided telephone poles from orbit, only then can you be sure.

  • RRS

    Nuke –

    Not to fear, if I Understand from childhood devices and later days physics lab, the motion of the projectile is impelled not propelled, much the same as the “MagLev” trains.

    Except for air (or other fluid) impedance and “track” friction (if any after Lev)) there is no resistence beyond inertia.

    Most I have read about are linear, leaving open the question of whether the energy requirements can be modified to a reduced Hadron Collider type for acceleration. We shall see.

  • Railguns mounted on heavy weapons platforms, metal storm mounted on light weapons platforms.

    I’m staying away from battlefields in the future.

  • Dishman

    I’m staying away from battlefields in the future.

    I believe that’s the point, to make sure that the battlefield is the other guy’s location.

  • Scooby

    Nuke & RRS- there is an equal and opposite reaction, and the force on the railgun is equal in magnitude to the force on the projectile.

    Since the railgun is mounted to a ship (or on the ground), the mass that is accelerated by the reaction force is many orders of magnitude greater than the mass of the projectile.

    Firing the gun mounted to the earth does have an effect on the ground, but it is miniscule- probably somewhere between that of a crowd of people simultaneously hopping one meter to the east and that of the start of an auto race (30+ 2,000 kg all accelerating in the same direction at the same time). It will exert a force on the plate they are on, but not very much of one.

  • H man

    Let me know when they use this technology to launch material into space.

  • In Taiwan’s case, the question is surely whether a short-range railgun (<50km), with the requisite radar kit, could effectively defend against low-altitude cruise missiles? You're trading off the low RCS of the missile and hence limited reaction time against the speed of the railgun.

  • Bugger (must remember to type “less than”).

    … (less than 50km) could knock out incoming low altitude cruise missiles. The low altitude (20m or so above sea) and small RCS of the missile means short reaction time – but that’s precisely the advantage of a railgun.

  • Sigivald

    As Scooby said, it’s just physics – it has the same overall effect on the landmass as a non-railgun exerting the same force on a projectile*. The only difference is how the force is generated, not how it acts.

    My question is why they said “EM railgun” – doesn’t railgun imply electromagnetic?

    Is there some other kind I was unaware of, despite following the technology for years, from science fiction to prototypes to working models?

    (* Now, railguns have the potential to exert more force than conventional explosive guns, but still not so much as to be relevant at the geologic scale.

    Mostly the focus these days is on moving a smaller projectile really, really, really fast, rather than something the mass of a Volkswagen more slowly, like a 16 inch battleship gun – and without the high explosives, since you don’t need them at Mach Whatever.)

  • RRS

    Hey you physicists – enlighten us as to those equal and opposite “forces” where no propulsion is exerted; that is when successive points on the projectile are induced (attracted) to the next point ahead, etc. at increasing rates. Does increasing the rate create some reaction?

    As I recall, the “ruler” never moved on the minature sets.

    I don’t believe these developments are based on the use of a “carrier” for the projectile, just huge amounts of energy (resultant heat?)

  • Dale Amon

    Think of the fields like a powerful hand attached to the launcher. The force it exerts forwards on the small mass of the projectile gives it a lot of forward momentum; but the act of pushing also imports an equal and opposite push on the large mass of the launcher. The balance of forces, ignoring friction and such is just

    Mass_projectile * Acceleration_projectile = Mass_launcher * Acceleration_launcher

    If the launcher is attached to an aircraft carrier and the projectile is a hundred pounds… Not a big problem.

    Note that when an A-10 Warthog fires its depleted Uranium slugs from its GAU-8, the aircraft in that case *is* noticeable affected. One would expect the same from a weapon of this sort as well. It’s all just the balance of forces. ‘To every action there is an equal and opposite reaction’. F=ma. (unless you want to go all relativistic on me, in which case the equation gets a bit more complex).

  • Eric Tavenner

    US Navy receives EM railgun prototype. The US Navy (USN) has taken delivery and started testing a prototype electromagnetic (EM) railgun from BAE Systems as the service continues to develop a surface ship gun that can fire a projectile 50-100 n miles (93-185 km) without using propellants. General Atomics is due to deliver its competing prototype to the USN’s Office of Naval Research (ONR) in April

    That’s rather behind the times, I have seen the official ONR video(Link) of the full power rail gun. It looks like it would fit into a standard MK45 gun turret and would certainly fit into a MK42 turret. Both of those currently house a 5″ 54 naval rifle.

  • RRS

    Dale –

    TKS, but, if this is like the instrument tested at Dahlgren,
    does it really “push?”

    I will suggest the example at CERN for acceleration.

    I am asking, not challenging. I’ll also ask my grandson who has followed this a bit.

  • JDN

    Looking at the funnel shaped indentation at the back of the projectile, my understanding is that a plasma burst is induced in that space (analogous to rocket fuel within a combustion chamber) and is sustained as the projectile travels down the rail. The expanding plasma is directed by the funnel to the rear of the gun propelling the round forward, just like exhaust does to a rocket. “Fuel” is sustained by sublimation (?) of the metal projectile to plasma inside the funnel. Therefore, does the rail gun itself experience recoil?

    Put another way, is the projectile propelled solely by the magnetic field generated by the gun (recoil = yes), or the expanding plasma at the back of the projectile (recoil = no), or a combination of both (recoil = some).

    The huge electrical energy involved certainly creates large stresses within the gun itself, but I doubt that that translates directly into recoil.

  • Dale Amon

    It really depends on the kind of gun. I would have to do a bit more research. If it is a mass-driver type, it can be either push, pull or both, although my understanding is that pull-only is the most efficient. It doesn’t really matter in terms of the force vector diagram.

    There is also what was at once time ‘the’ rail gun, in which the pushing was essentially a plasma arc that followed the projectile all the way up the tube. There were issues with that technique so I suspect that what is in use now is closer to the lunar mass driver work that O’Neill’s team (which included Eric Drexler, the father of Nanotechnology) did back in the 1970’s.

  • Dale Amon

    Okay, so it is a ‘classical’ rail gun and not a mass driver (electromagnetic launcer). I guess that means they solved the problems with the electrode life. I seem to remember that many years ago that was a big issue.

  • RRS

    Sipping from the Pierian Spring, I read that the motive force is the Lorentz Force.

    The Plasma is created as the “armature” conducting the current that generates the Lorentz Force.

    The lateral part of the 3D of that force tends to push the rails apart (at 90 degrees to the impelled force.

    Currently they propose to use a “carrier” (sabot) for projectiles. That will eliminate the Plasma (vaporized foil).

    Perhaps super-cooling will come next?

  • the other rob

    This is somewhat peripheral, but the mere fact that a privately held company called “General Atomics” exists has put a smile on my face.

    If only more in life were like Mr Heinlein’s novels.

  • bloke in spain

    Correct me if I’m wrong, but I thought one of the big problems with hypersonic projectiles was the aerodynamics. There’s nothing much stopping the firing of very high velocity projectiles using chemical propellants but isn’t there some sort of problem with them ‘toppling’ in flight? S’pose you could fire spherical objects to avoid this but for maximum range you need something with a small cross section relative to mass to reduce atmospheric drag. ie a needle shape, ideally.

  • RRS

    Thou in Spain-

    Whence came the name of Fletcher?

  • bloke in spain

    á la Molly Millions? Not sure if a fletcher was electromagnetic though. Seem to remember it took cartridges so presumably chemical propellent.
    I’ve actually tried loading a shotgun cartridge with a load of needles. Even with flights they don’t fly very well.

  • RRS

    A fletcher put the feather on an arrow to stabilize its flight.