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Railgun test shot  (Source: U.S. Navy on YouTube)
Goal is to create a 64 MJ cannon capable of firing ten high impact metal slugs per minute

The U.S. Navy is anticipating the railgun will play a key role in battlefields of the future.  To that end it's investing deeply in the technology, gunning to make the U.S. the first to deploy the wild weapons technology.  The U.S. Navy and its research wing -- the Office of Naval Research (ONR) -- announced this week that in 2016 the railgun efforts will see a crucial test: the first live fire demonstration at sea.
I. A Brief History of Railguns
France’s Louis Octave Fauchon-Villeplee first proposed the concept of an “electric gun” in 1918, later getting a patent on the technology in the U.S. in 1922.  Railguns have long been speculated to potentially have critical advantages over traditional guns.  Like missiles and other propellant based high-speed projectiles, they can achieve much higher velocities that traditional projectiles which lack internal propulsion.  However, railguns are expected to be much cheaper than rockets, given that their ammo can be crude metal slugs.
Railguns operate by utilizing the Lorentz force or "Lorenz (sic) force" as the U.S. Navy refers to it as in a press release.  This phenomenon involves the application of force from electromagnetism on point charge.
A railgun operates via a homopolar motor armature, typically a conducting metal rod.
[Image Source: Wikimedia Commons]

The simplest form of the railgun -- the one the U.S. Navy will likely look to first deploy -- involves a sliding metallic conductor that acts as a homopolar motor in the cannon, accelerating down a pair of magnetized rails of opposite charges.  The armature can be integrated into the projectile itself, but typically it is attached to the rails so that nonmagnetized projectiles can be fired from the cannon.
More exotic variants use electrical arcs across ionizing gas to create a propellant effect similar to a traditional chemical (e.g. firepowder) based cannon.
Given the benefits, military designers worldwide have long been chasing after railguns.  In World War II, the Nazis hatched designs to build anti-aircraft railguns.  Recent analyses suggest these plans may have been technically feasible, however, they would have used as much power as half the city of Chicago, making them somewhat farfetched.  They were never built.
II. Railguns Approach the Battlefield
With the advent of high-energy solid-state switches and high-energy-density capacitors, at last the power necessary to rapidly magnetize the rails and eject the projectile has been at least made a practical reality.
The U.S. Navy has been kicking around prototypes for some time.  Its plan is to deploy a 64 Megajoule cannon to warships sometime around 2020-2025.  That device will use tungsten slugs and will fire at speeds of around 5,800 m/s (19,000 ft/s or roughly 13,000 miles per hour).  At that rate the cannon will be able to accurately to hit a 5-meter (16 ft) target from roughly 200 nmi (370 km) away.  The goal is to be able to fire 10 shots per minute.
The tungsten slugs are expected to have enough kinetic force to punch through even the best tank armor of today.  Line of site is a problem with railguns, but the advent of drone sighting technology -- a key area of research at the U.S. Navy -- will likely nullify this disadvantage by the time the tech hits the high seas.
Currently the Navy's prototypes are being tested on land by the Dahlgren Division of the Naval Surface Warfare Center (NAVSEA), a team based in Dahlgren, Virginia.  The Surface Warfare Center -- which targets nearer term warfare solutions -- collaborates with the Naval Research Lab (NRL), which handles more speculative and pure research projects.
After much land-based testing, the cannon will soon be ready to test at its desired destination -- on the high seas.  In 2016 the U.S. Navy plans to deploy a prototype cannon with a range of 110 nmi (204 km) aboard one of the Navy's Spearhead-class joint high speed vessel (JHSV) for live fire testing.

HSV Swift
The second JHSV vessel, the U.S.S. Swift [Image Source: Florida Times-Union]

The JHSV is the Navy's next generation troop ship.  Currently, 10 are either built or under construction and another 13 will be added by the year 2041.
The JHSV is technically a non-combatant, however, it was selected for this test due to its flexibility and roomy deck.

BAE railgun
BAE's prototype railgun [Image Source: U.S. Navy]

One of the biggest challenges facing railgun designers is to shrink the cannons down to the size of traditional naval artillery.  Currently a team at UK-based BAE Systems plc (LON:BA) and the Electromagnetic Systems (EMS) Division at privately-owned U.S. defense contractor General Atomics, have both delivered the Navy competing prototype designs.
It's possible that both companies' railguns will be deployed in 2016.

General Atomics Railgun
A railgun prototype from General Atomics [Image Source: U.S. Navy]

Rear Adm. Bryant Fuller, the Navy's chief engineer, comments on the upcoming tests:

The electromagnetic railgun represents an incredible new offensive capability for the U.S. Navy.  This capability will allow us to effectively counter a wide-range of threats at a relatively low cost, while keeping our ships and sailors safer by removing the need to carry as many high-explosive weapons.

Rear Adm. Matt Klunder, the chief of naval research, adds:

Energetic weapons, such as EM railguns, are the future of naval combat.  The U.S. Navy is at the forefront of this game-changing technology.

The Navy has been actively developing the railgun technology since at least 2005, according to a press release.  The Navy says it does not plan to deploy railguns permanently aboard the JHSVs, due to their noncombatant status.  It has not decided on the final destination for the cannons; one possibility is the Littoral combat ship (LCS), a newer class of naval vessels that are expected to comprise a key portion of the U.S. Navy's future combat fleet.

Source: The U.S. Navy [press release]

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RE: Sweet technology
By drycrust3 on 4/11/2014 2:53:30 PM , Rating: 2
Another thing here is that rail guns I don't think will need air to operate, it can be operated in a vacuum, I think. Gunpowder stills needs air to explode.

Firstly, most explosives rely on chemical methods to produce a lot of heat in a short amount of time. Usually the explosive has its own oxidising agent, although an internal combustion engine uses the oxygen within the air as the oxidiser. Any explosive that carries its own oxidiser, e.g. Gunpowder, Dynamite, TNT, etc, can operate in a vacuum, while any explosive that doesn't, e.g. Petrol, diesel, natural gas, won't work in a vacuum.
A nuclear bomb doesn't use the electrons around an atom as the means to generate heat, it uses an uncontrolled chain reaction involving either fission or fusion of atomic nuclei to generate heat. A nuclear bomb will work regardless of whether it is in a vacuum or not (provided the trigger can operate in that environment).
A rail gun, like a nuclear weapon, relies on trigger to get it going, it needs something to start the projectile moving, but after that the electromagnetic forces are what accelerate the projectile, so whether a rail gun can work in a vacuum, for the first firing at least anyway, or not depends entirely upon the nature of the primary moving force.
Why do I say "for the first firing ... anyway"? The big drawback with a rail gun is the massive amount of current required. This generates a large amount of heat at any point of "high resistance" (in the context of rail guns, "high resistance" could be 0.01 Ohms) e.g. between the projectile and the sides of the cannon, where the cables between the capacitor bank and the rails are attached, etc. This heat is enough to melt the metal on both the rails and the projectile, thus the rails are eroded with each firing. If you look at the closeup picture you will see what looks like a huge number of electrical cables. It wouldn't surprise me if that is exactly what they are. As an example, look at the size of the cable that goes between the battery and the starter motor on your car, it is also very thick, while most other wiring in your car is quite thin. Why? Current! Large current + thinness of conductor + distance = low voltage = power loss.
The same applies to a rail gun. Every point where heat is generated is also a point where there is power loss, meaning your projectile goes slower = less range.
For a rail gun in space, there wouldn't be any heat generated until the first projectile is fired, the problem then is the time taken to fire the second projectile is governed by the time to charge up the capacitors (which would depend on the size of the rechargeable batteries and the solar cells) and the time taken for the heat generated by the first firing to dissipate. By contrast, and land or sea based rail gun could use some compressed air to flush away the heat.
If you look in the background to those pictures you can see what looks like a huge capacitor bank, and on the side is a huge transformer (and I guess somewhere are some massive diodes) to charge up the capacitors.

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