Railgun
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February 2012 test
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A railgun is an electromagnetic projectile launcher based on principles similar to those of the homopolar motor. A railgun uses a pair of parallel conductors, or rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail.
Railguns are being researched as weapons that would use neither explosives nor propellant, but rather rely on electromagnetic forces to impart a very high kinetic energy to a projectile, (e.g. APFSDS). While explosive-powered military guns cannot readily achieve a muzzle velocity of more than about 2 km/s, railguns can readily exceed 3 km/s, and perhaps exceed conventionally delivered munitions in range and destructive force. The absence of explosive propellants or warheads to store and handle, as well as the low cost of projectiles compared to conventional weaponry come as additional advantages.
Nevertheless, any cost-benefit analysis between chemical propellant and electromagnetic (EM) propulsion systems for weapons applications should also factor in the reliability and survivability of the EM power supply that must be co-located with the projectile launch system. In addition, many arguments in favor of EM guns revolve around the questionable assumption that greater muzzle velocity is always better. Parametric relationships between range, payload weight, and launch velocity show that this is not a strong argument for many suggested EM gun applications. For example, due to lower aerodynamic drag at launch, a slower but heavier projectile may actually fly farther than a lighter faster one, making the velocity limitations of chemical propulsion perfectly acceptable. In addition, explosive fragmentary warhead lethality is largely unaffected by velocity and does not require more demanding hit-to-kill guidance electronics that may not survive extremely high gun launch accelerations. Significantly, explosively formed penetrator and shaped charge warheads already drive what is technically a kinetic energy penetrator to velocities well in excess of EM gun launch capabilities, up to 8 km/s for a shaped charge, upon detonation with the target; and it has been demonstrated that with respect to armor penetration, increased impact velocity much above 2 km/s does not necessarily result in a deeper hole; (although the crater may be wider as more energy is deposited with increased impact velocity).
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