The electromagnetic (EM) railgun in many respects sits in the fuzzy boundary between conventional and emerging military technologies. It is an emerging technology in that it is yet not practical, but does promises much. However, in many ways it is offering more of the same. Compared to conventional bullets, shells, and most tactical missiles, it offers a revolution in speed, indeed the point of much of this work is to push a projectile to speeds where the destructive power of the projectile's kinetic energy (KE), its energy of motion, is greater than that which can be carried in the projectile. On the other hand these supersonic and hypersonic velocities are not comparable to the light-speed performance of EM weapons such as lasers. Like directed energy weapon (DEW) systems, it faces competition from existing technologies that can achieve many of the same effects, but without the many technical challenges that may not be overcome in the near and medium term.
In conventional guns, the bullet or shell is propelled by expanding gases from the rapid combustion of a propellant such as gunpowder, and are limited by the physics of the burning propellant and the resulting gas. Among the limitations is that the propellant burn in a gun is deflagration, which is burning at or below the speed of sound within the material. A detonation, combustion propagated by a shockwave that is above the speed of sound in the material, would be counterproductive as it would turn the gun into an expensive pipe bomb. Chemical-powered guns can overcome these limitations by using the deflagration process to drive a piston that compresses a large quantity of light gas, such as helium, which when released can achieve higher velocity than the combustion gases can achieve. Light gas guns are found in laboratories that study high-velocity impacts, such as in meteorite impact research, but are impractically large and cumbersome to be useful as weapons.
In an EM railgun, a powerful electric current is run from one rail to another through a conductive portion of the projectile, the armature, generating a powerful Lorentz force, which accelerates the projectile along the two rails. Not being limited by the characteristics of a chemical propellant, EM railguns have achieved hypersonic (above Mach 5) muzzle velocities from relatively small guns.1 The KE of a mass increases by the square of its velocity. Doubling the mass of the projectile merely doubles the KE. Doubling its velocity quadruples the KE. Therefore if one wants to use KE purely as a destructive mechanism, velocity at impact is paramount.
KE = 1/2 (Mass) (Velocity ^ 2)
The extreme “muzzle” velocity of railguns has drawn military interest for years. Early in the Reagan-era Strategic Defense Initiative (SDI), orbiting railgun batteries were a possible means of launching guided KE interceptors. Earth-based applications, such as long-range artillery aboard warships, or even mobile ground pieces, avoid many of the power, mass, and volume restrictions found in space basing. As of 2012, working test beds, not laboratory experiments, were being demonstrated by BAE Systems and General Atomics2 under the Office of Naval Research's Electromagnetic Railgun Innovative Naval Prototype (INP) program that started in 2005.3
Like DEW, cited applications for the U.S. Navy's railgun research include defense against missiles and aircraft; however, but unlike DEW, there is also open discussion about its use as a strike weapon. Unlike the novel effects of a laser or high-power radio-frequency weapon, the effects of being hit by a hypersonic projectile are unambiguously destructive. This of course puts this technology in competition with existing missile systems. Notwithstanding the research and development costs, the per-shot cost of a railgun would only involve a projectile and the energy source. Unlike electrically powered DEW systems, there would not be a “limitless magazine,” a fact that puts the railgun conceptually in between existing gun and potentially revolutionary DEW systems.
Although the U.S. Army, U.S. Navy, and their contractors have produced spectacular media presentations hinting at the promise of this technology, it must be remembered that challenges remain. The weapons being worked on now are power hungry, requiring pulses of energy measured in multidozen megajoules. Naval power plants and ground-based generators are capable of recharging such system, but the sudden release of this type of energy requires advance capacitors, and other novel energy storage systems. The heat generated by this much energy being driven through a weapon system is destructive, and current goals involve developing cooling systems to allow for firing the railgun several times a minute. Then there is the problem of the rails themselves, they must be incredibly strong to survive the effects of firing. An armature must be in electrical contact with the rails, whether the armature remains solid or is intentionally transformed into superheated conductive plasma,4 putting significant wear and tear on the rails. Present critics of this research have cited the short life span of current barrels, which have life spans measured in only hundreds of shots.5 Finally there is the problem of constructing a guided projectile that can survive being fired from a railgun. Accelerating to hypersonic velocities in only meters creates high g-loads that would crush most available components today. Again there are the EM and thermal effects of EM railgun operation that would fry (in both senses of the word) electronics unless they were shielded.
Solutions to these challenges overlap with other emerging technologies. Electrically powered DEWs also require large pulses of energy to operate. Solutions to the energy problem may involve nanotechnology structures that can increase the energy density of capacitors and other forms of electrical energy storage. Barrel sustainability is in part a material-engineering problem, and again nanotechnology is a potential solution. Robust electronics that can survive the accelerations and hostile thermal and EM environment of being fired likewise combine advance electronics with nanotechnology.
That there are potential solutions to these challenges makes the EM railgun an emerging military technology instead of science fantasy. If they can be overcome, this technology's backers claim a potential military revolution of even lower cost precision firepower at longer standoff ranges. However, if railgun technology works as advertises it will still need to prove its advantages against existing weapons’ concepts, such as the old-fashioned chemically driven guns and missiles. The excitement around emerging technologies is part about dreams of the future, and part about the thrill of the gamble—with the ironic payoff of becoming commonplace.
Notes
1. Grace Jean, Office of Naval Research. “With a Bang, Navy Begins Tests on Electromagnetic Railgun Prototype Launcher,” February 28, 2012, http://www.onr.navy.mil/Media-Center/Press-Releases/2012/Electromagnetic-Railgun-BAE-Prototype-Launcher.aspx.
2. Ibid.
3. United States Navy, Office of Naval Research. “Electromagnetic Railgun,” http://www.onr.navy.mil/en/Science-Technology/Departments/Code-35/All-Programs/air-warfare-352/Electromagnetic-Railgun.aspx.
4. David Hobbs, An Illustrated Guide to Space Warfare (New York: Prentice Hall, 1986), 121.
5. Spencer Ackerman, “Navy's Rail Gun Blasts through Budget Restrictions,” Wired, February 10, 2012, http://www.wired.com/dangerroom/2012/02/rail-gun/.