Railguns are a class of electromagnetic launcher and are known more formally as Linear Magnetic Accelerators. Along with their cousins, coilguns, railguns are also called Mass Drivers (particularly in their artillery versions) and Gauss Guns (in their firearm versions). Using Railguns as an orbital launch technology is discussed in the Launch Guns article in the Orbital Travel section.
The first railgun was constructed by Joachim Hänsler in 1944, and various researchers experimented with the idea in the ensuing decades. Scientists at the Australian National University in 1972 were able to accelerate a 3 gram projectile at speeds of over 5000 meters per second. In the 1980s, railguns became part of the Reagan administrationís SDI program. Today, railguns are being actively researched by a number of private interests, NASA, and by a collaborative effort between the US Naval Sea Systems Command in Washington, D.C. and the British Ministry of Defence.
Railguns are also a popular weapon system in science fiction, appearing in a great many table-top RPGs such as Cyberpunk and Rifts and combat-oriented videogames such as Mechwarrior and Halo. Theyíve also been seen in the TV series Stargate: Atlantis and the movie Eraser.
|Simplified diagram of railgun operation|
A railgun consists of a pair of long, parallel, electrically conductive rails, mounted in an insulating barrel, with the rails connected to a rapidly switching high current source. An armature on the projectile to be fired completes the circuit, resulting in a magnetic force that drives the projectile down the barrel. In more advanced designs, this armature is actually a plasma arc created by the vaporization of metal brush-like armatures. The metal-plasma arc still conducts electricity, but since it is no longer solid it greatly reduces friction.
The projectile "rides" the magnetic field it creates as it connects these two rapidly-alternating electrical sources down the length of the barrel. Think of the electrical arcs riding up paired antennae in a mad scientistís laboratory, only moving much faster and propelling a bullet at the top of its arc. More detailed technical explanations for their operation are given in the links at the end of this article.
The muzzle velocities railguns are capable of are astonishing. Railgun systems in laboratories have achieved projectile speeds exceeding 21,000 kph and are projected to eventually be able to obtain even greater velocities of over 8000 meters per second.
However, railguns have a number of drawbacks. Most significantly is their enormous power requirements and the need for large amounts of direct current. One of the main stumbling blocks to their being implemented as a practical weapon system is that engineering an energy source both mobile and potent enough to power the system has proven enormously difficult. Advanced forms of flywheel batteries and explosive power generators may work, but both technologies would have to be developed to a much greater degree than they are now.
Another problem is the constant wear and tear on the acceleration rails. Passing the huge amounts of current through the rails creates heat, and that excess heat can build up and warp the rails if theyíre used often enough. Also, the arcs that propel the projectile tend to superheat the metal of the rails, resulting in various problems, such as warping the rails through "spot welding" effects and vaporizing the top layer of the metal as the arc passes over. The vaporization of the armatures to create the electrical arc may also result in the accumulation of metal residue on the rails over time.
Some innovations in the basic railgun design have gone a ways to correcting these problems. Cryonic cooling systems are being explored. Altering the composition and cross-section of the rails themselves (circular rail cross-sections seem to be the configuration that works best with latest models) may help, as well as "pre-accelerating" rounds. The "pre-acceleration" means basically using more conventional means of firing a round, such as the gas-expansion method used in modern firearms, then running the round through the rails to further augment its velocity. This way, the projectile spends less overall time between the rails, reducing the heat applied to them by the electrical arc.
Even with these techniques, however, rails would have to be replaced fairly frequently in order to ensure optimal performance. This may tend to make railguns comparatively expensive weapon systems to maintain.
Ammunition for railguns are usually envisioned in terms of discarding sabot rounds. This means that the projectile itself is surrounded by a protective casing which it sheds as soon as it leaves the barrel, helping not only to protect it from the extreme conditions of the weapon firing but to also give it an additional velocity push. Even so, the projectiles have to be unusually resistant and specially designed. They would have to be near-needle-like in cross-section in order to slice through the air at the tremendous velocities quoted without disintegrating, and they would have to be specially reinforced to withstand the thousands of Gís of acceleration they would undergo upon firing.
Because of their configuration, railgun projectiles will be smaller and easier to store than conventional rounds. Typical magazines could hold up to six times as many railgun rounds as standard rounds, depending on their exact design. Also, because railguns do not need to eject a casing, mechanical reloading can be simplified and lead to much higher rates of fire than what modern weapons are capable of.
Because of their enormous power requirements, early railgun armaments would most likely be large point-defense weapons, designed primarily to take down incoming missiles or attack aircraft. A railgun can put a lot of hyper-velocity rounds into the air fast, making them ideal for intercepting rapidly-approaching targets.
Point Defense Railguns would be large artillery-like emplacements, turreted and gimbaled to provide fire rapidly over a broad arc if need be, and tied directly into a dedicated but non-mobile power source nearby. They would be guided by a powerful array of sensors and most likely controlled directly by a computer (as opposed to a human gunner) in order to ensure the fastest possible response times to incoming threats.
Tech Level: 12
|The US Navy's DD-X destroyer firing its railguns. Image (c) Lockheed-Martin|
The main thrust of current railgun research is to produce railgun-powered artillery, especially for use on naval ships. The US Navyís advanced DD-X Destroyer project, being developed with the cooperation of the British Ministry of Defense, is developing a railgun version of a main shipís gun, designed to hurl shells inland over 290 miles in under six minutes. The rounds fired would be travelling at over seven times the speed of sound in sub-orbital parabolic arcs. They would be guided via satellite and would hit the ground with such force that explosive warheads would superfluous. In 2003, a facility in Kirkcudbright, Scotland, hosted a 1/8-scale test of an electromagnetic railgun that produced stable flight in a projectile fired out of the barrel at Mach 6.
Current naval guns cannot hit targets further inland than 12 miles and have only a fraction of the DD-X railgunsí projected accuracy. The other primary armament that can reach such ranges, cruise missiles, currently cost a cool million dollars apiece. Railgun ammunition can hit just as hard and with just as much accuracy as a cruise missile, but can deliver hundreds of rounds for the same price as a single missile.
Because the DD-X destroyer would use an all-electric drive, the ship would be designed to divert most of the power from its generators to its railguns, giving the weapons sufficient power for a number of devastating barrages. However, this has the disadvantage of forcing the ship to stop to fire its main weapon, but since the DDX is designed primarily as a long-range bombardment vehicle, this would be required of it any way. Future naval vessels using railguns will probably be designed to overcome this limitation.
Land-bound versions of the DD-X railgun are sure to be developed. The major impediment foreseen in producing railgun artillery is their enormous power requirements. Mobile land-bound railgun artillery will at first probably be fairly massive, little more than a large, mobile electric generator (probably at least truck-sized) of one design or another attached to a mobile chassis and the weapon itself. The arrangement would likely be too bulky and clumsy for any first-line use, and would probably be assigned only to long-range bombardment duties.
Another possibility is to design the system as modular; the gun as one separate mobile unit, and the generator as another. This may ultimately make the system easier to transport and use, and in fact multiple railgun units could be powered off of a single mobile generator. However, this would also make the mobile generators prime targets as they would be seen as the railgunsí achillesí heel.
If railroad lines are available, its also possible railgun artillery could be fitted onto rail cars. Multiple guns could be loaded onto a flatbed with one or more generators carried as separate cars. Because of the railgunsí range of hundreds of miles, dependence on rail lines would not be an impediment in many theaters of battle.
Its assumed that if railguns can prove themselves as large scale-weapons, efforts to scale them down for a wider variety of uses would be an inevitable development. But again, the largest stumbling block to achieving this is coming up with a small but potent enough source for steady current to charge the gunís rails.
Ever more compact and efficient power generation and storage technologies is a field that is seeing constant refinement and research. Its almost certain better mobile power sources will be developed alongside railgun technology in the decades to come. But by the time railguns are ready for deployment on tanks and fighting aircraft, will the proper power generation and propagation technology be there for them to take advantage of?
One good candidate for an effective mobile power source is advanced flywheel batteries. Current research into such systems would have future military-grade models composed of tough advanced composite alloys, enough to spin at hundreds of thousands of rpms in a frictionless vacuum environment and provide enough juice for up to several dozen railgun shots. An array of such batteries would provide vehicles with all the power needed for their railgun weapons.
As power sources become more mobile, railgun weapons can be scaled down accordingly, and be fitted onto tanks, armored fighting vehicles, fighter jets, and attack helicopters. Using a railgun as a main weapon on a tank would mean an increase not only in effective firing range but also in overall rate of fire for such vehicles, as well as potentially higher penetration with direct shots. Like with the DD-X naval guns, rounds fired by tank railguns would probably be guided via satellite.
Aircraft employing scaled-down railguns would make use of them for direct fire, especially in air-to-air combat where hypersonic projectiles would have vastly greater speed and rates of fire than missiles. In order to offset recoil considerations for aircraft, railgun anti-aircraft rounds would probably be smaller than machine gun rounds, but at the velocities they would be travelling they would still deliver crippling damage to enemy aircraft. Airborne railguns can also be used for ground strafing, but with their increased range, such strafing would be able to hit targets on the ground several kilometers away with reasonable accuracy.
RAILGUN SPACE SYSTEMS|
Tech Level: 13
|The Reagan-era SDI vision for a railgun-armed anti-ICBM satellite. Image courtesy the US Department of Defense|
The Reagan Administrationís SDI program in the 1980s made railguns one of its top research priorities. Unfortunately, like most of the weapon systems investigated in that program, they proved unworkable with then-current technology. The SDI programís ambitions were simply too far ahead of their time.
However, 50 or so years from now (tech level 13), many of the technologies sought after by SDI are envisioned to not only be available, but be well-tested and proven. These include the railguns themselves, potent mobile power sources, improved heavy-lift space launch capabilities, and vastly improved sensors, fire control, and targeting computer systems. The railgun-armed satellite could become reality.
As with their original SDI vision, the primary mission of railgun satellites would be ballistic missile defense. As it would be operating in a microgravity environment in orbit, a railgunsí projectiles could effectively travel thousands of kilometers to intercept their targets. As soon as an enemy missile left the atmosphere behind on a sub-orbital parabolic arc, the railgun would acquire it and shoot a swarm of hyper-velocity rounds at it. This is much trickier than it seems in the telling, as there are a number of factors at work in low earth orbit that affect the trajectory of both missile and railgun rounds. However, such engagements are workable with sufficiently advanced and high-speed computer systems.
SDI railguns could also target more than just missiles. High-altitude aircraft, satellites, and spacecraft would all be viable targets. They would also be able to draw upon potentially more potent power sources than their land-bound cousins, such as nuclear reactors with a large array of flywheel batteries as possible back-up.
Railguns are also likely to be one of the primary weapons systems on the first armed spaceships. Because the distances involved in space combat are assumed to be enormous, the railgunís role would primarily be defensive, as missile and shrapnel defense. However, its also possible that they would be used offensively on targets relatively close, or to strafe non-maneuverable targets such as satellites and space stations. Large spaceship-mounted railguns may also be used to launch missiles as well, to give them an added oomph of acceleration.
At this tech level, an innovation may come online that would make man-portable high-energy-consumption weapons like railguns a possibility: compact explosive power generators.
Explosive power generators use specially-created charges to propagate a dense wave of high-energy electrons when detonated. Their current weapon application is to initiate experimental non-nuclear EMP bombs. Its possible that with decades of refinement such systems can become compact and powerful enough to serve as energy sources for small railguns.
The explosive charge would be built into the round itself, acting as both initial propellant and a quick-pulse power source to charge the rails for a single shot. Projectile, propellant, and power source would all be integrated into a single round, and a soldier would only have to worry about carrying around clips of ammunition to power their weapons, as they do today. This would eliminate the need for bulky and heavy external power sources.
Its also possible should these explosive power generators not prove practical, advanced flywheel batteries could become small enough to be carried in a backpack by this time, still allowing for a man-portable weapon system, though this configuration would prove much clumsier and may be impractical for all but the most specialized uses.
Even with the explosive power generator solution, the first man-portable railguns would likely be big, bulky affairs, used primarily for anti-tank and squad support roles. Individual soldier would also have to deal with fierce recoil from the weapons. In order to help offset this, railgun projectiles would be made as light as practical. Three to four gram needle-like flechettes encased in discarding sabot rounds have been cited in several science fiction sources as the likely type of ammunition. Even so, recoil compensators and steady-cam-like body harnesses may be necessary to help reduce this problem.
And thus we come to what may be the holy grail of the rail: practical railgun rifles usable by the average soldier. Pistols and other small configurations may never be very practical using this technology. Even with powerful current running through them, the rails in railguns need a certain amount of length in order to get its projectile up to speed. Make them too short, and their performance would fall below whatís achievable by modern gas-expansion firearms.
Another problem that may arise is that lighter and smaller railguns means lighter and thinner rails, which may be much more prone to the warping and wear problems than their larger cousins. Advances in material technology between now and their implementation could offset this, but even so one can foresee having to replace the rails in a railgun rifle more frequently than in larger railgun weapons.
Railgun combat rifles would almost certainly be heavier and bulkier (or at least longer) than modern combat rifles, but would make up for that with greatly increased range, penetration, and rates of fire. Railgun firearms could defeat any personalized armor now available and with specialized armor-piercing ammunition could conceivably be a threat to armored vehicles such as modern light tanks.
Still, given the prevalence of other types of more reliable advanced firearms sure to be present by the time railgun firearms are developed, these weapons may end up having only a very limited role in combat. Because it may be inevitable that the smaller, thinner rails will deform quickly, railgun rifles might take the form of cheap, disposable one-shot weapons with specific armor piercing rounds, designed primarily to be direct-fire anti-armored-vehicle weapons.
Compact but potent power systems are an absolute must to make railgun firearms a reality. Besides compact explosive power generators, at this tech level options such as super-conducting batteries and loops may become available, and at higher tech levels science-fiction-type power systems such as compact fusor units could supply all the energy a soldierís weapon could conceivably need.
http://www.angelfire.com/fl2/quantum/history.htmlhttp://www.powerlabs.org/railgun2.htm http://www.railgun.org/ http://www.navweaps.com/Weapons/WNUS_Rail_Gun.htm http://www.popsci.com/popsci/technology/generaltechnology/64669aa138b84010vgnvcm1000004eecbccdrcrd.html http://www.military.com/soldiertech/0,14632,Soldiertech_RailGuns,,00.html http://www.onr.navy.mil/media/releases/image_gallery/default.asp?categoryID=9
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