Coilguns are a type of electromagnetic launcher which, along with their cousins, railguns, are sometimes called Mass Drivers (especially pertaining to their artillery versions) and Gauss Guns (especially pertaining to their firearm versions). They are more formally known as electromagnetic linear accelerators. Using coilguns as a means of shooting a payload into orbit is detailed in the Launch Guns article in the Orbital Travel section.
The first coilgun was patented in 1900 by Norwegian researcher Kristian Birkeland. However, his attempts to produce a practical weapon proved disappointing, and the concept was abandoned and languished for many decades. Interest in the concept revived in the wake of the Reagan Administrationís SDI program, and NASA began looking into the possibility of using coilguns to launch orbital payloads. The NASA program has designed and built an experimental coilgun that can accelerate a 10 kilogram projectile to 39,600 kph. Today, many hobbyists and private interests build home-made coilguns, and the concept has gathered a great many enthusiastic supporters.
Coilguns consist of a series of electromagnetic coils that accelerate a metal projectile to high velocity. They are more mechanically complicated than railguns, but since there is no direct contact between the projectile and the coils they avoid the erosion and arc-over problems of railguns.
Each coil section along the barrelís length is switched on rapidly in sequence, pulling the projectile forward, then switched off as the projectile passes so the next coil section can grab it with its magnetic field. Rapidly switching from one coil to the next in sequence can accelerate a projectile to astounding velocities unobtainable by modern gas-expansion weapons.
Unlike railguns, coilguns can be made arbitrarily long, allowing for greater potential velocities using gentler accelerations. The main engineering obstacle to this technology is not so much producing enough power or strong enough magnetic fields, but overcoming timing and switching problems.
Because the projectile zooms so rapidly through the barrel, the magnetic fields switching on and off have to be precisely timed. Also, the current and voltage needed to produce the fields do themselves take time to build to strength and to fade away, especially in the bullet-time microseconds the projectile will typically be in the launch barrel. This can result in a loss of velocity, both from less-than-optimal field strength as well as slow-fading fields behind the projectile tugging on it and slowing it down. Precision timing programs and compatible hardware are therefore an essential component of any coilgun, and one of the main reasons why they have proven much harder to engineer than their conceptual cousin, the railgun.
Coilguns do pose a number of advantages over railguns, however, and many believe that while railguns will see practical use at first, coilguns will eventually supplant them. Coilguns use less overall power, are quieter, can be scaled down much more easily, and require far less maintenance (no rails to replace after so many firings) and will therefore prove cheaper to operate and maintain. Because a coilgun projectile does not actually come in contact with the barrel, there is very little friction and coilgun projectiles can potentially be accelerated to much greater velocities. And because rail wear is not an issue, coilguns can also be fired much more often and with a much greater rate of fire.
However, coilguns use up an enormous amount of current with every shot. Portable but potent power sources and energy transfer technologies are required in order for them to be made practical. Emerging devices such as compulsators, flywheel batteries, ultracapacitors, explosive power generators, superconducting batteries, and so on may be the key to making this technology battlefield-ready.
Coilguns also have a large amount of recoil, at least equal to that of modern artillery and firearms of comparable size. Ways to counter or lessen this recoil would have to be integrated into the weapon. And because of all the current eaten up by the coils, the weapon will also generate a large amount of heat. Passive and active cooling systems may also become a necessary part of coilgun designs.
The first practical application of coilgun technology will most likely be in the form of artillery, the "Mass Driver" often mentioned in science fiction. Their performance is expected to at least equal the railguns currently being developed by the US Navy for their DD-X destroyer project, which has a muzzle velocity in excess of Mach 7 and a range of 290 miles.
Projectiles would likely be somewhat needle-like cross section and be made as frictionless as practical. They need to be able to slice through the lower atmosphere as efficiently as they can, as air friction will sap over 20% of their muzzle velocity just in the first 16 meters of flight. Explosive warheads would be superfluous, as the projectile is expected to hit its target at over 5000 feet per second, and explosives would only be needed in certain specialized circumstances. The damage done is expected to come purely from the enormous kinetic energy of the impact from the dense projectile.
Coilgun artillery would shoot their projectiles in sub-orbital parabolic arcs which could reach over 80 miles high. During flight, the projectile can pick up navigational data from GPS satellites and adjust its trajectory accordingly with small maneuvering fins on its aft section.
Supplying power to the coilgun would be problematic but can be achieved with several different schemes. If used on naval ships, the shipís engines could supply the large amount of current needed directly. Land-based artillery would need a mobile generator and compulsator/flywheel arrays built into its chassis, making them potentially huge lumbering vehicles.
Alternately, the power source could be built into a separate vehicle, mainly a truck with a mobile generator complimented with banks of capacitors and compulsators. The coilgun itself would be a separate mobile unit. This could make the system much more mobile, and generator trucks could service multiple coilgun units simultaneously.
In areas where railway service is available, coilguns could be mounted and deployed on train cars. A generator could be carried in a separate car, or it could draw power off of the main train engine itself. Because of their enormous potential range of hundreds of miles, a coilgun mounted on a flatbed railcar could still be useful in battlefields far from the rail line.
At tech Level 13, circa 50 years from now, it seems likely space launch systems will become sophisticated and common enough that the cost of orbital launches falls dramatically. This would allow the lifting of large weapon payloads into orbit that previously were considered to be too cost prohibitive to be practical. Since coilguns would also be emerging at this time, an orbital coilgun anti-ballistic missile satellite like that originally envisioned during the SDI program seems inevitable.
Orbital coilguns have a tremendous advantage over orbital railguns, as they would have no rails to replace on a regular basis, plus would need less overall power in order to deliver the same performance. Such satellites could be powered by nuclear plants or by solar panels, and could store their energy in banks of long-term flywheel batteries. The flywheels would be aligned in counter-rotating pairs along different axes, both to minimize progressional instability as well as do double duty as gyroscopic stabilizers.
These coilgun ABM satellites would acquire targets rising over the atmosphere on suborbital parabolic arcs, and fire at the enemy vehicle is at or near the apex of its flight. This is much more complex than it sounds, as everything in orbit is moving at very high relative speed. Any one ABM satellite would probably only get a handful of chances to target a bogey as it whips by on its orbit, so the coilgun satellite would probably fire large bursts to ensure it could take down whatever it was aiming at.
The recoil from the shots would also act as thrust, meaning the satellite would have to readjust its aim after every burst. However, it can also use its gun as a mass driver in the space propulsion sense, and correct its orbit with it while on the other side of the planet. This would be in addition to whatever additional thruster system it may have.
The coilgun satellite could also target objects rising into higher orbit-bound trajectories or other objects in space.
Coilguns are sure to be incorporated into armed spaceships when such vehicles become available, and would be employed as both an anti-missile defense as well as a short range offensive weapon to use against non-maneuvering targets such as satellites and stations.
Scaling coilguns down small enough to be used in armored fighting vehicles and aircraft would be a daunting but not impossible task. Because barrel lengths would be shorter, more power would have to be applied to the coils to maintain their relatively high muzzle velocities.
At this Tech Level, a key technology comes into play that can supply this added power in a compact form: explosive power generators (EPGs). These come in two general forms. In the first, an explosive charge induces large spin in a flywheel or compulsator near-instantaneously, which in turn is used to create the power needed for the shot. The second kind uses a specific mix of elements to produce an electron dense, high-energy shockwave whose energy is fed directly into capacitors.
In order to keep the weapon system as simplified to use as possible, the explosives for the EPGs would be incorporated into the round itself, eliminating (or at least greatly decreasing) the need for a bulky independent power sources for the weapon. Like in modern weapons, the only thing soldiers would need to power the weapons would be the ammunition. The weapon ignites the charge and uses it to power its coils, while that same impulse is used to impart initial velocity to the projectile as it starts down the barrel.
In use as frontline weapons, direct-fire coilgun projectiles would fly much faster than missiles and have much higher potential penetration than modern conventional arms. They would be able to reload and fire at much faster rates as well.
Using coilguns as aircraft armament would require some special considerations. Coilgun projectiles would travel and hit their targets much faster than air-to-air missiles, making them very attractive armaments for aerial combat. What they would lack in maneuverability they would make up for in raw velocity.
In order to offset recoil adversely affecting the aircraft, the projectiles would be small and needle-like with minimal inertial kickback per shot. At the velocities they would be travelling, even such small projectiles would still cause massive damage should they hit.
Coilguns would still be large, heavy, and bulky, but it would be possible at this point to reduce their size enough for a single soldier with a specialized harness to carry one into the field. Its main purpose would be to act as a squad support and, coupled with armor-piercing rounds, as a direct fire anti-vehicle weapon.
As its assumed power supply in the form of EPGs can be made compact enough to at least carry in backpack form, the two main problems of a man-portable unit become recoil compensation and heat regulation.
Even scaled-down coilguns would deliver a large kickback per shot. A steady-cam like body harness for the gun would be needed. These are full-torso, rigid harnesses with a free-swinging articulated arm designed to bear the brunt of the weaponís weight and recoil. A famous example is the harnesses worn by the heavy gunners in the movie Aliens. Still, these may not be enough, and active recoil compensation systems, such as directing the waste gas from the EPGs and sliding counterweights may be needed to make these workable.
Heat regulation may become a serious consideration. While there is no friction produced by shooting the projectile itself, the constant charging and discharging of the coils would produce a lot of waste heat. In order to prevent performance degradation or even extreme damage such as melting, an active cooling system may be needed. Even if the power system is small enough to be incorporated into the magazines or rounds themselves, a small backpack-sized cooling system may still be required to make the weapon system practical.
This particular weapon comes from the Traveller RPG universe, where it is more properly known as a VRF Gauss Gun, and does seem to be a natural outgrowth of coilgun capabilities.
As was stated previously, engineering the coordinated rapid on-off switching of the accelerator coils is one of the major hurdles facing researchers in making coilguns a feasible weapon system. Eventually, though, this problem is expected to be fully solved and even perfected to the point that the on-off sequencing would take milliseconds at most. The weapon could fire projectiles as fast as they could be fed into the barrel. Combined with a high-speed ammo feed system, a weapon can be designed that would prove to be an entirely new class of devastating autofire weapon.
A VRF Coilgun would have a rate of fire dwarfing even the most prolific modern systems. It would be capable of continuously firing dozens of rounds per second, which when combined with a coilgunís extremely high penetration and muzzle velocity, creates a very formidable anti-personnel and area denial weapon. Even targets armored against single shots from coilguns may buckle when hit by hundred round bursts. It could devastate even the most heavily armored infantry.
But even such a formidable weapon system would have some drawbacks. First and foremost would be its power requirements. It would need an extremely potent source to fire so many projectiles so fast. Because needing to evacuate the waste gasses from EPGs would slow the weapon down, an array of advanced flywheel batteries or a more high tech source, such as superconductor batteries, would probably be used instead.
The weapon would also generate helacious heat as it fired, both from the electricity in the coils as well as superheated air in the barrel. VRF coilguns, their barrels especially, would therefore need to be cryogenically cooled. Without a sophisticated active cooling system, its likely the weapon would start melting after only a single burst.
Recoil would also be a major problem. Thousands of rounds firing per minute, even if they are small needle-like projectiles, creates a tremendous amount of force. A VRF Coilgun would have to be heavily anchored and compensated for its recoil just as well as modern artillery pieces twice their size.
Thereís also the issue of ammo capacity. VRF coilguns would eat ammunition voraciously, so their rounds would probably come in hoppers of a thousand or more.
All these considerations would preclude VRF coilguns from ever becoming man-portable; the weapon would simply be too heavy and unwieldy for any unaugmented soldier to carry, much less employ effectively. However, they would make an ideal vehicle and support weapon.
The Traveller version of the VRF coilgun fires 4000 rounds per minute, and each pull of the trigger unleashes a hundred-round burst. It is supplied ammunition in 1000-round hoppers, and typically vehicles sporting the weapon carry over 30 interconnected hoppers for it.
These are the gauss guns, gauss rifles, and gauss pistols often referred to by a number of science fiction sources.
Coilgun rifles and pistols would represent a quantum leap forward in small arms lethality and capability. Even though with their shorter barrels they wouldnít be able to come close to the performance of the larger, more powerful versions of this technology, they would still be significantly more powerful than any equivalent modern firearm. They would not only be able to shoot their rounds much at a much greater velocity (a theoretical maximum of 8500 mps in an atmosphere), they could also do so with a greater rate of fire and significantly increased range.
Powering such weapons while making sure the energy source is not bulky or heavy enough to act as a detriment to handling the gun is always an issue with this technology. However, its is assumed that by the time coilgun firearms become practical, so too will power sources compact enough to be incorporated into the guns. One possibility are compact, high-efficiency EPGs, with the tailored explosive charge incorporated into the individual round. Other possibilities include flywheel generators carried in backpacks or belt packs, and disposable superconductor batteries and/or ultracapacitors built into the base of a coilgunís ammunition magazine.
Recoil will be a problem that would have to be addressed in coilgun firearm design. These weapons may in fact be deliberately designed to be under-powered to a degree in order to make them easier for an unaugmented soldier to handle.
Heat regulation is another issue, but because these weapons would be smaller and use less power, heat build-up in the coils may not become a significant factor, at least to the point where it would risk degrading weapon performance. Still, the weaponís barrel after firing would be a very bright infrared source, and if used often enough in a short period of time might even start glowing red-hot. A compact recyclable coolant system would be ideal, perhaps with a recharge of the chemicals needed included in the weapon magazine. Combined with air cooling and radiator fins, heat buildup can be handled readily.
So even though coilgun rounds would be lighter and smaller than conventional rounds, the need to couple them with an explosive charge for the gunís EPG, as well as working a coolant recharge into each ammunition cassette, would mean that their magazines may actually prove just as large and heavy than a modern gunís, if not more so.
A coilgun that does not use EPGs would be significantly quieter than modern firearms, as there is no explosive charge needed to propel the round. The projectile would still create a loud report as it breaks the sound barrier, but the gunís coils can be powered down to subsonic performance if stealth is necessary. Running is such a "quiet mode" would result in greatly reduced performance, but on the plus side the weapon would make virtually no noise when fired.
http://www.coilgun.eclipse.co.uk/http://www.powerlabs.org/gaussgun.htm http://www.thinkbotics.com/military.htm http://traveller.wikia.com/wiki/Gauss_Weapons
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