ETC stands for ElectroThermal Chemical weapons, an idea that is being actively developed by the US and other nations.
Electrothermal chemical is a complex phrasing for a weapon that uses the same basic principle as a car engine to propel ammunition. In an internal combustion engine, a spark plug ignites a small volume of gasoline in a confined space. The force of this detonation drives the chamber's piston up, supplying mechanical force to turn the vehicle's drive shaft. An ETC weapon uses this sparkplug-fuel concept to propel bullets instead of pistons, but the guns use a much more advanced fuel systems, materials, and combustion chamber designs.
Like in a modern rifle or pistol, rapidly expanding gasses in the firing chamber propel the bullet forward. However, unlike contemporary weapons, the bullet itself does not contain the igniting charge. Rather, a highly-combustible fuel is injected into the firing chamber behind it and ignited into plasma by an electronic ignition system sometimes called a plasma cartridge--basically a souped-up spark plug. This fuel may be a solid or liquid propellant, depending on the exact design of the gun, though liquid fuels are the most often discussed with this technology. Either way, the weapon does not have to eject a casing afterward, somewhat simplifying some aspects of its mechanical design.
Another advantage of ETC technology is the ability of the plasma detonation to "follow" the projectile up the gun barrel while continually imparting energy to it. In a conventional solid propellant weapon, the initial detonation of the propellant sets the projectile on its way, but the force of the expanding gasses drops off with distance as the bullet shoots down the gun barrel. However, the electrical charge causing the plasma to burn ever hotter in an ETC weapon can remain engaged the entire time the bullet is in the barrel, forcing the burning gasses to constantly expand at even faster rates and constantly exert pressure on the projectile. This phenomenon combined with the much higher burn rate of the propellant fuel makes ETC weapons a significant improvement over conventional solid propellant weapons in both range and muzzle energy for a given caliber of weapon, in some cases by 50% or greater.
There are a number of different liquid propellant mixes for use in ETC guns, ranging from basic hydrocarbons such as gasoline to high-burning fuels such as hydrogen. They are all superheated into a rapidly-expanding plasma by the electric igniter. In fact, the system is set up so that the more juice is pumped into the weapon, the hotter the plasma burns and the more explosive a force its able to produce. Hence ETC weapons can be "dialed" up or down selectively in performance. Guns can fire rounds with as much force as their physical manufacture is capable of handling, instead of the set pre-packaged level of propellant each modern bullet contains.
The hotter the propellant burns, the less fuel needed per shot, and the less juice is drained from its electrical source to push it to that temperature. High-burning fuels would be ideal, but their toxicity, expense, and difficulty in handling may preclude their wide-spread use in the weapons. Hydrocarbons are a viable, cheap, and readily available alternative, especially if doped with inert material to coax them into a higher burn, but even with such a modification don't offer the higher performance and efficiency of the higher quality fuels. The choice of fuel in the weapon will depend on a number of factors, including availability, cost, compatibility with desired performance, and details of its storage and handling.
Real tests conducted by the military have shown that blends of nitromethane and methanol and blends of octane and hydrogen peroxide work best for large-caliber guns. Whether these mixtures are the ones that will actually be used should the weapons go into mass production remains to be seen, and will depend on how well they can be stored and handled in quantity in practical usage. Since research into smaller calibers is not yet being seriously pursued, it is unknown what fuel mixtures would work best for bullet-sized projectiles.
ETC weapons also need a fairly potent electrical power source, but unlike other electromagnetic weapons such as railguns and coilguns, their power requirements are well within the capabilities of current battery and capacitor technology, at least for artillery versions.
The biggest hurdle in seeing ETC weapons adapted for wide-spread use will likely have much more to do with economics than with any technical problems that still need to be solved. ETC weapons are an entirely new class of gun. The militaries employing them will have to retool their production, deployment, maintenance, and logistics regimens to accommodate them, and that usually takes quite a bit of effort and resources to bring about. Of special concern is the handling of potentially toxic propellant chemicals by large numbers of individual soldiers. New safety procedures and technologies would have to be developed to prevent potential health hazards and accidents.
Also, if this technology becomes widespread, there would be a strong push to make weapon materials, their ignition chambers and barrels especially, much stronger, in order to contain and channel hotter burning propellant plasmas.
With ongoing programs in the US, Britain, and other countries to develop ETC weapons, it is likely that the first battlefield-ready versions will be produced sometime in the next decade or so. ETC weapons are an integral part of the US military's ongoing Future Combat System (FCS) project.
ETC technology will first see deployment as artillery and vehicle weaponry. The first one of these planned by the US is the XM291, one of the main tank guns designed for the FCS's replacement of the M1A2 Abrams Main Battle Tank. Designed to be in the 60-80mm range, it will have as much muzzle velocity and range as a modern solid-propellant 140mm gun, with a rate of fire of about 10 to 15 rounds per minute. In other words it will be able to do the work of a solid propellant gun almost twice its size, while allowing for a lighter, more mobile, and more fuel-efficient vehicle.
However, use of an ETC weapon will probably be a more complicated affair, at least until the weapons are more streamlined in the future for mainstream use. The gunner will have to keep track of both liquid propellant and the amount of electrical current each shot will consume. A computer system will likely be in place to make the task much easier, as well as knowing how much of each to use to get a desired shot, but the gunner will have to be trained to know the system inside and out to oversee the firing computer as well as be able to operate the system manually should the main computer ever go out.
For pure artillery versions of ETC guns, where the weapons would be well back from any front-line danger zones, a more modular system of deploying the weapons may be used. The gun itself may not be equipped with its own combustion-plasma fuel tank nor with a high-current power source. Instead, rows of multiple ETC artillery guns may be serviced by a single separate generator truck and a tanker fuel truck each. This way, a great deal of weight and volume in the artillery vehicles can be given over to other design features, such as recoil absorption and hardening, as well as making the entire system much more mobile.
SP stands for Solid Propellant. This is a proposal to combine existing SP artillery guns with emerging ETC technology in order to produce much better performing weapons by retooling weapons that currently exist. This would require new cartridges and modified gun chambers, as well as the addition of plasma regenerative injector and combustion control to a standard combustion chamber. This means, basically, that standard artillery guns would have to have a liquid fuel injector added to the combustion chamber, so the liquid fuel would enhance the solid propellant by making it burn hotter. Both the gun barrel and the projectile would have to be modified to handle this increase in power, which some estimates put at 30% or more above what current SP artillery is capable of.
While workable, the biggest barrier to such a retooling would most likely be economic. Many military commanders would not believe that the increased performance would be worth the expense of the modifications to a large proportion of the artillery weapons out there. If done at all, it would probably only come after ETC stand-alone weapons have proven their mettle.
Eventually, ETC weaponry can be streamlined and scaled down to the point where the technology can be used safely by the individual soldier, both as squad support weapons and as combat rifles. Scaling them down for practical man-portable use will take some extensive modifications, however.
In order to simplify use, the various consumable components of the weapon--projectiles, fuel, and current source--will probably be combined into a single magazine. This magazine will contain enough fuel for each shot at a preset maximum level, as well as a rechargeable battery or ultracapacitor in its base. Even though ETC ammunition does not contain casings or solid propellant, the presence of the liquid fuel and a battery will likely make ETC magazines bulkier and heavier than magazines for modern-day weapons.
Reloading the magazine With the necessary consumables would be a complicated affair and may need a specialized machinery or automated stations to speed up the process. Otherwise, the magazine itself can be made modular, breaking into its three main components of projectile sub-magazine, fuel cylinder, and battery, allowing soldiers on the battlefield to swap needed components quickly if a full-service reloader is not available.
The weapons themselves, while made thicker to handle hotter combustion plasmas, are also likely to be made of more advanced composite material to make them as light as possible without giving up material strength. Thus, an ETC rifle or squad support weapon will probably not be any heavier than it modern SP equivalent except for its magazines.
In order to simply its use, each ETC weapon will likely come with pre-set power levels for its shots. Artillery and vehicle versions would have their power levels completely customizable on the field by their attending crews with full computer readouts, but an infantry soldier in a combat situation will not often have the luxury of adjusting weapon settings on a large user-friendly computer screen. Instead, the power levels of the shots will literally be set on a small dial, probably near the trigger or some other spot on the gun the soldier can readily reach while in firing position. An indicator light or readout on the weapon would display the level of the shot he has selected.
One of the main design concerns for ETC firearms will be recoil absorption. That profound increase in potential muzzle velocity also means a profound increase in the amount of recoil the weapon produces. "Dialed up", ETC guns can be expected to have the kick of SP guns twice their size or worse. And unlike modern firearms, which have a preset amount of recoil that the soldier can readily adjust to, an ETC firearm's recoil will vary with how far up or down its power level is set.
Thermal regulation issues also rear their ugly heads with this type of firearm. Unlike tank and artillery versions, to be practical as an individual soldier's weapon on today's battlefield, rapid automatic fire is a must-have feature. However, this gives the weapon almost no time to cool down between shots, and with the super-hot combustion plasmas ETC are designed to propagate, heat build up may become a very serious concern. Because of their anticipated more advanced construction materials, ETC weapons will be more tolerant of higher temperatures than modern firearms, but its easy to foresee circumstances when the weapon will be asked to perform even beyond this level of tolerance.
One solution may be as simple as supplementary air-cooling fins, such as those seen on many fanciful golden-era sci-fi ray guns. The fins in this case may be simple thin sheets of heat-conductive material along the gun's barrel, and may be designed to "pop-out" mechanically only if the gun is dialed up to a power level where heat regulation may become an issue.
Alternatively, active coolants may be used, but this may add another level of complication to an already complicated soldier's weapon. Some fuels, such as hydrogen, can double as a coolant, and could be pumped through the weapon before being used as propellant fuel. In this case, fuel cartridges for the weapon would always have a bit more fuel than needed for all its projectiles, to ensure that some can always be injected into the gun to act as a coolant.
A separate coolant may be necessary, however, and worked into the gun's magazine as with its other consumable components. The disadvantage to this would be that the magazine becomes even heavier and bulkier, especially since coolant may not be necessary at every set power level. A solution would be to have one type of magazine with no coolant meant only for low to mid level shots, and another special magazine with coolant designed for high-power, high-temp shots. The weapon would be set so that it would not be able to fire at certain power levels unless the right type of magazine is in place.
Because the propellant plasma "follows" the projectile up the barrel of the gun, at the upper power levels each shot will be accompanied by a very bright plasma discharge from gun barrel, looking very much like a miniature flame-thrower to an unschooled eye. Because of this and other factors, ETC guns will not be appropriate for stealth work, and some mission areas, such as sniper work, will likely remain in the realm of solid propellant rifles.
http://www.powerlabs.org/electrothermal.htmhttp://www.freepatentsonline.com/5188682.html http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel1/20/5024/00195648.pdf?arnumber=195648 http://www.fas.org/man/dod-101/sys/land/fcs.htm http://220.127.116.11/search?q=cache:q-PJby6W8xMJ:www.globalsecurity.org/military/library/news/1997/5fcs97.pdf+xm291&hl=en&ct=clnk&cd=2&gl=us&client=opera
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