Electrothermal-chemical technology
Electrothermal-chemical (ETC) technology is an attempt to increase accuracy and muzzle energy of future tank, artillery, and close-in weapon system
An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy to trigger the process. ETC increases the performance of conventional solid propellants, reduces the effect of temperature on propellant expansion and allows for more advanced, higher density propellants to be used.
The technology has been under development since the mid-1980s and in 1993 was actively being researched in the United States by the Army Research Laboratory, Sandia National Laboratories and defense industry contractors, including FMC Corporation, General Dynamics Land Systems, Olin Ordnance, and Soreq Nuclear Research Center.
Background
The constant battle between armour and armor-piercing round has led to continuous development of the main battle tank design. The evolution of American anti-tank weapons can be traced back to requirements to combat Soviet tanks. In the late 1980s, it was thought that the protection level of the Future Soviet Tank (FST) could exceed 700 mm of rolled homogeneous armour equivalence at its maximum thickness, which was effectively immune against the contemporary M829 armour piercing fin stabilized discarding sabot.
Most proposed advances in gun technology are based on the assumption that the solid propellant as a stand-alone propulsion system is no longer capable of delivering the required muzzle energy. This requirement has been underscored by the appearance of the Russian T-90 main battle tank. The elongation of current gun tubes, such as the new German 120 mm L/55,
ETC technology offers a medium-risk upgrade and is developed to the point that further improvements are so minor that it can be considered mature.
Operational Principle
An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy as a catalyst to begin the process. Originally researched by Dr. Jon Parmentola for the U.S. Army, it has grown into a very plausible successor to a standard solid propellant tank gun. Since the beginning of research the United States has funded the XM291 gun project with USD 4,000,000, basic research with USD 300,000, and applied research with USD 600,000.
Flashboard large area emitter
Flashboards run in several parallel strings to provide a large area of plasma or ultraviolet radiation and uses the breakdown and vaporization of gaps of diamonds to produce the required plasma. These parallel strings are mounted in tubes and oriented to have their gaps azimuthal to the tube's axis. It discharges by using high pressure air to move air out of the way.
Triple coaxial plasma igniter
A coaxial igniter consists of a fully insulated conductor, covered by four strips of aluminium foil. All of this is further insulated in a tube about 1.6 cm in diameter that is perforated with small holes. The idea is to use an electrical flow through the conductor and then exploding the flow into vapour and then breaking it down into plasma. Consequently, the plasma escapes through the constant perforations throughout the insulating tube and initiates the surrounding propellant. A TCPI igniter is fitted in individual propellant cases for each round of ammunition. However, TCPI is no longer considered a viable method of propellant ignition because it may damage the fins and does not deliver energy as efficiently as a FLARE igniter.
Feasibility
The XM291 is the best existing example of a working electrothermal-chemical gun. It was an alternative technology to the heavier caliber 140 mm gun by using the dual-caliber approach. It uses a breech that is large enough to accept 140 mm ammunition and be mounted with both a 120 mm barrel and a 135 mm or 140 mm barrel. The XM291 also mounts a larger gun tube and a larger ignition chamber than the existing M256 L/44 main gun.
ETC is also a more viable option than other alternatives by definition. ETC requires much less energy input from outside sources, like a battery, than a railgun or a coilgun would. Tests have shown that energy output by the propellant is higher than energy input from outside sources on ETC guns.
Furthermore, ETC technology is not only applicable to solid propellants. To increase muzzle velocity even further electrothermal-chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. ETC technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. Understandably, recoil of a gun firing a projectile at 17 MJ or more will increase directly with the increase in muzzle energy in accordance to Newton's third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an ETC powered gun in an existing vehicle design. For example, OTO Melara's new lightweight 120 mm L/45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism (550 mm) and a pepperpot muzzle brake.