Electrothermal-chemical Technology - Feasibility

Feasibility

The XM-291 is the best existing example of a working electrothermal-chemical gun. It was an alternate 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 XM-291 also mounts a larger gun tube and a larger ignition chamber than the existing M256 L/44 main gun. Through the application of electrothermal-chemical technology the XM-291 has been able to achieve muzzle energy outputs that equate that to a low-level 140 mm gun, while achieving muzzle velocities greater than those of the larger 140 mm gun. Although the XM-291 does not immediately mean that ETC technology is viable at this current point in time it does offer an example that it is possible and that continued research in the area is worth the advantages reaped if such a system was to be successfully implemented on a modern tank.

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. In comparison, a railgun currently cannot achieve a higher muzzle velocity than the amount of energy input. Even at 50% efficiency a rail gun launching a projectile with a kinetic energy of 20 MJ would require an energy input into the rails of 40 MJ, and 50% efficiency has not yet been achieved. To put this into perspective, a rail gun launching at 9 MJ of energy would need roughly 32 MJ worth of energy from capacitors. Current advances in energy storage allow for energy densities as high as 2.5 MJ/m³, which means that a battery delivering 32 MJ of energy would require a volume of 12.8 m³; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. There has even been discussion about eliminating the necessity for an outside electrical source in ETC ignition by initiating the plasma cartridge through a small explosive force.

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. Reduction in recoil can also be achieved through mass attenuation of the thermal sleeve. The ability of ETC technology to be applied to existing gun designs means that for future gun upgrades there's no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel.

Several countries have already determined that ETC technology is viable for the future and have funded indigenous projects considerably. These include the United States, Germany and the United Kingdom, amongst others. The United States' XM360, which is planned to equip the Future Combat Systems Mounted Combat System light tank and may be the M1 Abrams' next gun upgrade, is reportedly based on the XM291 and may include ETC technology, or portions of ETC technology. Tests of this gun have been performed using "precision ignition" technology, which may refer to ETC ignition.