March 04, 2017

Plans for a new US super tank with an electrothermal chemical gun

The Army cancelled a future Ground Combat Vehicle but, some of the innovations, technologies and weapons systems may get into a new tank design. Design specs, engineering, weapons and other innovations envisioned for the GCV are now being analyzed for the new tank. In particular, the new tank may use an emerging 30mm cannon weapon planned for the GCV – the ATK-built XM813. XM813 is computer-controlled and electronically driven weapon can fire up to 200 rounds per minute, uses a dual-recoil firing system and a semi-closed bolt firing mode. The new tank will emerge after the Army first fields its M1A2 SEP v4 upgraded Abrams tank in the 2020s

The Army’s MCS program developed and test-fired a super lightweight 120mm cannon, called the XM360, able to fire existing and emerging next-generation tank rounds. The lightweight weapon being developed for the MCS was two-tons, roughly one-half the weight of the existing Abrams 120mm cannon. The XM360 used 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 guns by improving the predictability and rate of expansion of propellants inside the 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 (cancelled in 2009) was 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.

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 mean that ETC technology is viable it does offer an example that it is possible.

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/dm³, which means that a battery delivering 32 MJ of energy would require a volume of 12.8 dm³ per shot; 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.

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.

SOURCES - National Interest,

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