Thursday, March 8, 2012


The US Navy is working on railguns, electromagnetic launchers capable of fantastic muzzle velocity. Conventional guns are limited by the speed of sound. The projectile is pushed up the barrel by combustion gas. That combustion gas only expands at the speed of sound. Grant that the speed of sound in white hot gas at enormous pressure is much higher than the speed of sound in air, but muzzle velocity in conventional guns is still limited to about 4000 ft/sec.
Railguns have no such limit and can achieve much much higher muzzle velocities. The Navy project is working on 32 Megajoule rail guns. To put that into real numbers, 32 Megajoule is 23.6 Mega foot/pounds. For comparison, the conventional 5 inch cannon has a muzzle energy of 0.185 Mega foot/pounds. The rail gun has 127 times the muzzle energy of the conventional cannon. This translates into amazing range, like 100 miles.
To power the railgun, the Navy is talking about a battery bank. That ought to be quite something. An ordinary car battery (still the best there is for this kind of application) holds only 4560 joules. Each 32 Megajoule shot would totally flatten 7017 car batteries. The Aviation Week article talked about a battery bank good for 20 shots. That's a LOT of car batteries.
Another science fiction project gets funding.

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