Future Naval Guns

by Davy Jones

Future naval guns

Student thesis looks ahead to next generation naval gun

by JO2 Davy Jones

Much of the student research in the Navy's university's engineering programs focuses on fleet applicable technology. This couldn't be more true for Lt. Cmdr. Fred Beach, a combat systems student working toward his master's degree in applied physics, who is building an electromagnetic rail gun.

The rail gun is a weapon that uses electrical current to propel a projectile, said Beach. "There are no moving parts, except the projectile, of course."

Beach has known about the technology for a while now; the concept of a rail gun is not new. He became interested in the weapon while working a problem in physics class, then built a miniature gun with off-the-shelf equipment for his robot's weapon in last spring's Robot Wars IV.

"I built the robot's rail gun as more of a challenge to myself, to see if it could be done," Beach explained.

The weapon itself consists of two parallel copper rails and a electrical current source; in Beach's case, the source is a battery that charges up a bank of capacitors. The projectile is placed between the two rails, and actually completes the circuit.

"This means the projectile must be able to conduct electricity," added Beach. "I use graphite, instead of copper or aluminum, because it is almost as good as a conductor as the other metals, but doesn't erode the rails." Aluminum or copper projectiles cause higher temperatures inside the barrel of the gun and slowly eat away the rail surface.

When the gun is fired, energy from the capacitor bank is discharged, and the current will flow from one rail, through the projectile, to the other. This generates a directional magnetic field, called "Lorentz Force," that propels the projectile.

"The robot's gun fires a projectile with a barrel velocity of 40 meters per second," Beach said, "and that was toned down for Robot Wars." The robot's capacitors take two seconds to charge and 2.5 milliseconds to discharge.

Beach's goal, as part of his thesis, is to build a meter long rail gun that can fire a projectile at a barrel velocity of two kilometers per second, about 6,500 feet per second -- more than twice as fast as the SR-71 Blackbird spy plane can fly.

"If I can get the money to buy them, I'd like to get a pair of more powerful capacitors," said Beach, citing that, so far, his project is on a zero budget. The new capacitors would produce four times the power and increase the barrel velocity to six kilometers per second.

"A two-pound projectile fired at that speed could conceivably flip a tank over on a direct hit," Beach added. Beach's thesis isn't concerned with the gun's accuracy, however. His bullets are washers, and aren't very stable projectiles. Beach will be concentrating on the effects of a graphite projectile on bore erosion in a larger weapon.

"Although graphite is brittle, the entire projectile doesn't need to be made of one material," the lieutenant commander explained. "You could use a strip of graphite as the conductor on a tungsten- molybdenum alloy slug, for example."

The future of this weapon could be bright, if the money was there to fund it, Beach said. "The rail gun is comparably better than the 5-inch, 54 caliber, naval gun that dominates the fleet now."

The rail gun's largest component would be the power supply, but it would fit into the space normally taken up by a powder or ammunition magazine, according to Beach. These would be unnecessary, because the projectile wouldn't need a chemical propellant nor explosive charge. The kinetic energy of the slug itself would be enough to destroy the tank or damage the ship.

"The projectile would also be smaller and lighter -- a 10-pound slug vice the 70-pound shell used in today's 5-inch guns," Beach said.

"It's also a very safe technology. There are no weapons magazines, no explosives. The entire weapon is insensitive to magazine hits," Beach explained. "It also saves on logistics, reducing the amount of explosives carried on ammunition and other supply ships."

Rail gun technology is very mature, Beach said, only two to three years away from being able to field a weapon, assuming the money is there, of course. Demonstration devices have been built at the University of Texas at Austin.

The main drawback to the rail gun is its rate of fire. Although the time required to charge up the power supply is fine for naval and artillery gunfire, aviators won't be seeing the weapon on the F-14 Tomcat anytime soon.

"Air-to-air combat requires a high rate of fire to track an opponent down in a gunfight," Beach concluded, "we won't see electromagnetic machine guns until the power supply can be made much smaller and much stronger."