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Fast steel on target? Electric guns on Navy ships: not yet on the horizon.


SOME CALL IT ZEUS' LIGHTNING bolt--a weapon that relies upon electricity and magnetic force to launch projectiles at hypersonic speeds to hit targets hundreds of miles away in a matter of minutes.

Scientists have been researching the electromagnetic rail gun for decades and as it slowly develops, analysts question when and if it will come to fruition in the face of ongoing engineering challenges.

Because of its promise to revolutionize warfare, as many as 20 countries, including the United States, are in pursuit of the technology. The Navy in recent years has invested $70 million in the concept in hopes of deploying the weapon aboard its ships in the 2020s.

Current naval gun technologies are limited in range, with firing distances of 12 to 15 miles. The rail gun would give the Navy an unprecedented ability to provide indirect fire support to ground troops operating as far away as 250 nautical miles.

The Marine Corps is especially eager for the technology, says Elizabeth D'Andrea, program manager of the Office of Naval Research's innovative naval prototype rail gun program.

Analyst Norman Polmar says the technology, if put on a ship, would be the only gun that could meet the Marine Corps' requirement to hit targets from the sea more than 150 miles away from the coast.

"I think it would be tremendously valuable for next generation warships," says Scott Truvet, a Washington-based naval analyst. "But the devil's in the details."

The rail gun looks like a conventional ship-based gun system with round barrels several meters long, says Ray Zowarka, associate director of the Center for Electromechanics at the University of Texas at Austin. But it diverges from current, naval weapon technologies at the back end with two parallel rail segments that are bridged by a sliding armature. Electric current runs down one rail, through the armature and back up the other rail. The voltage generates magnetic fields around the rails and the interaction between those fields, called the Lorentz force, accelerates the projectile from the gun.

Standing just over five feet tall, the rail gun projectile will be much shorter than that of conventional weapons, says D'Andrea at a science and technology conference. Because all the energy to propel the projectile to the target is located on the ship, the projectile itself contains no chemicals or explosives for launching and can be stacked below deck without worries of secondary explosions.

As envisioned by the Navy, the rail gun would fire the projectile at Mach 7, or seven times the speed of sound. It would accelerate into the sky at 2,500 feet per second and leave the atmosphere for four minutes. After re-entry, on board electronics would acquire target information from the Global Positioning System and the projectile would strike at Mach 5 velocity. Ships would be able to fire six rounds per minute.

But to reach that point will take a lot of research, analysts say.

"It's a very tough technology. The United States has been working on rail guns for decades and there's a number of technical problems," says Philip Coyle, senior adviser at the Center for Defense Information.

Rail guns require high power sources, such as capacitors and other pulse power systems, that can be difficult to build and are not necessarily compatible with the maritime environment, he says.

To accelerate a projectile to 2,500 meters per second requires six million amps of electric current running through the gun.

"When you start your car in the morning, to make the battery turn your engine and have the starter do the electromechanical conversion, that takes about 300 amps. So you can see the orders of magnitude we're talking about to fire these guns," says Zowarka.

Because of its high power requirements, the rail gun's energy supply would have to be drawn from the ship's generators over time and stored. Several storage technologies, including capacitors, inductive devices and batteries, have been demonstrated in the United States and abroad. Researchers at the University of Texas have successfully placed 60 megajoules in inductive storage, says Zowarka. But storage is only half the issue. The energy must be quickly converted into large currents and discharged in a short period.

"The gun fires in something like 10 to 20 milliseconds, so what the ship puts out in minutes, it now gives up in thousandths of a minute," says Zowarka.

The Navy wants the projectiles to have a kinetic energy of 64 megajoules, about as much as a locomotive traveling at 60 miles an hour, he says. A joule is a measure of work or energy, equivalent to the work done by one newton of force acting through a distance of one meter. A megajoule is one million joules.

Firing the gun at that muzzle energy level will require an even greater input of energy into the system itself, says Zowarka. If the weapon fires at 50 percent efficiency, then the amount of energy will have to be doubled at the input of the gun. For example, a muzzle energy of 64 megajoules requires an input of more than 120 megajoules.

"We've demonstrated about half of what's required to eventually do the job," he says.

To achieve the goals of the rail gun, about 40 gigawatts, or 40 billion watts, of electricity is necessary. In 1995, when a heat wave claimed hundreds of lives in Chicago on a particularly blistering day, the city was generating 19 gigawatts of power.

"If you took all the power plants in Chicago, routed all their wires to one location, and then supplied the whole power to run Chicago, you still would be a factor of two short to fire this gun," says Zowarka.

In laboratories, scientists have demonstrated the art of the possible: muzzle energy of 9 megajoules, currents of three million amps and velocities dose to the Navy's specifications, says Zowarka. But boosting the muzzle energy from 9 to 64 megajoules, the amps from 3 million to 6 million and the bore size from four inches in diameter to six or seven inches remain a challenge.

"It's a scale up, but there's been a lot of good demonstrations that give you the feeling that we can probably get there with the right amount of research and effort," he says.

Major research efforts are focused on materials to extend the bore life of the gun to allow multiple firings of the high-speed projectiles. Other efforts are underway to prevent a phenomenon in the armature called transitioning. When the armature slides against the rails to launch projectiles at such high velocities, it can create plasma--a very hot gas--that can cause damage, says Zowarka.

The rails also pose a problem. Anything traveling at thousands of miles an hour will tear raw metal. "If one of the advantages you're hoping to get is multiple firings, that's a problem that has to be overcome," says Coyle.

On top of the research challenges, there are engineering difficulties.

"You have to get the current there, and then you have to manage these tremendous forces between the rails," says Zowarka.

Transferring the energy to the gun requires numerous current-carrying cables, and the placement and routing of those cables becomes a tricky design issue. Also of concern is the magnetic pressure inside the gun barrel, which comes up to 60,000 pounds per square inch, says Zowarka.

Any electronics in the projectile would have to be hardened so that they can withstand the setback accelerations, says Coyle. The projectile also must be able to fly through the atmosphere without overheating, adds Zowarka.

In the overall system, the challenge is thermal management for a continuous rate of fire operations at high rates of fire, says Amir Chaboki, the rail gun program manager at BAE Systems, which is developing a 32 megajoule laboratory launcher for the Naval Surface Warfare Center at Dahlgren, Va., and designing a 32 megajoule advanced launcher prototype for the Office of Naval Research's rail gun program.

There also is a debate about the lethality of projectiles that rely upon velocity, rather than explosives, to make a kill.

"A solid slug of metal isn't going to do much damage. It will stir up the dirt where it lands. But if you want a bigger projectile to do some damage, then you've got to be able to put explosives inside," says Coyle. If U.S. forces are trying to hit tunnels buried beneath the ground, for example, high-speed projectiles alone will not do the job.

"It's got to be more than a lead brick--it's got to be a bomb with explosive force," he says.

But certain targets, such as a command center inside a building, could be destroyed by sheer kinetic force.

"You don't have to have an explosive. Just that slug hitting it will devastate the building," says Polmar.

At the Naval Surface Warfare Center in Dahlgren, Va., researchers are experimenting with a 32 megajoule laboratory rail gun. It is designed to allow scientists easy access to components so that they can quickly test different parts and look at new concepts, says D'Andrea. "We are systematically testing through the materials," and will look at insulators and the armature the same way, she adds.

Using blunt projectiles, the team has fired 66 shots at two megajoules of muzzle energy on a single set of rails. It has acquired more than seven months of data using eight megajoules of muzzle energy.

This month, the researchers plan to take a world-record shot, firing a projectile at 11 megajoules of muzzle energy. The lab plans to begin firing the gun at 16 to 32 megajoules shortly after.

In August 2009, there will be a "go" or "no-go" decision on the rail gun, says D'Andrea. If it passes muster, the technology will advance into testing phases, with a feasibility demonstration in 2011, a system demonstration in 2016 and initial operating capability in 2020 to 2025.

Analysts question whether the technology will mature enough under that schedule, but scientists including Zowarka, who has worked on rail gun technologies for more than 20 years, have confidence that it will.

"Given the time frame, if it is indeed 2020, it sounds like more than enough time to me," he says.

The Navy has not yet determined whether it will put the rail gun on any ship. But any combat vessel that would carry a rail gun must have advanced electrical distribution systems capable of powering both electric propulsion motors and supporting the full range of shipboard electrical loads, including weapons.

The first warship to meet those power requirements is the DDG-1000 Zumwalt class destroyer. Some reports have linked the rail gun to that ship. The Navy originally had planned on incorporating the rail gun onto the 7th or 8th ship in the class, but because the number of ships has been cut back, it may not be a viable option. The Office of Naval Research is adamant that the two programs are not at all connected and stresses that its work is independent of shipbuilding programs.

But there are other options for the rail gun technology, analysts say.

"It's not like you need a battleship," says Polmar.

The gun will size to fit onto Arleigh Burkeclass destroyers, and it could be backfitted onto the ships when they are brought in for their half-life updates.

"If we can put the vertical launch system in a Spruance class hull, then you sure as hell can do this," he says.

Some shipbuilding experts disagree and argue that a new ship design would be required.

If the rail gun falls through, the Navy will have to rely upon existing close range weapons, guided extended range munitions and aircraft to do the job, says Truver. But with a rail gun, "you don't have to worry about stealth. You don't have to worry about survivability. You don't have to worry about a lot of different things that you would worry about with a crewed asset, like an airplane," he says.

Scientists and some analysts say that while there are a number of hurdles to overcome, rail gun technology is viable.

"We know how to do it--it's just an engineering challenge," says Polmar.

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Title Annotation:FUTURE NAVY
Comment:Fast steel on target? Electric guns on Navy ships: not yet on the horizon.(FUTURE NAVY)
Author:Jean, Grace
Publication:National Defense
Date:Nov 1, 2007
Previous Article:Sea services: facing uncertainty, Navy contemplates 'alternative futures'.
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