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Navy Railgun Program Takes Aim

January 2007
By Henry S. Kenyon

 
 
 
The Office of Naval Research (ONR) is developing electromagnetic (EM) railguns as a weapons system for future warships. EM railguns use electrical current to accelerate a projectile at extremely high speeds magnetically. This research launcher is powered by 8 megajoules; a megajoule is a measure of electrical, mechanical and thermal energy. The launcher is in use at the U.S. Naval Surface Warfare Center but will be replaced with a more powerful 32-megajoule system.
High-speed electromagnetic launchers promise accurate, lethal weapons system.

In coming decades, warfighters could rely on artillery support from U.S. Navy warships more than 200 miles away. Instead of conventional cannons or rockets, these ships would use electromagnetic launchers to accelerate projectiles to many times the speed of sound. Using electricity instead of gunpowder to fire guided munitions, the weapons offer the potential of rapid, highly accurate precision attacks without the logistics and safety issues of conventional naval guns.

Although electromagnetic (EM) railguns have existed in laboratories for decades, recent power system and materials developments now make the weapons’ fielding more feasible. The U.S. Navy has initiated an effort to produce a technology demonstrator by 2011. According to Dr. Amir Chaboki, program manager for BAE Systems’ Navy EM gun initiative, Minneapolis, the project began with a ship integration study funded by the Navy’s DD(X) destroyer program office in early 2003. The six-month study examined the feasibility of integrating an EM railgun into a next-generation electric ship, which is a design concept for future military vessels. Many of the mechanical systems on these ships would be replaced with fuel cells, electrical generators and actuators dispersed around the vessel to create more space for weapons and sensors and to enhance survivability in the event of damage to the ship.

Based on the study’s results, the Office of Naval Research (ONR), Arlington, Virginia, is exploring the development of a prototype weapon. BAE Systems was awarded two ONR-funded contracts, one through the NavalSurfaceWarfareCenter at Dahlgren, Virginia. The Dahlgren program is for a 32-megajoule laboratory launcher, including its detailed design, fabrication and installation. A megajoule is a measure of electrical, mechanical and thermal energy.

The second contract is for an innovative naval prototype of an EM railgun for tactical shipboard applications. BAE Systems and General Atomics, San Diego, are developing competing systems for the first phase of the shipboard contract, which also is managed by the ONR. The laboratory program is intended to solve bore life issues and to develop a practical bore and projectile design, while the tactical program seeks a lightweight solution that can be mounted on a platform. Chaboki manages both programs for BAE Systems.

The Navy’s final plans for the railgun are not concrete, says Chaboki, adding that the ONR program balances the service’s needs against the readiness of the weapons system’s technology. The 32-megajoule railgun is an intermediate step toward a 64-megajoule shipboard tactical weapons system. He explains that this is still the program’s goal but cautions that additional studies are needed to determine the best system for the service’s requirements.

As envisioned by the ONR, the 64-megajoule weapon would be able to launch a projectile as far as 250 miles downrange in six minutes. Traveling at around seven times the speed of sound (Mach 7) when launched, the ordnance would hit targets at speeds up to Mach 5, delivering tremendous kinetic force. The program envisions a variety of projectiles that would use global positioning system guidance.

Railguns offer several advantages over conventional guns, according to the ONR. Because the projectiles do not need propellant, logistics is simplified and greater shipboard magazine capacity is possible. The high speed of the ordnance will provide ground forces with accurate offshore artillery support and will allow warships to engage enemy surface vessels with rapid precision fire.

Several engineering challenges must be met before an operational EM railgun system can be fielded. The main impediment to developing an effective weapon is barrel life. Designers must be able to fire hundreds of consecutive shots without damaging the rails and insulators making up the gun’s bore.

The 32-megajoule laboratory launcher is intended to have a high-performance capability four times greater than any other laboratory-built railgun. It is planned as a flexible, adaptable and robust test platform to determine the best bore configuration and construction for an operational system. This test gun will accommodate different-size bores made of varying materials, allowing researchers to address bore life challenges. A near-term goal is to allow 100 consecutive firings at the 2,500-meter-per-second level without any damage to the bore.

Another development issue is the separation or damage of the rails. When a railgun launches a projectile, it generates an electromagnetic field around the rails, accelerating the ordnance out of the barrel at high speed without the need for propellant. An armature connects the current between both rails as it pushes the projectile out of the barrel. But the magnetic process that launches the projectile also forces the rails away from each other. This force must be contained to prevent the rails from being separated or broken.

The forces the rails are subjected to during a launch combined with the electrical current flowing through the system and the armature, which is in contact with the rails, all contribute to wear. Compared with a standard cannon, which sustains wear in its barrel from mechanical contact with the projectile, EM railguns are worn by the electrical current. Chaboki admits that maintaining this high-current sliding contact without damage is challenging.

He explains that two rail containment methods are being examined. The first is to use a heavy, laminated steel structure to reinforce the rails. The 32-megajoule laboratory launcher will apply this type of containment. But such a steel frame makes the barrel too massive for tactical applications. BAE Systems researchers instead are examining the use of advanced composites and other lightweight yet strong materials to contain the rails.

The gun’s breach and muzzle management also must be considered. Chaboki notes that with a conventional cannon, the escaping gas from the propellant causes pressure around the breach of the gun during firing. With a railgun, it is the current that propels the projectile, but after a launch, there is residual current at the muzzle that must be managed. Engineers will work on the weapon’s muzzle and its breach as well as ways to power the barrel, contain the system and mount the device.

BAE Systems currently is building a small-scale 2-megajoule launcher for testing purposes. Chaboki notes that it will be fired at the Yuma Proving Ground in Arizona. Some of the system’s components will be tested at the Dahlgren facility as the gun is developed and assembled. This is the location where the 32-megajoule launcher will be housed.

The gun’s projectiles and their guidance systems also must survive massive acceleration. Although a final design for the projectiles has not been determined, Chaboki notes that any object launched from the EM railgun will sustain between 35 to 40 kilo Gs, or units of acceleration, with up to 50 kilo Gs for the operational version of the weapon. This is double the acceleration conventional shells experience when fired from a cannon. The ONR has two contracts, one with the Boeing Company, Chicago, and one with the Charles Stark Draper Laboratory, Cambridge, Massachusetts, to develop a projectile. 

 
The EM railguns being
developed by the ONR may one day be installed in warships such as the U.S. Navy’s DD(X) Zumwalt-class destroyers.
EM railguns are attractive to the military because they have lower power requirements than direct energy weapons such as lasers. One of the conclusions of the DD(X) destroyer program office’s 2003 feasibility study was that coming generations of warships will have the power to operate EM railguns. The weapons will be fired with large pulses of electrical power 9- to 10-milliseconds long. “There is enough power, but managing the power quality and problems in other areas is still under investigation. But it’s much more possible and feasible than directed energy power supply,” Chaboki says.

The U.S. Army also has been developing EM railguns for several decades. Because of the weapons’ size and weight, Army researchers have been examining pulse alternators and a rotating machine-type energy for power supply. But Chaboki notes that the Navy does not have the same size limitations because ships have enough room to use capacitors to store energy for the weapons.

The Navy is considering two power options: capacitors and pulse alternators. Capacitors are a more mature technology, but they are larger and heavier, although Chaboki observes that there is ongoing research to develop more compact systems. Pulse alternator technology is being developed by General Atomics; pulse alternators use high-speed flywheels to generate multiple megawatts of power.

Chaboki adds that both the Navy and U.S. Army are sharing information between their respective railgun programs. He notes that the Navy is closely observing the Army’s work on pulse alternators, and the Army is studying the Navy’s gun development.

The program’s first phase, demonstrating the weapon’s feasibility, is scheduled to end in 2011. Based on the success of the first stage, a system demonstration will occur in 2015 followed by an initial operational capability in the 2020 to 2025 time period.

 

Web Resources
Office of Naval Research: www.onr.navy.mil
BAE Systems: www.baesystems.com
General Atomics: www.ga.com
Charles Stark Draper Laboratory: www.draper.com