Reforging the Thunderbolt: How Railguns Can Revolutionize the Weapons of War

Historical Development of Electromagnetic Weapons1 In the year 1132, the Chinese documented the firing of primitive mortar weapons using gunpowder charges, bamboo tubes, and shrapnel-producing materials.2 After nearly 1,000 years of advances in the tools of warfare, warriors today fire bullets with this same basic technology. By igniting a chemical propellant behind a projectile, trigger pullers release the energy necessary to propel bullets across the battlefield. There is a compelling vision to revolutionize future military capabilities with the development of electromagnetic weapons. Instead of burning propellant, this type of weapon uses electrical energy to accelerate projectiles to velocities of interest. The most technologically mature class of electromagnetic weapons is the railgun. Railguns promise to expand warfighter capability with increased lethality, improved survivability, and enhanced effects over competing advanced weapons technologies.

The theory of electromagnetic weapons dates back nearly a century. In the early 1900s, the general fascination with electrical energy inspired the theoretical design of various classes of electric guns. One of the more advanced designs of the time was that of Louis Octave Fauchon-Villeplee. His 1916 concept for the Canons Electriques had a 30-meter barrel, intended to fire a 100-kilogram projectile at 1.6 kilometers per second (km/s).3 In 1920, he received a U. S. patent for his invention. Due to inadequate power supply and unsuitable materials for a full-size cannon, Fauchon-Villeplee built his design as a small-scale demonstration piece.4 The impetus for further developing electromagnetic launch technology remains the same today as it was 100 years ago. Given the ther-modynamic limits inherent in the combustion and expansion process associated with conventional powder cannons, electromagnetic forces enable faster acceleration and high speeds for the object of interest. While expanding gases operate in velocities associated with the sound speed of the working fluid, electrons move at rates approaching the speed of light. This fact serves as the basis to pursue a launch technology that expands the performance envelope in a revolutionary manner. Laboratory railguns operated by researchers routinely achieve muzzle velocities of 2.4 km/s. There are advanced powder cannon concepts that use longer barrels and larger chamber volumes to gain incremental advances in projectile speed, but none offer the leap in performance afforded by the railgun concept. To achieve a velocity of 1 km/s with a conventional cannon, a weapons designer will plan to use a powder charge weighing approximately three times the mass of the projectile; to achieve 2 km/s, the powder charge jumps to nearly nine times the mass of the projectile; and at 3 km/s, the mass of the powder charge is greater than 27 times that of the projectile.7 These examples demonstrate the theoretical limit and physical impracticality of conventional cannons achieving velocities greater than what impact physicists refer to as “ordnance velocity.” Impact physicists generally define ordnance velocity for direct-fire, large-caliber cannons as 1,600 m/s, or about a mile per second. Hypervelocity is therefore defined as speeds in excess of ordnance velocity. The advantages of operating in the hypervelocity range are substantial enough to justify the continued development of the railgun.

Physics of a Railgun8 The science of a railgun is very straightforward; a simple railgun consists of two parallel electrical conductors, called “rails,” and a moving electrical connecting bridge, called an “armature.” Current introduced at the breech end of the rail flows through the armature and returns via the second rail. Current flow in the rails generates a magnetic field Figure 1: Louis Octave Fauchon-Villeplee’s cannon design, circa 1916.5 Figure 2: Victor Appleton’s book Tom Swift and his Electric Rifle, circa 1911.6 Figure 3: Simple square-bore railgun with propellant force F, inductance gradient L, electrical current I, and magnetic field depicted with black dots.10 in the region between the rails. In both the rails and the armature, the current flows at right angles to the magnetic field, thereby exerting a force. Since the armature is free to slide along the rails, the electromagnetic forces can accelerate the projectile to extremely high velocity. The force imparted into the projectile is proportional to the product of the current I squared and the inductance gradient L.9 These are the same forces at work in your common rotating electric motor. In this sense, one can consider the operation of a simple railgun as a one-turn, linear, direct-current (DC) motor.12 “In an ordinary motor, there are hundreds of turns so the current is used hundreds of times as it were. With the (simple) single-turn railgun, the current is ‘used once’ so it must be ‘hundreds of times’ higher to enable reasonable propelling forces to be obtained.”13 Railguns therefore require very high levels of electric current flow to fire sizeable projectiles. The requirements for megajoule energy discharge and gigawatt power generation place extreme demands on both the launcher and power supply.14 Military Significance of a Tactical Railgun Weapons System15 The kinetic energy imparted into a target is described as the product of one-half the mass of the projectile and the velocity squared (KE = ½mv2). Since the velocity term is raised to a power, in this case two, even modest gains in speed can greatly improve the ability of around to destroy a threat. At hypervelocity, the results are a dramatic increase in kinetic energy. In a direct-fire or line-of-site (LOS) application, this velocity increase translates to improved penetration efficiency. This means that the same size round traveling at greater velocity has greater destruction capability. This also means that one can induce the same kinetic energy on a threat with a smaller piece of ammunition. Greater efficiency eases the requirements on launcher size, mobile weapons platform, and logistics train. Hypervelocity also dramatically increases what is referred to as “behind armor debris (BAD).” When a projectile penetrates the target, the BAD includes the metal fragments that spray in a nearly hemispherical pattern from the exit hole inside the vehicle or structure. It is the BAD that often dis-ables or destroys the threat by creating sympathetic ammunition detonation, severing hydraulic lines and electrical cabling, and disabling or killing crew members.

In the indirect, beyond-line-of-sight (BLOS) and non-line-of-sight (NLOS) employment, in-Figure 5: Railgun concept with concave rails and an integrated launch package.16 Hypervelocity Increases Penetrator Efficiency penetration depth exceeds penetrator length P L P/L cross section of target penetrated by hypervelocity projectile (P/L > 1) Velocity, km/s creased launch velocity means that these systems can operate with unprecedented increases in range. These ranges are currently available with complex and expen- sive rocket systems and bombs delivered by aircraft. Improvements in the direct- and indirect-fire capability of the weapons system are considered first-order, tactical ben- efits of the railgun. A second-order benefit of an electromagnetic weapon is improved safety associated with removing propellants from the combat vehicle and the supply chain that supports them. These propellants are especially hazardous since they contain both the fuel and oxidizer necessary to burn inside the cannon chamber and bore. Vehicle fires result- ing from sympathetic detonation and deflagration of ammunition are nearly impossi- ble to extinguish and place both the crew and combat platform at high risk. A third-order benefit is the potential reduction of collateral damage on the battlefield. The capabilities of a hypervelocity kinet- ic energy projectile are focused at the point of impact, as opposed to high-explosive ammunition, which dissipates a large portion of its exploding warhead to the environment. Additionally, the energy associated with high explosives decreases as a function of the distance or radius from the point of impact cubed, since the free expansion of the blast occurs in air.

Veterans of Operation Iraqi Freedom have had a great deal of experience with the advantages and challenges associated with heavy armored units operating on the modern battlefield. There is great truth in the simple statement: “when you need a tank, you need a tank.” The addition of the M1028 canister round to the family of Abrams main gun ammunition, and the highly effective and versatile high-explosive (HE) bullets for the Brad- ley, reinforce the assets these heavy-hitters bring to the counterinsurgency fight. A combat system equipped with a railgun could further bolster mounted forces in the contemporary operating environment. Firing a railgun generates a significantly reduced overpressure region near the muzzle of the weapon primarily because it does not use an expanding column of gas as a means of propulsion. Operating this type of cannon in tightly congested urban areas would reduce the potential for collateral damage to adjacent structures caused by the expanding gas shockwave. From a mobility perspective, the railgun has additional advantages. The length of breech inside the turret of a railgun-equipped vehicle is reduced considerably, allowing the gun tube freedom to elevate higher and conceivably articulate from side to side indepen- dent of the turret within a band of considerable azimuth. This could be a major benefit in tight urban areas. From the standpoint of projectile velocity and lethality, the added flexibility of the railgun is clearly superior to conventional cannons. A theoretical railgun system would afford gunners the ability to dial in a lethality setting by controlling the amount of discharge energy to the cannon system before the shot. The muzzle velocity of a railgun can be reduced to deliver a large-caliber, nonlethal projectile, whose effects would be much more dramatic than current options, and potentially have added uses such as a highly effective dynamic breaching tool for raid teams. Soldiers must always be cognizant of the second- and third-order effects of the actions they take during a counterinsurgency fight, and adjusting projectile velocity to limit effects to a specific target area would be a tremendous advantage. Many com- manders have dealt with negative outcomes when bullets continue beyond their initial target and do further unintended dam- age. The ability to mitigate these problems before they happen is something all soldiers would greatly appreciate. Considering a reconnaissance and surveillance perspective, the acoustic and visual stealth operation of a railgun is a strong benefit. We should not construct our force to face only a single threat, and stealth is just as important in traditional high-intensity combat as it is in the counterinsurgency fight. Additionally, an unobvious potential benefit to this technology is the varied possible uses of the electric power such a system produces; power generation at the company level is always a major issue. From a purely tactical perspective, running a company-level suite of communications and operations support equipment consumes a tremendous amount of electricity. Establishing semi-permanent patrol bases in counterinsurgency environments, especially those that provide luxuries, such as climate control for sleep areas, is very difficult from a power availability standpoint under current modified table of organization and equipment (MTOE) authorizations. Having MTOE vehicles capable of handling these generation needs is clearly a major tactical advantage. Also, during counterinsurgency operations, controlling local power generation is often a tool employed by the enemy; ground commanders with the ability to provide quick reaction power generation to a local clinic, police station, or other such key infrastructure could surely swing the local population’s opinion in favor of friendly forces.

Challenges and Opportunities While there remain many areas of active research and room for growth in current railgun design, power generation and switching are two elements of the concept that must be addressed to make this a viable system for a tactical combat platform. For an Abrams-scaled railgun, the system must generate gigawatt (GW, or one-billion watts) levels of power and discharge megajoule (MJ, or one million joules) levels of energy. Power is the rate at which energy is consumed. As a practical example, a household electric stove requires about 10,000 watts to operate. While the GW value is quite staggering and represents the output of a typical electrical power plant, the railgun system would require this for a very short duration in what is described as a pulsed power application. Energy is a measure of work and can be considered in the future (potential) or present (kinetic). Smashing an average-sized car into a wall at 80 miles per hour is about equivalent to a MJ. In the laboratory, most railguns operate with a series of capacitor banks. The size and weight make them impractical for an Army system. The focus of current power generation research is on compulsators, or rotating machines, which can be thought of as very high-speed generators. The bridge between a railgun power generator and cannon is a switching mechanism. Safely and efficiently turning on and off GW levels of electrical power is not a trivial matter. Advancements in material science research may yield the formulation for a material that can survive the rigors of a railgun switching application.

Throughout military history, there have been revolutionary designs in the machines of warfare. The technological and capability leaps from sail to steam, horse to vehicle, and propeller to jet all afforded warfighters with dramatic increases in performance. The railgun falls into this same category. Electromagnetic cannons are a revolutionary weapons system that comprise all the attributes of current large-caliber guns and improve them, giving them flexibility to deal effectively with everything from a rioting crowd of civilians to the most formidable enemy tank on the battlefield.

With the advantages afforded by the railgun with respect to lethality, survivability, and effects, this class of electromagnetic weapons warrants the continued support of its research and development to ensure we retain our capability overmatch against current and future threats. In closing, the following quote by Alexander von Humboldt offers some insight into the challenges associated with adopting revolutionary concepts. Recent events make it quite possible we are entering stage three regarding the development of railguns.

“There are three stages in scientific discovery: first people deny that it is true; then they deny that it is important; finally they credit the wrong person.”19 Notes 1Joshua M. Keena, Experimental Analysis and Predictive Modeling of Thermal Loading in a Railgun, Institute for Advanced Technology, University of Texas at Austin, 2008, pp. 1-3, 2Jacques Gernet, translated by J. R. Foster and Charles Hartman, A History of Chinese Civilization Cambridge, Massachusetts, 1996, p. 311. 3Richard A. Marshall and Wang Ying, Railguns: Their Science and Technology, China Machine Press, Beijing, China, 2004 p. 31.

4Ian R. McNab, “Early Electric Gun Research,” IEEE Transactions on Magnetics, January 1999, pp. 251-253.

5Harry Fair, EM Launcher History and Basics, Institute for Advanced Technology, Austin, Texas, 2007, p. 27.

6James D. Keeline, “Who Invented Tom Swift’s Electric Rifle?” 1988, available at http://www. keeline.com/Electric_Rifle.pdf.

7Don Berry, A “Primer” (not pr-eye-mer) On Guns, Institute for Advanced Technology, Austin, Texas, 1992, p. 14.

8Keena, Experimental Analysis and Predictive Modeling of Thermal Loading in a Railgun, pp. 3-4.

9Ian R. McNab, Pulsed Power, Institute for Advanced Technology, Austin, TX, 1996, p. 8. 10Jerald Parker, Railgun Launch and Modeling Principles, Institute for Advanced Technology, Austin, Texas, 2007, p. 19.

11Sikhanda Satapathy, IAT-T-1492, Institute for Advanced Technology, Austin, Texas, 2008, pp. 3-4.

12Wang Ying, Richard Marshall, and Cheng Shukang Physics of Electric Launch, China Machine Press, Beijing, China, 2004, p. 21. 13Marshall and Ying, Railguns: Their Science and Technology, p. 5. 14Ian R. McNab, Pulsed Power for Railguns, Institute for Advanced Technology, Austin, Texas, 2007, p. 1-3.

15Keena, Experimental Analysis and Predictive Modeling of Thermal Loading in a Railgun, pp. 5-6.

16Fair, EM Launcher History and Basics, p. 24. 17Source data and graph provided by Hypervelocity Impact Physics Division, Institute for Advanced Technology, Austin, Texas; and Fair, EM Launcher History and Basics, p. 15. 18Fair, EM Launcher History and Basics, p. 18. 19Friedrich Wilhelm Heinrich Alexander von Humboldt, 1837. Major Joshua M. Keena is currently pursuing a PhD in mechanical engineering as a uniformed Army scientist and engineer, U. S. Army Acquisition Corps. He received a B. S. from the U. S. Military Academy and an M. S. from the University of Texas at Austin. His military education includes U. S. Army Command and General Staff College, Armor Officer Basic Course, Armor Captain Career Course, Acquisition Basic Course, Combined Arms and Services Staff School, and Intermediate Logistics Course. He has served in various command and staff positions, to include commander, Headquarters and Headquarters Company, 2d Battalion, 81st (2-81) Armor, Fort Knox, KY; commander, F Company, 2-81 Armor, Fort Knox; support platoon leader, Aviation Brigade, 25th Infantry Division (Light), Wheeler Army Airfield, HI; and scout platoon leader, A Troop, 3d Squadron, 4th Cavalry, 25th Infantry Division, Schofield Barracks, HI.

Captain Jonathan Bodenhamer is currently a graduate student, U. S. Army Student Detachment, Cockrell School of Engineering, University of Texas at Austin. He received a B. S. from the U. S. Military Academy. His military education includes Armor Officer Basic Course, Armor Captain Career Course, and Airborne School. He has served in various command and staff positions, to include commander, A Troop, 1st Squadron, 10th (1-10) Cavalry, 2d Brigade Combat Team (2BCT), 4th Infantry Division (4ID) (Mechanized), Fort Hood, TX, and Iraq; assistant S3, 1-10 Cavalry, 2BCT, 4ID, Fort Hood; S5, 1st Squadron, 1st Cavalry (1-1 CAV), 1st Armored Division (1AD), Iraq; XO, B Troop, 1-1 CAV, 1AD, Budingen, Germany, and Iraq; and platoon leader, A Troop, 1-1 CAV, 1AD, Budingen.