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Further Reading

Electromagnetic Rail Gun (EMRG)

Electric drives on future US Navy ships will make possible significant advances in ship design, fuel efficiency, and numerous shipboard systems, including innovative weapon systems. One such weapon system is the electromagnetic rail gun (EMRG), which uses electricity, rather than chemical propellants, to launch projectiles at long-range targets. The EMRG is one in a family of the Office of Naval Research's Innovative Naval Prototypes (INPs). An INP is characterized by high-risk, high-payoff technologies. If successful, an INP will lead to significant advances in Navy or Marine Corps capabilities.

The launcher (barrel) contains a pair of metal conducting rails embedded in a structure made of composite materials. Very strong opposing magnetic fields are generated within the launcher by a high current pulse that flows through the rails and a bridging armature positioned behind the projectile when the rail gun is fired. These fields create a propulsive force that accelerates the armature and projectile out of the barrel. The GPS-guided projectile will exit the launcher at approximately 2500 meters/second. On the way to its target, the projectile would leave the Earth's atmosphere, making it less susceptible to jamming or interception, and minimizing interference with friendly aircraft upon re-entry into airspace.

When operational, the EMRG will provide high-volume, precise, and time-critical fires in all-weather conditions. The goal of the Office of Naval Research rail gun project is to develop and smoothly transition prototype system that can deliver fires with high accuracy and lethality at distances greater than 200 nautical miles. The rounds will contain little or no high explosive material. Instead, they will inflict damage bway of high-velocity impact. With no explosives or propellants, the logistics of supporting the weapon will be simplified and crew and shsafety will be enhanced.

Railguns provide a capability for sustained, offensive power projection, complementary to missiles and tactical aircraft. Railguns may be a cost-effective solution to the Marine Corps Naval Surface Warfare Support future assault requirements for expeditionary maneuver warfare because of their unique capability to simultaneously satisfy three key warfighting objectives: (1) extremely long ranges; (2) short time-of-flight; and (3) high lethality (energy-on-target).

One important distinction between railguns and propellant-based guns is the difference in muzzle velocity. The 5-inch/54and 5-inch/62guns of today achieve muzzle velocities of approximately 800 m/s. In contrast, a railgun can accelerate a projectile to hypersonic velocities of 2500 m/s or Mach 7 and greater, enabling more that 200 nautical mile ranges within a six-minute time of flight. Such high muzzle velocities preclude the need for post-launch rocket-assist to achieve extended ranges. In an indirect fire mode, the projectile flight profile is predominantly exo-atmospheric, reducing the deconfliction problem and potential for Global Positioning System jamming.

However, railguns could also be used in a direct fire mode against surface targets, with only seconds from time of launch to impact. A notional 15 kg railgun flight body arrives on target with a 1500 m/s or Mach 5 terminal velocity, which equates to 17 MJ of available kinetic energy. This is about twice the kinetic energy available from a conventional 5-inch KE warhead from a projectile at half the weight.

The amount of power required for a railgun depends on the rate of fire. With an expected 80 megawatts of installed electrical power, electric warships such as the DDG-1000 will have ample power to supply a railgun with the 15-30 MW necessary for sustained fires at 6-12 rounds per minute.

Key tasks are the development of a launcher, rail gun modeling and simulation toolset, GPS-guided projectile, pulse power system, and integration into a yet-to-be-determined ship class. A 100-shot bore demonstration is planned for 2011 and a long-range integrated system demonstration is planned for 2015. A fully functioning weapon system aboard a deployable ship is planned in the 2020-25 timeframe.

The Naval Research Advisory Committee was asked in May 2003 to conduct an assessment of the current maturity of electromagnetic (EM) gun technology for the Assistant Secretary of the Navy (Research, Development & Acquisition). Specifically, the Committee was tasked to: review and assess the technical and operational performance capabilities necessary to achieve a militarily effective EM gun system for naval application; review the current and anticipated state of the technology and provide an assessment of the performance, manufacturability and maintainability of an EM gun system; and evaluate the technical and developmental risks in producing a projectile that will perform throughout the mission profile, i.e., launch to precision impact on target. The study panel concluded that while there were significant engineering challenges that must be overcome to produce an operational naval EM gun, there were no new technology issues to be solved. Additionally, the study panel provided a strawman roadmap that would enable the Department of the Navy to within four years have sufficient technical basis to decide whether or not to proceed with a development program that could be completed in an additional four years. If limited to the weight and volume envelopes allocated to the Advanced Gun System (AGS), the Committee believed that a railgun capable of putting lethal fires on targets more than 200 nm from the ship, and accommodating more than 2400 rounds of non-explosive ammunition can be developed and fielded.

Broad Agency Announcement (BAA) # 05-003 was issued by the Office of Naval Research (ONR), Code 351, in cooperation with the US Army, Army Research, Development and Engineering Command (ARDEC), as part of a collaborative effort. Specific Research Areas of Interest include (but are not limited to): Weapons systems research with applications of direct and indirect fire, in medium to large calibers bore sizes (1 inch to 6 inches, or 25mm to 155mm), such as those relating to accelerating a launch package by using Electromagnetic (EM) Rail Gun technologies to velocities greater than those typically considered feasible with conventional energetic gun propellants. Examples of these technologies may include pulse forming networks, integrated launch package and/or projectile component research and development, and launcher research and development. For reference, typical kinetic energy levels for proposals under the technical efforts are expected to be between two (2) and sixty-four (64) mega-joules.

The objective of the Electromagnetic launch, delivery, and lethality S&T Program is to develop and demonstrate technologies that contribute to: (1) the neutralization of threat targets by increasing probability of kill in all scenarios, including countering enemy troops, emplacements, tanks, and artillery, (2) providing the ability to conduct long range strike engagements from off shore assets, (3) providing weapon-target matching/pairing studies, (4) and reducing costs.

Launcher research is currently focused on the three mechanisms known to cause damage when accelerating high-speed launches of projectiles inside a gun bore: 1) excessive heating of the rail/armature interface; 2) hypervelocity gouging of rails by the passage of the armature; and 3) erosion of rails near the muzzle at projectile exit from the barrel. In these cases, increases to the launcher life over the currently demonstrated state of the art - for high speed Integrated Launch Package acceleration of the resulting lethal projectile is necessary.

Research and engineering issues which are desired to be immediately addressed as part of a notional launcher design, build, and test effort might be expected to include but are not limited to barrel issues of a)Method of assembly, b) Bore compression pressure, c) Stability of bore compression, d) Bore straightness, dimensional stability and overall barrel assembly stability, e) Rigidity for slewing, or training of gun barrel from mount, f) Barrel Electromagnetic Interference(EMI) and muzzle arc or blast management, and g) ILP-induced dynamic effects. Similarly, issues for Breech power feed might include concepts for a) Interleaved compact breech assembly, b) Flexible cables or slip ring for recoil and traverse of the mounted barrel, c) Breech swing arc in degrees (0 to plus/minus 360 degrees,) and d) Recoil management. Also, technical approaches relating to maintenance and repair, such as a) ability access to examine components in the field or at sea, and b) issues addressing lifetime component replacement needs are of great interest.

With respect to pulsed power technologies, two approaches are currently being considered to produce the high current pulses required over short time frames to accelerate the projectile primarily by magnetic Lorenz force generation. First, by developing pulsed alternator technology as the main energy storage device and second - high energy, dense capacitor storage. Because the Army is focused on a direct fire weapon mounted in an armored vehicle, the greatest technical challenge is achieving significantly higher energy and power densities. For the Navy, lower power densities are typically required, but over longer sustained rates of fire with requirements for quick recharging the pulse forming network from naval ship power is required to fulfill NSFS applications where gains in response time, range and magazine capacity provide new capabilities desired under the Naval Sea Power 21 objectives for Sea Strike and Sea Shield missions. Keen interest is noted for similar design methods, however differing technologies may be needed due to the disparate power requirements for the individual service mission requirements.

With respect to integrated launch packages (ILP's), the primary issue is to accelerate a projectile within the launcher, and maintain delivery of lethal performance. The performance of the electromagnetic armature, the sabot, and the projectile as one unit within the barrel is crucial. For longer ranges, guidance is required and includes critical survivability of projectile electronics through the high Gee acceleration profile, when high fluxing electromagnetic environments exist. After launch, Aero-stability, aero-thermal heating, effective and survivable guidance and control, and lethality issues will be crucial to determine feasibility of an EM weapon for both short direct and longer range indirect fire support missions.

The near term collaborative program will focus on the identification of technical objectives, quantified technical barriers, and enabling technologies associated with development of the objective EM gun systems. Academic and Commercial Industry collaborative ventures are requested to identify themselves and show the extents of their agreements as clearly and completely as possible. And while other complementary technologies may exist for other applications, and may be acceptable for risk reduction purposes, only those applications with a clearly defined relation to direct and indirect gun fire systems are under consideration in this announcement and are expected to be considered for award.

For purposes of clarity, direct fire engagements are typically considered line of sight (LOS) or near line of sight (NLOS). Engagements are from one to forty (1-40) kilometers in range and can be either defensive or offensive in nature and depending on application include a mix of fix and moving air, sea surface or land targets. Indirect fire, or non-line of sight for cannon (NLOS-C) or naval artillery systems, are typically distances starting from hundreds (100's) of kilometers or more and primary interest currently is in land based targets mobile or fixed target sets. The envisioned systems and potential solutions will help meet the needs of each of the Military Departments future war fighting needs and, in so doing, identify opportunities for development of common components or subsystems.

By early 2005 work had commenced on construction of the new test launcher facility at Dahlgren, VA and technical development work continued at various sites including Kirkcudbright, Scotland and the Institute for Advanced Technology at University of Texas (Austin). The Army began research in 1985 to develop a mobile, ground-based electromagnetic system capable of defeating future armored combat vehicles. It is the refurbished SDI launcher that was installed at NSWC Dahlgren, while the program awaited delivery in June 2007 of a gun being built by BAE Systems. The new gun is a "laboratory" version with removable rails that weighs in at 40 tons.

The next generation of naval guns was launched Oct. 2, 2006, with the successful test and stand up of an electromagnetic (EM) railgun facility at the Naval Surface Warfare Center Dahlgren Division (NSWCDD) Laboratory. Under the auspices of the Office of Naval Research (ONR), engineers at the laboratory fired a low energy shot, the first in a series of tests required to bring the facility online. Using a 90 mm bore launcher with a copper rail and a power plant capable of delivering 8 mega joules (MJ) of muzzle energy, a 2.4kg projectile was fired at 830 m/s, yielding an energy of 0.8 MJ. With the potential to deliver lethal, hypersonic projectiles at ranges in excess of 200 nautical miles within six minutes, a naval railgun offers a transformational solution for volume fires and time-critical strike. Understanding the technical dimensions of ships, ship systems and weapons, allows the Navy to deliver innovative and affordable capability to the nationd. As part of ONR's electromagnetic railgun program, the stored energy, launcher and terminal area will be increased in size to accommodate a 32MJ muzzle energy gun by fiscal year 2009. This facility provides the first steps toward the envisioned tactical Navy system of 64MJ of muzzle energy.

There are a number of things the Navy still doesn't know how to do. How is it possible to shoot more than about three or four rounds out of an EM rail gun before having to change the barrel? How is it possible to build the kind of pulse forming networks that are needed to be able to shoot not direct fire weapons, but 200 mile indirect fire weapons? There is a lot of potential that a capability like EM rail gun could bring. But there are many risk to EM rail gun.