Buzz
Image provided by Sam Barros from PowerLabsFor centuries, gunpowder has been the go-to propellant for firing projectiles from weapons. However, this fine gray powder comes with three significant drawbacks:
- Gunpowder needs to be transported alongside the projectile, increasing the overall weight of the ammunition.
- Black powder-based ordnance is highly unstable, posing challenges in handling and transportation.
- The speed of projectiles driven by gunpowder typically caps at around 4,000 feet (approximately 1,219 meters) per second.
Can these limitations be overcome? Enter the electromagnetic rail gun, commonly known as a rail gun. By harnessing electricity to generate a magnetic field, a rail gun can propel a projectile at speeds reaching 52,493 feet (16,000 meters) per second. While traditional Navy guns max out at 12 miles, rail guns can accurately strike targets 250 miles away in just six minutes.
This article explores the mechanics of rail guns, their potential applications, and the challenges associated with this advanced technology.
Special thanks to Sam Barros from PowerLabs for contributing to this article. Sam, a Mechanical Engineering student at Michigan Technological University, has developed his own rail guns, coil guns, and numerous other innovative devices.
Rail Gun Basics
A rail gun essentially functions as a large electrical circuit, comprising three key components: a power source, a pair of parallel rails, and a movable armature. Let’s delve deeper into each of these elements.
The power supply serves as the source of electric current. In medium- to large-caliber rail guns, the current typically reaches millions of amperes.
The rails consist of conductive metal strips, such as copper, with lengths varying between four and 30 feet (approximately 9 meters).
The armature connects the two rails, bridging the gap. It can be a solid conductive metal piece or a conductive sabot — a carrier designed to hold a dart or similar projectile. Some rail guns utilize a plasma armature, where a thin metal foil is placed behind a non-conductive projectile. When electricity passes through the foil, it vaporizes into plasma, which then conducts the current.
Here’s how these components interact:
Electric current travels from the power supply’s positive terminal, up the positive rail, across the armature, and down the negative rail, returning to the power supply.
Current flowing through any wire generates a surrounding magnetic field — an area where magnetic force is exerted. This force has both strength and direction. In a rail gun, the two rails function like wires, each producing a magnetic field. The positive rail’s magnetic field circulates counterclockwise, while the negative rail’s field moves clockwise. The resulting magnetic field between the rails is oriented vertically.
Similar to how a charged wire reacts in an electric field, the projectile is subjected to a force referred to as the Lorentz force (named after the Dutch physicist Hendrik A. Lorentz). This force is oriented at a right angle to both the magnetic field and the current's direction through the armature. The accompanying diagram illustrates this mechanism.
Observe that the Lorentz force runs parallel to the rails, pushing away from the power source. The force's strength is calculated using the formula F = (i)(L)(B), where F represents the total force, i the current, L the rail length, and B the magnetic field. Enhancing either the rail length or the current can amplify the force.
Given the complexities of designing long rails, most rail guns utilize intense currents—approximately a million amps—to produce massive force. Propelled by the Lorentz force, the projectile speeds toward the rail end farthest from the power source and exits through an opening, thereby interrupting the current flow.
To achieve projectile speeds of Mach 5 or beyond, rail guns demand enormous currents. This poses significant challenges for conventional battleships, as power cannot be rerouted from the propulsion systems. However, the Navy's future all-electric DD(X) battleship will be capable of generating such currents. For firing, power would be temporarily redirected from the ship's engine to the gun turret, allowing for a firing rate of up to six rounds per minute as needed, before reverting power back to the engine.
Challenges Facing Rail Guns
Rail guns are theoretically ideal for delivering firepower across both short and long distances. However, in practice, they come with significant challenges:
- Power supply: Supplying the immense power needed to propel rail gun projectiles is a major hurdle. Capacitors, which store electrical charge, must be large enough to accumulate the required current. For rail guns, these capacitors are enormous, often occupying several cubic meters.
- Resistive heating: As electric current flows through the rails, it encounters resistance, causing the rail molecules to vibrate and generate heat. In rail guns, this results in extreme temperatures.
- Melting: The combination of high-speed armature movement and resistive heating causes significant damage to the rail surfaces.
- Repulsion: The opposing currents in each rail create a repulsive force proportional to the current, pushing the rails apart. Given the massive currents involved, this repulsion is substantial. Wear and tear are critical issues, with many rail guns failing after just a few uses, and some being single-use only.
Coil guns, also known as Gauss guns, provide certain benefits over rail guns. Their barrel consists of a sequence of copper coils energized in succession, creating a moving magnetic field inside the barrel. This field pulls a ferromagnetic projectile through the barrel without physical contact, reducing wear and operating silently. While coil guns have achieved supersonic speeds, they are less efficient and powerful compared to rail guns.
Rail Gun Applications
An artist's depiction of a U.S. Navy aircraft carrier featuring a rail gun.
Photo courtesy ONRThe military is particularly intrigued by rail guns as a potential replacement for traditional large artillery. Rail gun ammunition, consisting of compact tungsten missiles, would be lightweight, easy to transport, and simple to manage. Thanks to their high speeds, rail gun projectiles would experience less bullet drop and wind interference compared to conventional artillery shells. While course adjustments would still be necessary, all rail gun missiles would be satellite-guided for precision.
Developing small arms rail guns poses significant challenges, primarily due to recoil. Recoil, the backward force generated when a weapon is fired, depends on the projectile's momentum. For rail guns, the momentum of high-velocity projectiles would be substantial, making recoil a major issue. A potential solution could be a portable rail gun firing tiny bullets, which would minimize recoil while retaining enough kinetic energy to cause significant damage.
Rail guns have also been suggested as key elements of the Strategic Defense Initiative, commonly referred to as Star Wars. This U.S. government program focuses on creating a space-based defense system to protect against ballistic missile attacks. Rail guns could be used to launch projectiles capable of intercepting incoming missiles. Additionally, some scientists propose that rail guns could defend Earth from rogue asteroids by firing high-speed projectiles from orbit, either destroying the asteroid or altering its path upon impact.
Beyond military uses, rail guns have fascinating non-military applications. They could potentially launch satellites or space shuttles into the upper atmosphere, where secondary rockets would take over. On airless celestial bodies like the moon, rail guns could propel objects into space without the need for chemical propellants, which rely on atmospheric oxygen to function.
An artist's depiction of a space-based rail gun intercepting and destroying nuclear-armed re-entry vehicles.
Photo courtesy Department of Defense Visual Information CenterRail guns could also play a role in initiating fusion reactions. Fusion happens when two small atomic nuclei merge to form a larger nucleus, releasing vast amounts of energy. Achieving this requires atomic nuclei to travel at extremely high speeds. Some scientists suggest using rail guns to fire pellets of fusible material at each other on Earth. The collision of these high-speed pellets would generate the extreme temperatures and pressures needed for fusion.
Many of these potential applications are still theoretical or in the experimental stage. For instance, current rail guns cannot produce the energy levels required for nuclear fusion. Additionally, it may not be until 2015 that an all-electric battleship deploys a rail gun to fire projectiles at an enemy.
Despite these challenges, the technology shows great promise. In 2003, the British Ministry of Defense conducted a one-eighth-scale test of an electromagnetic rail gun, achieving a muzzle velocity of Mach 6, or roughly 2,040 meters per second.
With ongoing advancements like these, rail guns could eventually become the preferred weapon on the battlefield and the go-to propulsion method for space launches.
For additional details on rail guns and related subjects, explore the links provided below.
Rail guns might feel oddly familiar because similar weapons have been a staple in popular culture. In Robert Heinlein's *The Moon is a Harsh Mistress*, lunar colonists fighting for independence employ an electromagnetic launcher to hurl iron containers filled with rocks at Earth. In the film *Eraser*, Arnold Schwarzenegger plays a Witness Protection agent who uncovers a government conspiracy to supply rail guns to terrorists. Similarly, in *Battlestar Galactica*, the vintage warship is equipped with rail guns that combine electromagnetic and traditional technologies.
These imaginative weapons have also made their way into video games like *Quake*, *Metal Gear Solid*, and *Red Faction*.
