Abstract
Railguns are often viewed as fictitious weapons that futuristic civilization could only use. They are weapon choices in any video games and sci-fi movies depicted with a futuristic timeline. They seem just out of reach in today’s times but a not too distant future to the common American. Many research articles and test trials are here to address that they are already here and a very viable option in means of military offense and defense. 2Railguns can conduct large quantities of electrical energy into kinetic energy to the projectile. 1Railguns are more than able to exceed the muzzle energy of current naval deck guns today and with more focused planning, testing and awareness in the physics behind railguns, it will definitely continue to be the weapon of the future. The physics behind a railgun can be tested simply and correctly increasing the energy to larger and larger velocities to prove to readers the future of weapons is already here.
Introduction
11 Since 1918, rail gun schematics have existed as experimental technology, but the mass, size, and cost of the required power supplies have prevented it from becoming practical military arsenal. In the last decades there have been significant advances toward the development as realizable military technology. A rail gun is comprised of parallel conducting rails, along which a sliding armature is accelerated by the current of the electromagnetic force connected to a pulsed direct current power supply (figure 1). In contrast to traditional methods of explosive or gas expansion propulsion, the muzzle velocity is only dependent to the aerodynamic properties of the projectile and the energy of the power supply. The force acting on the armature, is known as the Lorentz force. It appears through the magnetic field of the rails. There are various complications that arise like mobility, abrasion of the rails due to the heat and friction, but they will be addressed later in the article. 11 The uses of rail guns are mostly viewed as military offense and defense, but they can also be used to assist the launch of spacecrafts out of the atmosphere into orbit and even for the initiation of a nuclear fusion.
4 The rail gun is a type of weapon projectile. The basic structure for a rail gun is depicted in figure 1. A rail gun gets its name because it consists of twin rails made to accelerate a projectile to high velocities as fast as possible using electromagnetic force. A massive current is delivered along one of the two parallel conducting rails across a conducting armature to complete the circuit between the rails. It then heads back to the conducting source along the second rail like a large battery. The armature, that is to be shot out, has the projectile on the end of it which should fit loosely between the rails. The current in the rails produces magnetic fields between the rails. The total magnetic field sends a force on the armature because of the current that runs through it connecting it all together. The force is directed outward along the rails and pushes the projectile, gaining momentum and hurling it at very high velocities up to mach 7.
Lorentz Force
11 When a rail gun has a conductive projectile inserted between the rails it completes the circuit and allows the electrons to flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply. This current makes the railgun behave as an electromagnet, creating a magnetic field inside the loop formed by the length of the rails up to the position of the armature. In accordance with the right hand rule Dr. Casey Johnson taught in Physics 112, the magnetic field circulates around each conductor demonstrated in figure 5. Since the current is in the opposite direction along each rail, the net magnetic field between the rails (B) is directed toward right angles to the plane formed by the central axes of the rails and the armature. This, combined with the current (I) in the armature, produces a Lorentz force which accelerates the projectile along the rails, away from the power supply. Lorentz forces also act on the rails and attempt to push them apart, but as long as the rails are mounted firmly, they should not move (figure 5).
The Lorentz force (F) is defined as the force that is exerted by a magnetic field (B) on a moving electric charge. The Lorentz force is given by the average magnetic field on the railgun armature and is a result of the Biot-Savart-Law.
B= µ0I / 2πd (ln r/d)
Is the permeability constant, I is the current through the rails, d is the distance between the centre points of the rails and r is the radius of the rails. Now we insert the result for the magnetic field in the Lorentz force law and we get the following solution for the Lorentz force.
F= µ0I2 / 2π (ln r/d)
We can understand that the force, accelerating the projectile, is going with the square of the current. Therefore, the higher the current, the higher the velocity of the projectile.
Motivation for an electromagnetic rail gun
5 The argument today for the naval electromagnetic rail gun depends upon two principles of necessity and feasibility. The question of whether or not the Navy needs to add a rail gun to it’s arsenal and the pros and cons to placing a rail gun onboard a naval ship. Needless to say, a naval rail gun must prove to be useful in warfare tactics and still fall into the guidelines of technology available out today, such as a viable power supply and structural design. Therefore, although an electromagnetic rail gun has the potential to revolutionize naval warfare, the use of this caliber of weapon must prove to be efficient as well as practical.
6 Over the past decade the Navy has invested considerable resources into the development of hypervelocity electric launcher technology. The program has been immensely successful, demonstrating a multimegajoule hypersonic railgun launch. A prototype weapon system is expected to be on a naval ship within the next decade. The navy rail gun, when fully developed will provide new capabilities for multiple navy missions. These include long-range fire support for littoral missions, naval anti ship or small craft surface warfare, and ship self-defense against air threats. High performance electric launch weapons will dictate new strategies and provide different tactics to help ensure the safety of the naval officers.
Though the main efforts for a rail gun are military reasons, the wonders of space exploration are just one of many subjects that would benefit from the trickling down effect of understanding and harnessing the power of controlling electromagnetic fields. 13 For a spaceship to be launched into orbit it would need to be accelerated at speeds greater than 1000 gees to reach the required velocities. Considering that it would only be possible to launch rugged payloads such as fuel, water, food, and other materials. A railgun concept would be much more efficient because it would approximately cut costs from greater than $20,000/kg to less than $600/kg.
Transition
5 The U.S. Navy has recently used three main weapons against targets ashore: manned aircraft, tactical missiles, and conventional guns. The cost of manned aircraft missiles or tactical missiles is a major factor for why this path is not usually first resort. Because of this, the Navy must rely on it’s conventional guns to accomplish missions ashore. The average muzzle velocity of the 5”/54 naval gun is about .81 km/s, which results in a range of about 12-15 nautical miles. This range is close enough to worry the Navy about safety precautions and it may be in the Navy’s best interest to rely on a weapon with an increased muzzle velocity and longer range capabilities. 1A rail gun has the potential to use long range warfare propelling projectiles to velocities above 2 km/s and to reach targets at distances of 200km or more depending on the size of the rail gun and the strength of the current. 5 Limitations set on other chemical propellants such as gunpowder or rocket fuel are not issues with electromagnetic launchers therefore making it easier to surpass restrictions set on velocity and distance. Friction in the atmosphere causes velocities over 3 km/s to be impractical, but a velocity range of 2.5-3 km/s would still be fast and strong enough to carry the projectile to around 300-400 nautical miles, fulfilling the Navy’s long range requirements. A standard velocity of 2.5 km/s, a 60 kg projectile would have 180 MJ of kinetic energy, which is about 15 times the chemical energy of a high round explosive of 5 inches. Apart from being a lethal round, the armature and projectile would potentially replace hazardous and explosive rounds stored in the ships compartments. That makes the naval electromagnetic gun the new weapon of choice not only for lethality, but also for the safety of the naval ship. This would allow the Navy to store more projectiles for more artillery, but a safer storage center hundreds of miles off shore.
Armature and Projectile
The armature is the most important part of the launch package and it has two common types of shapes where the electromagnetic force is generated. There is a c-shaped armature and brush armature. The conductivity of the armature leads to the acceleration of the launch package so the more responsive it is to the magnetic forces, the faster the acceleration. 7 There were a series of experiments conducted testing both armatures in an energy range between 0.8 MJ and 1.13 MJ corresponding to a speed range between 950 m/s and 1400 m/s. The results of the experiments were then analyzed qualitatively and quantitatively. The results show that the total losses are higher for the C-shaped armature technology than for the brush armature technology. On the other hand our results show that launch packages based on the C-shaped technology convert better electrical energy into kinetic energy.
9 On December 10th 2010, the U.S. Navy made history at the Naval Surface Warfare Center-Dahlgren Division with the BAE Systems developed Laboratory Railgun. A 33-MJ shot was fired, the energy equivalent of 110 nautical mile range. When fully weaponized, the electromagnetic rail gun will deliver hypervelocity projectiles in support of U.S. Marines, ground forces, and ship defense. The electromagnetic rail gun technology uses high-power electromagnetic energy instead of explosive chemical propellants (energetics) to propel a projectile farther and faster than any preceding gun. At full capability, the electromagnetic rail gun mounted on U.S. naval vessels will be able to fire a projectile 100 nautical miles at a muzzle velocity up to Mach 7.5 and impacting the target at Mach 5. The high velocity projectile will be able to destroy land, sea, and air targets due to its kinetic energy, rather than with conventional explosives. The safety aspect of the railgun is one of the greatest potential advantages of the electromagnetic rail gun. No propellant is required to fire the projectile, and no explosive rounds are stored in the ship’s magazine.
Engineering Systems
8 A tactical railgun system will require an unheard of amount of electrical power for it to be operational, so the development of an integrated power system in Naval warships is necessary to make operational rail gun weaponry a reality. As figure 3 illustrates, a railgun weapon can be hundreds of miles from it’s target to fire at land, sea or aerial targets. The railgun weapon system will draw on the ships power to have enough current going through the rail gun to be fired at mach 7. This core shift needing immense electromagnetic power could shift to an all electric warship to ensure enough power will be readily available to power the rail gun. This alternative can promise to cause a fundamental change in future naval force capacities paving the way for other directed energy weapons.
The ability to propel guided missiles for hundreds of miles offers major tactical and strategic advantages and is considered quite common, but should not be overlooked. 7Figure 4 shows the basic architecture of what a top-level rail gun weapon is structured as. The major challenges associated with a projectile guidance system with the rail gun includes one that can withstand and still function after the high g forces placed upon the launch, the enormous amounts of electromagnetic energy needed for firing, an unprecedented thermal management requirements because of the heat released during these launches, resisting electromagnetic interference with the highly conductive materials the rail gun is made of, and many others. Different materials that can withstand and dissipate energy are a viable response these issues, but need further testing to be made into a reality.
Future Naval Platforms
10 Future designs for warships are considering electric drive systems. Already employed in some commercial cruise ships, electric drive trains offer improvements and advantages of increased ship design flexibility, improved energy efficiency, reduced maintenance and it allows the ships prime power to be easily diverted to other electrical loads when needed such as a rail gun. The ability to use the ships prime power generation, which normally ranges between 40 and 150 MegaWatts depending on the vessel class. Other electric loads provide the option to have everything be electric such as possibilities for new electromagnetic weapons or upgraded performance enhancing systems.
As we talked about earlier, electromagnetic guns aboard naval warships would be an immensely powerful asset for surface support on shore. 10 As the U.S. force structure is reduced in size and moved closer to home as forward bases are eliminated, the need for rapid response to regional crisis situations becomes more probable. The fact that 85% of the worlds population resides within 200 miles of a shoreline proves how many of these critical situations will arise in locations where surface fire can be effective in supporting ground forces or disrupting threat forces. The U.S. naval force would provide adequate retaliation force from littoral threats that threaten the safety and security of Americans at a capability of 100 to 400 nautical miles. Presently, fire support at this range is only provided by tactical aircraft operators such as carriers or medium range guided missiles. Medium range guided missiles are not affordable for large volume fires, while naval aircraft delivery puts aircrews at risk, introducing numerous complex national policy issues. Aircrafts also require relatively long times to fly to their targets, and have a daily ordinance delivery rates limited by the number of available aircraft carriers and the men flying them.
Firing Rate and Charging Power
12 Charging power determines the firing rate because if the railgun fires 30 MegaJoule shots at a rate of 6 rounds per minute, that is equal to 3 MegaWatts. Burst firing rate of 12 rounds per minute would require double the wattage at 6 MegaWatts. At 30% efficiency, this leads to 18 MegaWatts peak charging power requirement. If 60 MegaJoule rounds are fired this would require double the peak charging power requirement at 36 MegaWatts which is almost equal to the electrical power output of MT30 or LM2500 + G4 which are marine gas turbine engines. This just puts things into perspective of how viable of a solution it would be to put a rail gun on an all electric naval warship that could power the rail gun with ease. All the charging power would not be able to come directly from the turbine and alternator, but has to be battery based as well. The power output of the power distribution model is fixed, but a suitable energy storage module would be a lithium iron phosphate battery because of its safety relative to lithium ion battery in high discharge condition, and much longer recharge lifetime. In 2015, The U.S. Navy Naval Sea Systems Command awarded an 81$ million contract to K2 Energy Solutions, a developer and manufacturer of lithium-iron phosphate batter technology based in Henderson, Nevada, to design an energy storage system capable of powering a large modular capacitor bank for the electromagnetic rail gun.
Conclusion
It may seem that rail gun technology is in sight, but out of reach. It is not, and there are so many programs and steps that have already been taken to achieve this future as a reality, but we have to keep going. Railguns are a very intriguing technology and have several exciting potential applications. We have to continue testing different materials that are possibly more conductive so they react with greater velocities, or material that is conductive with cooling properties so that it doesn’t heat up as fast as normal materials used for a rail gun. So many tests and trials have been conducted to further understand the physics behind electromagnetism and how they work on rail guns, but we need to understand it better. While the physics of the electromagnetic phenomena are fairly simple, implementation of the technology has proven to be very difficult. The laws of physics we are continually trying to understand better and better are what governs our universe. We can harness this power of electromagnetic energy that is in abundance to power and create a world that runs on renewable energy. It is a viable alternative to leading a safer, cleaner future and I truly believe it is taking a step in the right direction for humanity as a whole. The future of railgun development depends not only on continued development of technology, but also on continued financial support of railgun research. Though we may spend what may seem like large amounts of money on funding the research behind the rail gun it will ultimately help us save money. This was one of the biggest, if not the biggest, driving factors behind trials on the rail gun. Each round would cost the material of the armature, projectile and charge which would be in the thousands compared to missiles ranging in the millions. They are safer to store in large amounts of artillery compared to explosives that could detonate at any time. A long distance attack is optional with a rail gun of up to 400 nautical miles to keep your loved ones safe while they protect the country on a naval warship. Understanding the physics behind this rail gun will help us understand the universe and ourselves on a deeper level of why things happen a certain way.