A Railgun (more precisely Electromagnetic Railgun / EMRG , German rail gun or rail cannon ) is a weapon that accelerates steel projectiles by means of a current-carrying slide along two parallel rails. The acceleration of the projectiles is caused by the magnetic field generated by the current flow. Depending on the acceleration distance (rail length) and the strength of the current, but also on the arrangement of the rails, speeds of several kilometers per second can be achieved. With conventional weapons, the muzzle velocity is around 2 km / s (corresponds to around 6 Mach ). In experiments with railguns during the US Strategic Defense Initiative (SDI), speeds of over Mach 7.5 were reached.
A railgun accelerates the projectile through the magnetic interaction of an electric current, which flows over the rails onto the projectile itself or onto a driver charged behind the projectile, with the magnetic field of the rail current itself. The projectile itself can also serve as a slide, this is but because of the contradicting requirements (the projectile must be slim for aerodynamics, the slide, however, wide and flat), it is uncommon in professional / military designs.
The accelerating force is the Lorentz force : The opposite rail currents generate a magnetic field between the rails that is perpendicular to the surface between the rails . The slide current flows orthogonally to this B-field, which generates a constant force perpendicular to the slide current and B-field. Due to the right-handedness of the Lorentz force, the projectile is accelerated out of the rail. The force on the projectile is only dependent on the strength of the magnetic field and the flow of current and is therefore independent of the speed.
Supercapacitors in the form of pulse generators are used as a power source or energy store . Alternatively, flywheels are used as energy storage devices, in this special case unipolar machines or their further development, the compulsators .
The drive is not to be confused with that of a Gauss rifle (also coil cannon or coil gun), in which a conductive or ferromagnetic projectile is accelerated by a traveling magnetic field without current flowing through it.
Target and development status
At TARDEC, a US Army research institute for armored vehicles based in Detroit , a railgun research project was carried out until 2015 with the aim of developing a prototype of a functioning tank cannon with a caliber of 60 millimeters. In addition to the power supply, wear and tear was an unsolved problem. The rails suffer massively from the great heating caused by the current flow. Until 2006, only a few shots were possible with all of the experimental setups before the systems failed. At that time (2006) 200 experts discussed the current state of technology at a symposium in Potsdam. In 2016, General Atomics tested a railgun mounted on a truck for the first time with a projectile speed of 9,600 km / h (= 2667 m / s). The prototype is completely transportable.
In Washington, the US Navy is researching railgun ship guns whose projectiles are accelerated up to Mach 7, re-enter the earth's atmosphere at Mach 5 and are expected to reach a range of at least 200 nautical miles (approx. 370 km). The most important company partner is BAE Systems . BAE set the goal of completing a first prototype with an energy of 32 megajoules with a range of 100 nautical miles (approx. 185 km) by 2011 and one with 64 megajoules by 2016 to achieve the 200 miles, while the Navy assumes that it will be in 2016 To be able to test a first operational prototype with associated support systems in 2018. The first railgun is to be installed on a ship between 2020 and 2024. There should also be a variant for defense against ICBMs . By 2009 around 36 million US dollars had been invested in the project, and by 2011 another 240 million had been planned. A $ 21 million contract signed by BAE with the Office of Naval Research (ONR) in early 2009 began development of a 2011 operational prototype that will finally (in the 64 megajoule version) shoot 200 nautical miles (370 kilometers) should be able to. Phase II, which began in 2012, aims to advance the technology for the transition to an acquisition program. The aim of the Phase II technology is to achieve a rate of fire of 10 rounds per minute and the development of thermal management techniques, which are necessary for sustained rates of fire, for both the carrier system and the pulsed energy system.
At the end of January 2008, the Navy reported on a test set-up that is said to have produced the best performance results to date. In the Naval Surface Warfare Center in Dahlgren , Virginia, a 32-megajoule system is said to have accelerated a projectile to 2520 meters per second. The aluminum projectile achieved an energy of 10.68 megajoules. The bullet mass was a little more than 3 kg. This kinetic energy is comparable to that of a bullet , such as that fired by the Leopard 2 main battle tank ( m ≈ 8 kg, v ≈ 1,700 m / s). On December 10, 2010, an improved version of the plant in Virginia accelerated a projectile to 2163 m / s (7786 km / h) with a projectile energy of 33 megajoules, which marked the first milestone (32 MJ projectile by 2011). In the summer of 2010, a sabot bullet was first used in the General Atomics and Boeing Railgun project to collect data under mission-like conditions. After seven kilometers of flight, the projectile penetrated a 30 centimeter thick steel plate.
Arleigh Burke-class destroyers by 2020 at the latest .General Atomics estimates that the weapon can be used regularly on
In April 2014 declared Rear Admiral Matt Klunder that one of the proposed 18-inch projectiles about 25,000 US dollars will cost a considerable saving compared to previously used cruise missiles. A single Tomahawk costs $ 650,000. In July 2014, a prototype is to be demonstrated to the public at Naval Base San Diego.
In February 2015, a prototype ready for use on ships was presented at the “Naval Future Force: Science & Technology Expo”. The weapon accelerates a 5-inch (12.7 cm) projectile to Mach 7 (approximately 2382 m / s) and can attack targets up to 110 miles (177 km). In 2016, the prototype was to be tested on a Spearhead-class ship , the USNS Millinocket ; the first series use is planned on Zumwalt-class ships , as these can currently provide more electricity than the Arleigh Burke class.
The first patent application was made in 1918 by the French Louis Octave Fauchon-Villeplee. During the Second World War there were attempts by German and Japanese scientists, but these were largely unsuccessful and were taken over by the Allies after the war. Although attempts were made to design high-performance railguns as early as the beginning of the 20th century, they are still in a development phase.
In the United States, the Strategic Defense Initiative (SDI), which has existed since the Cold War (officially since 1983 ), worked on the development of a space-based electromagnetic cannon, the Space-Based Hypervelocity Railgun (SBHRG) . It should serve as missile defense and as an anti-satellite weapon . Nuclear reactors were intended as the energy source at that time .
Railguns were also discussed as a propulsion method for space travel.
In addition to the military, there is a private hobby community that deals with the construction of railguns. These projects mostly work with graphite projectiles in order to maintain the sliding properties at the high temperatures that occur at the points of contact with the rails. However, the parameters achieved have the character of demonstrators .
Reasons for development
The Office of Naval Research calls the Railgun a "game changer". The motivation for the development of electromagnetic weapons lies in the advantages that exist in principle over conventional firearms : the exit speed is only subject to aerodynamic limits, whereas conventional ammunition can never be faster than the expanding propellant gas (in general this is the speed of sound of the respective gas, am fastest with light gas cannons ). The higher speed brings with it a multiple of destructive power, since the kinetic energy grows squared with the speed. In addition, the noise development is limited to the sonic boom , which is militarily advantageous. In addition, there are fewer moving parts, which reduces possible wear and failure to just a few parts and thus makes them less maintenance-free.
The use of railguns appears to be of particular interest where a high rate of fire and range is required, e.g. B. in air defense. Because the rate of fire is not limited by the replacement of propellant charges, the speed of the projectile with a correspondingly high current is only reduced by air friction.
Problems of principle
The biggest problem with the construction lies in the required energy storage device, which has to briefly deliver an output of several megawatts to around 1 gigawatt. Among other things, strong capacitors are used for this . This makes the weapon very heavy. At the moment, electromagnetic weapons are at least as heavy as conventional ones with the same firepower.
Another main problem is the wear and tear on the busbars that conduct electricity to the floor and have to contact it. The rails are subjected to extremely high mechanical loads, and on the other hand, the high currents - these are in the range of mega-amperes - cause great wear, so that they can only be used once. In recent years, however, some progress has been made on these points.
Within the earth's atmosphere, the bullet can burn up due to the frictional heat.
Railguns in popular culture
Railguns are found in literature, films, and computer games. The feature film Eraser with Arnold Schwarzenegger in the leading role revolves around fictional railguns as infantry weapons. In the tabletop game Warhammer 40,000 , the extraterrestrial people of the Tau have such guns that are called mass accelerators in the German translation. Railguns are used as weapons in many computer games. For example as a sniper rifle in the Quake game series , the first-person shooter in the Halo series or in Call of Duty: Advanced Warfare . Railguns also appear in the science fiction series of the Stargate series. In addition, a railgun is used as a ship gun in the movie Transformers - Revenge .
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