Railguns


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Railguns

 

An electromagnetic railgun is a technology that is currently under development by the U.S. Navy and the Universities and Corporations associated with it, like the University of Texas in Austin and BAE Systems. Railguns are essentially cannons that discharge projectiles at enormous velocities by means of electromagnetism alone. Recently, on December 10th 2010, the world's record for muzzle energy was broken by the 33-megajoule railgun that the U.S. Navy is developing, it was able to send a projectile at least 110 nautical miles and still be traveling at Mach 5. It broke the previous record by a factor of three, and coincidentally the previous record was also held by a railgun. Railguns are a new type of weaponry that can destroy targets with kinetic energy alone.

 

How the Railguns Work

 

A railgun works simply by using Lorentz forces to rapidly accelerate an armature and propel the projectile out the muzzle. The Lorentz force was discovered by the Dutch physicist Hendrick A. Lorentz and is similar to what our class learned on April 19th. The design of a railgun is, as the name implies, two parallel rails roughly four to nine meters in length connected to a huge power source. The power source is huge because to attain these ridiculous velocities either length or current is needed, but since increasing the length will cause complications the easier solution is to increase the current. The two rails will be made of a conductive metal and one will be positive conducting and the other negative conducting. In between the rails is the armature, when in place it creates a circuit between the two rails as the diagram will show. When the current goes through the circuit is creates electromagnets, and the net magnetic field will be pointing upwards in the middle of the rails.

 

(Sorry, but this diagram applies the right hand rule)

 

When the circuit is made there will be magnetic fields pointing upwards and a current moving perpendicular to them at the armature, this will create a Lorentz force on the projectile. As the diagram shows, the force is coming out perpendicular to both the current and the magnetic field, thus accelerating the projectile out of the railgun. Lorentz forces can be quite complex, but in a simplified equation the force would follow be represented by the following where I is the current in amperes(A), L is the length of the rails in meters(m) and B is the magnetic field in tesla(T).

 

Formula

 

(This diagram too applies the right hand rule)

 


Applications

 

Obviously railguns are a technology developed primarily for military use. They are a possible replacement for warheads and other explosive weapons that are reliant on chemical reactions. These types of weapons are costly and add an additional risk factor to the ship containing them. Alternatively, railguns don't require any combustible material and the only risky thing would be the huge capacitors needed to supply the current, but since they're planning on using nuclear reactors to power the railgun it makes the point moot. Other advantages include the overall damage that a railgun can deal and the velocity of which it does this. Since the velocities exceed 2'000m/s the Navy can move their ships far out of harms way and still effectively destroy the target, and even then the wind effect is still negligible. Its velocity is the reason why the railgun projectile doesn't need additional explosives, it relies solely on kinetic energy, and as we all know in the kinetic energy equation velocity affects the equation more than mass does. The projectile will be a tungsten rod because of the properties of tungsten, much like the theoretical weapon Rod of God. The current plan for the U.S. Navy is to mount railguns to battleships as artillery, but other ideas such as a low orbit satellite railgun acting as an anti-nuclear missile defense system have been theorized. Scientist even theorize that railguns satellites could be used to defend earth against rogue asteroids by either nudging them off course or obliterating them. This seems ideal but there are still a few complications, and mainly two major complications. The first is that the current in the railgun is so powerful that there is a huge force of repulsion between the rails. This complication makes it so each railgun can be shot only a few time before the rails need switching. The energy supply is huge for a single railgun shot, and even with proper power generators in place the capacitors and charge up times are long. The U.S. Navy has stated that efficient railguns will be functional around 2020 or 2025.

 

Other than weaponry, railguns have some other theoretical applications such as initiating nuclear fusion reactors. That is to have to two railguns shoot fusible material at each other and at the high velocities that the materials would be going the kinetic force may be enough to cause nuclear fusion to occur.

 

Sources

 

 

Links and Cool Stuff

 

Word Problem:

Railgun Word Problem of Science.docx

 

Amazing animation of the electromagnetic fields during for a railgun

http://www.comsol.com/showroom/animations/2023/

 

Previous World Record

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December 10th 2010's Record Breaking Demo

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