High current is passed through two fixed rails and through a movable armature placed between them. The high current induces a tremendous force against both the rails and the armature. The rails are fixed in place, but the armature is forced with great acceleration down the length of the rails and out the bore of the gun, pushing the projectile with it.
Although certainly impressive, the achieved speeds were no more remarkable than those of the chemical propellants of the time. The relatively slow speed of Hänsler's railgun can be traced to the type of material that he had used in the projectile. In his trials, he used a metallic conductor as the armature this presented two major problems. The first was that as the armature was a solid, it was impossible to ensure that the armature constantly maintained contact with both rails. The dynamics of the projectile's motion meant that at times the armature lost contact, stopping the flow of the circuit and hence losing the acceleration during that time. The only way that the armature could be made to maintain contact with both rails would be to use brushes or some other contact device, all of which would have created an unacceptable increase in friction. The second problem with solid armatures was that at high speeds they tended to melt, resulting in a rather messy gunk at the muzzle. As the current ran through the fuse it vaporized the metal and established the initial plasma arc. The plasma arc is moved forward by Lorentz's Force, and pushes the nylon cube forward along with it. The plasma arc is confined behind the nylon cube by a dielectric container enveloping the entire setup. Using plasma arcs over solid metallic armatures eliminated the problems that had previously limited railgun velocities to 1-3 km per second, consequently muzzle velocities of 5-6 km/s were achieved.
The rails can be made of any conductive material. However, the best rail material will depend on your specific design. Important characteristics of a good rail material are high conductivity, high strength, high machinability, resistance to corrosion, high melting point, availability, compatibility with slug material, and finally price.
Because the rails in a rail gun are not super conductors they have a resistance. Since the current that must go into a rail gun is so massive the amount of heat that is produced this way is very high and thus may fuse the projectile to the rails which will either render the rail gun useless or slow down the acceleration of the projectile. A solution to this problem is to make the rails in a rail gun super conductors. Each rail in a rail gun carries a current anti-parallel to the current in the other rail. The laws of physics show that two anti-parallel currents repel each other. Since the currents in a rail gun are large the repulsion between the two rails is very large. Rail guns thus have the tendancy to break after a few uses, which makes them not very cost effective.
where Maxwell Laboratories' 32Megajoule gun fires a 1.6kilogram projectile at 3300m/s (that's 9megajoules of kinetic energy!) at Green Farm research facility. Their ability to propel objects at speeds which are simply impossible for conventional (chemical or mechanical) means makes them extremely useful for a range of functions. They hold the record for fastest object accelerated of a significant mass, for the 16000m/s firing of a .1 gram object by Sandia National Research Laboratories' 6mm Hypervelocity Launcher
If a rail gun was able to be implemented on a battleship or a tank, the fire power of that vehicle would be immensly increased because of the velocity (and thus energy) a projectile would be shot at. If it were possible to have a rail gun in a hand weapon form, the destructive power of handguns would be increased ten fold. Luckily we do not have power sources small enough to power a hand held rail gun. Back in the 1980's there was a military program called Star Wars in which the government planned to make an automated computer system which could intercept incoming enemy rockets before they hit US soil. In this plan rail guns would be used to fire projectiles to intercept the rockets. The project was canceled because making an automated system that could track incoming missiles and fire proper counter measures was not possible As seen in many sci-fi movies, asteroids do have the possibility of hitting earth, which would in turn cause massive damage to the planet and human race. Scientists theorize that by using a rail gun to fire high-velocity projectils from orbit at incoming asteroids they can either destroy or change the trajectory of those asteroids. Magnetic trains use the concept of a rail gun. Metal plates (the rails) are placed beneath a train and then current is run through them which will will in turn move the train at velocities up to 300 miles per hour. Rail guns have the ability to fire projectiles at such high velocities that they can feasibly take orbit. If this is true then rail guns could be used to launch space shuttles and satellites without the need of chemical fuel.
Aerodynamic drag along with a million amps of current heats the bullet to 1,000 °C, igniting aluminum particles and leaving a trail of flame in its wake. The researchers estimate the muzzle energy based on the mass and velocity of the bullet in the barrel and from precisely timed x-ray snapshots during flight.
Ashutosh Kumar Rai
B. Tech. Part-IV
What is a Rail Gun?
• Simply put, a rail gun is a gun that launches shells
(projectiles) using magnetic fields and current
instead of consumed fuel.
• Railgun theory is based on the Lorenz force
• In 1944, using batteries as his
power source, Joachim
Hänsler created the first
working railgun, which was
able to propel a 10 g mass to
speeds of about 1mile/s.
• 1964-MB Associates used a
28kJ Capacitor to accelerate 5
and 31 mg nylon cubes with a
plasma arc as the armature
with speeds of 5-6 mile/s.
The best rail material will depend on specific
design. Important characteristics of a good rail
material are high conductivity, high strength,
high machinability, resistance to corrosion, high
melting point, availability, compatibility with slug
material, and finally price.
• The contact patch between rail and shell.
• Dependent on shape and type of shell.
• The structural rigidity of the rail in the horizontal plane
(in plane with but perpendicular to projectile motion).
• The shape and size of shell determine the speeds that
can be achieved by it.
• The armature, which drives the shell, closes the
electromagnetic loop between the rails and is forced
along their length at extremely high speed.
– Solid piece of conductive metal
(Conductive sabot housing a dart or
– Metallic plasma for very high
The Sabot (proposed design)
• optimum current
and heat dissipation.
• projectile itself may
be designed for
more stability and
• Speeds up to
The Power Supply and Firing
• Rail guns require tremendous currents to fire a projectile
at great speed. Typically, the current used in mediumlarge calibre rail guns is in the millions of amperes, while
the duration will be less than 10ms. Maintaining a high
current as long as possible increases the amount of
energy input to the projectile.
• It can be shown from the Biot-Savart law that the magnetic
field at a given distance s from an infinite current-carrying
wire is given by:
• So, in the space between two infinite wires separated by a
distance, d, the magnitude of the field is:
• To obtain an approximate expression for the average
magnetic field on a rail gun armature, we assume that the rail
radius r is small compared with the rail separation d and, by
assuming that the rail gun rails can be modelled as a pair of
semi-infinite conductors, we compute the following integral:
• By the Lorentz force law, the magnetic force on a currentcarrying wire is given by IdB, so since the width of the
conductive projectile is d, we have (assuming l>3d):
• a(acceleration)=IdB/M(mass of shell)
• So, Acceleration directly proportional to charge
• Each rail in a rail gun carries a current anti-parallel to the
current in the other rail. The laws of physics show that two
anti-parallel currents repel each other. Since the currents in a
rail gun are large the repulsion between the two rails is very
large. Rail guns thus have the tendency to break after a few
uses, which makes them not very cost effective.
• F = q . (v X B)
• High Temperatures
Because the rails in a rail gun are not super conductors they
have a resistance. Since the current that must go into a rail
gun is so massive the amount of heat that is produced this
way is very high and thus may fuse the projectile to the rails
which will either render the rail gun useless or slow down the
acceleration of the projectile. A solution to this problem is to
make the rails in a rail gun super conductors.
• Extremely Fast
• hold the record for fastest object
accelerated of a significant mass,
for the 16000m/s firing of a .1
• Can propel large masses
• 32Megajoule gun fires a
1.6kilogram projectile at 3300m/s
• Extremely Accurate
• Military Applications
Destroying Asteroids and
• Destroying planes (Anti
• Peaceful Applications
• Electric Trains: Using magnetic levitation and linear
motors for building fast locos.
• Space launch: In place of shell rockets, satellites can be
launched from appropriate carriers.
• Nuclear Fusion is triggered by very high temperature and
pressure at the core:
-- Lasers, usually over 100, to concurrently strike a
fuel pellet, creating a symmetrical compressive pressure.
-- Rail guns may be able to trigger fusion by firing
energetic plasma from multiple directions.
Seven-pound bullet emerged from a truck-sized contraption at seven
times the speed of sound and sent a visible shockwave through the
air before crashing into a metal bunker filled with sand. With 10.6
mega joules of kinetic energy, this aluminium slug was propelled not
by explosives but by an electric field,
making this the most powerful
electromagnetic rail gun ever fired.
The device is part of the US navy’s
rail gun development program.
Showing launch of rail gun at US naval warfare center
• Normal Guns (Naval
• Range of 20 miles
• Speed: Subsonic. Less than
• Explosives have limit upto
which they can provide speed
to the shell.
• Rail Gun
• Range of 200 miles and above.
• Speed: Mach 7-8 (Hypersonic)
• No such speed limit.
The capabilities of Rail gun are even greater than
that of cruise missiles like TomaHawk and
Junya Kitamura,” Formation And Analysis of Dense Boron Carbide
Coatings with A Low Porosity Formed by Electomagnetically
Accelerated Plasma Sprying,” August 6,2001,pp.632-635.