The Science of Rail Guns

Ubiquitous in science fiction, rail guns are a hot area of military research in real life too. But will we ever really get to use them the way people in science fiction do? And could rail guns be used for a non-violent reason — inexpensively launching payload into space?

Halo Reach ends with your Spartan taking up a mounted rail gun to destroy an incoming Covenant ship. Rail guns are the basis for a funny aside in Mass Effect 2. They're used in Babylon 5 and Stargate Atlantis and The Last Starfighter. And they're a devastating hand-held weapon in the Metal Gear Solid and Quake series. Now, let's discover the real science behind rail guns.

Ejecting pieces of metal at phenomenal velocities
The initial theory leading to modern rail guns owes itself to Louis Octave Fauchon-Villeplee, an early 20th Century French scientist who was awarded the patent, Electric Apparatus for Propelling Projectiles. The patent proposed passing current through two strips of aluminum, with an induced force pushing a metal block forward.

Modern rail guns typically make use of two metal rails, a movable armature, and a power supply. Current passes from a positive conducting rail, over the armature, and to a negative conducting rail, creating a magnetic field in the process that sends a projectile resting on or within the armature forward. Laboratory conditions produced velocities of up to 9 kilometers per second using small mass projectiles; nearing the velocity needed for an object on the surface of the planet to escape the gravitational pull of Earth.

Not surprisingly, research into the creation of modern electromagnetic rail guns owes its existence to military applications. A four kilogram chunk of metal projected at extremely high speeds could inflict damage on par with that of a conventional explosive weapon, but with lower cost ammunition.

The use of "non-explosive" ammunition frees up space and makes an aircraft carrier or naval vessel a safer place for personnel — no more worry about accidental explosions or chemical leakage from warheads.

The Science of Rail Guns

Scaling up is the problem
While launching a small piece of metal at 9 kilometers per second is a wonderful achievement in itself, in order to be of any use for military (and possibly space) applications, the size of the ammunition and rail gun itself must be increased drastically

A February 2012 U.S. Navy test produced 32 Megajoules of energy in ejecting an 18 kilogram projectile at 2.5 km per second, allowing a target several hundred miles away to be reached within minutes. Artillery guns currently on board naval gunships allow for a maximum target strike distance of 13 kilometers. In addition to the United States, the former Yugoslavia and the United Kingdom also are known to have pursued the creation of a weaponized rail gun. The U.S. Navy expects to implement rail gun technology on warships by 2025.

Increasing the size of a rail gun poses a number of problems. The friction accompanying the movement of the ammunition and armature along the rails creates intense heat and possibly a plasma discharge. The presence of opposite magnetic polarity between the rails themselves constantly force the rails away from each other; leading to significant damage to the rails. A plug-and-play launch system with exchangeable or disposable rails attached to a reusable electric energy source would be ideal for military use, but is at least a decade away.

Space exploration
Dr. Ian McNab, director of the Institute for Advanced Technology at The University of Texas at Austin, proposes a modified rail system that would allow for payload deposits to orbiting craft, or, with adequate propulsion after launch, bases on the moon.

The launch system uses a set of rotating rails along a 1.6 kilometer barrel outfitted with modified rail gun technology. The track would be used to launch 300 kg payloads inside of a 1250 kg cone shaped projectile. The 1250 kg projectile will also carry propulsion equipment that guides the cone to its destination.

The benefit of using an extremely long track is a decrease in the rate of acceleration. Much smaller increases in acceleration are needed to reach the desired velocity due to the extreme length of the track.

McNab's proposal estimates the cost of the project at roughly 1.3 billion. With a lifetime of 10,000 uses, the infrastructure put in place by the project costs coming out to a little over $500 per kilogram of payload material launched into space. This is a significant decrease from the current cost of $22,000 to place a kilogram of payload into space. I doubt the rail gun system would be used to transport humans into space (the launch scene from Running Man immediately jumps to mind), but it would be useful for sending additional supplies to space stations, or with sufficient after-launch propulsion systems, moon bases.

The Science of Rail Guns

Handheld rail guns
The likelihood of seeing handheld rail guns in the future, like the ones used in the Quake and Metal Gear Solid series is quite low. A handheld rail gun would need to be both small, use low mass ammunition, thus decreasing the force of the projectile, and come with a lightweight, small power supply as well.

Contemporary explosive ballistics are already at our disposal, exist in a portable fashion, and achieve lethal results. A handheld rail gun would likely be a "one and done" munition, akin to the M72 LAW, a disposable rocket launcher. No ongoing research into the use of easily portable or hand held rail gun is publicly known.

Military dollars and research are paving the way for leaps in rail gun technology, allowing for movement in the technology that could also benefits space exploration efforts. Most uses of rail guns in science fiction implement stationary rail guns, however, the likelihood of blowing someone away with a handheld rail gun as in the Quake series is small.