Geek Answers: How do rail guns work? (with video)
By Graham Templeton 05.16.2014 :: 8:29AM EDT 05.16.2014
Rail guns are fun. They fall somewhere between cannons and RPGs in terms of their utility, and despite concerted campaigning by the Quake series they still are not the backbone of US military armaments. Believe it or not, some have spent decades arguing that railguns will eventually replace a good portion of traditional naval armaments — that's how fundamental some of its advantages truly are. Yet railguns are still fairly niche devices. Why?
Firstly, a railgun is essentially a real gun that's switched out the explosive power of combustibles for the magnetic power of electricity. Instead of hurling a piece of metal by packing an explosion behind it, railguns create a huge magnetic differential between two rails (Hey, that's what they're called!), and place the round in between. The firing mechanism is simply magnetism: as a round of, say, 3 kilograms accelerates due to the overall magnetic force, it can acquire speeds of Mach 7 or more! Next-gen versions could have a range of more than 160 kilometers (100 miles), making them extremely versatile.
A very basic diagram of a railgun's internal design.
Some railguns have been known to send out rounds carrying up to 50 million joules of kinetic energy — to put that into perspective, the enormous .50 BMG sniper rifle has a muzzle energy of about 15,000 joules. Still, a railgun round does more damage than a few hundred super-rifles all firing at the same spot. The reason is that, by shooting one large projectile, a railgun can fundamentally change the physics of the "bullet" impact.
The speed of sound (vibration) in metal is quite a bit higher than it is in air. However, at railgun speeds (and starting well below those speeds, actually), something different happens: when the projectile hits a target, the back end of the metal projectile continues to move forward without any way of knowing that the front has stopped; the force of the impact has not yet rippled back through the whole round. As a result, large railgun rounds tend to produce explosions even without explosive material. The super-compression of the metal allows it to ignite in the presence of oxygen, potentially producing a lot of outward energy. One particular US Navy railgun acquired the motto "Velocitas Eradico," or, "I, who am speed, eradicate."
Unrealistic – at least, for a while.
Since a piece of metal is easier to produce than a complex explosive round, the assumption has been that rail guns have the ability to not just provide all the strategic abilities of conventional weapons, but to do so for far less money. The problem has never been the round though — it's the gun. The sheer power needed to so powerfully accelerate a hunk of metal are simply prohibitive. Something on the order of a million amperes is required to accelerate a metal mass so powerfully. This is less of an issue for super-heavy naval vessels like the latest, dual-nuclear aircraft carriers, but railguns won't be eligible for truly widespread use until low-cost, high-termperature superconductors become available.
Another major downside of railguns is that they are extremely hard on themselves; railgun maintenance is their biggest financial disadvantage.
Railgun technology has been proposed for all sorts of non-military applications, from launching spacecraft to fusion power. The basic principle is simple enough to be generalizable: an extremely powerful way to launch projectiles is going to be useful to all sorts of industries.
Check out an ad for the Blitzer railgun below, almost comical in its similarity to satirical works like Starship Troopers.
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railguns
superconductors
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