This episode of Real Engineering is brought to you by brilliant.org, a problem solving website that helps you think like an engineer. Guns are a technology whose roots can be traced all the way back to 12th century China. And although the technology has advanced beyond recognition: with the guns growing in size and power their ammunition has evolved from spherical to the more familiar bullet shape to make them more efficient at supersonic speeds; the barrels have been bored with twists to impart a spin on the round to make it more accurate; and the method of their transportation has revolutionized how they're used. But there has been one constant for this technology through the centuries. Today we're going to learn how this technology looks set to be revolutionized by its largest iteration to date with the invention of the rail gun. Rail guns are guns that use electromagnetic force to propel a projectile instead of an explosive. Using explosives to power artillery has some drawbacks. Perhaps the most glaring one, being that naval ships have to carry huge caches of explosives on board to power their guns. This has backfired several times throughout history, particularly during World War II when on multiple occasions Japanese attacks detonated huge stores of ammunitions within ships, with the most horrifying case being the kamikaze attack on the USS John Burke, where the resulting explosion dwarfed the gigantic ships in its convoy. Obviously, avoiding future cases of this would be ideal; but this isn't the only advantage. Current railgun designs are doubling the muzzle velocity of all naval artillery with hypersonic speeds up to Mach 6 -- most naval artillery max out at Mach 3. This would extend the range and reduce the time to impact by nearly double too if it wasn't for the elevated air resistance at these speeds. This technology has been a focus of the US military for decades, and for good reason. So let's see how it works and what needs to improve before we see it introduced to service. Rail guns use electromagnetism to propel a conductive armature, housing the projectile, downrange. The physics is quite simple, however the math is not. Two parallel rods are connected to a power source -- these two rods can be considered the weapon's barrel. Connecting these two rods and completing the circuit is the armature. As the current passes through the rails, it generates a magnetic field. The same happens as it passes through the armature. The interaction of these perpendicular currents through the magnetic field produces something called the Lorentz Force. This force acts both perpendicular to the flow of the current and the magnetic field. In the case of the railgun, this force is what pushes the projectile through the barrel and downrange. The beauty of the Lorentz Force is that it's consistent, meaning the longer the barrel the higher the muzzle velocity. but the power required to simply overcome the static friction within the barrel of a miniature railgun can require significant amounts of energy most individuals don't easily have access to. This is when things start to get extremely interesting or extremely challenging because both solving for the Lorentz Force and generating sufficient Lorentz Force are both huge engineering challenges that have only been made possible and sustainable in the last 20 years. The Lorentz Force, in the case of a railgun, is simply the current multiplied by the armature width, the magnetic field in Teslas, and sine theta, where theta is the angle of the current, which in this case is 90 degrees. The magnetic field, B, is a property of the railguns design, such as materials, rail separation, and diameter and overall design geometry. With some assumptions, the equations clean up a bit, but for actual railgun design, these assumptions can't be made. While this technology has huge potential, there are some problems that need to be overcome to make this a serious weapon system. First and foremost, the same force that is applied to the armature also acts on the parallel rails. Quite literally, every time the weapon system is fired, the gun is actively trying to tear itself apart. On top of all this, the heat generated during each shot is so immense it is melting the rails. This can be seen during test fire drills with prototype railgun systems. That discharge you see behind the projectile is not the result of explosive propulsion, but a result of the resistive electric heating created by the huge current running through the rails and the frictional force between the armature and the rail, causing the rails to melt and shed material during each shot, causing more damage to the rail. These are unavoidable side effects, which are currently limiting the railgun to just a few shots before the damage breaks the gun entirely. Next, and possibly the most obvious limitation to the railgun design as a whole, is power. For this weapon to ever be introduced to service, it would have to be paired with a power source capable of providing the 25 megawatts needed to fire it. Even if previous generation ships had this capability, they would not have had enough power in reserve after satisfying the needs to the onboard systems and propulsion. But America's new futuristic Zumwalt-Class Destroyer is an all-electric composite ship that was slated to test this new weapon. With a generator capable of creating 78 megawatts, it would still have 58 megawatts of capacity available after providing for the rest of the ship's essential power requirements. Difficulties in railgun development and fiscal pull backs in Zumwalt construction have delayed their introduction. But they can, and likely will, be retrofitted in the coming years, once the current Durability problems have been solved. And while this technology is currently being funded by the military, it has far-reaching potential for other industries. We spoke recently of the challenges of intercepting ICBMs with traditional missiles. Rail guns could allow multiple interceptors to be quickly fired at a fraction of the cost and increase the chances of success. They have even been suggested as a means of protecting the earth from asteroids, with huge versions in orbit, to destroy or change the direction of incoming asteroids. Launching a satellite like this could also be made drastically cheaper too if we can deliver the materials to orbit with nothing more than the force a magnetic field imparts on a moving electric charge. If you'd like to learn more about electricity and magnetism and how they affect the world around us or any number of other scientific and mathematical principles, the best way to learn and understand principles like this is by applying them yourself, and that's exactly what brilliant.org allows you to do. One of my goals with this channel is to inspire my viewers to follow the path of past engineers to make this world a better place. But to do that you have to learn how to apply these principles yourself. Brilliant is a problem-solving site that helps you think like an engineer by guiding you through problems that are broken into digestible sections that bring you from knowing nothing to having a deep understanding of the topic. What I love is that when you answer something incorrectly, it even tells you exactly why so you can correct your misconceptions. To support Real Engineering and learn more about Brilliant, go to brilliant.org/realengineering and sign up for free. 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I'd like to quickly address a few common railgun myths.
That's actually not true anymore. Barrel life was up to 400 shots by March 2014. Goal is 1000 shots per barrel (ca 2019). That's plenty for missile defense. The mount may only hold 650 rounds anyway, according to this 2015 RFI. The program has already gone through thousands of projectile shots and 5,000 pulse shots.
That's why they use a secondary power supply, apparently LiFePO4 batteries, which store energy for ~20 shots. The battery power system at Dahlgren stores 50 shots. The current 32 MJ gun is actually sized to replace some 5" guns on Burkes/Ticos, not just Zumwalt #3.
Close. It's actually 20 MW for 10 rounds/min for continuous fire.
But again, the first 20 shots or so are "free," drawing 0 power from the ship's generators.
That's true for literally every gun, especially with hot, high-performance propellants for long-range rounds.
ONR hopes its railguns will have more barrel life for a given muzzle velocity or muzzle energy. Eg, 1000 shots through a 32 MJ gun firing at Mach 6 to 100+ nmi. Or... several 1000s at Mach 4 and 50 nmi.
It still is. USS LBJ (DDG-1002) is still marked to receive a railgun. The program timelines of both the Zumwalt and railgun happily coincide to make this possible. Zumwalt is also arguably the ideal test ship for a railgun.
Fun stuff
Ballistic missile defense is one of the main reasons railguns are being developed by the military.
But for midcourse defense, you'll need a new round: new propulsion (fins don't work in space), new guidance (command guidance isn't precise enough at 200 mi), and probably a much more powerful gun for more range and heavier payloads
Unless it's incredibly massive, a railgun powerful enough to destroy or deflect earth-threatening asteroids is also powerful enough to instantly deorbit itself every time it fires (or not). But if you can build a railgun that massive, you can probably build much smaller missiles to do the same job much more cheaply. In fact, it's already possible today with current rockets, telescopes, and nukes. Lawrence Livermore National Lab paper: "Use of Nuclear Explosives To Disrupt or Divert Asteroids".
This is pretty challenging. Difficulties include:
Technically, this is fairly doable, especially in the long time-frame implied, but reusable rockets will be more competitive for the foreseeable future.
For more, I wrote a Railgun FAQ: https://www.reddit.com/r/HephaestusAetnaean/wiki/railgunfaq
This video is using outdated information. the 2 main issues listed have already been solved for the most part.
If it's public knowledge, it's probably not their best. The best they have is shit we won't see for another 5-10 years in public use.
"Railguns even have potential outside the military. For instance, they're better at shooting down missiles." ...I'm pretty sure defensive technologies still qualify as military.
This technology has always interested me ever since I played Halo and found out about MAC cannons
Wow.. That USS John Burke explosion looked like an atomic bomb test footage..
...that we know about
Thanks for post OP! If anyone has any questions, shoot me a question here and I will do my best to answer.
ah yes the familiar bullet shaped bullet (spitzer bullet)