Saturday, December 11, 2010

Railgun: From the 1933 Electric Machine Gun to 2010 Cannon


Preface: It would be nice, in the Lemming's opinion, if everybody would always be nice. That doesn't happen. I've discussed niceness, war, and reality, in "War is Not Nice," Another War-on-Terror Blog. The Lemming will omit the customary hand-wringing in this post, regarding the need for weapons.

A railgun is a staple science fiction weapon. Unlike guns that use a small explosive charge, or compressed gas, to accelerate a projectile; a series of electromagnets in a railgun's 'barrel' act on a projectile, one after another.

As the projectile reaches each electromagnet, it shuts off and the next one is turned on.

Theoretically, very high muzzle velocities should be possible.

This isn't a new idea. A 1933 patent application describes a machine gun that uses magnetic flux instead of "gun powder or the like." We don't have electric machine guns today: quite likely because back in 1933 we didn't have high-output portable generators.

As David S. Zondy said, in his Tales of Future Past page on railguns, "...Mr. Virgil Grigsby of San Augustine Texas went for the small-scale version of what today is known as a "railgun" when he patented his electric machinegun, which would have revolutionised warfare if the extension cord had stretched a bit further...." ("Railgun," Tales of Future Past)

That was then. This is now:

U.S. Navy video by John Williams. U.S. Navy engineers at the Office of Naval Research prepared and test-fired a slug from their rail gun in a 2008 test firing. On Friday, December 9, the ONR will attempt to break its own record.
(U.S. Navy video by John Williams, via FoxNews.com, used w/o permission)

"Navy Sets World Record With Incredible, Sci-Fi Weapon"
John R. Quain, Military Tech, FoxNews.com (John R. Quain)

"A theoretical dream for decades, the railgun is unlike any other weapon used in warfare. And it's quite real too, as the U.S. Navy has proven in a record-setting test today in Dahlgren, VA.

"Rather than relying on a explosion to fire a projectile, the technology uses an electomagnetic current to accelerate a non-explosive bullet at several times the speed of sound. The conductive projectile zips along a set of electrically charged parallel rails and out of the barrel at speeds up to Mach 7.

"The result: a weapon that can hit a target 100 miles or more away within minutes.

" 'It's an over-used term, but it really changes several games,' Rear Admiral Nevin P. Carr, Jr., the chief of Naval Research, told FoxNews.com prior to the test.

"For a generation raised on shoot-'em-up video games, the word 'railgun' invokes sci-fi images of an impossibly destructive weapon annihilating monsters and aliens. But the railgun is nonetheless very real.

"An electromagnetic railgun offers a velocity previously unattainable in a conventional weapon, speeds that are incredibly powerful on their own. In fact, since the projectile doesn't have any explosives itself, it relies upon that kinetic energy to do damage. And at 11 a.m. today, the Navy produced a 33-megajoule firing -- more than three times the previous record set by the Navy in 2008...."

33 Mega-whats?!

The energy involved, 33 megajoules, may not seem like much: although "mega" is an impressive syllable. Briefly, a joule is a measure of energy. A megajoule is, what else? - 1,000,000 joules. A joule is the energy involved in moving one meter with the force of one newton. A newton is the force it takes to accelerate one kilogram at 1 meter per second per second.

Another way of putting it is that the energy in one kilowatt-hour is about 3.6 megajoules. On the unlikely chance that you want more of that, Australian Academy of Science and GCSE.com websites define these and other terms.

33 Megajoules: How Bad Can That Be?

If the Lemming did the math right, at typical American energy costs, that 33 megajoules of energy costs between 20 cents and two dollars. That's according to EnergyVortex.com. We're apparently supposed to feel guilty about the power grid, by the way. Destroying the environment and all that.

The FoxNews.com article translates the railgun's destructive potential in a less geeky, more readily understood way. In the Lemming's opinion.

"...A single megajoule is roughly equivalent to a 1-ton car traveling at 100 mph...."
(FoxNews.com)

So: let's say one of those semitrailers that carries maybe a dozen cars is barreling down a freeway at 100 miles an hour. And hits a bridge piling. It's going to be bad for the driver: also anybody driving nearby; the bridge piling; and quite possibly the bridge.

33 megajoules is a lot of energy.

Why Railguns?

The Lemming could insert the conventional hand-wringing about the not-niceness of violence here: but you've heard it all before. Moving on.

Since railgun projectiles are essentially solid pieces of metal, with no explosives: if one is dropped, it won't explode. Navy crews who handle munitions would have one less thing to worry about. The railguns themselves don't use explosives to accelerate the projectiles: so that's another worry gone.

There are logistical and tactical advantages, too - discussed briefly in the article.

Impossible? In 1933, Yes

Navy ships with railguns won't be around for several years. There are still very serious technical issues to be ironed out. Back to that article:

"...The projectile is no cannon ball, either. At speeds well above the sound barrier, aerodynamics and special materials must be considered so that it isn't destroyed coming out of the barrel or by heat as it travels at such terrific speeds.

"Then there's question of electrical requirements. Up until recently, those requirements simply weren't practical. However, the naval researchers believe they can solve that issue using newer Navy ships and capacitors to build up the charge necessary to blast a railgun projectile out at supersonic speeds. Ellis says they hope to be able to shoot 6 to 12 rounds per minute, 'but we're not there yet.'

"So when will the railgun become a working weapon? Both Ellis and Carr expect fully functional railguns on the decks of U.S. Navy ships in the 2025 time frame...."
(FoxNews.com)

Video, and the Boom Explained

A Wired article's video includes USN footage of the recent railgun test:
"Video: Navy's Mach 8 Railgun Obliterates Record"
Spencer Ackerman, Danger Room, Wired (December 10, 2010)

"There wasn't much left of the 23-pound bullet, just a scalded piece of squat metal. That's what happens when an enormous electromagnetic gun sends its ammo rocketing 5,500 feet in a single second.

"The gun that fired the bullet is the Navy's experimental railgun. The gun has no moving parts or propellants — just a king-sized burst of energy that sends a projectile flying. And today its parents at the Office of Naval Research sent 33 megajoules through it, setting a new world record and making it the most powerful railgun ever developed.

"Reporters were invited to watch the test at the Dalghren Naval Surface Warfare Center. A tangle of two-inch thick coaxial cables hooked up to stacks of refrigerator-sized capacitors took five minutes to power juice into a gun the size of a schoolbus built in a warehouse. With a 1.5-million-ampere spark of light and a boom audible in a room 50 feet away, the bullet left the gun at a speed of Mach 8.

"All that energy was 'dump[ed] in 10 milliseconds,' says Charles Garrett, project manager at Dahlgren for the railgun.

But since there no explosion powering the projectile, why should the railgun have made any noise at all? Answer: the bullet went so fast it released a sonic boom.
"

The video's been making the round: on usnavyresearch's YouTube channel and cosmiclog.msnbc.msn.com, for example.

Here's that YouTube video reduced to fit in this blog. The full-size display is on YouTube:

"Electromagnetic Railgun world record setting event"

usnavyresearch, YouTube (December 10, 2010)
video, 0:50

"The Office of Naval Research Electromagnetic Railgun located at the Naval Surface Warfare Center Dahlgren Division, fired a world-record setting 33 megajoule shot, breaking the previous record established January, 31, 2008."

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2 comments:

Nick Raymon said...

I feel like I’m constantly looking for interesting things to read about a variety of subjects, but I manage to include your blog among my reads every day because you have honest entries that I look forward to. Here’s hoping there’s a lot more great material coming!
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Brian, aka Aluwir, aka Norski said...

Nick Raymon,

Thanks for your kind words. I'll try to keep the material coming: there's no shortage of items, the trick's finding them.

Again, thanks!

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