Thursday, February 21, 2008

Railgun!

The Navy set a new record for the most powerful railgun shot, and brought my dream of cosmically powerful weaponry one step closer to reality.

From the story:
Thursday’s test produced a record 10.86 megajoules, which sent the 7-pound aluminum slug at Mach 7 (more than 5,000 mph) for 80 meters, a roughly 20-millisecond ride.

Before:


Check out the visible shock wave. That's what you get at almost 1.4 miles per second.

After:


According to the story, the shot trap was a steel box filled with 2.5 tons of sand, and after the projectile hit it, it was splayed open like a flower. I wish we had some pictures of that, instead of this stupid billboard getting blown to hell and gone. Ah well.

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11 Comments:

Anonymous Jerry D. Harris said...

I wish we had some pictures of that

It's probably classified.

5:13 PM  
Blogger TheBrummell said...

Confusion: I thought railguns worked by generating a rapidly-moving electromagnetic field in a series of magnets. The story mentions an Aluminium slug, which I understand to be a non-magnetic substance (I know there's some distinction here with diamagnetic and the other kind, but I can't remember how that works). Thus, I though railgun slugs had to be made of (alloys of) iron, cobalt and/or nickel.

Now that I've shown off my amazing physics ignorance, I'll go.

2:55 PM  
Blogger Dr. Vector said...

I think you're onto something. Wikipedia says the projectile needs to be conductive. However, I have thought of a couple of solutions to the apparent paradox. One is that the projectile was made of aluminum for its ablative properties, with a disk, skin, or slug of something ferrous attached or embedded. Or perhaps the shot used a ferrous discarding sabot to boost the non-conductive aluminum penetrator. One of the test shot emblems I saw had something that looked very much like a sabot round on it.

If you have no idea what I'm talking about, some antitank shells consist of a small, dense penetrator--a finned titanium dart, perhaps--encased in a lightweight tube that's big enough to fit the tank barrel. The lightweight tube, called a sabot (French for shoe), is split lengthwise and flies off as soon as the assembly exits the barrel, leaving the penetrator to fly to the target unhindered, and at incredible velocities. The full name for these shells is APFSDS, or Armor-Piercing Fin-Stabilized Discarding Sabot. They put the kinetic energy of a loaded semi (or lorry, if you prefer) onto a spot about the size of a quarter. According to one book I read, during the first gulf war one of our M1 tanks was disabled and had to be left behind, and the departing troops had to blow it up to keep it from falling into enemy hands. So another M1 shot it point blank with an APFSDS, and the shot bounced off. It took a second shot in the same place to get through. Now that's some serious armor.

3:15 PM  
Blogger TheBrummell said...

I've heard of Sabot rounds, yes. They even make them for modern shotguns - I've seen and handled "sabot" slugs for 12-gauge. Not sure why, exactly, you'd need a transonic slug when hunting deer, but anyways...

I think you're onto something. However, if the projectile merely needs to be conductive (electricity, right?), then Al would work - that's what long-distance electrical transmission wires are made out of, for example. Otherwise, I think a ferrous sabot would be the way to go. Are there trade-offs in aerodynamic shapes at low vs. high velocities? I'm thinking you could have the slug and the sabot be different shapes, as one needs to be accelerated from rest through or pushing out the air inside the barrel, the other needs to fly in a flat trajectory (fins, spin, both) at high, near-constant velocity. Note that a railgun doesn't need to have an enclosed barrel, as far as I am aware, so air could be forced out the sides of the barrel ahead of the projectile during its initial acceleration.

re: historical development. I have seen in a museum a German tank of WWII, a Panzer IV if I remember correctly, that had a scar in the gun mantel, the piece of armour attached to the base of gun barrel on the turret. Apparently, Allied tank gunners knew that German armour was very strong all around, except on top above the driver, right in front of the turret. Hull armour on a tank is always heaviest at the front, so faced with a German tank head-on, allied gunners tried to richochet their shots off of the bottom half of the gun mantel, straight down onto the top hull armour. This tank in the museum had probably encountered an allied tank that missed by inches that difficult shot. Sabot rounds have higher penetrating power against armor (usually), and I think were widely adopted only after WWII.

re: tangential science fiction and rail guns. Besides their uses for peaceful purposes (moon-based launcher for cargo), railguns feature heavily in military science fiction stories. I particularly recommend David Drake's Surface Action for a description of their widespread use in future wars.

Sorry for the long and rambling comment, I like railguns too.

1:55 PM  
Blogger Dr. Vector said...

OMG!! An evolutionary biologist who knows Surface Action? Join me, and we can rule the galaxy as father and son!

Seriously, now, have you read Henry Kuttner's story "Clash by Night", which established the 'universe' in which Surface Action is set? I read it in The Astounding Science Fiction Anthology when I was 12--used copies are a cinch on Amazon, and it's packed with good stuff, but Kuttner's story really stuck with me. It was reprinted with another Drake Venus novel, which to my acute embarrassment I have not read.

2:48 PM  
Blogger TheBrummell said...

An evolutionary biologist who knows Surface Action? Join me, and we can rule the galaxy as father and son!

1. I am rarely actually given the compliment of being addressed with the job description I think I have. That was long-winded: thanks for refering to me as an evolutionary biologist.
2. OK, I'll join you, but if you cut off my hand I'll cut off yours, too, and there's no way you'll get me to whine-yell "Nooooooo!!!11!!111!!" and fall off of a tall structure. Nor will I be kissing my sister.

...have you read Henry Kuttner's story "Clash by Night"...It was reprinted with another Drake Venus novel...

Hell and Damnation! No, I have not read anything by Henry Kuttner, I shall endeavor to do so at the earliest opportunity. AND, there's another novel by Drake set on that version of Venus?

I have a couple of rather silly life-time-achievement goals regarding books. I intend to own every story written by Larry Niven, and every story written by David Drake. Given both authors' propensities for writing short stories set in other people's universes (including each other's), this is a rather odd and difficult pair of goals. Note that I don't intend to own every reprinting of every story, just one version will be sufficient.

I didn't even know that Surface Action was set in somebody else's universe. grumblegrumblegrumble

OMG!!

The grammatically correct version of that expletetive in this situation is "ZOMG!!!11!!!11111"

9:10 AM  
Blogger Dr. Vector said...

OK, I'll join you, but if you cut off my hand I'll cut off yours, too,

Sounds fair, if a bit Old Testament.

and there's no way you'll get me to whine-yell "Nooooooo!!!11!!111!!" and fall off of a tall structure.

Okay, but if you happen to fall off a tall structure accidentally, I think you should consider whine-yelling "Noooooo!!!11!!111!!" just to see if anybody gets the reference.

Nor will I be kissing my sister.

There are a lot of ways I could go here, but most of them might bring our nascent galactic conquest to a quick and acrimonious end, so let's just have a mutual no-incest policy in the Vector-Brummell empire, hmmm?

BTW, I didn't mean to suggest that a fine specimen such as yourself didn't know what a sabot was, my explanation was for our future legions.

Anyway, Drake's second Venus book was The Jungle, and it was reprinted with Surface Action in the Seas of Venus duology. Drake says here that wrote the books mainly to get more people to read "Clash by Night". Incidentally, the full text of both books is apparently available for free at the above link, BUT the duology version does not include "Clash by Night", which the stand-alone version of The Jungle definitely did.

I like your ambition. My first Drake book was Rolling Hot, and I've reread it more times than I can count. Hovertanks, man. We gotta get some of those.

9:52 AM  
Blogger TheBrummell said...

I'll agree to the Vector-Brummell Imperial Policy of Inbreeding Avoidance. Any decent evolutionary biologist would agree to that, anyways.

BTW, I didn't mean to suggest that a fine specimen such as yourself didn't know what a sabot was, my explanation was for our future legions.

Yeah, I got that. I didn't mean to imply that I was affronted by your quite good explanation for the masses. Delegation will be an important part of the New Imperium, so I agree we should have well-educated officers and top beaurocrats.

I'm going to have to pick up The Jungle, even if it duplicates my stand-alone copy of Surface Action, since it contains such good historical accessories.

Hovertanks, man. We gotta get some of those.

Oh yeah, I'm all about the hovertanks. I assume you've read more of the Hammer's Slammers series?

My first Drake was probably whatever story appears first in The Fleet series of multi-author anthologies, which I borrowed from a friend long ago. That's a series I keep looking for, but can almost never find. The sequel series, Battlestation is also very good and very hard to find. I don't even know exactly how many books are in each series; I've seen books 1 thru 6 in The Fleet and 1 and 2 of Battlestation. Possibly because these are anthologies edited by David Drake, they don't seem to show up reliably under lists of works-written-by.

11:21 AM  
Blogger Dr. Vector said...

Ah, the Fleet. Top stuff. I read and loved all of the books. What were the names of the series of target planets? Target itself is the only one I remember. Oh, and Bullseye. I really dug the flashes of dinosaurs in the peripheral vision from the A-Potential rifles, too.

I assume you read the Crisis of Empire books. Evidently Drake wrote the outlines and his coauthors wrote the prose. I liked the first three and never got around to the fourth, which may have been by Chelsea Quinn Yarbro? My favorite of the lot is Cluster Command.

Speaking of balls-out action relatively unhindered by character development and so on, have you read In Death Ground and The Shiva Option by David Weber and Steve White? They are a little flatter than Drake's books (whose aren't?), but if you just want to read about vast fleets of space dreadnoughts duking it out with nukes and particle cannons, look no further.

I'd love to chat all day, but duty calls. Once the Western Hemisphere is firmly under our collective boot, we can discuss this at our imperial leisure.

11:50 AM  
Blogger TheBrummell said...

OK, now you're just listing off the books on my shelves.

I read the Crisis of Empire books a couple of years ago, 1 through 3 like you said. I didn't know there was a fourth, I consistently have great trouble finding information about these edited anthology series. I didn't know about Drake outlining then casting open the stories like that, sounds like a very cool way to structure a collaboration in fiction-writing.

Another great series in the same vein is Jerry Pournelle's War World. Dr. Pournelle (his PhD is still classified as far as I know) also did the similarly excellent series A Step Farther Out and There Will Be War, and a few others that I know less about.

I read a couple of Weber books a few years ago, and I remember liking them, even if they were a little fluffy. Good stuff.

9:07 AM  
Blogger Dr. Vector said...

Poop, I got no time, gotta get the kid to bed and then myself, just wanted to say that I enjoyed both War World and There Will Be War a LOT and that we will discuss this further. Oh yes.

9:54 PM  

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