January 31, 2008

US Navy Kills Level Boss, Grabs Power-Up: You Got The Lightning Gun
— Ace


A railgun projectile strikes a target.

The future and its enemies? The enemies should be worried.

A futuristic weapon getting a trial run by the Navy demonstrated its destructive power at the Naval Surface Warfare Center in Dahlgren.

In the demonstration Thursday, engineers fired the electromagnetic railgun at what they said was a record power level: 10 megajoules.

The previous railgun power-use record was about 9 megajoules of muzzle energy.

Railguns use electromagnetic energy to launch projectiles long distances — more than 200 nautical miles.

...

The Navy hopes the railgun will eventually replace the standard 5-inch gun on its ships. The weapon isn't expected to be deployed until at least 2020.

The railgun tested Thursday actually has a capacity of 32 megajoules, but the Navy is slowly building up the energy level in a series of tests.

...

According to the Navy, the railgun, when fully developed, will be able to launch solid projectiles at Mach 5, or about 3,700 mph.

Click on the link to find video of the railgun about midway through the article.

Thanks to Driver.

A Whole Lot of Hell: Defense Tech writes that a single destroyer armed with railguns could pretty much wipe out every strategic target in North Korea.

Maybe that's overstated. Okay, maybe it will take two or three.

I found that looking for proposition I think is true but haven't been able to establish yet: I think railgun projectiles are not tipped with chemical-explosive warheads, but rather rely on the awesome kinetic energy of a heavy metal object flying at Mach 6 or 7 for their explosive effects. Not sure of that yet; still searching.

My only evidence of this so far comes from this discussion of a railgun's statistics in the Champions/Hero role playing game, which of course I find utterly convincing.

Let's try a different approach wherein an attack is required to simply punch through hex after hex in a straight line to total up the damage done. Actually, I can see a major problem with this. the frontal area of the ship is 25*50=1,250 hexes, which means that punching a hole clean through the ship lengthwise would only do 30/1250=0.24 BODY to the ship, but would require (20+10)*2 + (8+6)*200 = 2,860 Body from a human scale attack. For comparison, that's the average damage on an 817d6+1 RKA (12,260 pts). I don't have that many dice and you still have to do that four times to inflict one BODY on the ship. This approach is not going to work, I think.

Real-world anti-ship weapons, such as mines, missiles, shells, and torpedoes all have one thing in common: the letter E, which stands for "explosives". Science-fictional weapons such as lasers and hypervelocity solid projectiles also tend to release their energy as an explosion. Let's see what happens if we use an attack with the Explosion advantage to try to destroy our quota of hexes.

5ER lists an option for RKAs which I'll be using here: subtract 2 points of damage for every hex of expansion. That will make things much easier to calculate.

We can see from the numbers in the last post that to inflict one point of BODY damage on the ship, we need to damage the component hexes of the ship out to a radius of 16 hexes, at which point the damage will be 32 less than the damage at the point of impact. To destroy an internal hex will require 14 Body. Therefore, the damage at the point of impact must be 46 Body, the average result of a 13d6+1 RKA, Explosion (+1/2) (300 pts).

On this same model, a 20d6 RKA, Explosion (+1/2) (450 pts) would do an average damage of 70 Body at the point of impact and would do 14 Body out to a radius of 28 hexes. Assuming a hemispherical damage pattern again, this would destroy 91,952 hexes for a total of 11 BODY to the ship.

It would also appear, at first glance, to pretty much cut the ship in half, but the hole in the hull will "only" be 20 hexes in radius.

Exactly. I wish the Navy would stop talking in abstract scientific gobbedly-gook like "10 Megajoules" and speak in terms that the average American can understand, like 10d6 Mega RKA + AoE Explosive Effect. Or old school, like +6 Vorpal Holy Avenger Shells.

Oooh...

Thanks to a bunch of folks for that, including Exurban Jon and Buzz.

Entropy writes like he knows what he's talking about (though on the Internet you could always be talking to a dog, of course):

They're not going fast enough for real 'explosive' effect yet. Mach 5 would be getting close, but that's with 3 times the power this one used. So how fast was this one?

Mach 8 is hypervelocity. That's when metal reacts more like liquid and you get giant meteor craters as the ground vaporizes on impact, causing the freaking dirt to explode.

Not 'blow up the dirt'. No. I mean 'the dirt blows up'. You don't hit the dirt with explosives, the dirt it hits becomes the explosive when it's hit, and turns into rapidly expanding gas.

We're not going nearly that fast yet though. But I guess it still counts for something beyond just your basic "holy shit" forcepower...which this seems to be exceeding.

Even still it has a shitload of power, but without the explosiony goodness one would think there'd be a high chance of just penetrating the target straight through and actually doing just a little damage.

Eleven writes that these projectiles can't be tipped with conventional chemical warheads, because they'd explode on launch due either to the electrical firing (I don't know about that; it's electromagnetic, not electric) or maybe just because the sudden acceleration is not really any different than sudden deceleration, like hitting something, that can easily set off an explosive round.

It's Old: So says Fresh Air. Well, obviously we've had these in the works for a while, but the new record is fresh.

Fresh Air points to this great article by Wretchard from 2004 about these coming weapons. A must read. (By the way: Wretchard confirms the projectiles are solid darts without chemical explosive tips.)

A first-order analysis comparing the 200-mile volume of fires capability of a single hypersonic naval rail gun to the ordnance delivery capacity of a carrier air wing of F/A-18s is instructive. In the first eight hours of conflict, a single naval rail gun could deliver twice the payload, three times the energy, to ten times as many fixed aim points as carrier aviation.

He writes that such capability is not decisive, however, without a valid military doctrine behind it -- what exactly do you actually do with such firepower? seems to be his point.

I'm only being somewhat glib and sophomoric when I say don't worry, grant us the firepower and we'll come up with as much doctrine as you like to justify it.

I have to admit that the subtlety of Wretchard's point eludes me, though.

(Oh, I see: He's talking about the will to use such a ferocious weapon, or, more accurately, the lack thereof.)


Posted by: Ace at 11:51 AM | Comments (76)
Post contains 1217 words, total size 8 kb.

1 I thought it was a gun that shot lightning.   Bah.

Rail guns are awesome, though.

Posted by: Synova at January 31, 2008 11:58 AM (KZJr+)

2 Lightning would be a bit tricky to aim, I would imagine.

Posted by: Eleven at January 31, 2008 12:01 PM (7DB+a)

3 I want one.

Posted by: runninrebel at January 31, 2008 12:02 PM (0n9wc)

4 Lets see how long it takes before Dick Chaney to get one of those and go hunting quail with it.....

Posted by: A Arizona Republican at January 31, 2008 12:03 PM (+7oCm)

5 32 MEGAJOULES!!!

Posted by: Doc Brown at January 31, 2008 12:03 PM (Lz6uE)

6 Lovely railgun... you had me at 9 megajoules.

Posted by: Exurban Jon at January 31, 2008 12:11 PM (N0doa)

7 Drooooool...  Now I'm just waiting for the 10 story tall mini-reactor powered robots with PPC cannons.

Posted by: Inner Sphere! at January 31, 2008 12:12 PM (+7oCm)

8 I'm pretty sure you're right, Ace, on the warhead issue. My understanding was that any explosives would be fried by the awesome electrical current passing through the slug.

And explode early.

So yeah, not a good idea.

Posted by: Mastiff at January 31, 2008 12:14 PM (lXkG4)

9 Here's the Video: http://youtube.com/watch?v=TWryzhGSM_U

Pretty.

Posted by: Exurban Jon at January 31, 2008 12:15 PM (N0doa)

10 http://www.youtube.com/watch?v=y54aLcC3G74

Link on the fox page is wmv, I mean, WHAT THE FUCK FOX???

Posted by: E Buzz Miller at January 31, 2008 12:15 PM (sf4Oe)

11 Why that would take a bolt of lightning!

Posted by: Doc Brown at January 31, 2008 12:17 PM (SXBHu)

12 http://www.youtube.com/watch?v=TWryzhGSM_U

Awesome...totally awwwesome...

Posted by: E Buzz Miller at January 31, 2008 12:18 PM (sf4Oe)

13 At a high enough velocity you wouldn't need an explosive warhead.  The impact would still be plenty explody.

Posted by: Eleven at January 31, 2008 12:18 PM (7DB+a)

14 That Video is pretty cool.. where can i get one those...

Posted by: A Arizona Republican at January 31, 2008 12:23 PM (+7oCm)

15 I hear the navy is ready to test the gun on more targets - I think Berkeley and San Francisco are the top choice.

Seriously drooolingly awesome war potential (the gun, not necessarily using in on SF)

Posted by: Defector01 at January 31, 2008 12:24 PM (ppm2I)

16 Great idea for ships, that's about the only thing on earth that could port around the energy supply for this kind of weapon at present.


The thing is, there are more commercial applications than military. Making a gun with a magnetic accelerator array is great, but imagine using a big one to fire raw materials into high orbit? You can't put people up there that way but you could launch all the heavy stuff that would cost millions to put up in a shuttle.

Posted by: Christopher Taylor at January 31, 2008 12:24 PM (hfyfI)

17 Anyone else thinking new battleship class with a bunch of jumbo rails?

Posted by: doubleplusundead at January 31, 2008 12:24 PM (68v+0)

18 Call me when out soldiers have Gears of War style chainsaw guns and Duke Nuke'em BFGs. THEN I'll be impressed!

Posted by: Max Power at January 31, 2008 12:28 PM (q177U)

19

Ha!  Your railgun still has nothing on me, bitches.


Posted by: BFG 9000 at January 31, 2008 12:32 PM (plsiE)

20

 I think railgun projectiles are not tipped with chemical-explosive warheads, but rather rely on the awesome kinetic energy of a heavy metal object flying at Mach 6 or 7 for their explosive effects.


I don't entirely get it either.


They're not going fast enough for real 'explosive' effect yet. Mach 5 would be getting close, but that's with 3 times the power this one used. So how fast was this one?


Mach 8 is hypervelocity. That's when metal reacts more like liquid and you get giant meteor craters as the ground vaporizes on impact, causing the freaking dirt to explode.


Not 'blow up the dirt'. No. I mean 'the dirt blows up'. You don't hit the dirt with explosives, the dirt it hits becomes the explosive when it's hit, and turns into rapidly expanding gas.


We're not going nearly that fast yet though. But I guess it still counts for something beyond just your basic "holy shit" forcepower...which this seems to be exceeding.


Even still it has a shitload of power, but without the explosiony goodness one would think there'd be a high chance of just penetrating the target straight through and actually doing just a little damage.


Posted by: Entropy at January 31, 2008 12:34 PM (m6c4H)

21

Weapons funding and procurement must be a job for adults only. I'd drop everything, like my son kicks aside his LEGO Millenium Falcon, and just buy these things. Forget all about jets and tanks and missile systems and get me some railguns like yesterday.


Until the robot warriors YouTube got linked anyway. But I'm like a little kid.


Posted by: spongeworthy at January 31, 2008 12:35 PM (a00go)

22 I'll be in my bunk.


Someone had to say it.

Posted by: Trimegistus at January 31, 2008 12:49 PM (HucaB)

23 Wretchard the Cat had it at the Belmont Club..four years ago. See here.

Posted by: Fresh Air at January 31, 2008 12:52 PM (4C6p2)

24 I am curious as to how a ship plans to hit anything other than a line of sight target.  Doing the ballistic calculations in my head leads to me to think that at that speed, the shell hasn't significantly started "falling" yet to hit a ground target.  Unless they plan on using these things like mortars and shooting them straight up into the air.

lets see, 3000mph, or 17400000 feet per second, 200 miles to target, that's 1/15 an hour, that's 4minutes or 240 seconds.  ok, nevermind, I guess thats plenty of time to start falling. 

But yeah, its a cool concept, taking advantage of the square function of energy to velocity.  Who cares about mass when you can geometrically gain energy?

Posted by: joeindc44 at January 31, 2008 01:02 PM (NXelq)

25 "(I don't know about that; it's electromagnetic, not electric)"

Electric fields always accompany electromagnetic fields.

Posted by: profligatewaste at January 31, 2008 01:05 PM (SSTpc)

26 6 of these things hitting you a minute.  very much like a finger of God weapon.

Posted by: joeindc44 at January 31, 2008 01:06 PM (NXelq)

27 Whats its plan, son?
Plan, sir?
Son, Railguns don't go boom without a plan. A railgun doesn't go to the bathroom without a valid military doctrine.

Posted by: joeindc44 at January 31, 2008 01:10 PM (NXelq)

28 turns into rapidly expanding gas.

Meh,  Mexico has been doing this for years.  Centuries, even.

Posted by: mesablue at January 31, 2008 01:16 PM (KCOdQ)

29

I am curious as to how a ship plans to hit anything other than a line of sight target.  Doing the ballistic calculations in my head leads to me to think that at that speed, the shell hasn't significantly started "falling" yet to hit a ground target.  Unless they plan on using these things like mortars and shooting them straight up into the air.


I seem to remember an article that said they shoot the things in a high arc into the upper atmosphere before they start falling.


Posted by: Hollowpoint at January 31, 2008 01:18 PM (plsiE)

30

Eleven writes that these projectiles can't be tipped with conventional chemical warheads, because they'd explode on launch due either to the electrical firing ...


Not me Ace.  Dunno who said it.  But it sounds right enough.


Posted by: Eleven at January 31, 2008 01:19 PM (7DB+a)

31 It must suck to be from another country and have to sit back and watch as the US of A creates weapons like this, and realize that your country will never have firepower like this.

Posted by: Ken at January 31, 2008 01:22 PM (e7rdm)

32 Bonus: Imagine you're inside an installation hit by one of these.  When the slug hits the wall, it vaporizes the structure, bringing superheated, unbreathable metal gas in with it.  Oh, and the shockwave as it rips through the air you can no longer breathe because it's hot enough to melt your lungs.  If that ain't shock and awe, I don't know what is.

Posted by: leoncaruthers at January 31, 2008 01:23 PM (JSO4h)

33 Hmmmm.

IMO I see this kind of weapon being upscaled into an intercontinental railgun based in Colorado capable of delivering kinetic strikes to anywhere on the planet, or earth orbit, without having to put a ship out to sea.


Posted by: memomachine at January 31, 2008 01:26 PM (3pvQO)

34 has anyone calculated energy loss as the thing spends 4 minutes in the air traveling to the target?

Posted by: joeindc44 at January 31, 2008 01:27 PM (NXelq)

35 Guess what I'M building in my garage this summer!

I swear I will use my science-fiction weaponry for good. And profit. But mostly for good. And profit.

Posted by: Merovign at January 31, 2008 01:31 PM (GLJe8)

36 Hmmm.

Let's face it.  If you can overcome the difficulties in working with ultra-high power it makes a lot of sense to create a railgun capable of delivering slugs via sub-orbit. Then it makes sense to put it into the side of a mountain and power it with a few military grade nuclear reactors.  By that point you realize that you aren't limited in either the size of the railgun or space restrictions on capacitors.

Hook it into JSTARS and Marines could call in GodStrikes from Afghanistan.

Posted by: memomachine at January 31, 2008 01:34 PM (3pvQO)

37 At that speed you don't need explosive. The M829A3 is a long depleted uranium spear that is used by the Abrams. It is able to defeat any tank armor in the battle field.

Posted by: jdun at January 31, 2008 01:37 PM (fHa57)

38 I am not that impressed. The rail gun can launch a screaming fast projectile, but how fast does the velocity bleed off? I would think the projectile would go from lightning bolt to brick fairly fast. I would also presume the projectile cannot directly contact the barrel at a certain point in its launch, or it will melt it.

Posted by: Mark at January 31, 2008 01:37 PM (Sth9k)

39 It must suck to be from another country and have to sit back and watch
as the US of A creates weapons like this, and realize that your country
will never have firepower like this.

It's not so bad.

Posted by: Asymmetry at January 31, 2008 01:39 PM (Lz6uE)

40 "has anyone calculated energy loss as the thing spends 4 minutes in the air traveling to the target?"

Oh, I'm sure somebody has.
The article I read a while back talked about calculating the trajectory to recover energy on reentry.
Basically shooting this big hunk of metal almost into orbit and having it free fall from 65 miles up into the target. Kinda like a meteor.

Posted by: A. Weasel at January 31, 2008 01:44 PM (bqcfE)

41 "speak in terms that the average American can understand, like 10d6 Mega RKA + AoE Explosive Effect"

Is this a Champions related comment? It has to be. I can probably calculate the power cost, plus special effects in my head.
You are like a god to me now.

For the non-geeks: Champions = superhero role-playing game. Being a math major wasn't a requirement, but it didn't hurt to have a calculator of hand at all times.

Posted by: Bert Godding at January 31, 2008 01:47 PM (XYM/m)

42 Everybody likes a splosion.

Posted by: ricpic at January 31, 2008 01:54 PM (+++MJ)

43 I would use it for hunting.

Posted by: Evil Otto at January 31, 2008 01:55 PM (08dnm)

44 For the non-geeks: Champions = superhero role-playing game. Being a
math major wasn't a requirement, but it didn't hurt to have a
calculator of hand at all times.


GURPS: Space was even worse.  OTOH, I kicked ass when I hit algebra after playing it.

Posted by: leoncaruthers at January 31, 2008 01:55 PM (JSO4h)

45 I'd hit it.

Posted by: 400 Year Old Clam at January 31, 2008 01:56 PM (3+0IS)

46 Without a valid military doctrine?  Ya mean like nuclear
weapons?  As Ace said, you invent the weapons and we'll develop
the doctrines.

Posted by: Ken at January 31, 2008 02:06 PM (e7rdm)

47 no, even better than Colorado, lets develop an space station to house one of these things.  Only big enough to destroy an entire planet.  I figure it should have a spherical shape and lots of trash compactors.  That way we can go from planet to plant, killing terrorists.  It could be the ultimate power in the universe.  I suggest we use it.

Posted by: joeindc44 at January 31, 2008 02:11 PM (NXelq)

48 valid military doctrine, like, "you get blowd up?"

Posted by: joeindc44 at January 31, 2008 02:12 PM (NXelq)

49 Why do you need a doctrine? It's just a gun that launch a projectile without the use of gun powder. Just faster and further then the current ones.

Posted by: jdun at January 31, 2008 02:15 PM (fHa57)

50

If you're dropping stuff from space you don't need a railgun - just a bunch of long DU rods with good guidance software and a small rocked motor. 


Posted by: holdfast at January 31, 2008 02:28 PM (Gzb30)

51 The moon is a harsh mistress.

Posted by: mr. frakypants at January 31, 2008 02:28 PM (bZAfL)

52 All i know is when i used the railgun in quake, it pwned.

Posted by: wahhaw at January 31, 2008 02:39 PM (OYPh2)

53 I'm not sure this weapon is much use for far inland targets.  At mach 8
it's going to get to a target 200 miles out in two minutes (ignoring
friction), but you have to lob it over any hills between you and the
target.  If the hills are too high, you have to slow down your shot. 
The article doesn't say, but I'll bet the projectile will have to have
some kind of on-board guidance, like little vanes sticking out into the
slipstream.  That would make it easier to hit the target with the full
kinetic punch.



Shooting almost straight up would work, but the projectile would go
about 240 miles up, taking about 18 minutes to hit the target. It's
like the old orbital crowbar concept (ah, holdfast mentions it just
above); hard to see why just sending a B-2 over with conventional bombs
isn't as good, and cheaper.  Of course, the Air Force owns the bombers,
and the Navy wants to be competitive.



And, of course, this is another example of fighting the last war.  Hard
to get all those guerrilla/insurgency fighters to stand in a row or a bunch so
that your railgun can shoot them all.  You're better off with a bunch of your own guys with rifles.

Posted by: Bob Munck at January 31, 2008 02:49 PM (n0BzT)

54 Now I want frikkin sharks with frikkin deathstars on their frikkin heads!

Posted by: JavaJoe at January 31, 2008 03:06 PM (Am6n/)

55 Well I guess since Bob M. has graced us with his opinion, the debate is over. He doesn't like it so there is no possible point in continuing. The folks who have worked on this for 20 years don't know what the hell they are doing. Thanks Bob. You couldn't have thought about this two decades ago when the dimwits who plan stuff for the Navy first started discussing the pros and cons of railguns?

Posted by: XBradTC at January 31, 2008 03:32 PM (H+PWn)

56

I don't think this is about counterinsurgency so much as saying hi to the Chinese.   They're getting aggressive and frisky.  


Posted by: Chip at January 31, 2008 03:40 PM (sOtz/)

57 You couldn't have thought about this two decades ago when the dimwits
who plan stuff for the Navy first started discussing the pros and cons
of railguns?


In fact, we did talk about railguns when I was working at NRL, but smaller ones, for ship-to-ship or anti-aircraft/missile under Aegis.  The kind of thing the Phalanx is used for now.  The big railguns were developed under Star Wars.  There's actually a civilian use for them, too: it's not impossible to build one with high enough velocity to put (high-g-proof) stuff into orbit cheaply.

And, of course, everybody really likes big guns.  Gerald Bull didn't live in vain.

Posted by: Bob Munck at January 31, 2008 03:45 PM (n0BzT)

58 The papers I read on this around the time of Wrechtard's article mentioned that they were guided. Not so much 'guided for the whole flight' as 'guided during the terminal attack phase'. I think it also mentioned that the 'useful range' of 150 miles was where it would drop below Mach 3 and start shedding velocity more quickly.

They also mentioned that along with the DD's getting these, the aircraft carriers would as well. So you'd have electromag catapults + railguns + nuclear powerplants for juice.

(And I can't help but think that this would rock on something like, say, the USS Jimmy Carter.)

Posted by: Al at January 31, 2008 04:06 PM (Lk931)

59 American ingenuity meets the catapult - rewired for "More Power"

Posted by: roy at January 31, 2008 04:28 PM (8tuJJ)

60
(And I can't help but think that this would rock on something like, say, the USS Jimmy Carter.)


You know she's a submarine, right?

Posted by: Bob Munck at January 31, 2008 04:36 PM (n0BzT)

61

Any projectile with such a long flight cannot help but be subject to unknowable wind changes, sheer, etc.  An unguided cannonball could be shot cheaper than our other systems but would be a lot less effective.


 


Going back a bit, I think Entropy has a point: a 100mph cannonball might do a lot more damage than a 3000mph one.  The first was able to break masts and bring down bulkheads and stuff; the faster one would go right through.


 


Going back even further, this is more like a modern trebuchet that was good for throwing heavy stuff against castle walls.  But, one of the best weapons ever was throwing a dead cow over the wall. 


 


So throwing the maximum energy at something does not always produce the best result. First, it has to hit the target, otherwise it is useless.  Second, it has to be effective.


Posted by: Robert at January 31, 2008 05:14 PM (Rb4Qc)

62 These won't be available until the "next war." And if at that point we are mistakenly fighing the last war, that means we'll be trying to use counterinsurgency tactics to fight a major, nation-state force. And if that's what we're facing, these ought to come in quite handy.

Posted by: Eric J at January 31, 2008 05:15 PM (ES8sY)

63

I respecfully disagree, Robert. I'd take a dead cow doing 8000 MPH any day. (If you can believe Lawrence, the dead camel was heavily preferred in the Empty Quarter).


Doubleplus, whadyamean "new class" of  battleship? We're not using New Jersey right now, are we? You can't buy that kind of armor belt today. Mmmm...Iowas. With death rays.


"and realize that your country will never have firepower like this." Yeah, like USSR until 1949, China until 1964,  Pakistan until 1998 and Iran until two weeks from Tuesday...have you no faith in espionage?


Line-of-sight shore targeting might not be so limiting. For one thing, it was said (Tuchman?) that on the eve of WWI, two-thirds of the world's population lay under the guns of the dreadnoughts. And those hills and stuff? They're only in the way until the second salvo.


 


 


 


 


=


Posted by: comatus at January 31, 2008 06:45 PM (VjNM6)

64 I'm late to the party here, Ace, but to give you an idea of the power of kinetic weapons, a projectile moving at 3000 meters per second (6696 MPH, or Mach 8.6 at sea level) will hit with the energy of the projectile's mass in exploding TNT.  In other words a 10 pound shell moving at 3 km/sec hits like 10 pounds of exploding TNT - but unlike regular explosives, all of that force is concentrated into the point of impact instead of blowing apart in all directions.

Posted by: J. Wilde at January 31, 2008 08:28 PM (i75Pv)

65 ... will hit with the energy of the projectile's mass in exploding TNT.

Yeah, but if the energy isn't released -- "coupled to the target," it's not the equivalent of TNT.   The projectile is going to be long and skinny, to get through the air without bleeding off its energy.  If it just punches through the target and takes most of its energy out the other side, like a cartoon character running through a wall and leaving a character-shaped hole, you would have been better off with slow TNT. A cheap laser-guided bomb dropped from 40,000 ft. is a better bet.

Posted by: Bob Munck at January 31, 2008 08:54 PM (n0BzT)

66 chips.navy.mil article

"A notional 15 kg railgun flight body arrives on target with a 1500 m/s or Mach 5 terminal velocity, which equates to 17 MJ of available kinetic energy. This is about twice the kinetic energy available from a conventional 5-inch KE warhead from a projectile at half the weight."

Posted by: Al at January 31, 2008 09:12 PM (Lk931)

67 If you've got your projectile moving at Mach 5 or so guided to the target, you've done the hard part. Getting from a solid shot that simply punches a 5 inch hole through armor to something that intentionally breaks apart just prior to impact to spread the damage doesn't seem quite as difficult. They're discussing 'guided projectile', so there's going to be electronics that know when would be best.

Fifteen kilos of Mach 5 shotgun shot with a variable choke.

Posted by: Al at January 31, 2008 09:21 PM (Lk931)

68 Here's some more data:

http://www.navweaps.com/Weapons/WNUS_Rail_Gun.htm

Posted by: Captain Ned at February 01, 2008 05:40 AM (2b8Uy)

69 Hmmmm.

"
Fifteen kilos of Mach 5 shotgun shot with a variable choke."

I'd use it to go quail hunting with Cheney.

Posted by: memomachine at February 01, 2008 08:13 AM (3pvQO)

70 Bob M, you need to go back and read up. Keywords: "hydrodynamic" and "hypervelocity".

At low velocity, a projectile without an explosive warhead has to push the target material out of the way ("plastic deformation").

At high enough velocity, pressure waves can't propagate through either the target or the projectile as fast as the projectile continues to arrive; the material can't get out of the way. The result is a shock wave containing a large fraction of the kinetic energy of the projectile. For the same reason (although at much lower energy) the speed of a ship displacing the water is restricted because above a certain speed the water can't get out of the way quickly enough.

This is also the point of a shaped charge -- some fraction of the explosive is accelerated above critical velocity and serves as the "projectile". But a shaped charge delivers only around a fifth of the explosive's power to the target in the form of a high-speed jet; a confined shaped charge can double that. A hypervelocity projectile without an explosive can deliver more than half, sometimes as much as three-quarters, of its kinetic energy in the form of heat, etc. to blow the target up.

The key is to keep the velocity above the critical value, about 1200 m/s or Mach 4. If you can regularly deliver velocities of 1500-2000 m/s at the target the concept of "armor" is essentially moot -- the only way of protecting a target is lots and lots of material, e.g. several feet of concrete, sandbags, etc. And if you can put a second and subsequent projectile on the same spot, even that doesn't help much -- it'll punch through eventually.

Tres cool.

Regards,
Ric

Posted by: Ric Locke at February 01, 2008 10:37 AM (DTj4I)

71 Bob M, you need to go back and read up.

I'll accept that; I'm a software guy, not hardware.

the material can't get out of the way. The result is a shock wave
containing a large fraction of the kinetic energy of the projectile.


I'm not entirely convinced.  What if it's hitting the thin aluminum skin of an airplane, say?  Sure, the cross-section it hits just vanishes, but I'd think the metal around that would simply deform or buckle.  I can't see how large amounts of energy would propagate through the skin to the airframe.  Anyway, that's what they were saying back at NRL.  A counter-argument was that the plane or missile would be coming right at the gun -- that being the reason we were shooting at it -- and the projectile would travel along its length, doing much more damage and transferring much more of its energy.

Posted by: Bob Munck at February 01, 2008 03:07 PM (n0BzT)

72

#54:


This is a smart projectile, not a ballistic one.


The muzzle blast is the gaseous remnants of the sabot.


Posted by: big G at February 02, 2008 09:09 PM (XtdhX)

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74

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