
France Is Dropping Concrete Bombs - riffer
http://www.theatlanticwire.com/global/2011/04/france-dropping-non-explosive-bombs-libya/37197/
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srean
Well directed kinetic energy can be devastating and has been used for such
effect since ages, for example the old canons with passive cannon balls. Rail
guns are their new sought after variants.

The famous bunker-busting smart-bombs circa first gulf-war were fin stabilized
old tank barrels packed with explosives. It is their weight, owing to the high
density metals used in the barrels and their small cross section (and hence
extremely high terminal velocity) that gave them their extreme penetrative
punch. Enough to pierce through tens of layers of strengthened concrete, each
several feet thick and explode with devastating effects underneath. It was
very important that they did not topple in flight though. So stabilization was
critical.

Even the modern anti-tank weapons are essentially glorified darts, but much,
much heavier. They kill tanks by sheer kinetic energy alone. They have been
found to be harder to defend against, compared to other variants like HEAT
that penetrate tank armor by the use of a high speed, dense jet of liquid
metal, or HESH which are sort of like cow-pies made of high explosives that
set off spalling bending moments inside the tank 'hull'.

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hollerith
>hence extremely high terminal velocity

the main benefit of the small cross section is not increased terminal velocity
through the air but rather to maintain velocity through the bunker (or armor
in the case of the "sabot" or APFSDS anti-tank round you mention)

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mmaunder
To generate the force of a 1 ton TNT explosion, a shell shaped bomb moving at
800 ft per second will need to weigh 311,000 pounds. [K.E.=1/2 x m x v x v]

It takes a fraction of this to dent a tank out of commission, provided you're
accurate. The overpressure wave bouncing around inside the tank cabin created
by a direct hit probably has stunning effects on the crew and may not kill
them if the cabin isn't crushed - although it could do terrible damage to the
ears, lungs and stomach.

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JofArnold
Or to look at it another way:

v^2 = u^2 + 2 _a_ s = 0 + 2 x 9.81 x 2,000 = 39,000

KE = 0.5 _m_ v^2 = 0.5 * 300 * 39,000 = 6MJ

I.e. about 1kg of TNT. "Crush"?? I'm with you on this one, mmaunder

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icegreentea
For another comparison, modern KE sabot anti-tank rounds (what tanks shoot at
other tanks) use penetrators weighing from 4 to 8kg, with a muzzle velocity of
around 1500m/s, giving a low of end of ~9MJ. Granted, this is ignoring air
friction, and must punch through the front armor (much much thicker) than the
top armor that bombs go through.

Also... as a cost comparison, JDAM (the US GPS guidance) kits cost 20-30k per
kit (you strap them onto 'dumb' bombs). For the actual bomb itself, you're
talking on the range of a buck or two per pound... the inert training versions
are much cheaper than that. Explosives are cheeapp. Silicon is pricey.

See link below for pricing information! (The Mk-84 is the 2000lb 'dumb' bomb,
it's listed along with its training/concrete version).

[http://www.fas.org/man/dod-101/usaf/docs/munition-
cost-11-1....](http://www.fas.org/man/dod-101/usaf/docs/munition-
cost-11-1.htm)

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AdamTReineke
Just a thought, but if the silicon is expensive, could you potentially
engineer the majority of the computerized parts into a UAV that could detach
at the last moment and fly back?

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tsotha
I wonder what they're using for guidance. GPS and inertial guidance aren't
accurate enough and anyway aren't useful against moving targets.

That leaves laser guidance kits, which tend to be pretty expensive. Probably
takes more than one attempt on average, too.

On the other hand, you probably don't need to worry much about temperature and
humidity when you store concrete munitions. Or maybe they mix up a batch of
bombs before the sortie - "You can't launch yet. The concrete isn't dry."

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Hominem
Pretty sure the US did this during the first gulf war to destroy stationary
targets without the pesky explosion.

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mnemonicsloth
Back in 1991, IIRC, missiles were smart but bombs were still dumb.

The US seems to have started using concrete bombs in 1999 (against Iraq, but
not during either gulf war).

[http://www.nytimes.com/1999/10/07/world/us-wields-defter-
wea...](http://www.nytimes.com/1999/10/07/world/us-wields-defter-weapon-
against-iraq-concrete-bomb.html)

~~~
icegreentea
They had 'smart' versions of bombs and missiles back in 91. They just didn't
have GPS guided ones/cheap guided munitions. They have both now (with cheap in
a relative term).

<http://en.wikipedia.org/wiki/Paveway>

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hollerith
To be specific, the relatively cheap GPS-guided bombs that became available
after the 1991 Gulf War consisted of new electronics and new tail sections
bolted onto ordinary "iron" bombs manufactured many years earlier.

<http://en.wikipedia.org/wiki/Joint_Direct_Attack_Munition>

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xsmasher
Shades of Heinlein's "Harsh Mistress" - launching is easy when you're "uphill"
from the earth, and rocks are cheap.

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tamersalama
I wonder how accurate you have to hit the target to get the intended
consequences.

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mynameishere
I think you have to be very accurate with almost any kind of bomb. The soviets
made 10+ megaton h bombs partly because they didn't have accurate delivery
systems.

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radagaisus
This is brilliant.

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merloen
Wasn't there a military program for dropping metal rods from space? Does this
sound at all familiar to anyone?

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neworbit
Yes - kinetic kill ideas are pretty sound.

[http://en.wikipedia.org/wiki/Kinetic_bombardment#Project_Tho...](http://en.wikipedia.org/wiki/Kinetic_bombardment#Project_Thor)

Lifting that much mass into orbit is pricy though.

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bifrost
This is an awesome idea. Even if the devices miss, they'll create terror in
people thinking about the unexploded bombs.

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nprincigalli
Soon: imaginary bombs, weighting sqrt(-1) t :)

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foob
But then those bombs would be highly susceptible to decay!

