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Air Defense: Mobile Centurion Opens Fire
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December 10, 2010: After two years of talking about it, and doing some tinkering, the U.S. Army finally mounted a Centurion anti-rocket/mortar system on a heavy truck, and successfully fired it. This  Centurion was originally developed six years ago, as "C-RAM". It is basically the Phalanx naval gun system with new software that enables it to take data from other radar systems, and shoot down just about any kind of artillery shell or rocket within range. Renamed Centurion, it uses high explosive 20mm shells, that detonate near the target, spraying it with fragments. By the time these fragments reach the ground, they are generally too small to injure anyone. At least that's been the experience in Iraq and Afghanistan. The original Phalanx used 20mm depleted uranium shells, to slice through incoming missiles. Phalanx fires shells at the rate of 75 per second. Another advantage of Centurion, is that it makes a distinctive noise when firing, warning people nearby that a mortar or rocket attack is underway, giving people an opportunity to duck inside if they are out and about.

The Mobile Centurion is basically the Centurion and a generator on a  U.S. Army HEMTT (for Heavy Expanded Mobility Tactical Truck, which is a flatbed truck). This enables the Centurion to be easily moved to protect areas that were suddenly getting hit with rocket or mortar fire. This keeps people in the target area safe until troops could hunt down and kill or arrest the attackers. It's usually a small group of people, or even an individual, responsible for these attacks. But with enough time, and the use of UAVs and special radars, the attackers can be located and caught.

The HEMTT is also known as the M-977. These vehicles have a diesel electric drive, thus there is plenty juice for the radar and electric motors of the Centurion system. The 8x8 HEMTT trucks are built for cross country operations and were able to keep up with armored formations during the 1991 and 2003 wars. Most of the 13,000 army HEMTT's normally haul ten tons of cargo or 2500 gallons (10,000 liters) of fuel. A Phalanx/Centurion system weighs six tons. The HEMTT began to enter service in the late 1980s, and cost about $200,000 each (depending on special equipment and configuration.) Starting five years ago, the HEMTT fleet began a refurbishment program (at about half their original cost) to give the trucks another ten years of life. This included development of a version that used the diesel-electric drive.

Meanwhile, the navy has upgraded the radar and heat sensors on its Phalanx CIWS (Close In Weapons System) so that that the sensors can detect speedboats, small aircraft and naval mines. The upgrades will cost $4.7 million per system. Of the 57 systems being upgraded to this Block B standard, 17 of them are the land based, Centurion, version of Phalanx.

The first Centurion was sent to Iraq in late 2006, to protect the Green Zone (the large area in Baghdad turned into an American base). It was found that C-RAM could knock down 70-80 percent of the rockets and mortar shells fired within range of its cannon. Since then, the U.S. Army has received 22 Centurion systems (and Britain got ten). The U.S. Centurions have so far defeated hundreds of  rocket and mortar attacks against American bases. Not bad, since it only took about a year to develop Centurion. Each one costs $15 million.

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math    Fragments   12/10/2010 3:34:24 PM
I've always had the question of what happens to flak once it blows up in the air, how exactly are the fragments too small to hurt anybody on the ground? a small hot piece of metal falling out of the sky into you doesn't seem too different from a bullet
 
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HeavyD       12/10/2010 5:04:32 PM

I've always had the question of what happens to flak once it blows up in the air, how exactly are the fragments too small to hurt anybody on the ground? a small hot piece of metal falling out of the sky into you doesn't seem too different from a bullet


Math - as the article said when you hear that brrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrp it's time to take cover.
 
I wonder if Israel is considering this type of system rather than sniping at hamas operatives with 120mm tank shells (and the resulting bad press).  Or for the border in Lebanon.  Seems like a no-brainer for them.
 
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mabie       12/10/2010 6:54:32 PM

they did something similar on 'mythbusters' IIRC. a bullet fired into the sky will follow a ballistic arc and can kill someone it hits on the ground. However a bullet fired straight up will lose momentum until it falls back to earth with only gravity acting on it. If this bullet hit you it could give you a nasty bruise but you would survive, I think the same would be true for flak fragments that fall from a high enough height.


I've always had the question of what happens to flak once it blows up in the air, how exactly are the fragments too small to hurt anybody on the ground? a small hot piece of metal falling out of the sky into you doesn't seem too different from a bullet


 
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History Buff    Ballistics of fragments   12/10/2010 10:49:23 PM
Hi
 
A couple of useful data points regarding the 20mm projectiles under discussion.
 
1.  Fragments or shrapnel that is created by explosions high in the air, will not fall nearly as fast as a bullet, due to the differences in their aerodynamic drag.  Bullets are extremely well designed to minimize drag, because that increases their residual velocity and maximum range.  And the heat originally contained in the fragments will be substantially reduced by the travel through the cooling air.  Thus neither the projectile or heat are likely to be especially dangerous.  Which is not to say that they pose zero danger.
 
2.  You may have also noticed the oft-cited data on the fragmentation lethality radius of various sizes of explosive projectiles.  Even for a really big bomb or artillery projectile, the lethal radius is surprisingly small, a few meters to a few dozens of meters (compared to the 1000+ meter lethal range of even the fairly small 5.56x45 NATO bullet as used in our M-16/M4 rifles).  The lethal distance for fragments is variable, but it is never very large, due to the poor aerodynamics of random pieces of fragments.  They lose velocity very quickly and thereby lose their penetrating/ wounding effect.  For a relatively small and light (~ 4 ounces) high-explosive projectile such as the 20mm cannon round, the typical size of any given fragment is usually less than 1 ounce.  A 1 ounce piece of metal falling on you from terminal velocity altitude could very well hurt you, but it isn't real likely to kill you since it has mediocre velocity and poor shape for penetration.  On the other hand, if a 1 pound fragment of a 155mm artillery projectile hits you at terminal aerodynamic velocity, it has major potential to crush your skull or break your bones, even if its velocity and poor shape are approximately the same as the 20mm fragment.  The basic way to make un-aerodynamic projectiles push their way through the air is to make them larger and heavier, which increases both their external ballistics AND their terminal ballistics effects after it hits flesh or barriers.  This is the way they made smoothbore muzzle-loading cannons more effective....bigger bores leading to bigger projectiles, thus overcoming some of their shape defects.   Some of the Civil War and Victorian-era cannon that used spherical projectiles had huge bores, yet their ranges and usable trajectories were still rather limited by aerodynamics.  The advent of rifling allowed the stabilization of elongated projectiles for greater accuracy, which also had greatly improved aerodynamics, and hence much greater range.
 
Incidentally, there are free online ballistics calculators that allow you to experiment and analyze the results from different shapes, bores, and weights.
 
 
 
 
 
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kirby1       12/15/2010 7:55:55 PM
Falling shrapnel won't weigh much or fall fast, but I bet a dud would fall pretty fast, and would make a heck of a UXO if found lying around.
 
I fore see a lot of one armed souvenir hunters in the future.
 
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Mikko    @ History Buff   12/16/2010 4:17:58 AM
Lethality of artillery fragments might have received a slight understatement there. I can't think of any artillery projectile, if for example 81 mm mortar shells are considered such, that's lethality would end at few meters. Only the lightest of ordnance stop killing you within few dozen meters. 

I am under the strong impression that standing up straight 100, or even 200 meters to a 155mm shell going off might very well cost you a limb or head. And even as 120 mm mortar shells might not have that dramatic effects at that distance you would still be much better of in a covered position.

Never been shot at with artillery, nor spotted it in war, so this is just what I've been taught. 

 
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WarNerd       12/17/2010 12:52:31 AM

I wonder if Israel is considering this type of system rather than sniping at hamas operatives with 120mm tank shells (and the resulting bad press).  Or for the border in Lebanon.  Seems like a no-brainer for them.

Israel is supposed to have a number of them. 
 
The problem is that the system is too short ranged for anything except point defense, i.e. it only protects the area around it, you cannot use these systems to build a wall at the border to protect everything behind them, because the long range stuff passes to high up to intercept.
 
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gf0012-aust       12/17/2010 2:45:22 AM

what happens to flak once it blows up in the air, how exactly are the fragments too small to hurt anybody on the ground? a small hot piece of metal falling out of the sky into you doesn't seem too different from a bullet
when the trials were being run around the green zone one of the issues was "what goes up does come down" (and there's a lot of it)

The SOPS were changed so that they were not used in and around "nn" populated areas

 
 
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