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Subject: Iron Dome Faces Bad Numbers
SYSOP    1/10/2013 5:35:56 AM
 
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Belisarius1234       1/12/2013 11:27:12 PM
Your numbers are a wee bit off for a Mach 10 system, about one order of magnitude effective range for an IRBM threat (60 kms slant.). FCS will be a little more expensive as you need two radars and a really good computer for a 3-d trajectory solution for predict lead in real time, about $65 for a firing battery of two guns, not including  the bullets to cover one engagement hemisphere 30 kms in radius.. 

So you can buy 1 missile system for $40M, or do the same job with 5 railgun system for $150M, not including ammo and barrels.

See above.

Moral of the story -- Ammo is cheap. Delivering it to the target is expensive.

Moral of the story is the same machine that WILL fling F-18s off the flight deck in the next American aircraft carrier class (electromagnetic catapult) which is a RAILGUN (i.e., LINAC) will shoot bullets very fast and very hard..
 
The only problem, in my humble opinion, is the usual problem with artillery, Heat dissipation and barrel (rail) wear.  
 
B.
 
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Belisarius1234    other half   1/12/2013 11:30:26 PM
I HATE this buggy HTML!
 
 



The one under current test fires bullets at Mach 8.

 

Think of a large electromagnetic machine gun with bullets traveling at 5600 mph.


And a gun barrel that is damaged beyond use in less than 4 rounds.
 
The problem is to make sure repulsion forces don't bend the rails. That is why the contact bushing to the rotor (slug) need refinement.  


Then think of the next generation railgun with double that performance. 


At 5kps your projectiles will burning up in the atmosphere.

 No it isn't. At those speeds, even aluminum survives long enough to survive the intended engagement.

That will kill ICBM RVs.


At what range? You are limited the accuracy of your gun mount, probably less than 6km.

More like 40 kms altitude. :Predict lead of 8 seconds difference is possible at 5000m/s  The RV can't jerk that much in descent unless you want to miss the carrier task force completely.  

Missiles have much longer effective ranges because the accuracy does not drop off.

 Hmmm. Missiles have an absolute upper bound in the lower atmosphere of Mach 10 (cylinder lift) before you have control problems, huge ones.

Bullets are cheap. Electricity is plentiful and easy to modulate. A gun is point and shoot. Missiles are expensive, have steer and  speed dropoff problems after burnout, and run out of supply too soon.


1 bullet may be cheap, but if it takes 100 to get the job done it gets more expensive. And you have to include rest of the costs – the system to fire it, especially the cost of the gun barrel which has a limited life, the weapon mount including power conditioning equipment, the sensors to point it, and the logistics to support it all.

Still cheaper than a missile and simpler to use. A stator round is the slug mass and the bushing carrier. a few dozen bucks per slug. The gun is R&D costs. Fire control is COTS. 

This is a railgun, so barrel life is big problem.  Let’s assume an order of magnitude increase in the number of rounds before replacement, say 50 rounds per barrel.

 More like 200. And the design feature of disposable rails that can be extruded like spent shell casings is one idea that is under review. the "Barrel" is not a barrel. It is more like an open  frame mount for those rails 
 
 
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WarNerd       1/13/2013 5:15:08 AM
The one under current test fires bullets at Mach 8.
 
Think of a large electromagnetic machine gun with bullets traveling at 5600 mph.
And a gun barrel that is damaged beyond use in less than 4 rounds.
The problem is to make sure repulsion forces don't bend the rails. That is why the contact bushing to the rotor (slug) need refinement.  
No, the problem is erosion of the rails by the plasma arc. The contact bushing on the slug is vaporized by the initial power surge to create a plasma arc and the slug is propelled by the resulting plasma arc between the rails.
That will kill ICBM RVs.
At what range? You are limited the accuracy of your gun mount, probably less than 6km.
More like 40 kms altitude. :Predict lead of 8 seconds difference is possible at 5000m/s  The RV can't jerk that much in descent unless you want to miss the carrier task force completely.  
And your CEP at that range is what? Probably in excess of 50m.
 
It is not how about far the gun can shoot, it is about whether or not you have a reasonable chance of hitting the target. The accuracy is limited by the mechanical system for pointing the gun, not the velocity.
 
And I was being generous, 6km is about the limit for engaging a missile with proximity fused rounds. The range limit for slugs that require a direct hit is much less.
Missiles have much longer effective ranges because the accuracy does not drop off.
 Hmmm. Missiles have an absolute upper bound in the lower atmosphere of Mach 10 (cylinder lift) before you have control problems, huge ones.
Again, it is accuracy, not velocity, that determines effective range.
 
Bullets are cheap. Electricity is plentiful and easy to modulate. A gun is point and shoot. Missiles are expensive, have steer and  speed dropoff problems after burnout, and run out of supply too soon.
1 bullet may be cheap, but if it takes 100 to get the job done it gets more expensive. And you have to include rest of the costs – the system to fire it, especially the cost of the gun barrel which has a limited life, the weapon mount including power conditioning equipment, the sensors to point it, and the logistics to support it all.
Still cheaper than a missile and simpler to use. A stator round is the slug mass and the bushing carrier. a few dozen bucks per slug. The gun is R&D costs. Fire control is COTS.
This is a railgun, so barrel life is big problem.  Let’s assume an order of magnitude increase in the number of rounds before replacement, say 50 rounds per barrel.
Again, it is accuracy, not speed, that determines effective range.
 More like 200. And the design feature of disposable rails that can be extruded like spent shell casings is one idea that is under review. the "Barrel" is not a barrel. It is more like an open  frame mount for those rails 
Where do you get that 200 round figure from? They just managed to fire 2 rounds in succession from the beast.
 
Correct, the ‘barrel’ is not a barrel. Have you come across another (practical and easy to remember) word that describes rail, framework, and bracing assembly? If not, then let’s just stick with ‘barrel’ for now.
 
Yanking a pair of white hot metal bars probably 6m+ long out of the barrel, shoving another cold pair in and then obtaining a firm seating and alignment so the gun doesn’t blow up in your face in under a minute? That is going to be a major technology breakthrough, and I am not talking just about railguns. Small wonder they are only talking about the possibility.
 
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WarNerd       1/13/2013 5:26:39 AM
Your numbers are a wee bit off for a Mach 10 system, about one order of magnitude effective range for an IRBM threat (60 kms slant.). FCS will be a little more expensive as you need two radars and a really good computer for a 3-d trajectory solution for predict lead in real time, about $65 for a firing battery of two guns, not including  the bullets to cover one engagement hemisphere 30 kms in radius.. 
I believe that the Iron Dome system has 2 radars. After all, they need accurate impact prediction so they can ignore the projectiles that won’t hit anything ‘important’.
Moral of the story is the same machine that WILL fling F-18s off the flight deck in the next American aircraft carrier class (electromagnetic catapult) which is a RAILGUN (i.e., LINAC) will shoot bullets very fast and very hard..
The electromagnetic catapult is a mass driver, not a railgun. The operating principles and mechanics are very different.
 
I assume your reference to the electromagnet catapult shooting bullets instead of launching aircraft is a typo.
The only problem, in my humble opinion, is the usual problem with artillery, Heat dissipation and barrel (rail) wear.  
Those are the problems with railguns.
 
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Belisarius1234       1/13/2013 11:58:22 AM
1. The predictive lead against an RV at Mach 10 is relatively straight forward. There is not that much of a ballistic problem when you can fairly predict an RV descent path-even as much as eight seconds into the future.
 
2. The primary problem of the plasma-arcing is the same as with any anode-cathode setup; surface pitting. Raul extrusion (cable?) is logical.
 
3. The slug, which is the atator, is the armature of a linear electric motor.  The rails are rails.
 
4. Since you are walking a slug stream into the weapon, can you explain to me how hit-to-kill doesn't work? The same principle that walks a laser into a missile is at work here.
 
5. If we do need a fragmentation option then lets us try an experiment. Run an RV into a cloud of aluminum dust at Mach 10 and let's see what happens to the missile warhead? That experiment should yield some useful data on what kind of 'sand' we might need our sabot to carry if we have a miss profile and if we have to use a BB cloud option.
 
Just some suggestions and observations.
 
B.
 
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WarNerd       1/13/2013 9:23:27 PM
1. The predictive lead against an RV at Mach 10 is relatively straight forward. There is not that much of a ballistic problem when you can fairly predict an RV descent path-even as much as eight seconds into the future.
The problem is not predicting the path of the RV or calculating the lead. The problem is your shots are scattered all over the place at that range.
2. The primary problem of the plasma-arcing is the same as with any anode-cathode setup; surface pitting. Raul extrusion (cable?) is logical.
Cannot find any references to “Raul extrusion”. Can you supply one? And what is it about (cable?)?
 
The problem is nothing like an anode-cathode setup. This is a “make-and-break” problem similar to the contacts in high power switches and relays. The voltages involved are modest, but the current is millions of amps, if short lived.
3. The slug, which is the atator, is the armature of a linear electric motor.  The rails are rails.
”atator”? Do you mean armature? Or stator?
4. Since you are walking a slug stream into the weapon, can you explain to me how hit-to-kill doesn't work? The same principle that walks a laser into a missile is at work here.
A laser does not generate recoil that cause the projector to vibrate and even whip, dispersing the shots.
 
”Walking a slug stream into the weapon” requires a high rate of fire, the ability to determine the miss direction, and the ability to incorporate the results into the gun laying solution. Railguns do not have high rates of fire (the Navy is trying for 2 rounds/minute). You can probably track the projectile and target for the miss data. The insurmountable problem is that the weapon’s aiming mechanism’s inherent limitations on accuracy at 40km give you’re a CEP > 40m.
5. If we do need a fragmentation option then lets us try an experiment. Run an RV into a cloud of aluminum dust at Mach 10 and let's see what happens to the missile warhead? That experiment should yield some useful data on what kind of 'sand' we might need our sabot to carry if we have a miss profile and if we have to use a BB cloud option.
Aluminum dust? Probably no significant effect. Try 10gm. heavy metal (tungsten or uranium) fragments instead.
 
Producing or dispensing those fragments will be tricky. A railgun exposes the projectiles to a big pulse of EMP when it is fires, so electronics and most explosives are out. Assuming you can come up with a way to disassemble the projectile in flight you will need a mechanical timing mechanism to activate it that can withstand more than 100,000 g’s and still be accurate to within 1 millisecond to get the burst in the right area (± 5 meters). They are being rather tight lipped about the research in this area, so the answer is probably no.
 
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Belisarius1234       1/14/2013 11:34:46 AM
1. Water droplets, alone, hit at Mach 10 would have profound kinetic effects on the solid that hit them. Aluminum sand would have a severe charge effect as well.
2. Rail, stator, armature.
3. Do you mean left-right scatter, or up-down scatter for the bullet stream? 
4. Pitting. That armature sparks as it moves down the rails. That is not just a simple contact short. The magnetic fields rotate.  
 
B.
 
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WarNerd       1/14/2013 7:48:53 PM
I think that we have a communications problem here. Your remarks frequently indicate that you are referring to a design generally classified as a mass driver, or electromagnetic catapult, not a rail gun.
1. Water droplets, alone, hit at Mach 10 would have profound kinetic effects on the solid that hit them. Aluminum sand would have a severe charge effect as well.
You said dust, I assumed similar to that used for paint pigment. Of course much larger sand size particles of aluminum would do more damage to the surface, but are unlikely to penetrate much because they vaporizes on impact. A multi-gram chunk of heavy metal, on the other hand, will punch deep into the weapon.
2. Rail, stator, armature.
So which is it? And what was the cable reference to?
3. Do you mean left-right scatter, or up-down scatter for the bullet stream? 
Both.
 
A railgun will have the same CEP as a normal gun in still air at that range. This is not a function of velocity, but of the inherent limitations of the gun training mechanism. You can get around it only by using guided projectiles. Yes, wind drift is reduced by the higher velocity, but since we a talking about a series of shots with feedback from tracking each shot that will not be a factor after the 1st shot.
4. Pitting. That armature sparks as it moves down the rails. That is not just a simple contact short. The magnetic fields rotate.  
It is a lot more than sparks, papers on the subject say the surface of the rail is shows signs of repeated melting. The expulsion of vaporized rail material from the muzzle is a safety and environmental concern. One of the biggest problems was the tendency of the projectile to weld to the rails, which was overcome by using a plasma arc for propulsion, but which damages the rails directly.
 
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Belisarius1234       1/15/2013 9:35:13 AM


I think that we have a communications problem here. Your remarks frequently indicate that you are referring to a design generally classified as a mass driver, or electromagnetic catapult, not a rail gun.


1. Water droplets, alone, hit at Mach 10 would have profound kinetic effects on the solid that hit them. Aluminum sand would have a severe charge effect as well.


You said dust, I assumed similar to that used for paint pigment. Of course much larger sand size particles of aluminum would do more damage to the surface, but are unlikely to penetrate much because they vaporizes on impact. A multi-gram chunk of heavy metal, on the other hand, will punch deep into the weapon.
Dust has erosive effects. At those speeds the heat and charge transfer at contact is significant. This deforms the shape of the moving object and its surface insulator properties (specially one that requires a heat and EM shield). BOOM! Even water vapor is a significant contributor.  

2. Rail, stator, armature.


So which is it? And what was the cable reference to?
 
The stator: self-contained unit of the magnetic pick-up, consisting of a permanent magnet, an inductive winding, and the pick-up core; the stator can be a disc-shaped pole piece with stator tooth or a simple pole piece.
 
The rail: is a track guide for the armature. That is all. 
 
The armature: is the slug or the conductive object that carries the slug that completes the LINAC rail-gun electric circuit between the rails.
 
A rail-gun is a linear accelerator that uses rails NOT coils. It IS a mass driver.
 
888888888888888888888888888888888
 
The problem was pitting. 
 
 
B.

3. Do you mean left-right scatter, or up-down scatter for the bullet stream? 


Both.

 

A railgun will have the same CEP as a normal gun in still air at that range. This is not a function of velocity, but of the inherent limitations of the gun training mechanism. You can get around it only by using guided projectiles. Yes, wind drift is reduced by the higher velocity, but since we a talking about a series of shots with feedback from tracking each shot that will not be a factor after the 1st shot.


4. Pitting. That armature sparks as it moves down the rails. That is not just a simple contact short. The magnetic fields rotate.  


It is a lot more than sparks, papers on the subject say the surface of the rail is shows signs of repeated melting. The expulsion of vaporized rail material from the muzzle is a safety and environmental concern. One of the biggest problems was the tendency of the projectile to weld to the rails, which was overcome by using a plasma arc for propulsion, but which damages the rails directly.

 
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Reactive       1/15/2013 12:54:55 PM
Hello H, good to see you're back. 
 
I think the issues pertaining to railgun functionality are largely a question of material science - it's going to be decades before compounds exist that can repeatedly withstand the arcing/erosion present in 40MJ railguns or the projectiles and their required acceleration , it's great to see testbeds being developed but imv expecting to see any useful return on that investment in the near future is futile - decades are needed to get to the point where those energy ranges can be reliably contained - same goes for ITER etc - panacea always seems just another prototype away and that is presumably not something that BAE et al are keen to dispel. 
With regards to application as a MIRV-killer, surely the problem with the mass-driver concept was that with a stream of particles drag was always an insurmountable problem (for objects moving at high velocity with very little mass). 
 
 
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