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Subject: Defense against railgun fire?
Habeed    9/24/2010 7:54:26 PM
Facts : the ship mounted 64 megajoule railgun the Navy wants will have a range of ~200 miles. A 32 megajoule prototype already exists, so the idea is less science fiction and more an engineering and integration challenge. The slugs will be guided, using guidance fins and some kind of sensor system. Guided artillery shells have existed for decades, and the electronics inside survive the acceleration just fine. I'm not sure how far along the Navy is in developing the ammunition but I think it can be taken for granted that they can do it. The Navy is planning on taking another decade to actually build ships sporting railguns but this is probably a matter of budget and priorities. If there was a pressing need for such a weapon I think it could be deployed within a few years. Once railguns become practical, would existing defenses work against the slugs? Railgun shots will be moving at several kilometers per second on a ballistic trajectory. They have to contain ferrous metals and will probably have a significant radar cross section (and stealthing them might not be possible with existing materials due to the frictional heat from traveling at mach 7+). Travel through the atmosphere at several kilometers/second would super-heat the projectile making it show up brightly on infrared and maybe even visible light. So you've got this glowing projectile streaking in from above, traveling several times faster than the bullets shot from a CWIS system. How would you defend against it? One last comment : railgun shots would not be able to fly around searching for a target like a missile can. To fire at a ship, you'd need to know it's exact position and possibly paint it with a targeting laser. I'm assuming a swarm of cheap, stealthy drone aircraft would search the seas looking for the enemy ships and act as a spotter. Also, railgun technology scales. Unlike chemical propellants where the explosion velocity limits your projectile velocity, if you throw more hardware into a railgun you can increase it's range and power smoothly and easily. Railguns with the same range as ICBMs are quite practical. I've been thinking that they would allow a nation without a decent Navy to build anti-ship "shore batteries".
 
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mabie       9/24/2010 10:04:27 PM
Offense is the best defense. Railguns are big and heavy.. make nice fat targets.
 
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Das Kardinal       9/25/2010 5:29:28 AM
That and simply denying your enemy the ability to pinpoint your location. It's not use having a 200+nm range munition railgun slug or otherwise) is your target's amoving one and you don't have real time targeting.
Against fixed targets, it's another matter. The pyramids of Gizeh are pretty much unmovable :-D
 
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WarNerd       9/25/2010 6:59:35 AM

Facts : the ship mounted 64 megajoule railgun the Navy wants will have a range of ~200 miles. A 32 megajoule prototype already exists, so the idea is less science fiction and more an engineering and integration challenge.

The slugs will be guided, using guidance fins and some kind of sensor system. Guided artillery shells have existed for decades, and the electronics inside survive the acceleration just fine. I'm not sure how far along the Navy is in developing the ammunition but I think it can be taken for granted that they can do it.
 
The ammunition development is the key element.  Current development seems to be for the GPS guided round only.  There seems to be some question of the ability to find a suitable material for a sensor window on a terminally guided round, including laser homing, and mid course target updates can only do so much.  A GPS only guided round would not be very effective against maneuvering surface targets at long range, as you noted.

Once railguns become practical, would existing defenses work against the slugs?

Railgun shots will be moving at several kilometers per second on a ballistic trajectory. They have to contain ferrous metals and will probably have a significant radar cross section (and stealthing them might not be possible with existing materials due to the frictional heat from traveling at mach 7+). Travel through the atmosphere at several kilometers/second would super-heat the projectile making it show up brightly on infrared and maybe even visible light.

So you've got this glowing projectile streaking in from above, traveling several times faster than the bullets shot from a CWIS system. How would you defend against it?

One last comment : railgun shots would not be able to fly around searching for a target like a missile can. To fire at a ship, you'd need to know it's exact position and possibly paint it with a targeting laser. I'm assuming a swarm of cheap, stealthy drone aircraft would search the seas looking for the enemy ships and act as a spotter.

These projectiles are much smaller than missiles, and therefore harder to hit, but coming in on predictable trajectories.  Destroying the projectile, particularly if you can hit it from the front where its own velocity will increase the effect, should not be to hard.  any significant damage and aerodynamics will tear it apart. 
 
CWIS (20mm) would probably prove ineffective, due to short range, intercepting the projectiles to close to the target to divert or dissipate (by atmospheric friction) the pieces, and low accuracy.  RAM would do better range wise, but require a different warhead and fusing.  A better, but somewhat specialized, system would certainly be designed and deployed before railguns became to too prevalent.
 
But in the end it may come down to barrel life of the rail gun versus the number of interceptors carried to see who wins.  Or whether the defending can take out either of the networks that is providing the targeting data or mid-course corrections to the projectiles.

Also, railgun technology scales. Unlike chemical propellants where the explosion velocity limits your projectile velocity, if you throw more hardware into a railgun you can increase it's range and power smoothly and easily. Railguns with the same range as ICBMs are quite practical. I've been thinking that they would allow a nation without a decent Navy to build anti-ship "shore batteries".

IRBM ranges maybe, ICBM ranges probably not, unless you lob a smart projectile into low orbit and it has a "retro-rocket" to de-orbit it to the target.  It is a matter of trajectories, atmosphere, and materials.  To achieve such long ranges the railgun would have to fire at a lower elevation and the projectile has to survive penetrating more dense atmosphere at the beginning and end of that trajectory. 
 
Immobile "shore batteries" are just targe
 
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Reactive       9/25/2010 9:08:17 AM
'Fraid you're looking at a lot longer than a decade for a railgun system to be put in operation...
 
Rail erosion is a huge concern for railguns  - the current flowing through the slug is several thousand degrees, hot enough to weld just about any conductive metal in thousandths of a second - one jam and your slug becomes a welding rod, your barrel is destroyed.
 
There's a lot of other problems but barrel erosion is the largest - the testbeds made thus far have indeed achieved far higher velocities relative to chemical propellants but they are also going to be far more expensive systems to maintain - in all honesty I think the benefits are somewhat limited until they manage to develop conductive alloys that can resist the temperatures generated in the barrel - the prototypes developed thus far have got a long way to go before they can be fielded operationally, my guess is closer to 20 years to see something that can be used repeatedly - the prototypes developed (however impressive) are still quite primitive testbeds that have yet to demonstrate any ability to fire repeatedly.

None of these problems are insurmountable, but the element of risk remains, if anything goes wrong the barrel is at risk of being rapidly destroyed - much like in the dawning era of ship gunnery when cannons would spontaneously explode as a result of the metallic impurities present in their barrels it will take time to make a system that is reliable and durable, with the increased investment one can only assume this will be in the near future, but don't hold your breath just yet - these systems have been touted as the imminent replacement for ship gunnery and missiles for a long time now.
 
And in respect to cost vs cruise missiles, these would be far cheaper per shot but as has been explained above, very limited in terms of trajectory, persistence and following a flight path that is essentially ballistic, any maneuvering has an energy penalty associated with it, any guidance mechanism has to withstand far higher G-forces than are present in other gunnery systems, my bet is 20 years till an operable system emerges.
 
R
 
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doggtag       9/25/2010 12:57:22 PM

......
The slugs will be guided, using guidance fins and some kind of sensor system. Guided artillery shells have existed for decades, and the electronics inside survive the acceleration just fine. I'm not sure how far along the Navy is in developing the ammunition but I think it can be taken for granted that they can do it.
......
Wishful thinking.
The US Navy has had a difficult enough time creating fieldable (in production) gun-fired precision guided shells since the notions of such PGMs began.
Conceptual gun-fired PGMs were tested coming out of the Mk71 8" MCLWG program (late Viet Nam era/early 1970s),
we saw the Copperhead CLGP fail during the 1980s because it got too expensive,
and half a dozen or more failed attempts at producing a gun-fired guided round for the current crop of 127mm ship guns,
still no in-service LRLAP for the still-not-in-service 155mm AGS for the ill-fated DDG-1000 "destroyers",
and add to that the fact that the USN, and in part the USMC, still haven't made up their minds as to what exactly are the priorities of naval gun fire support,
either as shore target engagement or used against sea borne (or aerial) targets...
 
For me to believe the USN can get built a functional, affordable PGM for rail guns that have considerably greater launch accelerations than any powder-propelled (and rocket boosted) gun-fired rounds,
I first think they need to prove they can get their act together (doctrine and, more importantly, budgeting know-how),
and prove they can do it in the less complex realm of gun-propellant-accelerated PGMs,
because the current ship guns (76-127mm) aren't generating anywhere near the launch stresses
that a 200mile range, high-Mach (6+?)  EM rail gun will,
in addition to the EM shielding needed for a rail gun guided projectile to even survive the launch to begin with...
 
Sorry,
too much wishful thinking on behalf of the USN,...
but it is nice that they are planning ahead for the USN of a half-century from now.
 
(/sarcasm off)
 
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Reactive       9/25/2010 7:13:36 PM
Yeah there's a long way to go - being realistic, the figures invested aren't nearly enough to create a completely revolutionary weapon system, I would guess that what they are doing right now is trying to work out whether the concept itself is actually feasible.
 
As you say, launch stresses will be enormous - to harden advanced seekers/sensors to the degree required will cost a vast amount if it is in fact posssible but so will erosion and heating of the barrel itself -
 
There is also a problem in that most of these systems chemically fire the slug through the barrel in the first place to prevent the slug from being stationary at any given point(and thus welding itself rather dramatically), there's a lot of potential failure modes...

Heat generated both by the vast currents flowing through the system and by friction from the slug's passage adds to the electrical impedence thus the barrel has to be cryogenically cooled somehow, such heating would also cause warping which could then cause jamming (goodbye railgun) or a reduced barrel velocity or overall accuracy, even if these problems can be overcome you still have to find a conductive barrel material that can withstand contact with a slug moving at mach 7+, does such a material actually exist?
 
Overall I'm very skeptical about the near-term possibilities, it seems like there'll need to be numerous developments in materials science, hardened electronics and all of this without mentioning the obvious problem of finding capacitors with good enough performance in the first place.
 
Missiles do the job just fine, they can't go quite as fast admittedly but they have far more options available for endgame.
 
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gf0012-aust       9/25/2010 7:23:19 PM
it seems like there'll need to be numerous developments in materials science, hardened electronics and all of this without mentioning the obvious problem of finding capacitors with good enough performance in the first place.


there's a few developments in the materials science side of the shop.  eg ceramics and titanium diboride. we're already seeing results in hypersonics tests at higher mach speeds.  although the friction and resistance issues are "different" - they're also similar across a number of vectors.

 
 
 
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Reactive    Sure enough...   9/25/2010 8:34:10 PM
"Titanium diboride (chemical formula TiB2) is an extremely hard ceramic compound composed of titanium and boron which has excellent resistance to mechanical erosion. TiB2 is also a reasonable electrical conductor,[1] an unusual property for a ceramic, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining."
 
 
So a conductive ceramic with high heat tolerance and resistance to erosion !
 
Thanks for the tip - I'd heard of it I seem to recall in usage in composite armour but had absolutely no idea it was conductive.. Is this material specifically in use in these sorts of applications or was it just an example of a material with suitable properties.
 
Cheers, 
 
 
R
 
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gf0012-aust       9/25/2010 10:35:52 PM
So a conductive ceramic with high heat tolerance and resistance to erosion ! 

Thanks for the tip - I'd heard of it I seem to recall in usage in composite armour but had absolutely no idea it was conductive.. Is this material specifically in use in these sorts of applications or was it just an example of a material with suitable properties.


no further comment.  :)

but, my last stint in the US (as a private citizen) was rather enjoyable - looking at what they were doing and what we are doing.

hypersonics, plasma boundary layers in ballistics and cavitation in subs all have a common denominator......

 

 
 
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WarNerd       9/27/2010 4:23:32 AM

"Titanium diboride (chemical formula TiB2) is an extremely hard ceramic compound composed of titanium and boron which has excellent resistance to mechanical erosion. TiB2 is also a reasonable electrical conductor,[1] an unusual property for a ceramic, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining."

So a conductive ceramic with high heat tolerance and resistance to erosion !

The electrical conductivity is similar to nichrome resistance wire -- good, not great.  The resistance to thermal shock and impact loads is probably poor given the hardness and the fact that it is a ceramic.
 
Potentially useful, but not the solution itself.
 
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