Defense against railgun fire?

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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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Reactive Re: 10/7/2010 12:38:47 PM

I'm not trying to be overly pessimistic, these things might well be commonplace in 2030 or 2040, i'm just saying in terms of a high velocity naval gun, there are more conventional, and applicable ways of skinning the cat... And again, none of this would matter except that R&D budgets often work to the detriment of other programs.

I think we're on the same page here.

my first view of anything is tactical need and imperative, then utility.

at a niche level then arguments can start to be made on LOS vignettes such as NGFS... but outside of this I'm not convinced that the time is right for railguns to have a significant role in a force artillery related model.

Me either !

there are better cats to skin to achieve the mission requirements. one then has to consider all those other techs which are undergoing parallel development, eg multi-stage hypersonics in a PGM artillery role will be steered and vectored to a range of targets within the field of opportunity. LOS railguns have a limitation already, and if the mantra for all weapons systems is about capacity to develop from initial concepts, the the railgun has some substantial limitations compared to other available solutions. some of which are further down the track.

That's definitely true - PGM developments are needed for almost all the options listed, it's possible they'll be the weak link in the chain - I think railguns when truly mature technology will be the system of choice - but there's going to need to be real developments in whole host of technologies that in my view will likely come from far larger funding sources - i..e. for a few hundred million dollars I don't see it as a likelihood that there'll be an end result that is fieldable, or within view of being fieldable - my guess is that it will be another programme cancellation at around 2015 and reinvented when materials science and plasma control models catch up with what they're trying to do.

i'm ecercising the privilege of temporal flux here, so things naturally could shift by 2030...

Absolutely, and I also appreciate there are probably many people inside this particular field of study who are far more informed about specific developments than I could hope to be, I guess what I'm doing is trying to outline just how far beyond currently predictable modelling a railgun is, plasma is hard or impossible to model, it all requires a lot of experimentation, if we can, in the near term use a solution that can hit 56MJ that is nearly mature (that is making an assumption based on the fact that the modelling required is fairly elementary compared to plasma for example) (and for an 18KG projectile the difference between 56MJ (CLGG) and 64MJ (for the railgun) is a paltry 166m/s increase in velocity!! (from 2500m/s to 2666m/s) then lets accept the long term limitations of chemical propellants and settle for something that can still fire out to 217 nautical miles.

I'm sure there are several practical limitations that I'm not aware of for the CLGG as an example, i'm not touting it as a cure-all system, but the fact that after minute levels of funding a very small (around 35 employees) company was able to demonstrate a system that not only had the required range, but was also able to demonstrate that the combustion process was consistent and predictable (see document posted earlier) and could replenish all of its own propellants in a timely fashion from seawater itself suggests to me that that, or similar programmes are fairly mature and could benefit from the sorts of funding pumped in to BAE's railgun programme.

I think the weaknesses in either case are likely to center around the guidance mechanisms and potentially the warhead itself, being limited to a kinetic kill is undesirable whatever mechanism is used, there's a whole range of effects that kinetic projectiles are no good for, they're great for smashing buildings or concrete but are very limited for providing the sort of area effects that artillery is expected to provide, even a flechette round needs fusing and guidance.

The interesting thing about some of the other chemical propellant

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Reactive Re: 10/7/2010 12:48:36 PM

One last question would be whether a railgun projectile could ever house explosive? Given that even insensitive munitions generally have one common mode of detonation : )

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VelocityVector 10/7/2010 4:31:02 PM

One last question would be whether a railgun projectile could ever house explosive? Given that even insensitive munitions generally have one common mode of detonation : )

A military explosive chain detonates the main charge by focusing energy on a small area inside the main charge. Rail gun launch energy would apply to the entire payload volume and at the local molecular level the shock experienced is less than with the explosive chain. Insensitive explosive compositions should be able to handle rail gun acceleration safely. 300k g is pretty dazzling though. 0.02

v^2

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Reactive 10/7/2010 6:48:44 PM

Thank you V2 for your excellent answer.

I am looking at the total energy delivered by the system relative to a TLAM...

I used to have an excellent ballistic calculator that could handle just about anything you put in, and accounted for atmosperic drag at varying altitudes on a ballistic trajectory as well as having a wide range of ballistic coefficient inputs.

This was a few years ago, and I forget the name of it - I can't seem to find it anywhere, (there are lots of small-arms calculators which are of little use) if anyone has any ideas please let me know, and the relevance is as follows.

The idea is that the long range naval gun of choice will deliver a slug at a muzzle energy of 64 Megajoules, I'm trying to work out what the energy (assuming kinetic only round) would be at target, I remember reading somewhere that the expected terminal velocity for a streamlined projectile would be ~1500m/s at 200nm which seems optimistic to me given the drag on a relatively flat trajectory, it's quite hard to solve for this manually as atmospheric density (therefore drag) differs radically with altitude.

Anyway, let's assume it's 1500m/s for a moment (and please correct me if I'm way out here) that means the kinetic energy at impact will be 20.25 Megajoules.

Cost for g-hardened guidance and fusing system on this projectile, GPS etc etc, well, lets say total projectile cost is around 50 000 USD

Which gives us a cost of $2469 per Megajoule for our railgun system merely in terms of cost per round if it is kinetic only (not factoring for cost of operation or the gun itself).

Let's assume that our shell comes in much cheaper, 10 000 USD (this is exceptionally unlikely in my view, even a single guided rocket costs more than this without requiring anything like the degree of hardening) $495/MJ delivered to target.

Remember none of these figures include operating/running/build costs for the gun itself, just the projectile cost.

Now we have a TLAM

Ignoring kinetic energy transferred it contains a 450KG warhead, assuming it uses an explosive that has about 1.2 times the power of TNT (conservative) that gives us about 6KJ/G or 6MJ/KG = 2700MJ (2GJ) energy transferred to target from warhead alone. (and not to mention the fact that there's several fusing modes, and the option of submunitions for area effects).

Cost per unit 1M USD, cost per MJ delivered: $370

These figures seem strange, an unguided projectile would be far cheaper but dumb munitions are not much use for most missions given the accuracy errors (i don't believe the CEP at 200nm would be anything like as low as 2-4m)

So I just don't get how it adds up, could someone explain this please?

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Reactive 10/7/2010 6:55:01 PM

One last question would be whether a railgun projectile could ever house explosive? Given that even insensitive munitions generally have one common mode of detonation : )

v^2

Sorry to repost, what I meant was in terms of the high voltage electrical charge flowing through the projectile, I was thinking that it would be very hard to insulate an explosive charge inside a projectile from this current?

Cheers,

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USN-MID 10/7/2010 9:59:04 PM

Anyway, let's assume it's 1500m/s for a moment (and please correct me if I'm way out here) that means the kinetic energy at impact will be 20.25 Megajoules.

Cost for g-hardened guidance and fusing system on this projectile, GPS etc etc, well, lets say total projectile cost is around 50 000 USD

Which gives us a cost of $2469 per Megajoule for our railgun system merely in terms of cost per round if it is kinetic only (not factoring for cost of operation or the gun itself).

Remember none of these figures include operating/running/build costs for the gun itself, just the projectile cost.

Now we have a TLAM

Cost per unit 1M USD, cost per MJ delivered: $370

So I just don't get how it adds up, could someone explain this please?

Well I'm not sure about the wisdom of using Dollars/MegaJoule as the primary means to compare efficacy.

For starters, I'm no expert, but you can look at attacking hardened targets. TLAM relies on warhead blast to generate the pressure needed to crack hardened targets. A high density object coming in at "Mach Ludicrous" with a tip shaped for penetration is ideal to penetrate hardened targets. Its energy will be more efficiently used for its mission than a TLAM.

Of course, roles are reversed for troops in the open in very soft terrain. You want fuzing to detonate rounds before they sink into the mud/gunk and have their blast/frag dampened, and you would need a rail gun with comparatively thin casing, and more explosive, in order to get more frag/blast on the unprotected targets.

There's also targeting. TLAMs are fine for hitting stationary targets, but they are next to useless for a mobile one. In other words, a ground unit needing fire support would much prefer the future rail gun to today's Tomahawk. Not to say of course, that there aren't newer TLAM variants that can't be retargeted, but the response time compared to a gun still isn't as good. When ranking timeliness, conventional artillery and on call CAS are ringside seats, while TLAMs are in the nosebleed section.

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gf0012-aust 10/8/2010 2:18:23 AM

One last question would be whether a railgun projectile could ever house explosive? Given that even insensitive munitions generally have one common mode of detonation : )

although not a rail gun, the principles of metalstorm weapons has close similarities.

I don't see any reason as to why explosive rounds couldn't be used. there's no reason why you couldn't include carriers such as sabots that broke up near termination - not just in the traditional model of exiting the crown.

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doggtag 10/8/2010 9:44:05 AM

.........

(1)

(2)

Anyway, let's assume it's 1500m/s for a moment (and please correct me if I'm way out here) that means the kinetic energy at impact will be 20.25 Megajoules.

(3)

Cost for g-hardened guidance and fusing system on this projectile, GPS etc etc, well, lets say total projectile cost is around 50 000 USD

(4)

(1) "...~1500m/sec @ 200nm..."

Well, you could just as well have an MBT 199nm away and have it shoot something 1nm away and still impact the target at ~1500m/sec...

What I'm getting at is: if you're shooting solid projectiles (slugs, but more likely sabots, as those would be the most aerodynamic long range design), a 1500m/sec impact at any range isn't going to be super spectacular on a target: yeah, MBTs kill each other with sabots all the time, but Desert Storm showed us that some thinner-skinned targets (older generation MBTs), the sabots literally passed cleanly thru without doing much actual damage inside the target, several instances showing the target MBTs needed multiple hits in order to ignite internal fuel and ammo storage for a total confirmed kill.

Point being: kinetic projectiles aren't the best thing for very target out there: you need explosives to do the damage in quite a number of scenarios.

(2) Keep in mind that we need to establish what exactly is the projectile weight, to accurately gauge the correct on-target energy....

(3) Optimistic.

We can't do Excaliburs now for that price.

They currently cost upwards of $100K.

And those are chemical-propellant-accelerated munitions, that don't exit the 155mm gun barrels at anywhere near railgun velocities: AIUI, a 52-cal gun tube like on the PzH2000 can fire an Excalibur at around 1000m/sec to get it to maximum range (over 40km).

(4) Even more optimistic.

The planned PGK Precision Guidance Kit program is/was hoping to get the technology to the point that the actual PGK could be produced for ~ $3000.

If massed produced like many consumer electronics, that could eventually happen.

But so far, that's still pie-in-the-sky best expectations for a program that, much like Excalibur, may easily face a reduced acquisition as numbers are cut to trim budgets.

As favorable as the PGK's capabilities are, it just isn't Big Ticket enough like programs such as the F-35 and LCS.

Even though a majority of our future wars are going to be ground-intensive like we're involved in now: conflicts where the F-35 and LCS won't really be required to make the most of the capabilities they were sold on (or even necessary at all).

As for concerns of muzzle energy of railguns, well,

it's a fair bet ships ever armed with such will never be broadsiding each other like Pirates of the Caribbean style,

and we'd probably save money on the projectile if we instead developed hypersonic missiles that had a smoother acceleration curve on their internal components.

Seeing as it's very doubtful we'll ever need ships with 200nm range railguns with 600round magazine capacity,

for battles where more than likely CAS/UAVs/air support will be available, or at least the USMC and/or Army can land some 155mm artillery and/or HIMARS types,

I'm still trying to wrap my mind around the perceived of weapons such as these railguns.

A nicety, but not a necessity.

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Reactive 10/8/2010 11:09:41 AM

One last question would be whether a railgun projectile could ever house explosive? Given that even insensitive munitions generally have one common mode of detonation : )

although not a rail gun, the principles of metalstorm weapons has close similarities.

I guess the difference at least insofar as I understand it is that the charges in metal storm systems only have to be powerful enough to ignite standard gun/grenade propellants, my thought was that the amount of volts and amps flowing through the projectile in a railgun system (and EM actually acting as the propellant force itself) would essentially be the same sort of current needed to detonate insensitive munitions..

However, I'm quite sure you and V2 have a more complete understanding of the applicable technology than I do and I respectfully submit to that : )

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Reactive 10/8/2010 11:40:22 AM

Well I'm not sure about the wisdom of using Dollars/MegaJoule as the primary means to compare efficacy.

But with the CEP of the round (assuming it's of similar performace to current guide-assist projectiles) being around 50m I find it unlikely that you would be able to reliably hit bunker/c31/radar/emplacement systems with the same sort of comprehensive lethality that you can with accurate high explosive ordnance, yes kinetic rounds are more efficient at penetrating armoured surfaces than high explosives, even HEAT rounds, but I'm not sure that also applies to concrete bunkers/buildings where you are ideally looking for high overpressures over a large area. HESH (high explosive squash-head) ammo on concrete structures is far more effective than APFSDS/HEAT rounds even though the former (HESH) is largely of limited effect against modern MBT's.

And that is something that GF and V2 believe is possible so I guess submunitions etc would also be an option.

I don't think the Railgun projectile is likely to be accuate enough for engaging single moving targets - the next generation gun round being developed by BAE for the zumwalt (DDG) class (LRLAP - long range land attack projectile, they'll never make that acronym roll of the tongue) reportedly has a <50m CEP which is of use for fire support but presumably not precision strikes against hardened or mobile targets, as far as I know it doesn't feature a laser designation mode (only INS/GPS).. . As to timelines, there is as you say a very clear benefit, at 200nm a TLAM will take around 20 minutes to arrive on target.

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