# Kinetic and Thermobaric Munitions



## GnyHwy (13 Sep 2011)

An even crazier idea.  Check out Project Thor.  Launching tungsten telephone poles from space.  The incoming mass and velocity would likely be similar to a nuke while penetrating 100s of meters into the ground.

Crazy effective idea, but not very practical.  I wouldn't even begin to guess how much a tungsten telephone pole would cost, let alone the cost to get it into orbit.  Suddenly makes the guidance package seem cheap.

http://en.wikipedia.org/wiki/Kinetic_bombardment#Project_Thor


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## cupper (13 Sep 2011)

Looking at thermobaric, is there a system available that would produce an effective result that would be feasible for use by troops on the ground? I know that there are man portable thermobaric weapons out there, but are there arty rounds or tank rounds on the market as well? Or is there a problem with the delivery system that precludes development of a thermobaric round? And failing all of the above, are we left with only thermobaric aerial bombs (guided or dumb) to achieve the best result?


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## vonGarvin (13 Sep 2011)

This is the 9K57 "Uragan" MLRS.  It's a Russian system.  It's very effective, but there is the whole "collateral damage" it can also cause.










Here's  a promo video of it.


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## vonGarvin (13 Sep 2011)

And don't forget the 9K58 "Smerch":


Video


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## cupper (13 Sep 2011)

Cool. I didn't think about the rocket option for arty.

Any thoughts on development of a shell that can deliver a thermobaric payload?


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## McG (13 Sep 2011)

cupper said:
			
		

> Looking at thermobaric, is there a system available that would produce an effective result that would be feasible for use by troops on the ground? I know that there are man portable thermobaric weapons out there, but are there arty rounds or tank rounds on the market as well? Or is there a problem with the delivery system that precludes development of a thermobaric round? And failing all of the above, are we left with only thermobaric aerial bombs (guided or dumb) to achieve the best result?


Back in the Cold War days, the west worked on munitions that killed through frag while the Soviets worked on munitions that killed through blast.
If you look at modern Russian munitions, they have many ways of putting thermobarics on a target.  And, the west is getting into it these days too.


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## GnyHwy (13 Sep 2011)

The main thing with thermobaric or fuel bomb is the volatility of the projectile itself.  It must be soft launched i.e. man portable rocket launcher or rocket artillery.  

It could not withstand the pressures of the inside of a gun (tank or arty barrel).


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## McG (13 Sep 2011)

I don't know about fuel-air bombs.  However, thermobaric should be fine for a gun launch- it is HE doped with an incendiary.


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## AmmoTech90 (13 Sep 2011)

MCG said:
			
		

> I don't know about fuel-air bombs.  However, thermobaric should be fine for a gun launch- it is HE doped with an incendiary.



Errr. Not quite.  It is an explosive that has a composition (normally more fuel, as in the fuel part of fuel/oxidizer mix) so that it produces a longer and usually higher pressure impulse.  Generally a larger fireball is the result, but this is incidental to the thermobaric effect.  It is not an incendiary as its purpose isn't to set things on fire.
Thermobaric weapons are more effective in some cases than straight HE, but it is just another tool in the box.  In some cases a thermobaric weapon would produce less damage than an fragmenting HE round.  Pressure drops off a hell of a lot faster than fragmentation so in an open field it would be less effective.


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## cupper (14 Sep 2011)

Thucydides said:
			
		

> (Just as an aside, the jet of a HEAT round is moving at @ Mach 25, which is similar to the speed of a deorbiting projectile proposed in the THOR project. When you consider the damage a few ounces of metal moving at that speed can do, then scale it up to dozens or hundreds of kilograms [tactical THOR penetrators are supposed to be small, the size of broom handles, while the strategic ones that can penetrate missile silos and deep bunkers are indeed the size of telephone poles] the effects will be dramatic, to say the least).



I would dare say that the energy release upon impact would rival a small low yield nuke.

A show I watched recently about the Tunguska event in the early 1900's discussed several theories, one of which was a small asteroid perhaps several dozen meters in diameter which air burst with an equivalent energy release of 10 to 15 Megatons.


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## BadEnoughDudeRescueRonny (15 Sep 2011)

cupper said:
			
		

> I would dare say that the energy release upon impact would rival a small low yield nuke.
> 
> A show I watched recently about the Tunguska event in the early 1900's discussed several theories, one of which was a small asteroid perhaps several dozen meters in diameter which air burst with an equivalent energy release of 10 to 15 Megatons.



I just read up on the Tunguska event on Wikipedia and some estimates go even as far as 30 megatons. 



Also, I used an online kinetic energy calculator to estimate the kinetic energy of a 600 kg THOR rod traveling at 10,000 m/s (THOR researchers state that the projectiles would be traveling at a rate of at least 9000 m/s).
Here was the result (in joules):

*30 000 000 000 joules* (or 30 gigajoules) of energy   (by comparison a 120 mm APFSDS-T exerts about 13 000 000 j.)

I did another conversion and this was equivalent to far less than a kiloton in explosive yield! I was puzzled about this at first and then I realized that none of these conversions take into consideration the sheer damage and shock waves exerted by something with that much potential kinetic energy hitting the ground or a target since energy is dissipated upon impact. However, about 4 gigajoules has the same explosive energy as a ton of TNT. So a 600 kg THOR rod would have the explosive power of 4.5 tons of TNT PLUS an insane amount of kinetic energy.


But then I thought some more, the 30 gigajoules of energy is only about 2300 times more powerful than a 120 mm sabot projectile, which doesn't make sense considering the higher mass and velocity of the THOR projectile, not to mention the thermal energy generated by its re-entry into the atmosphere. My only guess is that increases in kinetic energy are exponential and not linear and that the thermal energy of re-entry are the factors that would contribute to THOR's conceptual destructive capabilities. 

*EDIT: I did some more research and found out that increases in kinetic energy are quadratic (x^2), not exponential and certainly not linear as I had originally guessed. This means that a 600 kg THOR rod would be 5 290 000 times more powerful than a 120 mm sabot round *

Just my guess  .


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## lethalLemon (15 Sep 2011)

All of this math and talk of projectiles and explosives and tanks is making me giddy like a school girl at a Backstreet Boys Justin Bieber concert.

EDIT to add:



			
				BadEnoughDude said:
			
		

> *EDIT: I did some more research and found out that increases in kinetic energy are quadratic (x^2), not exponential and certainly not linear as I had originally guessed. This means that a 600 kg THOR rod would be 5 290 000 times more powerful than a 120 mm sabot round *



Why, why must you do this to me? Physics alone gets me all worked up, then you toss in explosions and military use... I'd kiss ya, if that was my kind of thing :rofl:

Anyway, the only problem with orbital kinetic weaponry is atmospheric reentry. Like Space Shuttles and those lander/return pods from rockets, the weapon and its targeting system will be subject to Planar/Debye (Plasma) Sheath. This presents a huge problem if they want to guide the weapon/munition even after it's been launched (like radio/video guided missiles and bombs), they targeting system will go blind. You have ions slamming against it at such insane velocities, electrons being reflected - trying to transfer from plasma state to solid state, it creates and an electrostatic field A.K.A. electrostatic shielding (basically acts as a localized EMP). So from Satellite to atmosphere, you know what your target is, where it is, and you are confident that the munition will strike. From atmosphere to target, you can hope that you hit your target. This would be especially frustrating for firing at moving targets - it moves, the munition will just kill a whole lot of evil rock/sand/water. There's also the risk that the munition will melt before it even reaches the target - so unless you build each sabot out of the materials that shuttles/satellites/pods are made out of (or something less expensive but will do the job, because you don't want to bankrupt the nation after one use), then your attempts are futile.


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## AmmoTech90 (15 Sep 2011)

BadEnoughDude said:
			
		

> I did another conversion and this was equivalent to far less than a kiloton in explosive yield! I was puzzled about this at first and then I realized that none of these conversions take into consideration the sheer damage and shock waves exerted by something with that much potential kinetic energy hitting the ground or a target since energy is dissipated upon impact. However, about 4 gigajoules has the same explosive energy as a ton of TNT. So a 600 kg THOR rod would have the explosive power of 4.5 tons of TNT PLUS an insane amount of kinetic energy.



Unless an item has an energetic filling the only energy you have to worry about is kinetic.  I think you should re-exmine your math.  The factor that increases exponentially is the velocity.


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## a_majoor (15 Sep 2011)

The formula is KE=1/2MV^2

Specific calculations about THOR depend on other factors like the angle of approach and if the penetrator is stabilized at some arbitrary velocity before impact, but in general the entire effect of THOR is the energy of impact, there is no warhead or explosive payload.

I recall the tactical THOR was supposed to have a nose cap of the same protective material used on the Space Shuttle, which would eject and expose the sensor after re-entry. Small pop out tabs at the rear would guide the penetrator to the target. For the most part, THOR was designed to be targetted at either fixed targets (a shower of small ones over an airfield or harbour, big ones at bunkers and missile silos) or slow moving ones like ships at sea. If the technology had been developed in the 1980's as planned, it may have been refined to the point a troop on the ground could attack a hard point by calling down a THOR today, but given the cost and factors like how big the constellation in orbit was (which defines how many THORs are in orbit and how long it takes for a satellite to come overhead), THOR would be a strategic/operational weapon rather than a tactical one.

For anyone who can work the math backwards, Jerry Pournelle once wrote that a single THOR projectile (broom handle sized) would hit with the energy of 250 kg of TNT, which should define the size and velocity...


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## lethalLemon (15 Sep 2011)

Thucydides said:
			
		

> The formula is KE=1/2MV^2
> 
> Specific calculations about THOR depend on other factors like the angle of approach and if the penetrator is stabilized at some arbitrary velocity before impact, but in general the entire effect of THOR is the energy of impact, there is no warhead or explosive payload.
> 
> ...



Such amazing stuff, I love it.


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## Retired AF Guy (15 Sep 2011)

Just something I put together. The source material is from 1982, so some of it may out of date. Enjoy. Any typos or formating mistakes are mine.


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## McG (15 Sep 2011)

The direct comparison of kinetic energy, chemical energy and nuclear energy is misleading.  These do not have the same terminal effects (heck, even within each energy category, engineers can design different terminal effects) and the energies are dissipated into the target & surrounding area differently.

Even assuming all KE was dumped into the target (no element of the penetrator remained having passed though to bury deeper in the ground or ocean), the direct comparison of energy does not work.  While I have no doubt the THOR concept could sink a warship, destroy an in-ground missile silo, or obliterate a skyscraper - there is no direct mathematical comparison to a nuclear weapon or mass of HE.


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## AmmoTech90 (15 Sep 2011)

MCG said:
			
		

> The direct comparison of kinetic energy, chemical energy and nuclear energy is misleading.  These do not have the same terminal effects (heck, even within each energy category, engineers can design different terminal effects) and the energies are dissipated into the target & surrounding area differently.
> 
> Even assuming all KE was dumped into the target (no element of the penetrator remained having passed though to bury deeper in the ground or ocean), the direct comparison of energy does not work.  While I have no doubt the THOR concept could sink a warship, destroy an in-ground missile silo, or obliterate a skyscraper - there is no direct mathematical comparison to a nuclear weapon or mass of HE.



Agreed, quoting things like joules in no way gives an accurate picture of the terminal effects.  The terminal effects are going to be very different if the munition hits a peat bog, sand dune, or skyscraper.

And just because a factor in an equation is squared does not mean it is a quadratic equation.


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## GnyHwy (15 Sep 2011)

Thucydides said:
			
		

> THOR would be a strategic/operational weapon rather than a tactical one.



I have no doubt about this.  We would need to come up with a new classification of target.  SDHVT (super-duper high value target).


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## cupper (15 Sep 2011)

AmmoTech90 said:
			
		

> And just because a factor in an equation is squared does not mean it is a quadratic equation.



Actually it does. Just that the coefficients of the X1 term = 0, and the constant = 0.


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## BadEnoughDudeRescueRonny (15 Sep 2011)

It seriously doesn't get any better than a discussion about the physics of a conceptual weapon  ;D.

AmmoTech90, is there any way to determine the terminal effects of a projectile besides the properties of whatever it hits? I agree that using joules to measure the force doesn't really describe anything in terms of effects and that's what I had the biggest issue with. It just seemed to me to be a number without any real meaning, which is why I tried converting it to explosive force values to try to make a guess as to the damage a THOR projectile could inflict.

 Can you ever gauge a projectile's terminal effects based purely upon its kinetic energy value?


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## GnyHwy (15 Sep 2011)

Perhaps think of it in terms of how far it can penetrate cement or steel.  I recall an equation similar to the KE formula, but the length of the projectile gets multipled into it as well.

I'll have look for it tomorrow.


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## GnyHwy (15 Sep 2011)

Found it.

For hyper velocity greater than 1200m/s. (Mach 3.5)

Penetration (P)=Length (L) x sqrt(density of penetrator(Dp)/density of target (Dt).  

P=L x sqrt(Dp/Dt).

Simply put, the length has alot to do with it but once the length to width ratio is greater than 7:1, it must be fin stabilized.

Not sure how that would be scaled up for higher machs in the teens.  It may not even matter.


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## cupper (15 Sep 2011)

Found this which goes into similar concepts while using the example of an asteroid colliding with earth.

http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/chapters%20(old)/1-Explosions.htm

/RANT
Also, I hate to pick nits, but can y'all stop using the word cement, when you mean concrete. I apologize for making an issue of it, but as a structural engineer it drives me around the bend when people call concrete cement. Point of fact, cement is a constituent of concrete, along with sand, crushed rock, water, and other chemicals. 
/rant.


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## GnyHwy (15 Sep 2011)

This reminds me of the bunker busters that were used in the first gulf war.  They were tank barrels with guidance systems attached.

UFI.  The time from conceiving the requirement to the time that the first one was dropped in operations was 3 weeks.  Kinda beats our procurement system.


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## vonGarvin (16 Sep 2011)

GnyHwy said:
			
		

> This reminds me of the bunker busters that were used in the first gulf war.



Were the bunkers _cement_ bunkers?


 >


(Apologies, cupper)


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## Franko (16 Sep 2011)

GnyHwy said:
			
		

> This reminds me of the bunker busters that were used in the first gulf war.  They were tank barrels with guidance systems attached.
> 
> UFI.  The time from conceiving the requirement to the time that the first one was dropped in operations was 3 weeks.  Kinda beats our procurement system.



Try to keep some perspective here.

When you have a defense budget of almost $400 billion and a President that wants someone dead, you get shit like that when you want it.

Regards


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## Petard (16 Sep 2011)

GnyHwy said:
			
		

> This reminds me of the bunker busters that were used in the first gulf war.  They were tank barrels with guidance systems attached.
> 
> UFI.  The time from conceiving the requirement to the time that the first one was dropped in operations was 3 weeks.  Kinda beats our procurement system.



A position awaits you on the ATWO, and an empty chair in DLR 2


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## GnyHwy (16 Sep 2011)

My procurement comment was meant with humour.  I have a fair grasp of what the procurement process entails and can appreciate the efforts that are involved.   

Some excellent examples of Canadian procurement would be the 777s and Leo 2s;  some of the pers kit that people hate wearing were excellent choices as well.  

Just to be clear, none of the above is sarcasm.

Cheers.


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## cupper (16 Sep 2011)

Technoviking said:
			
		

> Were the bunkers _cement_ bunkers?



Only if that's what they stored in it. :rofl:



			
				Technoviking said:
			
		

> (Apologies, cupper)


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## GnyHwy (16 Sep 2011)

Petard said:
			
		

> A position awaits you on the ATWO, and an empty chair in DLR 2



Ok, sounds good.  When should I expect my message?  ;D


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## a_majoor (16 Sep 2011)

From Wikipedia (yes, I know....)

http://en.wikipedia.org/wiki/Kinetic_bombardment



> *Project Thor*
> 
> Project Thor is an idea for a weapons system that launches kinetic projectiles from Earth orbit to damage targets on the ground. Jerry Pournelle originated the concept while working in operations research at Boeing in the 1950s before becoming a science-fiction writer.[1][2]
> 
> ...



(a 100kg projectile travelling at 7km/s would release about 2.5 gigajoules of kinetic energy, a tonne of TNT releases about 4.2 gigajoules)

The only comperable weapon would be hypervelocity railguns, such as the 42 Megajoule weapon being developed by the USN. Similar terminal effects can be calculated, including the idea of projectiles descending at high angles from near space trajectories...


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## GnyHwy (16 Sep 2011)

I just did it with the size of a real telephone pole.  I used 12m with a radius of 0.2m =  1.5 Sq metres ish.  With pure tungsten, that brings it in at about 18000 kg.  

This would produce 860,000,000,000 joules  or 860 gigjoules.

Wow, this is geeky.

Also, I did the penetration calculation with a 12m pole.  I couldn't find the density of cement.. er I mean concrete, so I used pure iron.

A 12m tungsten rod will pentrate 19m of pure iron.  I know 19m may not seem like a lot, but it is iron and chances are, the guys behind the iron would probably be a little unhappy.


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## cupper (17 Sep 2011)

FYI, concrete has a density of about 150 lb/cuft or 2400 kg / m3.


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## a_majoor (17 Sep 2011)

GnyHwy said:
			
		

> This reminds me of the bunker busters that were used in the first gulf war.  They were tank barrels with guidance systems attached.
> 
> UFI.  The time from conceiving the requirement to the time that the first one was dropped in operations was 3 weeks.  Kinda beats our procurement system.



Actually, I think they were surplus naval cannon barrels from 6" guns. Test articles were filled with concrete, and were able to penetrate test bunkers dug deep in the Nevada desert (including, I recall, ones which were made of reinforced concrete and surrounded by layers of gravel and earth to dissipate shock waves). 

Regardless, this was a very fast procurement and development project, and certainly a refreshing contrast to the process that takes a decade to develop and issue a new rucksack to the troops...


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## BadEnoughDudeRescueRonny (17 Sep 2011)

GnyHwy said:
			
		

> I just did it with the size of a real telephone pole.  I used 12m with a radius of 0.2m =  1.5 Sq metres ish.  With pure tungsten, that brings it in at about 18000 kg.
> 
> This would produce 860,000,000,000 joules  or 860 gigjoules.
> 
> ...



Definitely not geeky, IMO. More like pure outstanding when an Army forum is talking about the physics of experimental weapons. 


I got such a kick that a thread went from discussing the differences between two types of proven existing weapons technology to the physics of technology that doesn't even exist (yet)  ;D ;D ;D.


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## SeaKingTacco (17 Sep 2011)

Thucydides said:
			
		

> Actually, I think they were surplus naval cannon barrels from 6" guns. Test articles were filled with concrete, and were able to penetrate test bunkers dug deep in the Nevada desert (including, I recall, ones which were made of reinforced concrete and surrounded by layers of gravel and earth to dissipate shock waves).
> 
> Regardless, this was a very fast procurement and development project, and certainly a refreshing contrast to the process that takes a decade to develop and issue a new rucksack to the troops...



8 Inch Barrels, left over from WW2.


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## Nfld Sapper (17 Sep 2011)

cupper said:
			
		

> FYI, concrete has a density of about 150 lb/cuft or 2400 kg / m3.



A normal weight concrete weighs 2400 kg per cubic meter or 145 lbs per cubic foot (3915 lbs per cubic yard). 

The unit weight of concrete (density) varies depending on the amount and density of the aggregate, the amount of entrained air (and entrapped air), and the water and cement content.


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## Fishbone Jones (17 Sep 2011)

*THIS WAS POSTED BY RETIRED AF GUY AND MOVED HERE TO THE PROPER THREAD*



			
				Thucydides said:
			
		

> From Wikipedia (yes, I know....)
> 
> http://en.wikipedia.org/wiki/Kinetic_bombardment
> 
> ...



Since the projectile is being launched from outside the earth's atmosphere wouldn't there be a problem with the projectile burning-up on re-entry?


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## cupper (17 Sep 2011)

NFLD Sapper said:
			
		

> A normal weight concrete weighs 2400 kg per cubic meter or 145 lbs per cubic foot (3915 lbs per cubic yard).
> 
> The unit weight of concrete (density) varies depending on the amount and density of the aggregate, the amount of entrained air (and entrapped air), and the water and cement content.



I was quoting the generally accepted value used when doing structural calculations. My experience in the precast concrete industry has been that a "normal" concrete mix design can vary from 145 to 165 lb/cuft, particularly depending on the method of placement. I did tests of precat pipe that used a no slump dry cast mix used in a process called vibration under pressure. We took core samples along the pipe section and found that cores taken from the top end of the pipe (was cast vertically in the machine) were around 150, but one of the samples taken we got 165 lb / cuft.

We also made ballast mats to cover under water gas pipe lines which used iron ore (hematite) and steel shot as aggregate. In order to be accepted by the purchaser, the relative density needed to be 4.8 or greater (300 lb/ cuft or 4800 kg/m3 )


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## a_majoor (19 Sep 2011)

recceguy said:
			
		

> Since the projectile is being launched from outside the earth's atmosphere wouldn't there be a problem with the projectile burning-up on re-entry?



THOR projectiles were supposed to be protected by a layer of the same sort of material as used to protect the Space Shuttle. Once the projectile re entered the atmosphere and reache a stable velocity (say Mach 10), the nose cap would be jettisoned and the seeker exposed, while control tabs in the rear also popped out to provide final guidance. While the proponents of THOR tried to sell these as "flying crowbars", in actuality there were several fairly sophisticated systems attached to the metal projectile (or possibly inside; I think at least one proposal had the penetrator in the form of a hollow tube with the seeker, computer, control electronics and battery inside. It is kind of hard to imagine any other configuration that would survive reentry).


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## FlyingDutchman (19 Sep 2011)

How deep would one have to be underwater to not worry about one of these?


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## GnyHwy (19 Sep 2011)

recceguy said:
			
		

> *THIS WAS POSTED BY RETIRED AF GUY AND MOVED HERE TO THE PROPER THREAD*
> Since the projectile is being launched from outside the earth's atmosphere wouldn't there be a problem with the projectile burning-up on re-entry?



Tungsten does have the highest melting point for pure elements (except for carbon), but that doesn't address how to protect the guidance system.



			
				FlyingDutchman said:
			
		

> How deep would one have to be underwater to not worry about one of these?



On the wiki page for tungsten it says tungsten is 19.3 times denser than water so using the calculation on page one of this thread; that would be the sqrt of 19.3 (4.39) multiplied by  the length of the penetrator.  

So a 10m penetrator would go through 43.9m of water.


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## cupper (19 Sep 2011)

But how much of a pressure wave would that propagate for impact on a target below that depth? Obviously the pressure would dissipate the further away the target was from the point of impact with the water or the point where the penetrator velocity reaches zero, but would there be an optimum depth where it would still deliver damage to say an SSBN without making physical contact?

(am I the only one who has a problem with the spell check when typing penetrator?)


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## GnyHwy (19 Sep 2011)

cupper said:
			
		

> (am I the only one who has a problem with the spell check when typing penetrator?)


No, you're not.  Spellchecker doesn't recognize it.  I guess it's not a word.

As for your question, I am not sure it would have much force below at all.  The streamline of the bullet would produce minimal friction in order to penetrate, therefore causing little disruption.  Kind of like an olympic diver with a perfect dive.

I recall a Mythbusters episode that tests against projectiles going through water.  Water has some weird properties and dissipates the energy really well.  If I remember correctly, a shotgun blast penetrated deeper than a .50 cal. and the .50 only penetrated a couple feet (that was at a angle). I was waiting for an explanation but they never gave one.  Perhaps someone with a better memory of the show can correct me.


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## cupper (19 Sep 2011)

GnyHwy said:
			
		

> No, you're not.  Spellchecker doesn't recognize it.  I guess it's not a word.
> 
> As for your question, I am not sure it would have much force below at all.  The streamline of the bullet would produce minimal friction in order to penetrate, therefore causing little disruption.  Kind of like an olympic diver with a perfect dive.
> 
> I recall a Mythbusters episode that tests against projectiles going through water.  Water has some weird properties and dissipates the energy really well.  If I remember correctly, a shotgun blast penetrated deeper than a .50 cal. and the .50 only penetrated a couple feet (that was at a angle). I was waiting for an explanation but they never gave one.  Perhaps someone with a better memory of the show can correct me.



Saw that same one. In the back of my mind I thought the same thing. But for some reason I was stuck on the projectile to have a flat surface rather than an aerodynamic cross section which really would  make no sense at all.


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## Retired AF Guy (19 Sep 2011)

GnyHwy said:
			
		

> I recall a Mythbusters episode that tests against projectiles going through water.  Water has some weird properties and dissipates the energy really well.  If I remember correctly, a shotgun blast penetrated deeper than a .50 cal. and the .50 only penetrated a couple feet (that was at a angle). I was waiting for an explanation but they never gave one.  Perhaps someone with a better memory of the show can correct me.



Ask and You shall receive:



> They finally broke out the big gun, the .50 cal with armor-piercing rounds, which are shot at 3000 ft/s.
> 
> Adam: "Hopefully we'll be gone before the pool fully drains"
> 
> .50 cal @ 10 ft: even though the water exploded, the ballistics gel was intact. Water made it all the way up to the ceiling. As it was with the previous guns, the bullet round came apart on impact. It lost all of it's energy within the first 3 ft. You would be safe 14" underwater at a 23 angle from a .50 cal.



 Link. 

I remember watching the episode and I'm pretty sure they gave an explanation regarding their findings.  

A little off-topic, here is  link  to a clip from next weeks Mythbusters premiere that involves firing a RPG-7 rocket launcher (click on RPG 101} against a simple wooden trailer. Definitely not like you see on TV/movies.  For those who have been on the receiving end ....


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## FlyingDutchman (20 Sep 2011)

Mythbuster bullet explination: If I remember correctly it has to do with the mass of the object (bullets are small) compared with the speed it was travelling (very high) and surface tension (shot gun blast went farther due to the surface tension being disturbed by multiple objects.). Please feel free to correct me if I am wrong.


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## a_majoor (20 Sep 2011)

The simple explanation is water is @ 800X denser than air; the bullet decellerates suddenly and violently. The copper jacket gets torn off and the internal filler disintigrates (especially the soft lead in a conventional bullet). Most AP rounds that I know about have two or more parts to the internal composition, including the steel or alloy penetrator, ballistic "filling" to give the bullet its shape and so on, all of which is subject to massive forces of decelleration and yaw as the bullet violently upsets from the spin imparted by the rifling....

Just to add more fun to the mix; the former USSR had underwater "guns" for their Spetsnaz divers that fired what looked like steel darts, and several nations are experimenting with "supercavitating" projectiles which can move through the water even when fired from a weapon above the surface. Science and technology run wild.


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## FlyingDutchman (20 Sep 2011)

Yeah, for those who found my explination lacking, what he said.  Those soviet under water guns were just a heavily modified version of a spear gun, right?


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