Kinetic and Thermobaric Munitions

[a_majoor]

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).

 

[FlyingDutchman]

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

 

[GnyHwy]

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.

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.

 

[cupper]

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?)

 

[GnyHwy]

(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.

 

[cupper]

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.

 

[Retired AF Guy]

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 .... 

 

[FlyingDutchman]

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.

 

[a_majoor]

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.

 

[FlyingDutchman]

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?