Reel Physics: GI Joe Retaliation - Tungsten Rod Drop

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guys! next time you use the metric system contractions, please please please do NOT mix 'm' for milli and 'M'for Meaga

>.<

rcs619:
To be fair, the US currently thinks that dropping anti-tank missiles on random people it never even identifies, in nations it isn't even at war with, is a reasonable plan of attack. The only reason we probably don't use kinetic strikes instead of drone strikes is because the technology is currently nowhere near good enough to actually hit an individual (or at least hit with the same accuracy as a hellfire missile) from orbit. But just give it time, the way the US is going, I have to think rod-from-God kill-sats are inevitable.

Well in true fairness the comparison isn't really a proper one. The Hellfire is a tactical weapon intended to be used in (relatively) close ranges to the target letting you hit things that can move and such. The Rods From God system is a strategic weapons system more closely akin to an ICBM or a SLBM. The accuracy of those weapons is actually a lot better then you would think and the R.F.G. would use most of the same principles, gyroscopes and math. To give an analogy of the accuracy of say a Trident III MRV warhead, say you are aiming for the plate on the top of the pitcher's mound at Fenway you will drop the warhead somewhere on top of the mound itself. The problem with this you have to know the exact coordinates of the target and it can't move at all which is way you aim for buildings and such.

DVS BSTrD:

Mouse_Crouse:
Having watched the whole thing, I can safely say I have no idea what the final verdict was. Like I get that the movie went overboard, but by how far? What would the destruction have been? Are we talking a hole the size of a car or a city block?

Then you obviously didn't watch the whole thing.

They never stated what the destruction would be, simply it's relative energy compared to other devices.

ClockworkSailor:

rcs619:
To be fair, the US currently thinks that dropping anti-tank missiles on random people it never even identifies, in nations it isn't even at war with, is a reasonable plan of attack. The only reason we probably don't use kinetic strikes instead of drone strikes is because the technology is currently nowhere near good enough to actually hit an individual (or at least hit with the same accuracy as a hellfire missile) from orbit. But just give it time, the way the US is going, I have to think rod-from-God kill-sats are inevitable.

Well in true fairness the comparison isn't really a proper one. The Hellfire is a tactical weapon intended to be used in (relatively) close ranges to the target letting you hit things that can move and such. The Rods From God system is a strategic weapons system more closely akin to an ICBM or a SLBM. The accuracy of those weapons is actually a lot better then you would think and the R.F.G. would use most of the same principles, gyroscopes and math. To give an analogy of the accuracy of say a Trident III MRV warhead, say you are aiming for the plate on the top of the pitcher's mound at Fenway you will drop the warhead somewhere on top of the mound itself. The problem with this you have to know the exact coordinates of the target and it can't move at all which is way you aim for buildings and such.

I'd compare the R.F.G. more to an artillery piece than a tactical nuke or ICBM. It certainly could be a WMD-grade weapon, but in theory, you could dial the system up for any sort of yield you wanted. Either use smaller rods, or control the amount of juice passing through the mass-driver/railgun that launches it. That's both the big advantage and scary part of the system. If you go to war with someone that doesn't have the capability of shooting down satellites, you just roll your kill-sat up into a geostationary orbit with a line of fire on the enemy nation, and it's basically a predator drone, railgun artillery-piece and nuclear submarine all-in-one, hovering overhead all day every day.

Of course it really depends on the propulsion mechanism and how long it takes a kinetic projectile to get from orbit to impact. Hitting buildings, and bunkers and dug-in position is a given. But, really, all you'd need is a UAV spotting for it, and you could hit some moving targets. Armored columns and such that aren't going to be turning that much. Actually being able to control a planet's orbitals is a massive game-changer. That's why in most sci-fi where the author actually knows military stuff, planets just surrender when the bad guys grab orbit. The intelligence-gathering potential, alongside the ability for direct, potentially unstoppable fire-support, is a massive advantage.

Thankfully, tactical kinetic-strike platforms are still a decent ways off (although railguns are certainly on the horizon). So here's hoping we can sort ourselves out and stop being quite so dumb before then.

teebeeohh:

the US also build nuclear bazookas in the 50s.

and the queen/Cobra Commander thing was indeed great, everything is better with queen

My favourite crazy government project by far has to be Project Orion. "Hey, let's build a giant space ship powered by nuclear explosions! What do you mean, we can't find volunteer pilots?"

Best stinger yet!

would've loved to see a quick "the rod would have to be the size of a medium apartment building for it to work.", but aside from that I'm really enjoying the slightly more humour heavy route you guys are taking now.

Captcha: Take it all.

That's.. That's just.. do you want to take it now, captcha?

Easter Egg Found! Loved the use of the World in Conflict screenshot of a tactical nuke detonation.

I have actually looked this "weapon" in the past and it wouldn't work simply due to the fact that the rod would effectively vaporize on impact with most of the energy going down into the crust and not out along the surface,

mb16:
I have actually looked this "weapon" in the past and it wouldn't work simply due to the fact that the rod would effectively vaporize on impact with most of the energy going down into the crust and not out along the surface,

Well transferring the kinetic impact force directly into the Earth crust isn't all that of a bad thing. Instead of relying on the shock wave in the air to do the damage (this use by most bombs except those utilizing shaped charges) you instead have created a concept called an earthquake bomb, first theorized by Barnes Wallis. You transfer the force to the ground which is essentially in-compressible and the force then radiates outward from the impact point similar to the way seismic waves radiate outward from the point zero of an earthquake. Useful for destroying buildings and hardened structures alike.

rcs619:

I'd compare the R.F.G. more to an artillery piece than a tactical nuke or ICBM. It certainly could be a WMD-grade weapon, but in theory, you could dial the system up for any sort of yield you wanted. Either use smaller rods, or control the amount of juice passing through the mass-driver/railgun that launches it. That's both the big advantage and scary part of the system. If you go to war with someone that doesn't have the capability of shooting down satellites, you just roll your kill-sat up into a geostationary orbit with a line of fire on the enemy nation, and it's basically a predator drone, railgun artillery-piece and nuclear submarine all-in-one, hovering overhead all day every day.

Of course it really depends on the propulsion mechanism and how long it takes a kinetic projectile to get from orbit to impact. Hitting buildings, and bunkers and dug-in position is a given. But, really, all you'd need is a UAV spotting for it, and you could hit some moving targets. Armored columns and such that aren't going to be turning that much. Actually being able to control a planet's orbitals is a massive game-changer. That's why in most sci-fi where the author actually knows military stuff, planets just surrender when the bad guys grab orbit. The intelligence-gathering potential, alongside the ability for direct, potentially unstoppable fire-support, is a massive advantage.

Thankfully, tactical kinetic-strike platforms are still a decent ways off (although railguns are certainly on the horizon). So here's hoping we can sort ourselves out and stop being quite so dumb before then.

You make an excellent point, I honestly hadn't considered the possibility of on-station targeting and slow moving targets combined the shear speed the R.F.G. projectiles move. I have to say my own experience working around strategic weapons does make me a bit blind to other uses of planetary doom weapons

ClockworkSailor:

mb16:
I have actually looked this "weapon" in the past and it wouldn't work simply due to the fact that the rod would effectively vaporize on impact with most of the energy going down into the crust and not out along the surface,

Well transferring the kinetic impact force directly into the Earth crust isn't all that of a bad thing. Instead of relying on the shock wave in the air to do the damage (this use by most bombs except those utilizing shaped charges) you instead have created a concept called an earthquake bomb, first theorized by Barnes Wallis. You transfer the force to the ground which is essentially in-compressible and the force then radiates outward from the impact point similar to the way seismic waves radiate outward from the point zero of an earthquake. Useful for destroying buildings and hardened structures alike.

It would put on a nice show, vaporize anyone in the immediate vicinity, shake the ground, soil many pants etc. etc. but the actual effects on target won't be anywhere near as impressive as the sheer KE would imply. Throwing metal rods into the ground isn't a great way to destroy anything but bunkers to begin with and it's not even very good at that (aka it would probably vaporizes before it hit the bunker)

my gawd, please use LaTex or something to format the equations. reading ascii math is unpleasent. i think you can type equations in word.

wombat_of_war:
i still like the idea of a giant rock mass driver on the moon if you want to go doomsday. it has that whole 60's supervillian vibe about it.

This was in "The Moon Is A Harsh Mistress," published in the 60's.

One thing to note, a 2000 pounder does not contain 2000 pounds of explosives. The overall weight of a Mk 84 is 2039 lbs (from wikipedia, but it's generally on the money on these sort of things). Of this, the fill weight (amount of energetics cast into the bomb) is at 945 lbs. The difference is the weight of the steel bomb case, which delivers the lethality of the bomb.

The fill material is not TNT as well, as TNT is too sensitive. They don't even use Comp B (60/40 RDX/TNT with 1% wax added) anymore, because it is also too sensitive. If you want a rundown of why sensitivity is a problem with munitions, look up the fire on the Forestall in 1967.

Most of the modern explosives used in GP bombs are based on either RDX or HMX, bonded with a polymer of some sort to desensitize them. They may also have some powdered aluminum added, in order to increase the amount of energy delivered to the target. If we consider PBXN-5 fill, it is 95% HMX, which has an explosive energy yield of 1.70 of the yield of TNT. Crunching the numbers down, it would be 311 Mk. 84's required to lift that much water, not 237.

One more thing: fix your damn units. mJ is not megajoules, MJ is. The capitalization is important, as it is a difference of 6 orders of magnitude!

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