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Sirrobert

GI joe retaliation zeus weapon

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So in flight to my vacation a few weeks ago, I saw this movie. Not to relevent.

Than near the end (spoiler I gues?) they revealed the bad guy's 'super weapon'

A satelite that 'drops' a metal rod from a satelite down to earth, where it impacts and causes an explosion 'similar to a nuke'

This clip shows the details as named in the movie.

Now skipping over the obvious part that you can't drop something form a satelite in orbit and have it fall down to earth just like you would drop a ball.

What would it take to get such a rod to fall down to earth in that way, and what would happen to it? In the movie they say it touches down 8 times faster than a bullet, would that cause such an impact?

Third question: How long would you be able to keep such a satelite locked on a target? In the movie they just get into position, and than nothing happends to them until they launch

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Tor had one ton warhead similar to an one ton of explosives, so for an nuclear like effect you would need small asteroids if you just deorbit it.

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Basically Project Thor. I don't know how heavy the one in the movie would be, but the explosion would not be anything that large with the Thor weapon.

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

I've heard that while the explosion would be small, it would create quite the artificial Earthquake.

As for what it would take to get it down from orbit, just throw on some liquid fuel rockets to precisely retro burn so you can hit your target within a small enough radius to have a very high chance to hit the target. It would not however hit with that much velocity, as I would imagine that the resistance of the atmosphere would slow it down quite below that speed.

The satellite wouldn't really need to be the thing that locks on, the tungsten rod would have some RCS and a computer on-board to go away from the satellite, and then flip itself around until it points retrograde at the right point in time and space, and then burn. At this point, some aerodynamic surfaces for hypersonic control could deploy, and give fine adjustments to the projectile until it impacts the target.

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I also saw this movie, just the other night. When I saw what they were proposing as the workings of the weapon I laughed and tried explaining to my wife why it was completely ridiculous. In the film, the "bad guy" actually states that the tungsten rod is just "dropped."

First, as everyone has agreed so far, any projectile from a satellite in orbit would have to shed its orbital velocity to return to earth. And, being that it is just outside the atmosphere and not already traveling at 100,000 Km/h, such as an asteroid might, the projectile (even a very aerodynamically shaped object) would be slowed to it's terminal velocity, or at least slowing to that speed limit until impact.

This means it would hit the ground at perhaps a few hundred miles an hour, so something on the order of a small, very dense plane crashing into the ground nose first would result. Just my best guess.

--Nutty

edit: I split up the text instead of one long paragraph. Proper forum etiquette.

Edited by NuttyRob

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To address the satellite positioning question: "How long could one keep a satellite locked on target?"

Well, to be honest that wouldn't be necessary at all. We've already agreed that you can't simply "drop" a rod from an orbiting body and have it just drop to the earth. It would require some kind of propulsion to get itself into an impact trajectory. Since the projectile would have to de-orbit on its own, a launching satellite wouldn't need to be directly overhead of any target city.

In fact, in a lower than geosynchronous orbit, the satellite would have to "drop" the rod well before getting directly overhead. This would be in order to allow the projectile to de-orbit and reach the surface in time. Because of orbiting speed to a lesser extend planetary rotation, dropping an object directly overhead would cause a scenario where the projectile would not only have to slow its orbital speed to zero, but end up accelerating in retrograde direction to counteract the distance it traveled while slowing down in the prograde direction. That is an awful lot of Delta V capability, and completely unnecessary.

A satellite in orbit could easily be maneuvered over a certain location (provided it was between certain lattitudes between north and south poles of the body being orbited.) could remain thereabouts for several minutes depending on the actual range of position the sat would have to be in in order to still launch. A geostationary orbit has two requirements, must have zero inclination to the equator and have a circular orbit of just under 24 hours (like earth's rotation period) then the sat could stay there pretty much indefinitely with only minute corrections. If it were north or south of the equator though, even with the same orbital period as earth's rotation, it would only be over certain parts of the earth (the same parts) once every day for a few minutes. This could be altered so that it was over a new location, but would still only be over said location for a few minutes.

I hope I was clear enough, I have a tendency to overstate and restate points. Please feel free to smack me around if I go on too long.

--Nutty

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This means it would hit the ground at perhaps a few hundred miles an hour, so something on the order of a small, very dense plane crashing into the ground nose first would result. Just my best guess.

I have to disagree with this on the basis that it would be extremely ineffective if this was true and considering the military considered this as a weapons system means that it would have to work pretty well, at least theoretically.

As to its lethality, AFAIK it was generally envisioned as a bunker buster, probably to take out hardened ICBM launch sites. I don't know about their capability to create artificial earthquakes, although the idea seems reasonable, but according to wikipedia Project Thor allowed for a large version which would impact with 11.5 tons of TNT, significantly weaker than a nuclear bomb.

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One of the big factors in the Thor project, is also the fact that it would be very hard to shot down or interfeer with the projectile once it is launched. Very small radar cross-section, very small time window for detecting it, and even if it is detected then its a tungsten rod, so not terribly vulnurable to the various anti-missile devices currently existing (laser or ABM)

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Watching the clip my first thought was "Awesome!"

My second thought was, "PHYSICS DOES NOT WORK THAT WAY!!!"

Ignoring all the horrid orbital mechanics involved here, a rod that size would not flatten London, even if it was moving at 42,220 MPH (AKA, "eight times the speed of a bullet"). It might be able to take out the Buckingham Palace, and the explosion would be impressive from up close, but the city collapsing into nothing? Think more on the lines of a mid-size asteroid.

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Watching the clip my first thought was "Awesome!"

My second thought was, "PHYSICS DOES NOT WORK THAT WAY!!!"

Yea I had basicly the same thing.

Except I saw the movie in the plane TO my vacation, than spend 2 weeks there thinking about it.

Ofcourse it only took a few minutes to start doubting, than my internal kerbal quickly started yelling at me

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I have to disagree with this on the basis that it would be extremely ineffective if this was true and considering the military considered this as a weapons system means that it would have to work pretty well, at least theoretically.

As to its lethality, AFAIK it was generally envisioned as a bunker buster, probably to take out hardened ICBM launch sites. I don't know about their capability to create artificial earthquakes, although the idea seems reasonable, but according to wikipedia Project Thor allowed for a large version which would impact with 11.5 tons of TNT, significantly weaker than a nuclear bomb.

Actually, you are right...it would be significantly more destructive than the analogy I used. But the question is energy transfer. Essentially it would be transferring all the energy through a fairly small (give or take .5 meter at most??) diameter. I think it would be more of the kind of thing like you described, like a bunker buster or buried/hardened silos etc. It just wouldn't make much sense for the energy to transfer out to the order of kilometers wide, total destabilizing of the earth's crust. Though the collateral would not be insignificant, it wouldn't level a city.

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I have to disagree with this on the basis that it would be extremely ineffective if this was true and considering the military considered this as a weapons system means that it would have to work pretty well, at least theoretically.

As to its lethality, AFAIK it was generally envisioned as a bunker buster, probably to take out hardened ICBM launch sites. I don't know about their capability to create artificial earthquakes, although the idea seems reasonable, but according to wikipedia Project Thor allowed for a large version which would impact with 11.5 tons of TNT, significantly weaker than a nuclear bomb.

An fast moving rod of some dense metal is an perpetrator, 0.5 to 1 cm rods of tungsten or depleted uranium is the primary anti tank weapon.

An telephone pole of tungsten would be able to punch pretty deep and would probably to overkill against an hardened ICBM silo, however you has to hit pretty accurate.

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It seems like it would be far simpler to just "drop" a nuclear missile this way. Relatively modern nuclear weapons can actually be fairly clean, leaving the ground zero safe within hours.

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It seems like it would be far simpler to just "drop" a nuclear missile this way. Relatively modern nuclear weapons can actually be fairly clean, leaving the ground zero safe within hours.

I don't think they are THAT clean. Do you know any of the warhead models that are that clean by chance?

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It seems like it would be far simpler to just "drop" a nuclear missile this way. Relatively modern nuclear weapons can actually be fairly clean, leaving the ground zero safe within hours.

I find that very hard to believe. Do you have any examples?

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For example the neutron bomb and other fusion powered nuclear weapons produce very little fallout in comparison to their explosive power.

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I did a little of that thing called "math", and it turned out some interesting numbers.

First off, I went with the assumption that the projectile in the movie is the same size and shape as a telephonepole, and I went with a length of 15 meter and a radius of 12.7 cm, and made up of basic tungsten/wolfram (wichever sounds the coolest in your mind) at 19.25 g/cm3

Giving a volume of 760 062 cm3

for a grand total of 14 631 kg.

And I asumed the speed of a bullet to be 3 times the speed of sound, so 3 X 330 m/s = 990 m/s, and in this case, times 8

giving a speed at impact of some 7920 m/s.

So, using basic equation for energy in moving object (1/2XweightXspeed squared) I get:

1/2 X 14631 X (7920^2) = 458 874 979 200 kJ of energy at impact.

So, normalisation to TNT equivalents gives roughly:

458 874 979 200 kj impact energy / 4 184 000 kj per ton TNT = 109 673,752 tonns of TNT.

So it´s roughly the equivalent of a 110 KT warhead. As that random smiling evil henchman-like guy says in the movie, more powerfull than most nuclear weapons, if you consider "most" as being in the numerical sense, and then include tactical warheads, wich usualy counts in the lower of 25 KT size.

But, this brings up a small pile of new questions and problems where reality is conserned. Now, I´m not versed enough in the science of aerodynamics, since I only began reading about it properly half a year ago, but, the projectile is pretty dense, the ends, might just be flat, and then produce a shockbow in front, if it was kept stable on it´s descent, wich would give some protetion against heat, and considering it´s speed, if it came striaght down, would "only" spend some 10 seconds or so from the edge of space and down to the surface. And since only the lower 10% of that contains roughly 90% of the atmosphere, at that speed, atmosphere would only get a very short time to slow it down.

But this is where it gets realy hairy and ugly. First, the initial "drop", as mentioned by others, "physics don´t work that way". I´d be guessing an initial launch velocity of some 8-9 km/s retrograde for it to be able to "just fall". So, in free fall, when will an object falling towards earth reach such a velocity?

7920m/s / 9.8m/s = 808 seconds free fall.

808 seconds of free fall towards earth:

1/2 X 9.8m/s X (808^2) = 3199033.6 meter, i.e. dropped from an altitude of 3199 kilometer, and thereby defying orbital mechanics, since it´s orbital velocity is ignored. So, what would it´s orbital speed be?

I´ll try and give a rough estimate then, I realy want to see how much delta V we are missing here.

Semimajor axis:

Earth radius 6371 km

Orbital altitude 3199 km

6371km + 3199km = 9570km

Vo = sqr(398 600/9570km) = 6.45km/s retrograde "drop speed" then.

And all this is ignoring aerodynamic resistance for the last few seconds, assuming the pole is able to stay stable all the way down, and hit it´s target. Oh, and since the projectile is made up of a very dense material, it´s disintegration and deformation will be aimed downward. The energy at impact won´t resemble a nuclear detonation at all.

And I still very much doubt the impact speed until I see some figures taking aerodynamics into account.

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For example the neutron bomb and other fusion powered nuclear weapons produce very little fallout in comparison to their explosive power.

"very little fallout in comparison to their explosive power" does not mean "almost no fallout". It just means not as much as a normal nuke

And tnx for the numbers Thanial. 110 KT is still more than I expected from a metal rod. But as you said ofcourse, that thing would just burry itself deep underground, not explode with all that force on impact

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Yeah, I must say I was surprised at that high yeld myself. It´s at speeds we puny humans may relatively easily manage to accelerate something like that up to. But, we are talking about deep penetrating stuff, projectiles in the 14-15 ton size, wich in turn have to be accelerated a fair bit as well, and I expect them to have to hit pretty dead on, as a miss at that speed won´t inflict much harm far from the impact itself.

I´m not entirely sure I got the TNT equivalent right, but I am pretty sure I got the energy at impact right. I went over and recalculated those numbers a few times, weeded out a mistake where the rod was merely 15 cm tall and such. So if anyone spots a mistake, feel free to correct me. But I don´t think I´m too far off realy. After all, 24 times the speed of sound is pretty fast, and in this case, it is literaly as if a lokomotive traveling at that speed hits an area the size of a dinnerplate. There just have to be a lot of energy released in that.

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I don't think they are THAT clean. Do you know any of the warhead models that are that clean by chance?

The only way to get even relatively clean is an airburst high enough that no material from the ground is sucked up into the fireball. The problem there is that you give up a lot of your damage potential that way. (I.E. hard targets are out of the question.)

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Couldn't the force which the projectile is ejected from the sat be sufficient to deorbit it? Then you'd need a smaller propulsion package to change the trajectory.

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Couldn't the force which the projectile is ejected from the sat be sufficient to deorbit it? Then you'd need a smaller propulsion package to change the trajectory.

Well, yes and no. There are two possibilities/concerns here:

1. If the intenden "release" imparts enough energy to the projectile for it to reach the atmosphere on it's own, so it would deorbit properly, but not more energy for this than bare necesary, then the projectile would come in at a very shallow angle. This in turn would result in a mucher longer period of aerobreaking, resulting in a much lower speed, possibly as low as terminal velocity, and this again would mean appaling precission contra to actualy let something fall straight down, where it would experience a lot less time in our atmosphere, and at a much higher speed, before hitting it's target.

B. I forgot what I intended to write here, I think I got it in the first part though. Anyway, orbital bombardement isn't as fantastic as it sounds when you start taking orbital mechanics into the equation.

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Why am I not suprised Scott Manley has a video about this? He even called it Zeus

So 12 tons TNT, a pritty low number.

Also shows pritty good that dropping, or even shooting, would NOT result in something crashing straight down

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