What would a Kinetic Orbital Bombardment Strike looks like?

[RainDreamer]

I keep wondering about it when I see this:

Is that going to be how it look (inaccuracy in the stuff that is shown on their computer screen and the things they say aside)? Would it cause a massive shockwave that actually transform the ground in such dramatic fashion? or would it bore a deep hole into the ground and leaving more precise destruction?

[Deutherius]

(Please note that I cannot view the video with sound at this time) Unless it is a really powerful bomb, I think this is just overdramatized for the purposes of "hurr durr suparwepon". The projectile would most likely just bore itself REALLY deep into the ground, destroying everything in it's path. Probably some tremors, but not such a dramatic terraforming event.

I believe that was the original purpose of the rods from god (Project Thor If I recall correctly), right? To destroy underground bunkers.

[biohazard15]

The rod needs to be the size (and weight) of Empire State Building to produce such effects. The real "telegraph pole" would just bury itself deep in the ground, maybe with some sorts of explosion, but it would be something in range of heavy conventional bomb, not a megaton-class nuke.

[Tommygun]

From what I understand a 10 ton tungsten rod drop at orbital speeds (about 28,000 kph) would have the kinetic energy of a 10 ton bomb explosion.

The energy would only be released when it hits the ground, so a lot of energy, but not all is going into the ground and then reflect out and up too.

I don't know any percentages, but nothing like a land wave is going to happen. Even an atomic weapon doesn't create land waves like that.

[RainDreamer]

It is a good thing that we might never see such a weapon used in reality, but I am really curious about how it might really look...

[Deutherius]

Even an atomic weapon doesn't create land waves like that.

Most atomic weapons would be detonated in the air above target, because of the logistic problem that is getting the bomb in the ground below the target.

There have been nuclear bomb tests below ground level, but none that I have seen have produced such a dramatic effect.

And even if they did, a tungsten pole just doesn't release its energy in the same way that the nuclear bomb does.

EDIT: To clarify, I agree with Tommygun's post, just providing additional stuff

[Darnok]

You guys didn't seen electromagnetic cannons?

Having in orbit satellite with huge electromagnetic cannon you could speed up even few tons projectile, of course it would have to be built from alloys that won't burn down on re-entry.

And shock wave might be caused not by explosion or impact itself, but from seismic reaction. What if you shot few projectiles, few tons of metal each, into seismic rifts?

[K^2]

From what I understand a 10 ton tungsten rod drop at orbital speeds (about 28,000 kph) would have the kinetic energy of a 10 ton bomb explosion.

At the speeds you are quoting, it'd be closer to 70T. But there are significant losses in atmosphere. The impact is closer to 3km/s, which gives the 10T yield.

[Darnok]

One more thing what if we would shot from satellite orbiting around the Moon?

It should increase speed of projectile even further

[Streetwind]

The projectile would most likely just bore itself REALLY deep into the ground, destroying everything in it's path. Probably some tremors, but not such a dramatic terraforming event.

The real "telegraph pole" would just bury itself deep in the ground, (...)

Well, depends how you define "really deep". As Isaac Newton already showed, a typical impactor can embed itself no deeper into the target than its own length, times the difference in densities.

Now, tungsten has one of the highest densities recorded among the elements (but not the highest). It is about 8 times more dense then concrete, or 7 times more dense than solid rock (on average, because there are even more variants of concrete than there are of rock). So it could be argued that a "rod of god" about 3 meters in length* would bury no deeper than maybe 22 meters. The rod is also not a completely blunt impactor, but rather tapered specifically for penetration, so it'll go deeper than the first approximation suggests... but I don't know how much deeper. Maybe 10 to 12 times its own length. So about 35 meters at most.

Still makes it a useful bunker buster, but doesn't really carry it far below the surface, in absolute terms. Keep in mind: the rod is going to come down at an angle. A relatively flat angle. Certainly nowhere near vertically down. This is an object on a very fast suborbital trajectory that only juuuust grazes the surface where it is meant to hit (because that maximizes the speed and therefore the impact energy). So all that impact depth is going to go largely sideways. For a very good visualization - Scott Manley made a video on it where he tries to hit KSC with such an impactor. Spoiler: it's very difficult to pull off.

Assuming it hits nothing but solid ground on its way down, the energy released will go largely upwards, because that's the path of least resistance. I expect that the effect would not be unlike seeing a blurry flash of light lance down from the heavens, which impacted in a brief, extremely bright event that disappeared in the blink of an eye as it burrows in. But within that same blink of an eye you'd get a fountain of superheated rock getting thrown upwards - perhaps not unlike the water spray caused by a speeding object hitting the ocean at a flat angle and being suddenly slowerd down. It would be a single blast event, lasting a second at most. The resulting crater would be as "deep" as the projectile burrowed, if slanted very much sideways, and fairly sharply cone-shaped. The top section would likely be missing, though, so it might be more like a trench. Though that (and the crater size) depends on the surface material and the way it breaks up under stress. The blast wave would seriously damage surrounding buildings (and shatter all windows in a fairly large radius) but not collapse them.

Assuming the impactor hits something on its way down that it can release its energy into, then it will do so. For example, a bunker, if hit by such a projectile, will take a large portion of the impact energy because it's so conveniently empty (from the energy's point of view). An underground cavern system would be affected disastrously, likely leading to widespread collapse of the entire system. Such a thing could lead to the whole ground above suddenly falling a bit, or caving in in places, over an area much larger than the impact crater. This would naturally collapse most large buildings that relied on this ground for structural stability. If you assume that the ground below Westminster is sort of swiss cheese like (maye they have more catacombs than Paris? I dunno), then you could potentially get an effect somewhat similar to what is portrayed in the movie. But on the grand average, it seems like a rather contrived scenario and the single-blast, trench digging variant seems more likely. And the impact angle is wrong in every case.

* completely made up number for illustration purposes

Edited April 13, 2015 by Streetwind
Typos, typos everywhere!

[Tommygun]

At the speeds you are quoting, it'd be closer to 70T. But there are significant losses in atmosphere. The impact is closer to 3km/s, which gives the 10T yield.

I guess I should have been more specific, I meant dropped from orbit at orbital speeds of 28000 kph, not hitting the ground traveling at that speed.

[Rune]

snip

Pretty good description, and you make a point of mentioning the flash of light. Considering how fast the energy is deposited on the ground, a significant fraction must be spent creating a thermal flash, not to mention the column of superheated plasma the warhead leaves travelling at hypersonic speed in the low atmosphere. Hell, the shockwaves of the atmospheric portions of the flight will shatter some windows on the way to the target.

But on the other hand, a few kiloricks can't blow up London. These things have yields comparable with conventional explosives, after all. So we can conclude: a lot less rumble, but slightly more flashy.

Rune. And if someone suggests additional electromagnetic acceleration of the round, doing that to London would have ejected the station form orbit, because that round had to be relativistic to make such a mess. Expensive shot.

[lajoswinkler]

No, the video is just fancy but totally unrealistic. It assumes most of the kinetic energy would be converted to mechanical energy which is not correct. Most is converted into heat.

[RainDreamer]

Hmm...so a lot of heat in the area ( enough to melt stuff around it?) along with tremor similar to a light earthquake then? Wonder what would be the area of effect for such things.

[ChrisSpace]

What film is the clip from?

[KerikBalm]

Ummm it says on the video....

Anyway, one does not simply "drop it"

They would indeed need to launch it retrograde from the sat.

The next thing to consider, is that the impact can only be a small fraction of the power of the rocket that launched it.

Even though orbital rockets are big.... they don't make booms on the scale of nukes when they blow up.

And the amount of energy actually imparted to the payload is but a small fraction (most of the energy is imparted to the exhaust/reaction mass, and then the stages that don't make it to orbit with the payload).

Then you lose even more energy from air resistance on reentry.

I don't see how it could be more powerful than an ICBM carrying an inert payload instead of a nuclear warhead.

I of course mean a long range ICBM, one that reaches near orbital speeds (by the time the payload re-enters and nears the surface, the velocity difference should be negligable)

[RainDreamer]

I don't see how it could be more powerful than an ICBM carrying an inert payload instead of a nuclear warhead.

I of course mean a long range ICBM, one that reaches near orbital speeds (by the time the payload re-enters and nears the surface, the velocity difference should be negligable)

It is not going to be more powerful at all. The weapon platform simply take advantage of being an orbital platform that can attack from space with very little warning and difficult to counter, and slip through the space treaty that bans weapon of mass destruction in space (it is a conventional weapon by definition). But those are kind of negligible advantage, comparing to the cost of putting it in space, hence it is not going to appear in reality in anytime soon. And also the reason why I wonder what such an impact would look like as there is not going to be any real example.

[cicatrix]

You guys didn't seen electromagnetic cannons?

Having in orbit satellite with huge electromagnetic cannon you could speed up even few tons projectile, of course it would have to be built from alloys that won't burn down on re-entry.

And shock wave might be caused not by explosion or impact itself, but from seismic reaction. What if you shot few projectiles, few tons of metal each, into seismic rifts?

And of course this satellite should do something about the recoil force which will be equal to the force that have been applied to the projectile.

As for the original video - the laws of conservation are obviously violated. In order to deliver the energy capable of turning London upside down the bomb should have this energy in any form. E = mv²/2 if I'm not mistaken. Although the energy of the falling rod from the orbit would be quite large it would be several orders of magnitude less than what's been shown in the video.

- - - Updated - - -

At the speeds you are quoting, it'd be closer to 70T. But there are significant losses in atmosphere. The impact is closer to 3km/s, which gives the 10T yield.

Besides, the rod itself should lose some part of its mass as it burns through the atmosphere.

[tater]

Nukes are generally detonated in the air to maximize destructive area. Ground bursts (nukes) are typically used for hardened targets like missile silos.

Aside for the timing of the movie weapns being absurd, so clearly is the velocity. For a given mass weapon, we could easily calculate the velocity required for the KE to equal hundreds of kt of TNT.

[RainDreamer]

Well, I don't think there is any actual stats about the size and mass of the rod being dropped from space, and the perspective of the station in orbit can be deceiving. It could be a building-sized rod, eying it from the screencap of the drop alone. But..*shrug*

[cicatrix]

Well, I don't think there is any actual stats about the size and mass of the rod being dropped from space, and the perspective of the station in orbit can be deceiving. It could be a building-sized rod, eying it from the screencap of the drop alone. But..*shrug*

Don't give up hope, imagine the inside of the rod had several kilograms of antimatter suspended in electromagnetic field. But still it would be a fireball...

[YNM]

Why not a slightly huuge ball of water ice, akin of this ? The impacts for are quite, well...

[Streetwind]

Why not a slightly huuge ball of water ice, akin of this ? The impacts for are quite, well...

No no, you're doing it wrong. If you want to be unreasonable, this is the only way to be properly unreasonable.

Forgive me father for I have sinned.

[tomf]

I guess the 10-tonne of explosive makes sense

The rod isn't gong to have more energy than the chemical energy rocket that put it into orbit.

If a sensible sized rocket could throw an impactor that did nuclear levels of damage they wouldn't bother puttting nuclear weapons on top of them.

[impyre]

If you were to strike from space, you'd use explosives or some other destructive payload. "Kinetic" orbital strikes makes about as much sense as a space catapult. As others have pointed out, the amount of fuel spent establishing an advantageous orbit would be many times more effective when used established a depressed suborbital trajectory.