Nukes-Deep Impact Movie

Near the end of this movie the astronauts sacrifice themselves in order to save the world by setting off 4 nukes simultaneously. Ignoring the basic flaws of the movie, what would happen if these 4 nukes at 5,000 kilotons went off next to each other. Could they really be timed to go off simultaneously, or would one go off slightly before the others, destroying the nukes before they could all trigger nuclear reactions. How far apart do the weapons need to be to each detonate properly? Would it be a 20,000 kiloton blast, or do these kinds of reactions add differently?


WECOLME TO THE NEW MILLENIUM!, now go home.:rolleyes:

Those are good questions. I don’t know the answer to the timing question - I do know that fratricide is a major problem making it difficult to double-up warheads on the same target, unless they are timed to hit the target apart. That option is clearly out of the question when you’re planting bombs on an incoming object…

I think the answer to the last question is, multiple nuclear weapons add up to more than the sum of their parts, at least in terms of their radius. A little paradoxical perhaps, but four 50kt weapons will have a larger aggregated effective radius than a single 200 kt weapon. In terms of things other than blast radius, like how hot things are at the center, I don’t know, but anything near the center is going to go away in any case…

** fogmage** asks

Boris B answers, in part

The answer is correct, Boris, but you should mention that it is not because of odd addition characteristics of nuclear weapons, but because the explosive events take place over a larger area * when the centers are separated.* The case in point seems more to the opposite intent, the centers as close as possible.

The ignition of a group of nuclear explosions in near proximity is not specifically impossible for any reason of physics that I know of, it is the nuts and bolts of engineering such an event that are more difficult. With a specifically designed electronic timing set up, one could cause the detonation to be timed precisely enough that the four centers of explosion were already beyond the chain reaction threshold before shock and blast events were propagated far enough to disturb each other. However, jury-rigging a six pack of warheads by hand to accomplish that event might require a specific technological development. That would be a “plot device.”

By the way, having done so, you would have minimized, if not eliminated the additive advantages of multiple warheads which Boris B mentioned. Having confined the power of the greater number of centers to one location, it would be only as powerful as the sum of its parts.

This minor niggle must fall upon the heap among the many others one must suspend disbelief for in the case of the movie in question.

<P ALIGN=“CENTER”>Tris</P>

Ours is a world of nuclear giants and ethical infants. We know more about war than we know about peace, more about killing than we know about living.
– **General Omar Bradley **

Good point, Tris. I had forgotten really why multiple warheads add up so advantageously; it seems that it was much simpler than I expected. I was just remember some principle by which, if you double the tonnage of a bomb, you add a lot less than 100% to the effective radius. But if you put two warheads of the original size you can double the effected area.

I’m just reiterating what you’ve said, I suppose, but one question: Is this the inverse-square law?

Boris B asks

Kind of. Mostly it is the result of the huge overkill of nuclear weapons. While a megaton bomb may in fact destroy the center of its action a thousand times more efficiently than a kiloton bomb, it certainly does not create a blast radius a thousand times larger. Dresden was more thoroughly destroyed than Hiroshima, even though it was not hit by as much explosive force. The firestorm that was caused resulted from the placement of the bombs, not the power of them.

It also doesn’t take vaporization to compromise the usefulness of most of the accoutrements of civilization. Simply knocking them down, and setting them on fire is, in a military sense at least, sufficient. When you consider that concrete and steel are among the things which get set on fire in the firestorm which *follows * a nuclear explosion, you can understand why a little one is really all you generally need, in a given township.

If you want to sterilize, and obliterate a very large area, for some reason, you are far more likely to be successful if you place kiloton bombs on half mile centers over a five or six mile radius, than if you drop a big whomper in the center. For the same bang, you can set the entire five mile circle ablaze in a firestorm which will thereafter sweep outward for a mile or more, and the resulting counter blast of returning air will re-ignite anything which managed not to burn in the first holocaust.

Ideally you want your bombs to go off a thousand feet (assuming you are using 1 KT bombs) or so in the air, as well, since the fireball will rebound off the ground to a great extent, and even many megatons won’t vaporize all that much country rock, or reinforced bunker. The higher center allows your fireball to rebound in a more outwardly pointed vector, reinforcing the power of the blast, and the heat moves over a larger area of target. Secondary fires will be more widespread as well. Keeping the fireball from touching the ground will reduce the fallout by some amount, if that matters. Getting it above the troposphere will increase the EMP (electromotive pulse) effect, if that matters.

Now using nuclear explosions for propulsion is a bit different. You have to get up real close and personal, in space. The portion of the blast which moves away from the object to be accelerated is not a factor in the equation, and the further from the object, the higher that fraction is. Getting it above 50 per cent would mean having a concave target, and some spiffy impact reinforcements on that side of the object. If your asteroid is a big hunk of iron, all in one piece, it could work. If it is a pile of ice and gravel meandering around in space together, you create some amount of high speed shrapnel, and the rest of the pile moves along as before.

<P ALIGN=“CENTER”>Tris</P>

What goes: Clop, clop, clop, clop, Bang! Bang! Clop, clop, clop?
An Amish drive-by shooting.

I don’t want to turn this into a general critique of Deep Impact, but there was another thing the film-makers overlooked: That comet would have done considerable damage to the Earth even after being blown into smithereens. All of those particles would have released enormous heat as they entered the atmosphere. Whether as a single piece, or as powder, a billion tons of material hitting the atmosphere would release a lot of heat.

In other words, the Earth would’ve been fried.

Armageddon was another dumb movie, but at least they realized that you’d have to prevent most of the asteroid from hitting the Earth.


>< DARWIN >
__L___L

The law is known as the cube root law. Most of the primary effects of an explosion, such as overpressere and impulse, scale to the cube root of the explosive, as measured in lbs. of TNT equivalent (or ktons in the nuclear case). I don’t know if this is explainable through analysis, but it is verified by testing. That’s one reason why the unitary bomb has been replaced by the cluster bomb unit for soft targets, you get a lot more bang for your buck with multiple munitions carrying the same explosive weight.
To address another poster, if the explosion were made far enough out in space it could cause many of the fragments to miss the earth altogether.

Explosives aren’t very good at moving things, a nuclear powered mass driver would have been a much better mechanism for perturbing the orbit of the asteroid.