Neutron bombs and EMP

[Purple]

Thank you for the input so far. I am reading all you are posting including the contents behind the links.

[Shroom Man 777]

If your people have gigaton-level nuclear weapons, why can't they have super-awesome shielding to protect from super-EMPs? I mean, if it's in gigatons and it's obviously not modern tech but all futurey, why can't the RPG have general grievouses going "ACTIVATE RAY SHIELDS!" and something something. It's not remotely realistic anyway.

[Sea Skimmer]

US Army Field Manual chapter on EMP protection, field manual is about protection of command and computer systems from electromagentic interference in general.
140.194.76.129/publications/armytm/tm5-690/c-5.pdf

[Purple]

If your people have gigaton-level nuclear weapons, why can't they have super-awesome shielding to protect from super-EMPs? I mean, if it's in gigatons and it's obviously not modern tech but all futurey, why can't the RPG have general grievouses going "ACTIVATE RAY SHIELDS!" and something something. It's not remotely realistic anyway.

That is actualy a good point. I guess I should explain.

I am the GM there and I had to allow high level nuclear weapons since I wanted to avoid antimatter. I made a calculation on just how strong that thing is and realized that it would make space combat idiotically short and unfun. (think 1 star fighter with an AM machine gun killing star destroyers). So I allowed gigaton range nuclear weapons instead. They are still much below the efficiency of antimatter (think cylindrical shells 10m in diameter and 20m long) but they make for a more fun game. So our conditions regarding the efficiency of Nuclear weapons.

But other than that and FTL we like to keep things as close to the laws of physics as possible. Or rather, as close to SW and as far from ST as possible. All weapons and equipment (FTL excluded) in their design have to fallow the laws of physics and be quantifiable so that we can work out ways of countering one another.

As for shields, we only allow particle fields as described here: http://www.stardestroyer.net/Empire/Tec ... ature.html so there are no all purpose magical shielding like in Star Trek. Shields are usualy particle bariers held in place by an EM field. So my regular nukes would tend to take care of them prior to any EMP attack on a planet.

[Sarevok]

What manner of weapons do your "particle fields" stop ? A light breeze of electrons from a CRT ?

[phongn]

I am the GM there and I had to allow high level nuclear weapons since I wanted to avoid antimatter. I made a calculation on just how strong that thing is and realized that it would make space combat idiotically short and unfun. (think 1 star fighter with an AM machine gun killing star destroyers). So I allowed gigaton range nuclear weapons instead. They are still much below the efficiency of antimatter (think cylindrical shells 10m in diameter and 20m long) but they make for a more fun game. So our conditions regarding the efficiency of Nuclear weapons.

How is there any meaningful difference? Even defending kT-range enhanced-radiation weapons would be quite the trick.

But other than that and FTL we like to keep things as close to the laws of physics as possible. Or rather, as close to SW and as far from ST as possible. All weapons and equipment (FTL excluded) in their design have to fallow the laws of physics and be quantifiable so that we can work out ways of countering one another.

Uh, I hope you realize that SW is no more realistic than ST?

[Simon_Jester]

Less, in some ways, because the sheer scale of the energy levels involved is so far out. We can at least imagine being able to generate electrical power on the scale the Federation does; they use physical processes we can sort of understand for at least some of what they do (fusion reactions, antimatter). Star Wars doesn't use any technology we can really understand except computers; it's all handwaves from top to bottom.

[Purple]

How is there any meaningful difference? Even defending kT-range enhanced-radiation weapons would be quite the trick.

It's not. That is why almost no one has energy shields.

As for the Star Wars thing I have to explain.
What I meant to say is that we do not handwave away the laws of physics and actually use things like 3D strategy and thermodynamics and well you know the rest.

So, no antimatter weapons, no magic, no Omnipotent creatures, no magical force shields, no windows on starships, no generators that spontaneously blow the ship apart, no ships that blow up from a couple of hits, no machines that violate the conservation of mater and energy, no complete disregard for common sense.

[Stuart]

What I meant to say is that we do not handwave away the laws of physics and actually use things like 3D strategy and thermodynamics and well you know the rest.

Ummm, you do realize that means you can't make gigaton yield nuclear devices don't you? 100 megatons is about it; more than that and the device just blows itself apart before delivering additional yield.

[Purple]

Ummm, you do realize that means you can't make gigaton yield nuclear devices don't you? 100 megatons is about it; more than that and the device just blows itself apart before delivering additional yield.

As said, I am aware of that but that was one of a small list of abstractions I had to allow for the sake of gameplay.

[Seggybop]

What I meant to say is that we do not handwave away the laws of physics and actually use things like 3D strategy and thermodynamics and well you know the rest.

Ummm, you do realize that means you can't make gigaton yield nuclear devices don't you? 100 megatons is about it; more than that and the device just blows itself apart before delivering additional yield.

Is there any reason you can't stick 10 Tsar Bombas in a single gigantic pod and call it a single "bomb" ? If so, how far apart do the individual bombs need to be to release all of their energy before prematurely destroying eachother?

[Simon_Jester]

It's not. That is why almost no one has energy shields.

As for the Star Wars thing I have to explain.
What I meant to say is that we do not handwave away the laws of physics and actually use things like 3D strategy and thermodynamics and well you know the rest.

Star Wars typically doesn't. They have weapons that make antimatter look weak, magic (trust the Force, Luke!) magic force shields, windows (the Executor bridge), generators that spontaneously blow the ship apart (the Death Stars), ships that blow up from a couple of hits (the Death Stars), machines that apparently violate conservation of matter and energy (the Death Stars, by outputting truly unreasonable amounts of energy compared to their apparent mass), and complete disregard for common sense (see all of the above; to me, at least, the laws of physics are common sense).

I respect what you're doing. But the proper term is "hard science fiction," not "like Star Wars." Star Wars is the opposite of hard science fiction, just as much as Star Trek.

[Stuart]

Is there any reason you can't stick 10 Tsar Bombas in a single gigantic pod and call it a single "bomb" ?

I wouldn't call it a bomb at all. It's a device.

If so, how far apart do the individual bombs need to be to release all of their energy before prematurely destroying eachother?

The devices would need to be several tens of miles apart. It's a problem called fratricide. A really, really serious problem. The devices would all have to initiate in the same microsecond to make this work

[Guardsman Bass]

The devices would need to be several tens of miles apart. It's a problem called fratricide. A really, really serious problem. The devices would all have to initiate in the same microsecond to make this work

Now that introduces an interesting wrinkle for the use of nukes in hypothetical space combat. You'd have to use multiple missiles (or drone spacecraft) with warheads below that size as opposed to a smaller number of them with bigger nuclear bombs on-board, which probably drives the cost up.

[Simon_Jester]

The devices would need to be several tens of miles apart. It's a problem called fratricide. A really, really serious problem. The devices would all have to initiate in the same microsecond to make this work

Well... hmm.

I will assume for the sake of argument that an initiation takes one microsecond, with the nuclear reaction having proceeded to completion (or as close as possible) by that point. I will further assume that we can time all the devices to initiate in the same microsecond. Sending a signal to several widely separated devices at the same time, to a precision of a millisecond, really should be possible today... but only if we use an elaborate pre-arranged setup. So doing this would be the equivalent of wiring a structure for demolition, not the equivalent of firing a missile salvo at an enemy capable of defending itself.

If my assumptions above are true, then we can get all the devices to initiate as long as they're placed more than a light-microsecond apart: nothing from one initiation will reach any of the other devices before they go off in turn. One light-microsecond is 300 meters, so that's the minimum spacing between devices. So given that the devices take one microsecond or less to initiate, and that we can time the command signal to microsecond precision... we could reasonably assemble a grid of devices and get massive overlap.

But it wouldn't be practical to do this with a missile salvo. And if there's any more imprecision in the timing, or if the initiation takes more than a microsecond, we have to increase the spacing to give us more margin of error. So yeah, pretty limited. This might work if we were, say, trying to rig Cthulhu with nuclear demolition charges and there was no active opposition interfering with our setup. But it would be a lousy way to try something like overwhelming the energy shields of a science fictional spacecraft.

We only need "tens of miles" of spacing, though, if nuclear initiations take more than about a tenth of a millisecond to proceed to completion. Which strikes me as unreasonable, because many of the effects propagate at light speed and the device really should have been blown to bits long before that much time has passed.

[Purple]

What if I took a bunch of 5-10 KT bombs and spaced them out at about 2-5KM (2/3 of what ever that calculator says the combined range is) apart?

I think that under those conditions I could have a no fratricide situation.

[Simon_Jester]

Yes, but the cumulative effect wouldn't be all that much more substantial than using one big damn H-bomb to level everything out to the horizon. Might well be less.

[Stuart]

Yes, but the cumulative effect wouldn't be all that much more substantial than using one big damn H-bomb to level everything out to the horizon. Might well be less.

That depends; its better (for example) to use three 350 kiloton devices than one one megaton device when trying to take area targets out. That's because the big devices simply pile up more destruction in an area where destruction is already total while three smaller ones in a triangle spread the over-destruction out. To take out a point target though, I'd guess one would want a big device if said target is "protected" (as a point of reality the only way to protect oneself from a nuclear initiation is to be somewhere else). The center of a nuclear fireball is around 40 million degrees F.

On timing, the window for initiating devices in close proximity to eachother is 19 microseconds. The peaceful side of that and the first device to initiate will blow the rest apart, the noisy side of it and the sleet of radiation from other devices will destroy it. That's an important point by the way, the primary killing system of a nuclear initiation in space is the sleet of radiation in produces. What happens to that radiation is extremely complicated. All I can say that if a gigaton device was practical and some one let one off between a planet and its Van Allen Belt, it'll be a hot time in the old town tonight. It's rather fortunate that gigaton devices are impossible.

[Simon_Jester]

That depends; its better (for example) to use three 350 kiloton devices than one one megaton device when trying to take area targets out. That's because the big devices simply pile up more destruction in an area where destruction is already total while three smaller ones in a triangle spread the over-destruction out. To take out a point target though, I'd guess one would want a big device if said target is "protected" (as a point of reality the only way to protect oneself from a nuclear initiation is to be somewhere else). The center of a nuclear fireball is around 40 million degrees F.

Though there are still limits, surely; pile up enough reinforced concrete over your head and you can ride out kiloton-range airbursts, no? My impression is that this is why we relied on the nine megaton B53 for bunker busting for a while...

On timing, the window for initiating devices in close proximity to eachother is 19 microseconds. The peaceful side of that and the first device to initiate will blow the rest apart, the noisy side of it and the sleet of radiation from other devices will destroy it.

Synchronizing the initiation commands isn't the problem here (if this is a pre-wired and coordinated setup, again more like wiring something for demolition than launching a missile barrage). So... a minimum separation distance of 19 light-microseconds is about six kilometers, preferably more for margin of error.

Provided you can synchronize the setup properly, that places each initiation safely outside the light cone of all the others for 20 microseconds or more. And the radiation front from the next device over isn't going to get there any faster than c.

[muon]

(I haven't had time to follow the forums much recently, and missed this thread... my apologies for the week+ necro; I wasn't sure if I should start a new 'maximum achievable yield for a thermonuclear device' topic or just belatedly ask the question here)

Ummm, you do realize that means you can't make gigaton yield nuclear devices don't you? 100 megatons is about it; more than that and the device just blows itself apart before delivering additional yield.

It's rather fortunate that gigaton devices are impossible.

Stuart, are there any open-source references that would explain that?

Certainly ~100 MT is about the upper limit for an air-deliverable device due to size and mass constraints (and of course there are few if any military justifications for such high yields vs ground targets regardless). But, if bulk is not a design limitation (e.g. if the device was constructed in space, or a sea-based 'gigaton mine'), why could not staged implosion be extended to arbitrarily high yields (three-stage devices have been field proven, and adding additional stages still only requires a single primary)?

[Ariphaos]

I can easily picture the tamper required for such a device long enough would have to be so dense and thick that it would actually start to contain a meaningful fraction of the explosion.

[Starglider]

The devices would need to be several tens of miles apart. It's a problem called fratricide. A really, really serious problem. The devices would all have to initiate in the same microsecond to make this work

Wait, why is this a problem? Multi-point implosion fission primaries already start detonation of the HE at multiple points with microsecond precision. Why would multiple primaries be any different? The three stage TX-41 was supposed to have used two primaries synchronized in this manner, though I'm not sure how reliable that info is.