[Ultra-Tech] Mini-nuke TL

[Michael Thayne]

Some of the TL 9 devices in Ultra-Tech seem way ahead of what's otherwise implied to be available at that TL. Rigid armor values, for example, all over the place. Lately, I've been wondering if the mini-nuke is another example of this, something that should be booted to TL10.

Several possible trigger mechanisms are mentioned: "small laser diode, nuclear isomer, metallic hydrogen explosive, or microscopic pellet of antimatter". But many of these seem implausible. Antimatter traps are 20 lbs. and require continuous power to prevent them from exploding. Spaceships established metallic hydrogen exists for propulsion at TL9 (even though B415 puts metallic hydrogen weapons at TL10), but that would carry a high risk of unintended detonation. Nuclear isomers I've only seen in the "Ultra-Tech Too" article in Pyramid #3/51, but they're pegged as TL10. That leaves laser diodes, which I haven't seen referenced elsewhere in GURPS 4th edition products, and whose plausibility I'm unsure of.

You might think that fusion pulse drives imply the possibility of something like mini-nukes, but it's easy to imagine that instead of each fuel pellet having its own trigger, the drive uses a laser significantly larger than any 100mm warhead to detonate the pellets.

There's also the issue of general near-future plausibility. My understanding is that the US government would really like a pure fusion weapon, but has made little progress. Or maybe they've been making progress, just slowly? Or haven't actually taken it seriously in terms of funding? I'm no expert here.

Looking for everyone's opinions.

[AlexanderHowl]

An antimatter trap stores 10 micrograms for 20 lbs at TL9. A single nanogram of antimatter releases 180 kJ of energy when combined with an equal amount of matter, sufficient to fuse 200 micrograms of DT, which releases around 67 MJ of energy (~14 kg of TNT). In turn, the compression (and neutron bombardment) from that could cause 1 gram of uranium to detonate, releasing ~80 GJ of energy (~18 metric tons of TNT).

Working backwards, you would only needs 22 nanograms of antimatter to fuse 4.4 milligrams of DT to compress and detonate 22 grams of uranium to get a 1 kiloton explosion for up to 1 kiloton. You would 'dial-a-nuke' by releasing smaller amounts of antimatter into the DT, creating a smaller fusion trigger for th uranium detonation. At TL9, this would cost around $2000 in 'explosives', which is a fraction of the cost of the mininuke at TL9 ($40,000). A trap required for that little antimatter would cost $50, weight 25 grams, and could survive for 25,000 hours off of two B-cells.

[dcarson]

That assumes that a antimatter trap scales with how much antimatter it holds. The size listed might be the smallest you can make at that TL.

[Varyon]

Originally Posted by Michael Thayne

Spaceships established metallic hydrogen exists for propulsion at TL9 (even though B415 puts metallic hydrogen weapons at TL10), but that would carry a high risk of unintended detonation.

If you did want them available at TL 9, keep in mind both fission and fusion generally call for fairly precise geometries (in Heinlein's "The Long Watch," the main character wrecks the would-be usurper's nuclear arsenal by simply taking a hammer to the plutonium plates), so it may be a relatively simple matter for the nuclear fuel (be that deuterium, tritium, plutonium, uranium, or some mix) to typically be arranged such that it cannot sustain a nuclear detonation, but then be shifted into proper position once the nuke is armed. That would mean an accidental detonation of the metallic hydrogen fuse would wreck the warhead (and possibly the firing platform, depending on how powerful it needs to be), but not set off the nuke. You'd keep the fuse and warhead separate for transport, of course.

Originally Posted by Michael Thayne

That leaves laser diodes, which I haven't seen referenced elsewhere in GURPS 4th edition products, and whose plausibility I'm unsure of.

You'd need a fairly miniaturized laser to fit in a 100mm warhead, and at TL 9 laser weapons are pretty large (laser pistols and the like are TL 10), so I think you'd be justified in saying that solution would also call for TL 10.

Originally Posted by Michael Thayne

There's also the issue of general near-future plausibility. My understanding is that the US government would really like a pure fusion weapon, but has made little progress. Or maybe they've been making progress, just slowly? Or haven't actually taken it seriously in terms of funding? I'm no expert here.

Or they've been making quite a bit of progress, but it's too heavily-classified for us to know anything about it. That assumption could certainly work to justify having mininukes available at TL 9.

[Michael Thayne]

Originally Posted by Varyon

If you did want them available at TL 9, keep in mind both fission and fusion generally call for fairly precise geometries (in Heinlein's "The Long Watch," the main character wrecks the would-be usurper's nuclear arsenal by simply taking a hammer to the plutonium plates), so it may be a relatively simple matter for the nuclear fuel (be that deuterium, tritium, plutonium, uranium, or some mix) to typically be arranged such that it cannot sustain a nuclear detonation, but then be shifted into proper position once the nuke is armed. That would mean an accidental detonation of the metallic hydrogen fuse would wreck the warhead (and possibly the firing platform, depending on how powerful it needs to be), but not set off the nuke. You'd keep the fuse and warhead separate for transport, of course.

Yeah, I knew that. Though I suspect premature detonation of the trigger would damage not just the warhead but any other ordnance (and perhaps people) nearby. AlexanderHowl's design doesn't work if you are going for the "clean", pure-fusion device actually described in Ultra-Tech, but if his other numbers are right, I think you're looking at 5 or 6 pounds of TNT equivalent in the trigger, which is around 6dx2 or 7dx2 explosive damage, which could be worse but still isn't something you want going off unexpectedly.

[Rupert]

Originally Posted by Varyon

You'd need a fairly miniaturized laser to fit in a 100mm warhead, and at TL 9 laser weapons are pretty large (laser pistols and the like are TL 10), so I think you'd be justified in saying that solution would also call for TL 10.

However, a single-shot system of exceeding short active life that functions at very short range would be much more compact, needing neither large focussing systems nor any sort of cooling system.

I don't see any particular reason why mini-nukes shouldn't be a TL9 technology. Bear in mind that variable yield nukes are common today, and some have sub-kiloton minimum yields. The UT versions are just an extension of modern technology, and the only really questionable part is the 'clean' bit. So if they bother people on strict realism grounds (though remember that a lot of modern nukes are really TL7 designs, so the mininukes are actually +2TLs over what we consider current), just make them dirty and you're good.

[malloyd]

Originally Posted by dcarson

That assumes that a antimatter trap scales with how much antimatter it holds. The size listed might be the smallest you can make at that TL.

Not that that necessarily prevents using it for 100 mm mininukes. 100 mm ammunition generally is somewhere around 30 to 50 lbs. You can maybe fire one out of a tank gun or single shot shoulder missile launcher, but that's about as small as they go, and we were supposedly building 50 or 60 lb, 203 mm tactical nuclear weapons in the late 1950s for the M110 howitzer, so it's not all that dramatic an improvement.

[Michael Thayne]

I also wonder if metallic hydrogen would actually have the energy density to act as a fusion trigger.

[Fred Brackin]

Originally Posted by Michael Thayne

I also wonder if metallic hydrogen would actually have the energy density to act as a fusion trigger.

If you don't do anything to focus the energy very, very little would work as a fusion trigger. The question would be how well you could concentrate the energy into a small area.

Say that your fusion material is in the shape of a hollow sphere. You want to drive the material from the inner side of that sphere to collide in the middle and achieve high densities/temperatures even if only for an ininfinitesimally short time.

Exactly how high the temperatures you could achieve are wou;ld be a very technical question and probably no one here coudl answer it.

My antimatter triggered mini-nukes would be fission devices anyway. Fission is a lot easier to work with.

[johndallman]

Originally Posted by Rupert

Bear in mind that variable yield nukes are common today, and some have sub-kiloton minimum yields.

Typical yields are about 0.3Kt, 20Kt and 100+Kt. The 100+Kt yield is obtained by properly detonating the (two-stage, thermonuclear) device. 20Kt involves spoiling the geometry, or putting something in the way, so that the first stage detonates, but the second stage does not. 0.3Kt involves deliberately fizzling the first stage, by not adding the few grams of mixed deuterium-tritium gas that are used to "boost" the first stage to its full yield.

A device deliberately constructed for 0.3Kt yield would still need a critical mass of U-235 or Pu-239, which it would detonate in a very inefficient manner. Essentially, it's a device that can only fizzle. The US W54 warhead is an example, and weighed a minimum of about 50lb for the basic nuclear system. These have not seemed worth building in any quantity to any nuclear power. They consume lots of fissile material and are very dirty, far more so in proportion to their yield than any other kind of nuclear weapon. Their yield is also rather unpredictable: they may produce considerably less (or, rarely, more yield), depending on manufacturing tolerances.

Yes, these are TL7. Making them a lot better would require either far more powerful chemical explosives, or some other way of compressing dense metals.