Re: H bombs

Eugene Leitl (
Sun, 1 Mar 1998 17:14:37 +0300 (MSK)

On Sat, 28 Feb 1998, John K Clark wrote:

> >Unless you are a massive, unstructured superalloy sphere you won't
> >survive a nuke fireball from a few m distance virtually unscathed.
> It wouldn't matter what you did, at that distance nothing would be unscathed,
> not even atoms.

What I've heard from graphite-coated steel balls (can't asess the truth,
since coming from an electronic source -- probably the nanotech archives,
yet plausible-sounding), they survived just fine.

The typical inertia-confined nuke uses a massive metal lining to confine
the fissible device kernal during about one the microsecond the nuclear
reaction takes to completion (don't know much about thermonuclear weapons
just now). Accompanying release of neutrons (anybody know the typical
concentration?) flashes throught the device, and, getting absorbed, heats
it quite suddenly. After that by many absorbance/reradiation steps the
entire device turns into a more-or-less homogenous (?) ball of dense
plasma of roughly 20-100 MK, which radiates mostly in the Xray region.
Ignoring the effects of air, the graphite coated steel balls (few ten m
from ground zero) experience assymetric explosive ablation due to absorbed
EM radiation, and hence a strong acceleration. (It is probably not a good
idea for human observers to persist up to this stage). If ever the spheres
get engulfed by a nuke fireball, then at a much later, milder stage.

Don't ask me about the exact size, location, and composition of these
spheres, and on their weight loss after the experience, though.

> >nukes are pretty useless in space, especially against rad-shielded
> >floating and underground habitats.
> I think that's a big overstatement. It's true that in a vacuum you wouldn't

Well, ok, I have to admit that I'd rather be pretty far away from any such
business. There is always some nonzero chance you wind up playing ground
zero, and you can suffer death from explosive decompression due to
hermetic hull puncture by debris, rad sickness (neutron nukes), etc. War
is only fun in a movie, or in a theoretical treatise. Imo, the more
theoretical, the better.

> get hit by a shock wave caused by the pressure of matter, but you would have
> to worry about the enormous shock from radiation pressure. We usually think

That would seem to assume the event is pretty close. The good thing about
space habitats, especially orbiting ones, is that there is/have to be
plenty of space inbetween. Your eggs are most assuredly not in a single

> of radiation pressure as being very weak, after all, we'd need a solar sail
> miles across to slowly accelerate a small space ship, the feebleness is
> partly because the sun has a small angular size near the Earth but mostly
> because the of the sun is so cold, less than 10,000 degrees at the surface.
> When things get really hot the pressure becomes astronomical, literally
> astronomical, because just a small increase in temperature means a huge
> increase in radiation pressure, the two are related to the FOURTH power.

>From the very few things I remember from my Atkins, the energy radiated by
a blackbody is proportional to T^4. However, the emission maximum gets
shifted to short wavelengths with higher temperature, which makes matter
far from being a perfect reflector/absorber. So you've got quite a few mm
of material suddenly heated, comparatively slowly exploding into space.
Moreover the effect is brief, the nuke fireball in space cooling very
rapidly, I'd hazard a roughly exponential decay of the temperature. Also,
assuming wide habitat separation, on the average that means a few km
between me and ground zero.

I wouldn't want to face a nuke from that close while on a spacewalk (btw,
anybody knows whatever happened to these NASA study suits made from
several layers of thin rubber instead of bulky constant-volume-joint
monsters which are used now?), but it sounds highly survivable while
sitting in a large space habitat, shielded by several m of mineral/metal.
It would be interesting to assess the impacts of a deep-burrowing nuke
exploding in a few-km asteroid/comet kernal, the low density of the
material considered.

> If you heat up a tin can to temperature T the Black Body radiation pressure
> inside the can is 1/3 [QT^4] , Q is the radiation constant
> 7.56591* 10^-15 erg cm-3 Kelvin -4 . If you heated up the can to 90,000,000
> degrees the radiation pressure inside the can would be equal to the total
> pressure found at the center of the sun! Yes your target wouldn't be
> completely enveloped and would only receive the radiation from one side, but
> on the other hand, an H bomb can produce temperatures well over 200,000,000
> degrees, and the shock would be further enhanced because the outer layer of
> the target would vaporize and rocket outward and because momentum is
> conserved the inner parts would rocket inward.

Nothing new, so far.

> Incidentally, without radiation pressure an H bomb wouldn't work, the
> radiation from the fission trigger is the only way to compress deuterium
> enough to achieve fusion. You might think that photons of light couldn't
> evenly compress matter because of Rayleigh - Taylor instability, that's what
> would happen if you tried to support heavy mercury with a column of water,
> tiny tongs of mercury would force their way a small way into the water and
> then grow exponentially until the mercury had entirely fallen through the
> water. It's not at all obvious that the same thing wouldn't happen with light
> and matter, however detailed calculations by the military on the largest
> super computers of their day showed that this instability does not happen,
> photons really can compress matter evenly. This fact was kept top secret for
> many years, and when it was finally revealed, after painstakingly piecing it
> together in the early 1980's from hundreds of unclassified documents and
> after several people nearly went to jail, astronomers found it very
> interesting.

All very true, but really not applicable to my scenario described above. I
must play Dr. Strangelove's flamboyant rodeo to really experience the
dramatic effects you've just described. Antimatter pellets fired from a
matter catapult into a small spacecraft would probably demonstrate such

Btw, anybody knows what the highest achieved current in a proton
accelerator was? According data for record particle density in a neutral

> The interior of the sun is at a chilly 14 million degrees so radiation
> pressure is not very important, the gas pressure is about 1700 times greater,
> the same is true for most stars but not all, it is vitally important in
> super giantstars, supernovas, the accretion cloud around Black Holes, and in
> the H bomb it's the entire ball game.
> >What we should worry right now are not nukes nor nerve agents, but
> >engineered bioweapons (mostly viruses, not bacteriological bioweapons).
> That does worry me, another thing that worries me are the thousands of H bombs
> in the former USSR guarded by angry unhappy men who drink too much and make
> about a thousand dollars a year.

All true, but these poor blokes haven't got the arming codes. Assuming the
command-control structure is still centralistic, and the arming procedure
is similiar to the U.S. model, the launch commands must come from someone
standing pretty high in the hierarchy. Which, of course, doesn't mean it
can't happen.

Furthermore, the time fortunately works for us. As in the west, the
devices have not been designed to be recyclable. Aged nukes don't have
deterministic yield anymore (and are more dirty), nukes gone sour are
highly unreliable. Modern high-performance nukes, being high-tuned
devices, do not age gracefully.

While the nuke dangers are admittedly nonnegliegeable, the militant
molecular biologist Friends of the Earth or the walking virus bombs from
Jihad Unltd. scenario does worry me significantly more. Then the shit
hitting the fan always tends to hit you from an unexpected angle...