Re: H bombs

Eugene Leitl (
Mon, 2 Mar 1998 22:37:34 +0300 (MSK)

On Sun, 1 Mar 1998, John K Clark wrote:

> [...]
> >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.
> I don't see where you're going with this. If the target reflects a photon
> then it will receive a jolt equal to twice the photon's momentum of hc/w,

The reflecting plane is not flat, most photons do not get reflected but
absorbed (xRay mirror they are not), causing the surface material to turn
into a gas cloud exploding outwards. By the bulk, the counteractio is
pressure from hot, dense gas acting onto the surface, not from the photon
rebound. (Which is, btw, the chief problem of a nuke-driven solar sail:
you'd need a gas cloud to attenuate the xrays into the VIS scale where the
solar sail can act as a reflector). Surface turned into gas expands into
vacuum, relaxating by EM radiation into the environment, which, if not
sol-proximal, is few-K (Big Bang echo) cold space.

> h is Plank's constant c is the speed of light and w is the wavelength of the
> photon. If the photon is absorbed then it will only get half as much momentum
> but the energy absorbed will contribute to the rocket effect, exploding the

You do not account for energy relaxation by radiation into surroundings.

> outer layer of the target outward and compressing the inner layer. Either
> way if you're close to a H bomb so many photons will be encountered that

My point is that we are not so very close to ground zero.

> you'll feel a hell of a bang even in a vacuum.

See the escaping steel spheres.

> >Moreover the effect is brief, the nuke fireball in space cooling
> >very rapidly
> Granted, but when you're talking about pressures comparable to those at the
> center of the sun it wouldn't take long to shatter a target.

We are not riding the nuke, other relaxation pathways are not accounted
for -- and I'd like to see some numbers.

> >Also, assuming wide habitat separation, on the average that means a
> >few km between me and ground zero.
> Ok, if it's a few kilometers away then there are things you could do to
> protect yourself from a small H bomb, but even today ICBM's can achieve
> better accuracy that that.

Is 100 MT small enough? The difficulties we are talking about is hitting a
flurry of habitats/mosaic of subterranous settlings semisimultaneously,
requring a large number of brilliant warheads. And fissible material yield
should not scale very well in sub-kT range. Which does not mean it cannot
be done, of course. The more I think of it, the less I like it. Sneaky,
football-sized nukes.

> >Modern high-performance nukes, being high-tuned devices, do not age
> >gracefully.
> True, that's mainly because of the tritium, H bombs don't need a lot of it
> but they do need some and it's very expensive and has a half life of only
> 10 years.

A modern thermonuclear nuke would probably want to minimize the fissible
content, which would require high compression ratios and peachy-clean
isotopic compositon. Also, I think high explosives won't like prolonged
curing under high-rad conditions. Apart from that, the lithium
deuteride/tritide pellet homogenity should also suffer from transmutation.

> Wolfkin On Sun, 1 Mar 1998 Wrote:
> [...]
> means the foam further from the fission trigger must receive weaker X rays
> and explode with less power, this would compress the fusion cylinder unevenly
> making a dud.

Maybe that's why they took polymer foam instead of polymer solid, and
adjusted the geometry accordingly to compensate for that. There's a reason
thermonuclear devices are so difficult to build.

> It's clear that foam is important in an H bomb but probably not for the reason
> Morland's lawyers said. I don't know it for a fact but here is my theory.

Interesting thread. I'd like to see some design bluepauses, but I guess
that's still decades off.