Re: Why big ships are too good...

> Samuel Penn <sam@bifrost.demon.co.uk> said...
> [heavy editing]
> >(and exactly how is an EMP missile supposed to work in the vacuum of
> >space??? EMP is caused by an atmospheric effect after all).

And to this, various people replied: "You're talking bollocks!" :)

Okay, I don't claim to be an expert at this, I was just repeating
the conclusion of a discussion in rec.arts.sf.science about the
effects of nuclear weapons in space that happened a long time
ago. Anyway, since you've all challenged my statement, I though
I'd check the Nuclear Weapons FAQ for more details, 

(The FAQ is at http://astro.uchicago.edu/home/web/jeffb/abomb/nfaq0.html
for those interested - it is _very_ long though. Section 3.5 is the
bit which deals with Electromagnetic Effects).

My understanding of EMP is that it is caused by the absorption of
gamma rays in a particular way due to the different layers of the
atmosphere. Checking the FAQ seems to support this belief. Text
indented with "=" is taken from the FAQ (but edited for brevity):

= According to the FAQ, EMP is generated by the asymmetric absorption
= of instantaneous gamma rays produced by the explosion. Mid-altitude
= bursts don't produce much EMP, because the gamma rays are absorbed
= fairly uniformly. Low altitude and high altitude bursts do.

I would think space would absorb gamma rays pretty damn uniformly.
Anyway, the FAQ goes on to say:

= ...these gamma rays collide with electrons in air molecules, and eject
= the electrons at high energies through a process called Compton
= scattering, generating a cascade effect.

I think when Matthew said "no pesky molecules to scatter and
absorbe it" he summed it up pretty well, though not in quite
the way intended :)

= In low altitude bursts, the Earth acts a conductor...producing
= a strong magnetic field. High altitude explosions produce much
= more EMP, it being formed when the downwardly directed gamma rays
= ecounter denser layers of air below. The Earth's magnetic field
= causes the electrons to spiral as they travel producing a powerful
= downward directed magnetic pulse. A strong vertical electrical field
= is also generated between the Earth's surface and the ionised layer.

Anyway, the result of all this is that I still believe I'm right.
No mention is made of whether you do _need_ an atmosphere, but the
description of how EMP is created would seem to be invalidated if
you didn't have (a) an atmosphere and (b) ground.

Now, before anyone mentions it, space ships do have an atmosphere
inside them, so maybe a small EMP effect could be produced inside
them (though the atmosphere here would be pretty uniform), but it's
probably unlikely.

Having now put forward the case for the defence, I'll leave it
to someone else to show me where I've gone wrong. If I have gone
wrong, please tell me.

-- 
Be seeing you,
Sam.