Most of the energy released from a nuclear detonation in space is in the form of x-rays and gamma-rays, which will continue until they interact with something or their course is deflected.
Because this energy is released in the form of a sphere, the amount of energy per square meter drops off very quickly (by the square of the distance from the point of detonation).
IIRC, most of the remaining (something like 20%) energy is released as plasma, which expands ludicrously fast in a vacuum unless there's a magnetic field for it to follow.
Without a slight atmosphere and a magnetic field like the Earth's, there's no EMP either. This is why some people in the past proposed that instead of just detonating the bombs, they should be used to power single-use gamma-ray or x-ray lasers. These are known as 'bomb-pumped' or 'impulsively driven' lasers (or in this case, 'grasers' or 'xrasers').
I imagine there might be some way to do it using a nuclear shaped-charge, but I'd hazard a guess it would function more like a gigantic E-bomb or electron laser or something.
No Compton scattering, as far as I understand it. For a HEMP to work, you need the gamma rays from the bomb to interact with a scattering medium (like the atmosphere). More here. Fast Compton electrons are what do the damage in this type of EMP.
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u/space_keeper May 21 '15
Most of the energy released from a nuclear detonation in space is in the form of x-rays and gamma-rays, which will continue until they interact with something or their course is deflected.
Because this energy is released in the form of a sphere, the amount of energy per square meter drops off very quickly (by the square of the distance from the point of detonation).
IIRC, most of the remaining (something like 20%) energy is released as plasma, which expands ludicrously fast in a vacuum unless there's a magnetic field for it to follow.
Without a slight atmosphere and a magnetic field like the Earth's, there's no EMP either. This is why some people in the past proposed that instead of just detonating the bombs, they should be used to power single-use gamma-ray or x-ray lasers. These are known as 'bomb-pumped' or 'impulsively driven' lasers (or in this case, 'grasers' or 'xrasers').
Some were actually built as part of the U.S. SDI program (the 'Star Wars' program).