On Apr 18, 10:10 am, CharlesRCap...@[EMAIL PROTECTED]
wrote:
> On Apr 17, 2:45 pm, Luke Campbell <lwc...@[EMAIL PROTECTED]
> wrote:
>
> Sure, but that becomes much less plausible if you need tethered spin
> habs and thus any radiation shielding capable of dealing with
> Jupiter's radiation belts would require more extensive explanation.
My favorite design involves the spin habitat "pressure cans" on
tethers with superconducting cables forming two concentric loops -
once just to the outside of the habitat path and one just inside of
the path. Current flows along the two cables in the same direction,
the magnetic fields largely cancel in the region between the two
loops, and add outside that region. This leaves a relatively mag-
field free region for the habitats to orbit while deflecting charged
particles. In fact, this system is most effective with tethered spin
habs, there isn't much protection near the axis.
The limits on the effectiveness of this system are your ability to
cool the superconductors to below their transition temperature, the
critical magnetic field of the superconductors, and the attractive
force between the two loops due to the parallel currents. By spinning
the outer loop at high speeds, you can put the entire assembly under
tension, eliminating the need for compressive struts between the two
loops to keep them from collapsing into each other. Numerical
simulations I've done indicate you could protect the habitats from
protons with up to around a GeV in energy with moderate forces between
the loops (details are on another computer in another location, I can
post these later if anyone is interested).
This is far from the only design for electromagnetic shielding, just a
relatively simple radiation shield based off of magsail propulsion
concepts. I understand there are significantly more elaborate
proposals for electromagnetic radiation shielding in space.
> In any case if we are talking about "hard" SF you need to be careful
> about those throw away lines. If the reader doesn=92t agree with its
> plausibility you have a tough time maintaining that "hard" SF
> classification.
That's what appendices are for :-)
In any event, you can't be expected to describe all the details of
every technology that we don't have today. I would be quite happy
with hard scifi where a military spacecraft used UV lasers as
offensive weapons without a detailed explanation of how the UV beams
were generated or discussions of the tactics of beams vs missiles
(unless, of course, the latter was vital to the story). To my way of
thinking, electromagnetic shielding is similar. Charged particles can
be deflected by magnetic fields, magnetic fields can be generated by
electric currents and possibly manipulated by injecting and trapping
plasma into the field region resulting in an artificial magnetosphere
similar to that of earth. This is all known physics, and that's
sufficient for plausibility, no need to go into engineering details in
a work of fiction. Heck, if people can swallow fusion reactors
despite all the known problems (with no mention of how they operate),
electromagnetic or plasma shields should be fine with a brief
justification. Especially if the consequences are well though out
(the aforementioned radiation belts around the spacecraft, regions of
high magnetic field around the shielding loops where you need to be
careful with ferrous objects, possibly others). Just don't have your
electromagnetic shields protecting against neutrons or gammas or other
uncharged particles!
Luke
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