Second post, and allow me to put my 2 cents into the earlier discussion about Mars's magnetosphere
. For those interested :
http://www.newmars.com/forums/viewtopic.php?id=6122&p=1
It seems that making a magnetosphere would not be such a challenge for a human civilization as described in Outsider. To quote orionblade :
"I have done some back of the envelope calculations on this very topic recently, and I will post merely the results - if anyone's interested in seeing the actual calculations, I don't mind scanning and posting an image of my notes at some point.
In any case, I assumed the worst - a single loop of "wire" - the most malleable/ductile superconductor we have currently is niobium-tin, or in some cases niobium-tin-copper compositions. Assuming this is a single large cable to be unspooled in orbit around Mars, "spun up" as an MRI machine's magnet is powered up, and the whole thing encased in a fairly thin, thermally insulating conduit, and provided with a solar shield around its periphery, this should be able to maintain a low orbit at roughly 200-250Km.
I chose this altitude, versus geostationary, since we want to use the lowest current possible to generate a magnetic field, and the least amount of material possible. Further, the rotational motion of the coil relative to the spin of the planet may add a bit to the effective current, if only a negligible fraction.
My calculations left me somewhat disappointed: For an Earth-equivalent field of roughly 70 gauss, a one-meter diameter niobium-tin alloy superconducting cable, assumed to be solid for purposes of calculation, cooled with liquid helium, would be sufficient, but would require roughly 100% of our annual worldwide niobium mine output for a period of roughly a century, and nearly 10 years worth of Tin production. Taking into account mines that are planned or currently under construction, this could be reduced to roughly 65-70 years. The cost is astronomical, just for materials.
On the bright side, this technique is aided by the damn-near absolute-zero of outer space, so the portion of the cable eclipsed by the planet's shadow should provide enough cooling to allow something as simple as peltier junctions mounted every few meters to counteract any solar irradiation incurred beyond what a properly-spaced reflector could not handle on the day side. Since the whole cable would ride through the shadow every 90 minutes or so, and the solar shield/reflector could be composed of solar panels, the feasibility, if not the initial cost, becomes evident.
Further, the calculations assume that there is absolutely no planet in the middle of the coil. Since Mars has quite a bit of iron through its surface, mantle, and core, presumably, this would become a ferromagnetic core, increasing the field strength. Also, I neglected any plasmadynamic effects. If the field were caused to oscillate, or even held steady, but allowed to gather energy as an electric guitar pickup does, from the moving, time-varying plasma current, one could assume that the power for the coil could be had on-site, and only a minimal current required for start-up, with the current building in opposition to the solar wind, so long as seasonal variations were somewhat sizeable. Depending on the effective permeability of the planet as a magnetic core, the entire thing might well be scaled down by an order of magnitude or two. Further, with vastly superior deflection of electrons than protons, an electron-rich solar wind would allow the induced electric field to do most of the work. Another concept I failed to explore further, mathematically, would call for a non-single-loop coil geometry. Multiple turns wouldn't get you very far, but a helical or interlaced loop geometry could enhance local field strengths such that the aforementioned plasmadynamic effects could yeild a higher electric field strength, and thus better shielding. In any case, any shielding effected would be better than nothing, and the atmosphere should build.
Please consider this one key fact that is often overlooked: Mars' atmosphere is in a state of dynamic stability - it is continually losing atmospheric gas to nonthermal loss mechanisms, yet its atmosphere continues to remain at a stable, if low, pressure and density. If we inhibit even a small fraction of the loss, the atmosphere would build. If on the other hand, we build the atmosphere, we will be losing, perhaps the same percentage, but much more of the atmosphere. We'll be driving the reaction towards loss by adding gas to a lossy system. If we instead reduce loss mechanisms, the gases will add themselves, from whatever surface or subsurface sources are already in operation (anyone notice the detection of subsurface Methane sources not too long ago?). I'll have to look up the effective velocities, and calculate turning angles required for various orbits, perhaps writing up a system of equations and optimizing them for minimum material required (low loop current vs. shorter cable). It may very well be that a geostationary ring would require vastly lower current to achieve an adequate turning angle of maximum solar wind velocity, since it is further from the planet, or it could be that we would be better off with a larger diameter cable much lower in orbit, permitting a larger field but with considerably less cable length to encircle the planet at a lower altitude.
Either way, i would point out that any solution with a multitude of orbital components that are not physically connected, will be subject to magnetic attraction, or at least torques, which would require continual energy input to overcome. I think a single loop, or some variation on this Dyson-like ring is a better bet, since the loop would auto-inflate to a nearly perfect circle under the influence of its own magnetic field, much like a loop of string floating on a soap bubble. Individual magnets would pull together, and multitudes of loops would at the very least rotate to become a toroidal magnetic field, and the gaps between the loops would actually cause a degree of focusing.
It has also occurred to me that a slightly weak magnetic field might result in protection near the tropics, but deposition of solar wind components near the poles - thus heating the poles somewhat, but also adding hydrogen and helium to the atmosphere. Admtitedly, these would boil off rather quickly, but there should be enough radical production that water vapor would be created, and gravitationally retained within the atmosphere... I am uncertain as to the equilibrium state with high incidence angles for stellar wind particles on the atmosphere, if they would eject atmospheric particles more, or if they would be captured at a greater rate than the loss mechanisms... it's an interesting mathematical problem."
Seems like all we'd need is some tin and niobium. Well.....lots of it.