Author Topic: Recreating a magnetosphere by putting a coil on Mars’ equator: problems/solution  (Read 6084 times)

Offline Proponent

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Artificial Geomagnetic Field to Protect a Crewed Mars Facility from Cosmic Rays

Does "This is all still first-pass.  It needs magnetohydrodynamic modeling for completeness...." mean that that the modeling thus far consists of tracing the trajectories of individual particles subject to the magnetic field generated by the current loop?  If so, I might worry that MHD effects could dominate.  A quick reality check would be to compare the current flowing in the shield with the current in the incoming charged particles falling within it.

MHD effects, of course, would not invalidate the concept but could change the parameters quite a bit.
« Last Edit: 08/07/2018 02:07 PM by Proponent »

Offline LMT

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I suspect that a constant field which varies only gently from place to place is less dangerous than an intermittent or rapidly-varying field of similar intensity, because the electric fields and currents it will induce in the human body will be weaker.

Magnetostatic fields avoid unwanted induction, surely.  Did you think we designed something other than a magnetostatic shield for Mars?

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Abstract
We have designed an artificial local geomagnetic field, or magnetostatic shield, to protect a crewed Mars facility from cosmic rays.  The shield is modeled after the results and suggestions of Motojima and Yanagi 2008.  Modeling indicates that the shield is effective against protons to 1 GeV.  The shield deflects all solar storm protons, nearly all solar flare protons, and more than half of Galactic Cosmic Ray (GCR) protons.  The design applies existing technology from superconducting power lines, superconducting solenoids, and carbon nanotube (CNT) cables...

Notably, electrostatic shields can't work in the martian atmosphere due to its high conductivity.  This exhausts present E/M shielding options.  SpaceX et al. would use a magnetostatic shield for such reasons.

Offline LMT

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Artificial Geomagnetic Field to Protect a Crewed Mars Facility from Cosmic Rays

Does "This is all still first-pass.  It needs magnetohydrodynamic modeling for completeness...." mean that that the modeling thus far consists of tracing the trajectories of individual particles subject to the magnetic field generated by the current loop?  If so, I might worry that MHD effects could dominate.  A quick reality check would be to compare the current flowing in the shield with the current in the incoming charged particles falling within it.

MHD effects, of course, would not invalidate the concept but could change the parameters quite a bit.

Yes, the sim tracks individual protons.  Max shielding current is 6.4 MA, in cables envisioned as HTS cables, which presently have practical current density of ~ 1000 A/mm2.

re: MHD:  A flare's disturbance of the geomagnetic field might be the more useful first MHD check.  On Earth a flare disturbance ballparks 1E-6T as in Blanch et al. 2013.  The initial Omaha Field design exceeds 1E-1T near center.  That's 5 orders of magnitude in difference; so modeled MHD effects shouldn't change basic shield design parameters much.  MHD flare modeling would however produce an interesting sim animation of Omaha Field operation.

Refs.

Blanch, E., Marsal, S., Segarra, A., Torta, J. M., Altadill, D., & Curto, J. J. (2013). Space weather effects on Earth's environment associated to the 24–25 October 2011 geomagnetic storm. Space Weather, 11(4), 153-168.
« Last Edit: 08/09/2018 02:09 PM by LMT »

Offline Proponent

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I suspect that a constant field which varies only gently from place to place is less dangerous than an intermittent or rapidly-varying field of similar intensity, because the electric fields and currents it will induce in the human body will be weaker.

Magnetostatic fields avoid unwanted induction, surely.  Did you think we designed something other than a magnetostatic shield for Mars?

I wasn't commenting on your design at all but merely reflecting on ThereWasI3's musings about suggestions that fields much weaker than Earth's might be hazardous.  The static 500-μT field you envision for the crater floor does not strike me as anything to worry about, though of course I'm no expert.

Static magnetic fields will of course still induce currents as astronauts move through them, but, again, I'd have though these would be so small as to not be an issue (nothing like what happens inside an MRI machine).

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Notably, electrostatic shields can't work in the martian atmosphere due to its high conductivity.

I'm not disagreeing.  I think the magnetostatic shield is a promising idea.  I just think you may need to consider MHD effects even in a first-look analysis.

EDIT:  "yo0" -> "you"
« Last Edit: 08/12/2018 05:06 PM by Proponent »

Offline Proponent

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Yes, the sim tracks individual protons.  Max shielding current is 6.4 MA, in cables envisioned as HTS cables, which presently have practical current density of ~ 1000 A/mm2.

re: MHD:  A flare's disturbance of the geomagnetic field might be the more useful first MHD check.  On Earth a flare disturbance ballparks 1E-6T as in Blanch et al. 2013.  The initial Omaha Field design exceeds 1E-1T near center.  That's 5 orders of magnitude in difference; so modeled MHD effects shouldn't change basic shield design parameters much.  MHD flare modeling would however produce an interesting sim animation of Omaha Field operation.

I don't understand why the flare would relevant (are you assuming the that flare produces a plasma, whereas the usual, non-flare solar wind is essentially a stream of independent particles?).  The question is, can the incoming particle flux be treated as a diffuse hail of isolated particles, or is the MHD limit a better approximation.  If the aggregate incoming current is comparable to or greater than 6 MA, then I would think the stream's own magnetic field could be a major factor in its behavior.

EDIT:  "where as" -> "whereas"
« Last Edit: 08/12/2018 05:06 PM by Proponent »

Offline LMT

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Yes, the sim tracks individual protons.  Max shielding current is 6.4 MA, in cables envisioned as HTS cables, which presently have practical current density of ~ 1000 A/mm2.

re: MHD:  A flare's disturbance of the geomagnetic field might be the more useful first MHD check.  On Earth a flare disturbance ballparks 1E-6T as in Blanch et al. 2013.  The initial Omaha Field design exceeds 1E-1T near center.  That's 5 orders of magnitude in difference; so modeled MHD effects shouldn't change basic shield design parameters much.  MHD flare modeling would however produce an interesting sim animation of Omaha Field operation.

I don't understand why the flare would relevant (are you assuming the that flare produces a plasma, where as the usual, non-flare solar wind is essentially a stream of independent particles?).  The question is, can the incoming particle flux be treated as a diffuse hail of isolated particles, or is the MHD limit a better approximation.  If the aggregate incoming current is comparable to or greater than 6 MA, then I would think the stream's own magnetic field could be a major factor in its behavior.

Field disturbance is the relevant result, and indirect measure of currents.  Compare Omaha Field current density to the flare's Birkeland current density and proton flux.

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