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I was reading about the idea of using an electrodynamic tether to generate electricity for satellites in Earth's orbit using the planet's magnetic field, generating electricity but gradually lowering the satellite's orbit in the process. I had the idea to use a similar device on Europa, using it's motion through Jupiter's magnetic field.

Jupiter has a magnetic field much stronger than earth, with a magnetic moment 18,000 times higher, the moon Europa is well within the influence of this field. So presumably a conducting tether placed on Europa, which is orbiting at 13,743m/s on average with respect to Jupiter would convert some tiny fraction of Europa's virtually unlimited orbital kinetic energy into electricity which could then be used to power a lander, rover, or potentially some kind of heated "drill" designed to melt through the ice.

My questions are 1) is this actually possible? and 2) Could a useable amount of electricity be generated in this way, with present material limitations?, or would the tether have to be either too massive, long or superconductive in order to generate useful electricity?

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  • $\begingroup$ A huge consideration in space is weight. You aren't going to make a conductor on Europa, you've got to bring it, so could you make a tether-generator that's lighter and produces more electricity than a small nuclear reactor? $\endgroup$
    – GdD
    Oct 21, 2021 at 17:10
  • $\begingroup$ Probably not, the advantage would be that it would work permanently and passively, without needing to consider fuel running out or RTG's losing power as their isotopes decay, moving parts failing when using sterling engines, the need to produce expensive isotopes for rtgs, and it get's around public opposition to nuclear power in space. I am fairly confident it would be less massive than trying to use solar power at Jupiter though considering the meager strength of the sun that far out. $\endgroup$
    – Josh
    Oct 21, 2021 at 17:20
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    $\begingroup$ to add additional information: I found an old nasa paper from 1998 looking into using electrodynamic tethers in jupiter: ntrs.nasa.gov/api/citations/19980203952/downloads/… It seems like it's a viable way of generating power relatively close to Jupiter, but by the time you get out to Europa the strength of the magnetic field strength drops off too much for it to be really viable. Maybe in the far future it might prove to be useful though. $\endgroup$
    – Josh
    Oct 21, 2021 at 17:36
  • $\begingroup$ @GdD but a nuclear reactor requires fuel, and to the best of my knowledge there isn't a lot of plutonium around (or being produced) to power RTGs. So, "will there be more support to produce plutonium or create alternative power sources" might become part of the equation (certainly not the only one, and I am not arguing that tethers are feasible). $\endgroup$
    – Eike Pierstorff
    Oct 21, 2021 at 18:38

1 Answer 1

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You need a current flowing through a conductor loop to generate electric power. A single long conductor does not suffice, a closed loop is needed.

Electrodynamic tethers in Earth orbit use the space plasma to close the loop.

enter image description here

An electrodynamic tether can be described as a type of thermodynamically "open system". Electrodynamic tether circuits cannot be completed by simply using another wire, since another tether will develop a similar voltage. Fortunately, the Earth's magnetosphere is not "empty", and, in near-Earth regions (especially near the Earth's atmosphere) there exist highly electrically conductive plasmas which are kept partially ionized by solar radiation or other radiant energy. The electron and ion density varies according to various factors, such as the location, altitude, season, sunspot cycle, and contamination levels. It is known that a positively charged bare conductor can readily remove free electrons out of the plasma. Thus, to complete the electrical circuit, a sufficiently large area of uninsulated conductor is needed at the upper, positively charged end of the tether, thereby permitting current to flow through the tether.

Source https://en.wikipedia.org/wiki/Electrodynamic_tether

How are the electrons moved through the tether? There is the Lorentz-force shown in the following image:

enter image description here

Image source

The magnetic field B is vertical to both the current I in the conductor and the force F moving the conductor. The Lorentz-force effect may be reversed when the conductor is moved through the the magnetic field by an external force, the result is a current induced in the conductor. The loop for the current is closed by the vertical conductors outside of the magnetic field of the horseshoe magnet.

But for a tether moved through the magnetic field of Jupiter there is no outside of magnetic field, therefore the conductive space plasma is needed to close the loop for the current.

But I doubt there is a conductive space plasma on the surface or within the moon Europa.

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  • $\begingroup$ Thank you for the answer, I hadn't realized that, I'm guessing that the ice on the planet's surface would have too much resistance to close the loop, but could the tenuous 10^-12 bar atmosphere work? The atmosphere is mostly made of molecular oxygen generated by radiolysis of ice by Jupiter's radiation, perhaps not too dissimilar to earth's ionosphere. It also seems possible that charged particles may be able to make it down to the surface. $\endgroup$
    – Josh
    Oct 21, 2021 at 19:11
  • $\begingroup$ @Josh Ice with very low resistance would not help anyway. $\endgroup$
    – Uwe
    Oct 21, 2021 at 19:39

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