Science Nerds: Could Jupiter's Magnetic Field be harvested for energy?

[Anomalocaris]

What are you thinking of using Jupiter’s magnetic field to power?

A civilization. 

The Jovians live on orbital rings that they have built around the moons of Jupiter. Using a large "wire" (even several hundred kilometers long) would be possible for them to build. They are the most advanced civilization in the solar system. But I want it to be (theoretically) possible. Otherwise, I'll consider using fusion.

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Since it's science fiction, why bother making the power source plausible? Artificial gravity isn't plausible, nor phasers, transporters, light sabres, and so on and so on.

Since you're setting this far into the future, it stands to reason that there would be some significant scientific advancements during that time. Just postulate a synthetic element (you have my blessing to call it 'borudium') that transforms magnetic fields directly into usable electricity.

Boru

You could go two ways with science fiction. Most space operas do what you suggest and invent new science to make things (like faster than light travel) possible. Star trek is probably the best example of this. I'm trying to do "hard science" fiction, where everything is grounded in our current understanding of physics, but there is a technological advance that makes cool things possible.

What I'm trying to make unique about my setting is that there are many alien races (like Star Trek) but no interstellar travel in one lifetime (as most physicists think would always be the case). And even if you could, there'd be complications with abusing time dilation and such.

I suspect the problem with using wires in the Jovian magnetosphere to harness energy will always be that the act of inducing current in the wire for harnessing will always imparts a force on the wire.   The more the current, the greater the force.   

If the wire is rooted in an artificial object in orbit about Jupiter, such as your ring, that force pulling on the wire will be either be adding to or subtracting from the orbital energy of the object.   The problem once again becomes any energy you get out of the wire ultimately comes from orbital energy of the object. So eventually the object will either crash down into Jupiter or be pulled out its orbit about Jupiter.   If the object needs a lot of power from the wires, it will be pull out of its orbit that much sooner.    To fix the problem, you have to supply as much energy as you get out.   So I suspect wires moving in Jovian magnetosphere can not be a sustainable long term source of energy for any energy intensive artificial object in orbit about Jupiter.

However, I propose a slightly different use.     What if you tether the wire to something so massive all the energy you will ever need won’t make any practical difference to its orbital energy?   Something really massive, like a Galilean moon?    I imagine you can make carbon nano-tube wires really strong so it can be tends of thousands of miles long.   Remember the Jovian moons are phase locked to Jupiter.    You anchor one end to the surface of the moon antipodal to Jupiter.    Make the wire long enough so the other end if we’ll farther from the surface of the moon the synchronous orbit height of the moon.    The centrifugal force of acting on the distal end of the wire will keep it from falling back on to the moon and counteract the pull of the induced current in a magnetic field.     As the moon revolves around Jupiter, the wire will sweep through Jovian magnetosphere and continuously supply energy to the moon. 

Have to work out whether such a wire can be stable in the 4 moon Galilean satellite system of Jupiter, thou.

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A civilization. 

The Jovians live on orbital rings that they have built around the moons of Jupiter. Using a large "wire" (even several hundred kilometers long) would be possible for them to build. They are the most advanced civilization in the solar system. But I want it to be (theoretically) possible. Otherwise, I'll consider using fusion.

I think it would be possible.  I'm just not sure what engineering scale is needed to create enough energy for such a civilization.

Putting wires in space that generate energy causes drag.  The energy gained is your lost kinetic energy.  When ON a moon, the lost kinetic energy of the moon can be ignored, but in any orbital ring, you could be in trouble, unless the drag is directly in the direction of the moon's motion, and perpendicular to the ring (whereby the moon's gravitational field still pulls you along without upsetting the ring).

One thing about rings around things -- they aren't stable.  Larry Niven knew about this with his Ringworld series.  They need constant adjustments to stay in stable position, or they just drift and hit what they are moving around.  They aren't actually in an orbit.

Now, separate orbiting bodies (like rotating space stations) are stable because perturbations just change the eccentricity of the orbit -- but too much purturbation (like would be caused by an energy-generating wire) would eventually de-orbit you.  There is no free lunch there.

So, energy on the surface of the moons, is a YES.  On an orbiting body is a NO

Beat me to it.