# Thread: Can electric pwr be obtained from a planetary magnetosphere?

1. Ok, this is a complex set of questions.

Let's say that you're in orbit around Jupiter, riding one of the Galilean satellites. Then you build a space elevator there, which is roughly a gigantic rod protuding from the moon surface... as it spans across Jupiter's magnetosphere, it will behave as a gigantic antenna... am I right?

Then, this antenna will gather a huge electrical charge as the atoms in it are excited by Jupiter's magnetosphere... right?

And the final question is, would this charge, gathered by the space elevator/antenna, be enough to use the space elevator complex as a power source? Any clue on how to calculate the power output?

I repeat my questions...

- Is it right to think that a space elevator on a Galilean satlelite of Jupiter could behave as an antenna?
- Is it true that it could gather a massive electric charge?
- Could this charge be used as a power source? (where the antenna would play an anode and the moon a cathode)
- How can be estimated the power output of such power source?

2.

3. Originally Posted by Lucifer
Ok, this is a complex set of questions.

Let's say that you're in orbit around Jupiter, riding one of the Galilean satellites. Then you build a space elevator there, which is roughly a gigantic rod protuding from the moon surface... as it spans across Jupiter's magnetosphere, it will behave as a gigantic antenna... am I right?

Then, this antenna will gather a huge electrical charge as the atoms in it are excited by Jupiter's magnetosphere... right?

And the final question is, would this charge, gathered by the space elevator/antenna, be enough to use the space elevator complex as a power source? Any clue on how to calculate the power output?

I repeat my questions...

- Is it right to think that a space elevator on a Galilean satlelite of Jupiter could behave as an antenna?
- Is it true that it could gather a massive electric charge?
- Could this charge be used as a power source? (where the antenna would play an anode and the moon a cathode)
- How can be estimated the power output of such power source?

I don't see why not it could't be used as a power source.

4. Originally Posted by Lucifer
Ok, this is a complex set of questions.

Let's say that you're in orbit around Jupiter, riding one of the Galilean satellites. Then you build a space elevator there, which is roughly a gigantic rod protuding from the moon surface... as it spans across Jupiter's magnetosphere, it will behave as a gigantic antenna... am I right?

Then, this antenna will gather a huge electrical charge as the atoms in it are excited by Jupiter's magnetosphere... right?

And the final question is, would this charge, gathered by the space elevator/antenna, be enough to use the space elevator complex as a power source? Any clue on how to calculate the power output?

I repeat my questions...

- Is it right to think that a space elevator on a Galilean satlelite of Jupiter could behave as an antenna?
- Is it true that it could gather a massive electric charge?
- Could this charge be used as a power source? (where the antenna would play an anode and the moon a cathode)
- How can be estimated the power output of such power source?
No idea really, but... it would seem to me that a giant antenna would quickly get snapped off if it generated that much electrical charge, ie. it would be impossible to keep stable, or even whole.

5. Originally Posted by sunshinewarrio
Originally Posted by Lucifer
Ok, this is a complex set of questions.

Let's say that you're in orbit around Jupiter, riding one of the Galilean satellites. Then you build a space elevator there, which is roughly a gigantic rod protuding from the moon surface... as it spans across Jupiter's magnetosphere, it will behave as a gigantic antenna... am I right?

Then, this antenna will gather a huge electrical charge as the atoms in it are excited by Jupiter's magnetosphere... right?

And the final question is, would this charge, gathered by the space elevator/antenna, be enough to use the space elevator complex as a power source? Any clue on how to calculate the power output?

I repeat my questions...

- Is it right to think that a space elevator on a Galilean satlelite of Jupiter could behave as an antenna?
- Is it true that it could gather a massive electric charge?
- Could this charge be used as a power source? (where the antenna would play an anode and the moon a cathode)
- How can be estimated the power output of such power source?
No idea really, but... it would seem to me that a giant antenna would quickly get snapped off if it generated that much electrical charge, ie. it would be impossible to keep stable, or even whole.
It wouldn't be like a regular radio antenna, but an antenna shaped as a space elevator, or a space elevator playing as an antenna... with a counterweight in stationary orbit around the moon and the cable/antenna linking it to the surface of the moon. I guess it would be about 10,000 kilometers long (haven't done the calculations yet, but, on rough estimate would be about that).

Yet I am not enoguh fmailiar to antennas and Jupiter magnetosphere as to judge wether it would be practical, wether it would create a sizable electric current, and if the magnitude of such current would pay back for building the thing.

6. That sounds really cool, Then, they could transmit the energy over microwave transmitters to be converted for use on the moon or earth.

7. The way I see it, an antenna can only receive energy if the electric or magnetic field around it is alternating. So the moon would have to move around Jupiter in some orbit where the magnetosphere's strength varies with position.

Another idea would be to apply faraday's law, make a space elevator and wind a coil around it from the ground to the top of the elevator(the more coils the better). If there is a magnetic field moving over a coil then the amount of voltage generated would be
v= surface_integral(cross_product(velocity,B field))*turns
which comes from a book of mine, I wont bother with the derivation :P

Dont know how much power it will be but I think that for the cost of such a endeavour you would get more energy by putting solar panels near the sun.

8. Any conductor moving through a magnetic field (varying or not) will generate a current. Similar questions have been asked before. A few hundred feet of wire orbiting Earth generated enough charge to blow the wire away from its anchor when it arced.

9. I've been asking at another forum and there they told me it wouldn't work, as what inducts current is the variation of the magnetic field, not the movement. Although it moves very quickly, Jupiter's magnetospehre is quite homogeneous.

It woud work if the coil was moving in a polar orbit (although would need propulsion to counter the induced drag on the wire), but as the whole point was powering stuff on Jupiter's moons, then this is a dead end.

Additionally, building a space elevator on a Galilean moon would be quite difficult; L1 and L2 are pretty unstable due to the interference of the other moons and the only stable points for the counterweight would be L4 or L5... both of them 600,000 kilometers away in the case of Europa! Call that a wire too far...

10. Originally Posted by Lucifer
they told me it wouldn't work, as what inducts current is the variation of the magnetic field, not the movement.
So long as there is relative movement between the magnetic field and the conductor/antenna, then current will be induced. If the conductor is stationary, and the magnetic field is changing, then current will be induced (the basic principle of inductive coupling in antennas), If the magnetic field is uniform, but the conductor is moving through it, then current will be induced.

11. You need a closed loop or a coil moving in a static magnetic field to induce a current. As soon as the loop is loaded..(take power out of it) it would be a drag on the satellite and it would fall out of orbit..

12. Of course you know, the energy isn't totally free. The moon your antannae is attached to will lose momentum gradually over time (hopefully a very long time), and if you kept it going long enough (maybe millions of years, mind you), it would eventually fall into Jupiter's atmosphere.

13. But, if the magnetic field is constant, then this causes no induction... as much, they say, a constant magnetic field could cause Hall effect in the appropiate conditions.

What they says is:

, yet rotation varies as and so if is not parallel to then the flux will vary and a current will be inducted.

Whatever this means!

14. But, if the magnetic field is constant, then this causes no induction
Yes, but the moon will move through the field lines as it rotates around the planet and on its own axis. That is all that is needed. That is what they mean with the field changing.

15. Suppose we use a moon like Amalthea, which always faces the same side toward Jupiter? (Just like our moon always faces the same side toward us).

I don't think you'd get an electric current unless the wire/antenna were moving between areas of stronger and weaker magnetic force, though, so you might not get any electricity from an orbit. Well, the fact most orbits are elipses means that you'll be closer to Jupiter for some parts of the trip than others, but if it were a circular orbit, you might not get any actual electricity out of it.

16. It won't matter, the moon is still moving around the planet. As long as something's changing, you should still get some current.

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