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The NASA's space tether experiment in 2001,called for a scientific payload--a large, spherical satellite--to be deployed from the US space shuttle at the end of a conducting cable (tether) 20 km long. The idea was to let the shuttle drag the tether across the Earth's magnetic field, producing one part of a dynamo circuit. The return current, from the shuttle to the payload, would flow in the Earth's ionosphere, which also conducted electricity. The experiment, unfortunately, couldn't be realized at that time.

With the present technology, is it possible to put this into practical use? How much energy can be harnessed on the average from such tethered system typically? Could it be scaled up for gradually reducing the orbital velocity of spacecraft in orbit before reentry?

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  • $\begingroup$ I believe Scott Manley talked about this in one of his videos. $\endgroup$ May 10, 2021 at 7:30
  • $\begingroup$ I have heard of this and I’m not too sure how the system operated but I believe that was the attraction. The problem with this however is that once the mechanism leaves the magnetic magnetic in which it operates, it doesn’t work, and so unless the space craft has enough TWR, the acceleration will raise the orbit beyond the magnetic field before any meaningful acceleration can be gained. Bit of a generalisation however and I’m sure there are ways around it. $\endgroup$
    – R. Hall
    May 10, 2021 at 8:31
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    $\begingroup$ What is a "magnetic magnetic in which it operates"? How can "acceleration raise the orbit" before "any meaningful acceleration can be gained"? $\endgroup$ May 10, 2021 at 11:49
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    $\begingroup$ I don't get it either. $\endgroup$
    – seccpur
    May 10, 2021 at 11:52
  • $\begingroup$ The problem is the electrodynamic force that simply deorbits the device. There were even experiments of employing it specifically on cubesats to deorbit them. $\endgroup$
    – SF.
    Jun 9, 2021 at 15:11

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Space tethers have seen a fair bit of research and study but while a number of missions have flown there is a fair number of failures on that list.

Would suspect they are not particularly useful as a power source, since the energy coming out is just potential energy provided by the rocket that placed it in orbit in the first place, so you would generally be better using that fuel mass for some other power generation system.

The list of flown tether missions seems to focus more on achieving a controlled de-orbit at end of mission life, or as part of a re-boost system by running power into the tether.

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  • $\begingroup$ Although the magnitude of the Earth's MF is not significant, the length of the cable and the orbital velocity of the conductor should be able to generate sufficient emf imo. There was a missed accident with the Shuttle trying the setup and they dubbed it as dangerous and called off $\endgroup$
    – seccpur
    May 10, 2021 at 9:40
  • $\begingroup$ @seccpur - regardless of the mixture of current/voltage/tether length/clever termination the energy out of this system cannot exceed the kinetic energy put in by the rocket, unless you find energy from some other source (solar powered ion thruster say) and most cases directly using that will be more effective. Is possible there is a very small amount of additional energy harvestable from tidal effects. $\endgroup$ May 10, 2021 at 11:04
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A tether can serve as a power source, but the act of generating power in it causes a current/magnetic field which opposes the Earth's magnetic field, thus imparting a retarding force on the tether.

Indeed, one of the possible potential uses for such a tether would be to accelerate orbital decay for an old satellite.

Conversely, if you pump a current through the tether, you can cause a magnetic field in the tether which pushes on the Earth's magnetic field, thus accelerating the tether and its satellite in orbit, consuming power in the process.

Neither of these effects have been actually used with success so far, as apparently the handing and unspooling and orientation of a many metres (or kilometres) long conductive tether in space seems to be a bit more tricky that expected. There have been several proof-of-concept tests, with ....varied results.
It seems to be of similar ease on paper and similar difficulty in actual orbital space, as solar sail projects have been.

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  • $\begingroup$ Nice addition +1 $\endgroup$
    – seccpur
    Oct 7, 2021 at 13:28

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