In 1996, NASA performed an experiment with a tether attached to the shuttle. At the altitude the Shuttle flies at, the air is extremely rarefied but it is not a perfect vacuum. There is a voltage gradient with altitude and in addition, the shuttle is flying through Earth’s magnetic field.
The combination of these two effects was expected to generate electricity. Now I will admit to not fully understanding the theory here because my understanding of electricity is that it requires a completed circuit for current to flow. Now on the other end of the tether there was a small satellite but still I don’t understand what completes the circuit. If the circuit completed by ionic conduction in this rarefied atmosphere, then it’s cutting across the same magnetic field lines and so no net voltage should be generated.
The only way I can see this working is by tapping the voltage gradient present in the atmosphere, but if that were the case, I’m surprised that enough current was generated to actually sever the tether given the rarefied nature of the atmosphere at that altitude.
Also it was theorized that electricity could be sent into the tether and act as a motor increasing the orbital height of as satellite without having to expend propellant. There again, without a completed circuit I don’t understand how this would work.
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Shuttle Satellite
At any rate; somehow this was supposed to generate electricity, and apparently generated a lot more electricity than expected severing the tether.
An interesting aspect of this video is that the astronaut explains the floating things as debris from the shuttle in the foreground, but if you watch these floating things you can clearly see them go behind the tether.
There are a number of things I find interesting about this video. The tether remains taught even when it’s broken. I am unclear as to what force would keep it tight. I would have expected it to recoil when it broke, but clearly that is not the case in this video.
Then there is the question of the discrepancy between the amount of electricity expected and that actually generated. It would have made more sense to me to be measuring the current as you real the tether out so that if it expectantly approaches dangerous levels, you can stop before something catastrophic happens.
It is interesting to note that in eleven years they have not chosen to repeat this experiment.