Electrodynamic Compound Tether

guest blogger john hare

A variant on the compound tether is the electrodynamic tether with rotovator. In this one a long electrodynamic tether has solar panels and other counterweights high enough to get the center of mass to a 135 minute  orbit with the bottom end at LEO altitudes. With the bottom end at 2,500 m/s below local orbital velocity, a rotovator hub is attached with a tip speed of 2,500 m/s. The rotovator tips will cycle between 5,000 m/s below orbital velocity and local orbital velocity.


While this does not service the transportation hubs as in the earlier post, it might provide a way of getting a lot of volume into LEO. Two advantages to the system here compared to the last, electrodynamic tether can provide the reboost without propellant expenditure, and it is easier to visualize and model.

 As before, this is amatuer speculation.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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10 Responses to Electrodynamic Compound Tether

  1. john hare says:

    I threw this one out before seeing Kirk’s comment on the previous post. Unless a bulletproof way of preventing tether contact can be devised, these compound tether concepts are busted.

  2. Neil H. says:

    Random thought, and I’m not if you’ve already covered it: Might it be possible to use electrodynamic tethers with the basic space elevator concept, and use them to reduce the overall tensile strength required? For example, what if either the entire space elevator cable, or portions of it, were electrodynamic tethers powered by solar and/or nuclear… could the upwards “push” make other parts of the engineering easier?

  3. No. The electrodynamic tether has to move relative to the Earth’s magnetic field to function, and the space elevator concept does not move relative to the Earth’s magnetic field.

  4. Neil H. says:

    Oops, my bad. I guess one could alternatively imagine some sort of continuously orbiting space elevator which doesn’t actually touch the ground, although I guess a rotovator would probably be a better bet.

  5. PeterH says:

    I like the ability to release into the local circular orbit without having to climb along the tether.

    The spinning tether having a vertical or tilted rotation axis avoids the problem of tethers colliding, but makes capture and release a 3D compound pendulum problem. In addition, the spinning tether would have to precess if not in the orbital plane. Probably solvable engineering issues, but complications.

    Thinking of a vertical spin, ever play with spinning a chain or rope around so the lower end is on one side of the spin axis while the upper end is on the other? Hold one end with the chain hanging, and make small circles building up momentum. Find the right speed and you get the standing wave I described above.

  6. john hare says:

    I prefer a slight tilt to the standing wave. I think the various problems are solvable with considerable profit potential.

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  10. Marsha Crane Sias says:

    John Hare, we’re you born in california to Jane and Luther Hare? If so, I am your cousin Marsha Crane.

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