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I'm familiar with the concept of aerobraking. Consider an object like a star, or a planet with strong magnetic field (Earth, Jupiter, probably all of the gas/ice giants?) Could a probe use some kind of electromagnet (or maybe magnetic induction), to push against the magnetic field as it gets close to the planet, similar to aerobraking, but much farther out?

(Also, is this an old, well known idea?)

Even if there was lower deceleration, the much longer reach of the magnetic field might make it viable for starting to slow down much earlier.

I was watching a speculative video on YouTube about how tethers push against the earth's magnetic field. In that video, the idea was for a space station or skyhook or satellite to gain momentum to prevent gradual orbital decay.

But it occurred to me it might work just fine for slowing down instead.

There is some existing work for magnetic sails, to decelerate against a solar wind, but I don't really see anything comparing it to aerobraking, nor anything that considered it at the level of a planetary magnetic field.

Maybe the idea works just great, except the hardware is simply too heavy to be practical? Or if using induction — maybe the problem is if you decelerate too much, you build up too much charge and zap your space probe?

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  • $\begingroup$ ps. I did find a "Terminator Tether" product on google; designed as a way to de-orbit a satellite at the end of its life cycle, rather than leaving it as space junk. ( google for www.tethers.com ) $\endgroup$
    – Charles Teague
    Mar 24, 2017 at 18:36
  • $\begingroup$ A very interesting idea, not sure how viable though: the magnetic braking is fairly weak. OTOH the tether, per meter, is quite light and you should be able to pack a lot of it on the cheap. I'm quite curious how it compares, mass wise, to propulsive braking. $\endgroup$
    – SF.
    Mar 24, 2017 at 19:22
  • $\begingroup$ If you compare the earth magnetic field with the field of a coil with a diameter of 1 m, 100 turns and a current of 1 A, the earth field is huge in size but very weak in its intensity. You could try to suspend this coil in a way to allow visible movement of the coil when the direction of current is changed. It would not be easy because the field and the resulting force is so weak. $\endgroup$
    – Uwe
    Mar 24, 2017 at 20:02
  • $\begingroup$ You may find these two links helpful (Magnetic Monopole) en.wikipedia.org/wiki/Magnetic_monopole and phys.org/news/… $\endgroup$
    – Enigma Maitreya
    Mar 24, 2017 at 20:36

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Electrodynamic Tethers have the potential to do what you want. The long wire moving through the planet's magnetic field can either brake or boost the deploying craft.

That said, the history of tether experiments in space is...checkered, to say the least. Of electrodynamic tethers, I think only OEDIPUS and T-REX are considered unqualified successes.

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    $\begingroup$ I keep having to remind myself that the reason that a tethers can work is that they emit the induced current in the wire off of each end. Without some kind of electron emission at one end and an ion emission (or ionizer) at the other, they just build up a static charge and become ineffective. $\endgroup$
    – uhoh
    Mar 25, 2017 at 0:57
  • $\begingroup$ Thank you for your help. Tethers do cover the majority of what I'm looking for. <P> To Summarize for anyone interested -- in practice, the effect is generally small enough that it is probably not worth using for short-scale deceleration (ie as you approach) but it can be quite effective if you need to decelerate (or accelerate) over much longer timeframes (days / months). So you could use tethers to decay an orbit to get rid of junk. Or to maintain an orbit. <P> Also, there are conceptual Magnetic Solar Sails, but those are still conceptual. $\endgroup$
    – Charles Teague
    Mar 28, 2017 at 17:26

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