My thought process is that there is very little friction in space minus gravitational pull. Which could be a good thing if you wanted to go faster or slow down. The question is, is it possible to have a stong electo-magnet and grab onto the magnetic field of a random mass and use it to coast? Or to push away from the magnetic field of an object that is closer given that its gravity doesn’t pull you in?
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$\begingroup$ You can use magnets to do work (in the physics sense of the word), so, yes, you can use magnets for space travel. However, magnetic force (just like electrical and gravitational force) decreases with distance squared, so I'm not sure this is better than any other means of propulsion. $\endgroup$– user7073Commented Jun 13, 2018 at 15:57
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3$\begingroup$ @barrycarter: Not even squared. If you use a permanent magnet to pull against non-magnetized ferromagnetic metal, the force drops with 7th power of the distance. $\endgroup$– SF.Commented Jun 13, 2018 at 16:03
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3$\begingroup$ @Magic Octopus Urn: ...yeah, which is a good sign that it doesn't work. A rather more up to date article: arstechnica.com/science/2018/05/… $\endgroup$– Christopher James HuffCommented Jun 13, 2018 at 21:35
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1$\begingroup$ @ChristopherJamesHuff at least the space unicorns are magnetic! $\endgroup$– Organic MarbleCommented Jun 14, 2018 at 0:18
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1$\begingroup$ I still believe Em Drive is just an accidental ion drive, knocking copper ions off the chassis. It does produce thrust, and has wonderful specific impulse, but there's nothing magical about it and it does lose 'fuel' over time. $\endgroup$– SF.Commented Jun 14, 2018 at 12:12
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2 Answers
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So the short answer here is yes you could. However, there's not a justifiable advantage to using this. To propel yourself, you would constantly need an incredibly strong magnetic object near you. Now, electromagnetic forces are significantly stronger than gravity, but the extent of positive or negatively charged objects are relatively scarce. Additionally, the magnetic orientation of objects is also incredibly weak in general. Earth's magnetic field is 25-65 µT. To put that in perspective, a fridge magnet is about 1.5 mT and an MRI machine is about 1.5 T. This means that any force you could generate would be relatively small in comparison to the conventional Liquid Hydrogen and Liquid Oxygen reaction used. I can try to get the energy numbers if you need them, but I don't necessarily know how to go about calculating it properly. Regardless, the strength is likely 4 or 5 orders of magnitude ($10^4$ or $10^5$ times) weaker than conventional thrust methods.
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$\begingroup$ This is all new to me. Is that if you constantly power the magnet? Or do you need that much energy for a second of having it on? $\endgroup$ Commented Jun 13, 2018 at 19:28
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1$\begingroup$ Sorry I should've added this, but it's mainly weight. To generate even a N the weight would be far larger than we send up usually. And then you're trying to propel a huge block of material $\endgroup$ Commented Jun 13, 2018 at 20:17
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2$\begingroup$ Electrodynamic tethers should be mentioned. They only function in orbit around planets with strong magnetic fields and significant ionospheres, but can be used to raise or lower the orbit. Raising the orbit consumes electrical power, but the tether can be used to produce electrical power while lowering it, so such a tether could combine orbit maintenance and energy storage, as well as functioning as a deorbit mechanism at end of life. $\endgroup$ Commented Jun 13, 2018 at 21:42
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Magnetic "sails" have been proposed, that would achieve thrust by deflecting charged particles in the solar wind with the magnetic field of a superconducting loop. Also possible to deflect off solar and planetary magnetospheres.
I don't have any way to judge the feasibility. What I've read suggests they would need higher temp superconductors than currently available, at least in the inner solar system. It sounded like the current should persist in the loop.
