Engine theories developed and not used because they are not widely known

[Mad Rocket Scientist]

3 hours ago, Green Baron said:

Electromagnetic drives accelerate a reaction mass and through this method they produce thrust. They don't "push against Earth's magnetic field", though such a thing would theoretically fantastically be imaginable (it probably was the force they measured on poorly insulated plugs when testing the cannae thing), it is incredibly inefficient. Use as a propulsion device is improbable.

I wonder whether a magnetic field drive would be more efficient than a photon drive. Photon drives set the gold standard for energy inefficiency, so I suspect it would be better.

[K^2]

3 hours ago, DDE said:

since thrust is miniscule and gets weaker as you move to higher orbits... not a good plan.

Thrust from teather can actually be respectable. Way higher than ion. And nobody is stopping you from milking Oberth. Just keep raising apogee until you hit translunar, and a boost there can put you on a course to a Venus/Mars fly-by (via angular momentum trade in a self-fly-by with Earth.) From there, we know that free trajectory is available to anywhere in Sol or beyond for cost of minor correction burns. If you have the time to wait for all favorable alignments, there isn't a mission we've sent that we couldn't replicate with teather. Then again, we are an impatient bunch.

[Green Baron]

1 hour ago, Mad Rocket Scientist said:

I wonder whether a magnetic field drive would be more efficient than a photon drive. Photon drives set the gold standard for energy inefficiency, so I suspect it would be better.

If i put together the sparse info i can find on it, it seems to me that it is rather seen as a possible deorbit method or method to generate electricity. Though it might be working more nicely in a system with a strong magnetic field, like Jool Jupiter. But apparently nobody is working seriously on it as a means for propulsion. But this impression may be wrong, as i only did a brief search ...

I don't know how high the force actually is. These guys say <1N, but i did not look deeper for the conditions (length and material of tether, applied current).

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/83661/AIAA-2010-8844-783.pdf?sequence=1&amp;isAllowed=y

As @K^2 pointed out, one would have to do all the maneuvering with it as close to earth as possible, probably over a long time.

Idk how, but images of riders on the prairie swinging their bolas come to mind :-) Yippieh !

Edited December 16, 2018 by Green Baron

[Snark]

Sorry,  folks, but per forum rule 2.2.h, perpetual motion machines and similar fairy stories such as this one are not appropriate for the KSP forums. I'm sure there are plenty of crackpot websites where folks can discuss this sort of thing,  if they're inclined.

You're certainly welcome to discuss EM tethers and such, since those are real science, but if you'd like to do so, please give such discussions their own threads and don't mix them together with perpetual motion quackery.

Thank you for your understanding.