Academic. We don't currently have a pressing need for reactionless thrust in the magnetosphere. Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
> Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
That's certainly a pragmatic cost based argument for not using them in the fast moving world of commercial magnetosphere constellations.
> Academic.
I feel they've moved past academic and transitioned to deployed .. at some evolution of implementation. Not commercially relevant is certainly one state of play.
I guess I was more interested in the nonlinear control issue in a field of highly variable intensity.
I first encountered space tethers in 1980 reading an Introduction to Engineering text where the example was given of unrolling a flat spool of thin metal through shaping rollers to extrude a very long boom with a spring on the end to stabilise the orientation of a satellite.
That was one of the first times I noodled about with the dynamics of a pendulum in a potential field.
These days, of course, there's a few more tricks that can be done with a dangling lasso, including interacting with the magnetic field via a looped current.
That aside, I was curious about traditional magnetorquers and their variations actively providing force in the magnetosphere.
The Earths magnetic field has a lot of diurnal pulsing .. the gravitational field is lumpy but stable.
There's a control challenge in getting a smooth desired response from a choppy field.
Cheer's for the lookout though, it hadn't occurred to me that some would be talking about magnetic force against the field using "space tether" as the base description - my background was more about the field equations than the physical implementation.
( Magnetorquers are also used in the US Navy for twisting controls inside a fully sealed container. )