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Access to space using Momentum exchange tether (like Skyhook, Space elevator,...) is economical, but only to specific orbits.

And changing the inclination of the orbit is very uneconomical.

Is there an Momentum exchange tether protocol that can change the inclination of an orbit at will without paying too much?

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    $\begingroup$ Angular momentum ($L$) is conserved. Changing inclination of an object's orbit means changing its $L$ , so you have to cause an equal (and opposite) change of $L$ to something else. It might be possible (though fanciful) to have some kind of tether that raises the inclination of one orbit while lower that of another? But even if something were within the realm of engineering possibility, it seems like a very niche use case. $\endgroup$
    – ScienceSnake
    Commented Jul 5 at 13:24
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    $\begingroup$ @ScienceSnake Yeah, I thought it was a bit KSP-style tech too. $\endgroup$
    – Ember Edison
    Commented Jul 5 at 14:03
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    $\begingroup$ As a rule, the orbit of a skyhook and the transfer orbit it imposes on the cargo are co-planar, so no angular momentum transfer can occur. But angular momentum could be transferred from skyhook tether to an orbiting spacecraft if their orbital inclinations were different. This would require "pick-up" at ridiculous relative velocity and produce very exciting wobbles in the tether which would make release velocity unpredictable. I'd love to see a simulation. $\endgroup$
    – Woody
    Commented Jul 5 at 19:01
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    $\begingroup$ "exciting" is an interesting adjective to use there $\endgroup$
    – Darth Pseudonym
    Commented Jul 5 at 20:48

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One option is to do the inclination change at a high apoapsis.

For a full space elevator, it is comparatively easy to extend the counterweight side of the tether far enough out that releasing a spacecraft sets it on a near escape velocity trajectory. Velocity when reaching the apoapsis is very low, so inclination and periapsis height can be changed at close to no delta-v cost. In the same fashion, free-return trajectories from a lunar transfer orbit can typically also have an arbitrary inclination.

So as long as the target semi-major axis is high enough, yes, this can easily be achieved.

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  • $\begingroup$ @EmberEdison ... the angular momentum in question is not the angular momentum of the spacecraft, but the angular momentum of the spacecraft/planet system. The first can be managed by momentum wheels, the second cannot. $\endgroup$
    – Woody
    Commented Jul 5 at 21:02
  • $\begingroup$ firing the good guys … All true, but the tether (skyhook or elevator) only provides an orbital transfer orbit, not angular momentum for circularization or inclination change. The angular momentum for those must be supplied by old fashioned rockets. In the case of lunar transfer, the angular momentum is being supplied by gravity assist from the moon. $\endgroup$
    – Woody
    Commented Jul 6 at 1:08

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