These "orbits" so called are in reality unfathomably complex helical structures, with all kinds of retardation, constructive and destructive resonance etc etc.
Super duper complex. And all of this (all of what we perceive as reality) is explicate conjugate field perturbation modalities interplaying between the magnetic (space) from the dielectric (counterspace).
Yes. Close enough.
you don't really have to calculate any of the helical properties ((in terms of dimensional variables, that is - in terms of time series, yes)) in order to plot trajectories for a craft making inter-system journeys because it would be experiencing the same inertia that the rest of the solar system does, and to calculate orbits of bodies within the system, particularly with reference from the face of the earth, you don't need that information either.
what you're doing is approximate; of course, if for no other reason that there are masses and fields that aren't observable in interplanetary space that all contribute. but they can be shown to be relatively negligible, so that we
are able to make projections of sufficient accuracy to actually send craft on intercept courses between orbiting bodies. it is however, still necessary to have ongoing orbit maintenance ((attitude thrusters)) in any craft if you want to be able to keep intercepts within some usable margin, and especially if you want to enter orbit around another body. there's drag, which because of observational difficulties, isn't predicatable. for lack of knowledge, essentially.
take Musk's car, for example. he aimed it at mars. he missed. he was relatively close, 'relative' being a relative term, but not close enough to have gotten into orbit or been able to do science in a contributable way. no correcting thrusters; car had its fluids all removed.
'close enough' is a relative term. i believe Heisenberg discovered truth. human knowledge of he creation is limited, but even were it as complete as physically possible it would still be limited. that's Biblical - Ecclesiastes 3:11. it's a 'feature' of creation that we are incapable of comprehending and/or predicting it. 'close enough' is going to have to be enough, it is enough, pragmatically speaking, until Jesus brings the new heavens and the new earth.