Replace PyEphem with SkyField functions about orbitdeterminator

[AlexReido]

Yes I'll give it a go now, including testing of course :)

[AlexReido]

I don't have time right now but I believe ephem is only used to calculate the right asencion and declination from the topocentric coordinates. Should be an easy fix, I'll try tomorow.
I think this is the corresponding function in skyfield.
https://rhodesmill.org/skyfield/examples.html#what-is-the-right-ascension-and-declination-of-a-point-in-the-sky

[hornig]

I see it here being used here for the groundstation/observer location at a given time.

orbitdeterminator/orbitdeterminator/kep_determination/gauss_method.py

Lines 1236 to 1238 in 3c4ac10

	J0 = ephem.julian_date(0) #can be anything
	observer = ephem.Observer()

That is also what you said @AlexReido.
The other ephimerides in this function in there are done differently.

so, interested to work on this including a short test that is is equivalent in result?