Update spkezr call to put target and observer in correction positions and...

            ephem = self.ephemeris_time

            pos = []

            vel = []

            for time in ephem:

                state, _ = spice.spkezr(self.spacecraft_name,

                # spkezr returns a vector from the observer's location to the aberration-corrected

                # location of the target. For more information, see: 

                # https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/spicelib/spkezr.html

                state, _ = spice.spkezr(self.target_name,

                                       time,

                                       self.reference_frame,

                                       self.light_time_correction,

                                        self.target_name,)

                                       self.spacecraft_name,)

                pos.append(state[:3])

                vel.append(state[3:])

            # By default, spice works in km

            self._position = [p * 1000 for p in pos]

            self._velocity = [v * 1000 for v in vel]

            # By default, spice works in km, and the vector returned by spkezr points the opposite

            # direction to what ALE needs, so it must be multiplied by (-1) 

            self._position = [p * -1000 for p in pos]

            self._velocity = [v * -1000 for v in vel] 

        return self._position, self._velocity, self.ephemeris_time

    @property