aberration corrections are used, the states of
        target and observer relative to the solar system barycenter
        must be calculable from the available ephemeris data. Typically
        ephemeris data are made available by loading one or more SPK
        files via <a href="furnsh_c.html">furnsh_c</a>.
 
      - PCK data:  rotation data for the target body must
        be loaded.  These may be provided in a text or binary PCK file.
        Either type of file may be loaded via <a href="furnsh_c.html