KPL/FK
 
Voyager-2 ULS Frame Definition
===========================================================================

   BVS/NAIF, 02/16/22
 
   This FK file defines the ULS frame consistent with 

      Aurora and magnetic field of Uranus, Floyd Herbert
      14 November 2009 https://doi.org/10.1029/2009JA014394
      
      The aurorae of Uranus past equinox, L. Lamy, et al
      09 March 2017, https://doi.org/10.1002/2017JA023918  

   that describe this frame's relationship to the Uranus IAU frame 
   as follows:

      Herbert: This map is defined in the spin-aligned, rotating ULS 
         coordinate system [Ness et al., 1986]. In this system, the angular 
         velocity vector points to the north pole (opposite to the peculiar 
         IAU definition), so that the northern hemisphere was the sunward 
         side at Voyager encounter, and like Earth, the planet rotates to 
         the east. As at the other gas giant planets, an arbitrary point 
         (the subspacecraft point at closest approach was defined as ULS west 
         longitude 302 deg) on the planet, rotating with the magnetic field 
         period, is used to define the longitude system, so that the central 
         meridian longitude (CML) of a distant observer fixed in space 
         increases with time

      Lamy: Hereafter, longitudes refer to the Uranian Longitude System (ULS) 
         [Ness et al., 1986]. ULS longitudes are built from International 
         Astronomical Union (IAU)-defined longitudes, both increasing with 
         time, by referencing the 168.46 degrees sub-Voyager 2 IAU longitude
         on 24 January 1986 to 302 degrees according to the ULS definition.

   Based on this, the right-handed ULS frame can be defined as a fixed-offset
   frame w.r.t. to the IAU_URANUS frame, with the following two rotations 
   needed to align the IAU_URANUS frame with the ULS frame: first by 180 
   degrees about +X, then by -226.46 degrees about Z.

   Since the fixed-offset frame definitons store rotations from instrumenti
   to base, the order and signs of angles below are reversed.

      \begindata

         FRAME_VG2_ULS            = -32970
         FRAME_-32970_NAME        = 'VG2_ULS'
         FRAME_-32970_CLASS       = 4
         FRAME_-32970_CLASS_ID    = -32970
         FRAME_-32970_CENTER      = 799
         TKFRAME_-32970_SPEC      = 'ANGLES'
         TKFRAME_-32970_RELATIVE  = 'IAU_URANUS'
         TKFRAME_-32970_ANGLES    = (  180.0,      0.0,  226.46 )
         TKFRAME_-32970_AXES      = (      1,        2,       3 )
         TKFRAME_-32970_UNITS     = 'DEGREES'
        
      \begintext

End of FK.