The basic spacecraft attitude information, presented as quaternions, Euler angles, or a transformation matrix, is given in J2000 coordinates. Further information is given below. The GSE coordinate system is defined as: Planetary Solar Ecliptic, Planet centered X=Sun, V2=Orbital normal. X - Along the Planet->Sun line (S), positive towards the Sun. Y - V2 x X Z - Parallel to the Planetary orbital plane upward normal. The GSM coordinate system is defined as: Geocentric Solar Magnetic, Planet centered X=Sun, X - Along the Planet->Sun line (S), positive towards the Sun. Y - Z x X Z - The component of the Earth's geomagnetic centered north dipole vector which is orthogonal to X. The GSM coordinate system uses a temporally changing dipole, as defined in the SPICE MAG Frame. The Spacecraft UVW coordinate system has its UV axes rotated -35 degrees from the XY axes about the Z (or W) axis. The Solar Ecliptic Spacecraft Axes Matrix is similar to the Planetary Solar Ecliptic systems, with the X-Y plane in the Ecliptic. The X-axis is defined by the intersection of the Ecliptic Plane and the Earth's Dynamic Equator at the Jan. 1, 2000, epoch. That is, it is the X-axis of the J2000 coordinate system. The Z-axis is the Ecliptic normal. The GSQ coordinate system is Geocentric Solar Equatorial, defined as follows: Geocentric Solar Equatorial, Earth centered Z=Omega, V2=Earth-Sun vector. X - In the Earth->Sun plane, positive towards the Sun. Y - Z x X Z - Northward spin axis of Earth.
These coordinate systems are defined as they are for the Cassini mission. For more information, see Cassini Attitude.