ECI2ECEF & ECEF2ECI Transformations

Transformation from celestial to terrestrial reference system and vice versa

Computation of transformation from the International Celestial Reference System (or the mean equator and equinox of J2000) to the International Terrestrial Reference System (or the reference pole and Greenwich meridian) and vice versa.

Hint: Obtain Terrestrial Time (TT) and Universal Time 1 (UT1) as well as pole coordinates at the time of interest from the respective IERS bulletins. Employ the IAU 1976 precession theory and the IAU 1980 nutation theory to compute the instantaneous orientation of the Celestial Ephemeris Pole (neglecting any corrections to the nutation angles). In computing the Earth rotation transformation account for the conventional relation between UT1 and GMST as well as the first-order term of the equation of the equinoxes.