Influence of ITRS/GCRS implementation for astrodynamics: Coordinate transformations

Abstract

Converting between the Geocentric Celestial Reference System (GCRS) and International Terrestrial Reference System (ITRS) is necessary for many applications in astrodynamics, such as orbit determination and analyzing geoscience data from satellite missions. The implementation of this frame transformation and the manner in which the Earth orientation parameters (EOPs) are used have a notable impact on station coordinates and satellite positions. After briefly reviewing the various theories and their mathematical description, we investigate the impact of EOP interpolation methods, ocean tide corrections, precession-nutation simplifications, and Julian date handling on the ITRS/GCRS coordinate transformation. Estimates of the impact on position concern a range of altitudes, from the Earth's surface to geosynchronous orbit (GEO), and apply to a wide array of astrodynamics applications. We demonstrate that EOP interpolation methods and ocean tide corrections impact the ITRS/GCRS transformation between 5 cm and 20 cm on the surface of the Earth and at the Global Positioning System (GPS) altitude, respectively. We conclude with a summary of recommendations on EOP usage and bias-precession-nutation model implementations for achieving a wide range of transformation accuracies at several altitudes. This comprehensive set of recommendations allows astrodynamicists, flight software engineers, and Earth scientists to make informed decisions when choosing the best implementation for their application, balancing accuracy and computational complexity.

Improvement of Orbit Prediction Algorithm for Spacecraft Through Simplified Precession-Nutation Model Using Cubic Spline Interpolation Method

“…In the inertial coordinate system, the differential kinematic equation of the spacecraft can be described as: ¨ r = a earth + a others (1) where r is the positon of spacecraft in the inertial coordinate system, a earth is the acceleration caused by the gravitation of the Earth, a others is the acceleration caused by other perturbations.…”

“…The balance between computational complexity and accuracy affects the choice of coordinate conversion model. Among all the factors that affect coordinate conversion, precise computation of the bias-precession-nutation parameters is the most demanding on computation time and memory [1]. But the full model is not necessary for every application, such as real-time, on-board orbit determination.…”

Observing UT1-UTC with VGOS

“…The EOP that is most difficult to predict due to rapidly varying geophysical excitation is the daily rotation of the earth. It is usually reported as difference between UT1 and Universal Time Coordinated (UTC), and a precise and accurate monitoring of this parameter is of great importance for satellite navigation systems and satellite orbit determination (Bradley et al 2016).…”

Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14

“…Therefore, accurate UT1-UTC results allow detailed studies of geodynamical phenomena and excitation, see Brzezinski (2012). Also for the calculation of precise satellite orbits, UT1-UTC is a very crucial parameter, see Bradley et al (2015). Global Navigation Satellite Systems (GNSS) need VLBI-determined UT1-UTC since satellite techniques can only determine the time derivative of UT1-UTC.…”