High-fidelity orbit propagator for precise antenna pointing in LEO satellite operation

In this paper, the development of an antenna pointing control system for the operation of satellites orbiting in Low-Earth Orbit is presented. A high-fidelity orbital dynamics model is developed for the prediction of the satellite's position and velocity. It includes higher geo-potential harmonics of the non-spherical Earth, the gravitational attraction from the Sun and the Moon, and other non-conservative forces, such as atmospheric drag and solar radiation pressure. A high precision orbit integrator based on the Burlish-Stoer algorithm plays a crucial role in integrating the equations of motion and find the satellite's states advance in time. The states from the Earth-Centered Inertial Coordinate are transformed to the Topocentric Horizon Coordinate to find the satellite's motion viewed from the control station on the ground. The ephemeris file that comprises vital information for the satellite tracking, such as azimuth and elevation angles, can be generated when the pass is detected. The antenna pointing control system then tracks the predicted trajectory. The proposed system is verified during the operation of the Thaichote satellite. It is shown that the predicted orbital states are very close to those determined from the onboard GPS receiver. It exhibits only some small residuals in position and velocity. The tracking performance is also shown through the high signal level received from the S-band antenna throughout the tracking course.