S-band Antenna Angles Data Calibration using Spacecraft Tracking

Ground station’s antenna look angles (azimuth and elevation) is a crucial input for the precise tracking of satellite and launch vehicle during the launch. Antenna’s angle data calibration is an important activity where Telemetry Tracking & Commanding (TTC) stations antenna error coefficients are estimated and used for precise targeting of the space objects. The calibrated coefficients are also used for the initial orbit determination using range and angles data immediately after the launch to enhance the orbit determination accuracy. In this paper, we describe the angles data calibration computational process which is carried out periodically for ISTRAC S-band ground station antenna. The in-house developed satellite precise orbit propagator (SPOP) is incorporated for the precise ephemeris generation in the angles data calibration process to compute the predicted look angles corresponding to the measured one tracked through the auto mode tracking. The developed angles data calibration package estimates the antenna error coefficients and azimuth and elevation mean errors using linear least squares in the batch processing mode. The error coefficients are estimated making use of Indian Remote Sensing (IRS)-LEO satellite auto tracking and its operational orbit determination. Systematic errors of each ground station antenna are estimated by conducting tracking campaigns designed to collect data spread evenly in the azimuth-elevation domain.