Orbit determination of a LEO satellite using the Cranfield Ground Station

Cranfield University has been developing a ground station for many years, supported by the activity of many students and researchers, which realized projects involving its implementation. In the past years the station has been assembled in a permanent site: hardware and software parts has been tested and brought into operation. Since then, it is a functional laboratory at service of the Space University Centre. The activity presented in this thesis covers the realization of a software that estimates up to seven orbital elements from Doppler frequency data, in order to perform orbit determination for LEO satellites through one-way Doppler measurements. The objective of this work is to enable the ground station to autonomously acquire satellite trajectory and use it for further purposes. A side objective is to study the observability of the parameters estimated from Doppler data and the influence of perturbations. A model to propagate the trajectory of the satellite in time has been realized: it uses the orbital propagator SGP4 parametrized with Classical orbit elements semimajor axis a, eccentricity e, inclination i, right ascension of the ascending node RAAN, argument of the pericenter w, the time of passage at perigee tp and the TLE ballistic coefficient B*. This model has been used for simulating Doppler frequency data of a known orbit satellite. Then, a regression problem has been solved fitting the model to the real Doppler measurements, acquired at the Cranfield ground station. The fitting has been realized using the Levenberg-Marquardt algorithm, providing a least-square estimation of the parameters. Results has been verified and discussed by error analysis and chi-square test, to find the sensitivity of the model. Estimation has been performed from simulated data and real data.