Numerical simulations of the orbit determination of a small sat mission for gravity investigations based on Satellite-to-Satellite Tracking

In the recent years small satellites technology is growing up very fast. The use of a small sized spacecraft allows to reduce the costs of construction and launch without make particular compromise in terms of scientific objectives. Recently the small satellites have been used also as complement in a deep space mission and so new engineering challenges have born. The purpose of this master thesis rely on a particular small satellites mission concept that would improve the gravity investigations accuracy of a target body but with a lower cost. This mission case is based on the employment of a pair of small satellites that use the Satellite-to-Satellite Tracking technique to generates the observable quantities used for the orbit determination process and for the scientific analysis. These observables are two-way Doppler data obtained from the frequency shift of a stable microwave carrier transmitted between the two spacecrafts. Through these measurements it is possible to determine the static and dynamic gravity field of a body. The utilization of the SST, together with the small satellites technology, would certainly reduce the complexity and the costs, with an increment of estimation accuracy, but with the introduction of new potential engineering problems. The targets of the proposed SST mission concept are Titan, Enceladus and Europa. In each of these mission cases the two smallsats are placed on the same orbit, with a given angular separation. The objectives of this thesis were focused on the analysis of the SST technique, the numerical simulation of the orbit determination of the spacecrafts and the obtainable accuracy of the moon's gravity field estimation. Following these targets different orbital geometries were studied, to identify the most promising configurations. All the numerical evaluations have been conducted with the astro available at the Radio Science and Planetary Exploration Laboratory of the University of Bologna.