Differential orbit estimation for formation flying
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abstract
An interesting option to put heavy or large payloads into orbit is to distribute them on several smaller satellites orbiting in close formation. The formation flying, if it affords several advantages, also induces several challenges such as managing the formation as a unique vehicle. Within the ROMULUS ' research project, the Long-term Design and Systems Integration Department (DPRS) at ONERA2 is studying the estimation of the relative position of satellites within a formation from their relative observations. The relative orbit estimation is able to give very accurate relative positions which will be used, in particular, by control and command systems. This estimation of the relative state of the satellites is performed, within the scope of this study, by an Extended Kalman Filter. The objective is to determine continuously this state with high accuracy without any use of external reference. To do it, differential dynamic models and direct view sensors are envisaged. But the study proves that is not feasible if an accurate positioning is required. The study underlines also the influence of several parameters on the estimation accuracies: the orbit eccentricity, the observation system (optical, radar and/or differential GPS), the measurements rate and the initial estimation errors.
