Combined orbit determination (COD) is a new precise orbit determination (POD) method with the construction of space-based tracking telemetry and command (TTC) system and the development of POD technology, which seeks fusion and combination of multiple observation systems and orbit determination strategies by space-ground-based joint tracking, integrative COD models construction and COD strategies integrated application, and gains precise spacecraft trajectory to the greatest extent. This paper briefly summarizes the generation and development of COD conception, and puts forward a COD multi-layer data fusion model based on space-based TTC system and a hierarchical research method. Then the paper constructs COD models and designs the corresponding optimal weighing algorithms from observation data layer, model structures layer and strategies fusion layer, and carries out concrete simulation experiments. Simulation computation results show that COD strategy can improve LEO precision by constructing rational COD models and designing optimal COD weight, which proves the rationality and feasibility of multi-layer data fusion model in the paper from applied angle, and so can satisfy LEO high precision application requirements.
