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摘要


In recent decades, the concept of satellite flying in well-organized pattern or formation has captured the views of space mission analysts and designers. This is due to the multi-orientation capability of formation flight in accomplishing multiple space mission objectives. Until now, its full potential application has not been fully studied, particularly in the optimization of the overall space mission performance. Perhaps, one of the most renowned formation setups that is beneficial for Earth-observation mission is the projected circular orbit (PCO) configuration. The PCO formation uniqueness lies in the sense that circular locus trajectory would be created in the Y-Z plane of chief's local vertical local horizontal (LVLH) frame of reference where deputy satellite orbiting the chief satellite at constant distance. Following that, this paper highlights two main objectives to be achieved particularly related to the subject matter discussed. Firstly, the objective is to verify the usability of Earth spherical model assumption over the true-Earth ellipsoidal model for the accuracy in computation of ground track coverage performance. At a specific inclination and a near-circular formation orbital eccentricity, relationships between formation altitude, f_a and formation distance, f_d to the evolution of latitude differences using the spherical and ellipsoidal models were investigated. A set of data consist of formation distance and formation altitude information were used for computations of parametric latitude and geodetic latitude. Then, the differences between these two latitudes were plotted. In all cases, the analysis showed that the latitude argument between these two Earth's models does not exceed 0.04° threshold value corresponding to approximately ± 4.5 km over-the- ground distance. The second objective is to study the resulting pattern of relative motion geodesic locus while comparing it to the on-orbit relative distance. The geodesic lines for both satellites in the PCO formation can therefore be acquired to study the shape evolution of resulting ground locus. Computations for the geodesic inverse solution were done using Karney's method. The produced locus plots suggested the existence of geodesic shortening and lengthening effects whereby over the ground, the distance between sub-satellite points tend to distort and lengthen accordingly if compared to constant on-orbit formation distance. Based on these evidences, we seek to determine the reliability of close distance formation for the acquisition of consistent ground coverage patterns with relatively small off-distance errors.

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