| Formation flying and constellation station keeping, the innovative concept of distributing the functionality of monolithic satellites among less expensive, smaller, cooperative satellites, enables faster ground track repeats, provides higher degrees of system redundancy and, in the end, reduces the cost of the whole mission. However, the practical implementation of this concept is associated with the need to tightly design, measure, control and maintain the formation or relative distance, phasing and orientations among the participating satellites. Implementing, maintaining, and reconfiguring the cluster of satellites is so critical and complex, that it would be a big burden on the traditional ground-based orbital determination, navigation and command systems, and it also may impose stringent requirements on current control systems in terms of the energy consumption, precision, and the overall budget.; The research work in this dissertation addresses the problems in two parts: the first part, which discusses mainly how to design the relative orbits for formation flying and constellation station keeping; and the second part, which is about the exploitation of possible control algorithms for maintaining the formation and constellation.; Orbits are investigated for which there are no relative secular precessions or drifts due to the Earth's perturbations between the spacecraft. In this case the energy consumption could be largely decreased.; A general method is introduced to establish the relationship between a given orbit relative to a reference orbit. By analyzing a set of differential equations, relationships between the orbit design and all possible relative secular drifts due to perturbations in the Earth's gravitational field, can be derived. Mathematical singularities encountered at specific orbital inclination angles, such as polar inclinations, are discussed. By using the general approach, a solution for polar inclinations is found. Two solution sets are found as non-zero solutions, which is more useful in practice as compared with the zero solution.; In the second part of the dissertation, control algorithms, which have efficient energy consumption and higher automation, can be easily implemented on-board with little ground support and can adapt to the thrust level without compromising the mission task, are investigated to reduce the overall cost of the mission.; A multi-variable full-rank feedback compensator is designed for the in-plane motion. It can satisfy the required system response performance and at the same time can adapt to thrusters with different thrust levels by indirectly changing the execution time. An optimal control algorithm is proposed for the out-of-plane motion. (Abstract shortened by UMI.)... |
