Study On Optimal Design Methods Of Space Station Attitude Commands Based On Momentum-exchange

Space station is the largest manned spacecraft on low earth-orbit. The attitude control system plays the pivotal role in guaranteeing normal operations for space station. As one of the major attitude actuators, control momentum gyro (CMG) provides control torque with limited amplitude in the manner of momentum-exchange, which has the great advantage of saving fuel. However, CMG can only accumulate a small amount of momentum. For on-orbit operations via CMG, the momentum saturation of CMG should be considered as additional constraint, which brings great difficult. According to the operation demands and the dynamic constraints, designing attitude commands for space station based on the uniform attitude control platform is a practical scheme. On the background of executing on-orbit operations via momentum-exchange, the optimal attitude commands design methods are investigated in this paper.Firstly, the attitude model is established for the multi-body topological system of the space station, aiming at satisfying the space station design requirements on the initial phase. The CMG momentum-exchange model and the environmental torque models are also established.Secondly, in the task of CMG momentum-unloading via gravity gradient torque, the optimal design method for attitude commands is investigated. The attitude model of the space station is linearized on the torque equilibrium attitude which is acquired by the adjoint method. Then the optimal design problem of the attitude command for momentum-unloading is summarized considering attitude constrains. Based on the polytopic representation approach, the optimal design method for the attitude command is presented.Thirdly, to obtain the attitude command of the large angle maneuver via CMG and environmental torques, the optimal design method is investigated. Nonlinear models of the space station and the environmental influence are studied to depicting the large angle maneuver of the space station during the fixed structure mode. Then, the optimal design problem of the attitude command is summarized considering constraints from the solar panel rotation, the space station attitude and the CMG outputs. The optimal problem is solved via Gauss pseudospectral transcription.Fourthly, the optimal design method for the attitude command of the modular redocking task is investigated, which aims at fulfill the task by only using the CMG and environmental influence. In order to simplify the problem, the two-body relative rotation description for the modular redocking task is deduced from the multi-body topological system model. The attitude constraints, manipulator restrictions and the depth of discharge are studied, following which the optimal attitude design problem is summarized. The optimal problem is parameterized and then the solved via sequential quadratic programming method.Finally, referring to a certain type of space station, attitude commands are designed optimally for typical tasks during long-term operations. The construction periods of the space station are introduced and then the typical tasks during the Core-Lab1phase are analyzed. Then the attitude commands of these tasks are designed via methods from previous contents. The design results show the effectiveness of the optimal design methods.