Cubesats Attitude Control Problems Under Multi-constrains

Attitude control has always been an important part that cannot be ignored in spacecraft on-orbit operation.The attitude control system of Cube Sats,in general,is very sensitive to disturbances caused by external environmental torque or the failure of their internal components because of their small size,simple structure.If not properly addressed,these disturbances will lead to the failure of the entire space mission.Based on this background,this paper studies the attitude control problem of flywheel-driven CubeSats under multi-constraint conditions.First of all,the paper starts from dealing with the external environmental disturbances that affect the attitude control system of Cube Sats.In this chapter,the attitude regulation problem with bounded control for a class of satellites in the presence of large disturbances,with bounded moving average,is solved using a Lyapunov-like design.The analysis and design approaches are introduced in the case in which the underlying system is an integrator and are then applied to the satellite attitude regulation problem.The performance of the resulting closed-loop systems are studied in detail and it is shown that trajectories are ultimately bounded despite the effect of the persistent disturbance.Simulation results on a model of a small satellite subject to large,but bounded in moving average,disturbances are presented.Next,the internal factors that affect the attitude control of Cube Sats is studied.The attitude control problem for a class of nonlinear flexible Cube Sats with a redundant four reaction wheels’ setting and unknown actuator dead-zone is addressed firstly,and the configuration misalignment and external disturbance are considered simultaneously.By using the Takagi-Sugeno(T-S)fuzzy modelling method,the overall nonlinear attitude dynamics system is first reconstructed into several local linear ones.Then,an adaptive integral-type sliding mode control scheme is introduced based on a T-S fuzzy model to stabilize the considered attitude tracking control system of flexible Cube Sats.In this design,the external disturbance with unknown bound is counteracted in real-time by the adaptive estimate technique.Additionally,the integral sliding surface introduced is insured to be asymptotically stable under the condition of given matrix inequality.The proposed adaptive sliding mode controller guarantees the finite-time reachability of the specific sliding surface.A practical example with simulation results is given to verify the validity of the attitude tracking control strategy put forward in the chapter.By further considering the signal transmission limitation within the components of wireless Cube Sats.The attitude control problem for a class of flexible Cube Sats with signal quantization is studied.Considering the restrictions imposed by wireless network transmission and the energy-saving requirements of Cube Sats,a classical dynamic logarithmic sensor-to-controller quantizer and an event-triggered mechanism are introduced to perform the analysis and design work.The T-S fuzzy model is introduced to describe the nonlinear attitude dynamic property of the flexible Cube Sats,and an integral sliding surface is employed in this study.The robustness of the closed-loop attitude tracking control system and the finite-time reachability of the sliding surface domain are guaranteed by the presented quantized event-triggering adaptive sliding-mode control law.Simulation results are provided to verify the feasibility of the proposed attitude tracking control strategy.Based on the previous study,by taking into account the possible actuator and sensor failures that may occur during the operation of the satellite,two T-S fuzzy based observer design methods are developed to enhance the robustness of the Cube Sats attitude control system under two different network transmission environments.In the first case,the signal quantization effect is only considered on the channel between sensor and controller,and a sliding mode observer is designed,which can reconstruct the actuator faults.In the second case,the quantization effects are considered in both the sensor-controller side and the controller-actuator side,which is more difficult to be dealt with compared to the first case and the sliding mode observer method cannot be effective now since the discontinuous term is difficult to be designed.A descriptor reduced-order observer is presented to solve this problem,where the jumping behaviour resulted from the signal quantization is considered in the observer,which is novel and effective to compensate the quantization effects.Finally,two designed observers are applied to rigid-body and flexible satellite attitude control T-S fuzzy systems,respectively,to prove their effectiveness.