Research On Modeling And Control Techniques For Satellite Formation Flying

Satellite formation flying (SFF) is an enabling technology for future space science mission. The control of relative states of a formation is one of the key technologies that maintain satellite formation. The control performances of relative position and relative attitude are not only decided by the quality of the hardware, but also depend on the control algorithms. In this thesis, the control algorithms used to maintain the desired relative position and desired relative attitude of SFF were studied from aspects of dynamics and control.The model errors between the general nonlinear model of relative orbit motion for SFF,linearized model and C-W equations were analyzed. Based on the general nonlinear model, nonlinear robust control methods which adopted sliding mode control basede on power reaching law,power reaching law with boundary layer,exponential reaching law and exponential reaching law combined with neural network were designed respectively.The dynamics and kinematics models of relative attitude of SFF were derived to describe the relative motion between the body coordinate of the leader and the follower's body coordinate. Based on the relative attitude model, two control laws were derived from sliding mode control and integrator backstepping control respectively. Due to the load limits of satellite in a formation, as well as the angular velocity measuring equipment is expensive and easy to damage, control algorithms based on state observer were studied. One method was to design the observer using integrator backstepping method to get the angular velocity directively. And another is to design a differential observer to caculate the angular velocity from the observed state. In order to reduce the comunication between satellites in a formation, a parameters adaptive control combined neural network is deduced. The neural network is trained to estimate some parameters of the model.The coupled relationship between the relative orbit motion and the relative attitude was analyzed. And the 6-DOF coupled dynamic model was derived. Based on coupled dynamic model, the SFF 6-DOF full-state feedback control method and observer-based control methods were studied respectively.The characteristics of the relative orbit motion of uncooperative formation flying were also studied, and the relative model was established. Consider that the target satellite in the uncooperative formation would not actively provide us the parameters in the model which is related to it, the parameters adaptive control algorithms based on integrator backstepping and Lyapunov theory were derived respectively.In order to show the effectiveness of the control law designed in this thesis, the satellite formation flying composed of two satellites called Leader-Follower satellite formation was used to simulate. The simulation results denoted that: Sliding mode control can achieve the task requirement within the set time. And sliding mode control has good robustness against the model uncertainty and model parameters'variation. All the observers designed in this thesis could track the real state accurately less than 1000 seconds, which was a guarantee to the control of relative motion for SFF without some state measurement. For the uncooperative formation flying, the adaptive control law can complete the task even without information feedback from the target satellite.