Research On Spacecraft Integrated Position-Attitude Control Methods Based On Dual Quaternion Modeling

With the rapid development of aerospace industry in various countries and the increasing complexity of space missions,effective control of the position and attitude of spacecraft becomes a key enabling technology.Early space missions are relatively simple and usually only involve a single spacecraft,so the spacecraft position and attitude are mostly modeled and controlled independently.However,in consideration of safety and mission characteristics,it is necessary to control the relative position and relative attitude synchronously and accurately in some new space missions such as autonomous capture and on-orbit maintenance.In this case,the traditional strategies which address the attitude and position separately reflect some limitations.Based on the above background,this dissertation concentrates on the integrated pose control of relative motion between two spacecraft.The proposed control methods can be applied to various space proximity missions,such as hovering,autonomous capture and on-orbit maintenance.The dual quaternion,which can describe position and attitude at the same time,is adopted to establish the integrated kinematic and dynamic models of spacecraft relative motion.Considering pose unwinding,external disturbance,uncertainty of mass and inertial matrix,lack of angular velocity and linear velocity,several integrated pose control strategies are designed in the framework of dual quaternions to achieve high-precision pose tracking control,specifically:For the pose unwinding problem existing in the dual quaternion-based continuous controllers,and the steady-state error of the PD controller in the presence of constant disturbances,an anti-unwinding PID pose tracking controller based on hybrid feedback is designed.The hysteretic switching mechanism can solve the unwinding problem and avoid the noise sensitivity caused by discontinuous switching.The integral term in the PID controller can automatically compensate for the constant disturbance forces and torques.Based on the hybrid system stability theory,it is proved that the closed-loop system is globally asymptotically stable in the presence of constant disturbances and is robust to measurement noises.Finally,comparative simulations of hybrid,continuous,and discontinuous PID controllers are carried out to verify the effectiveness of the proposed hybrid pose control strategy.For the external disturbance,it is regarded as an uncertain parameter of the system.Then a dual disturbance force(including disturbance force and disturbance torque)estimator is designed based on the immersion and invariance adaptive control theory.The proposed disturbance estimator can effectively regulate the estimation process and avoid closed-loop performance degradation caused by large fluctuation in the parameter estimation of the certainty equivalent adaptive estimator.For constant and time-varying disturbances,it can ensure the estimation errors exponentially converge to zero and a small neighborhood near zero,respectively.Based on the proposed disturbance estimator,an adaptive pose tracing controller is designed.Comparative simulations with an adaptive controller based on certainty equivalent disturbance estimator and an ideal controller with known disturbance are conducted to verify the effectiveness of the proposed adaptive pose control strategy based on immersion and invariance disturbance estimator.For the uncertainty of spacecraft mass and inertial matrix,two adaptive pose tracking controllers are designed based on the immersion and invariance adaptive control theory,which use different methods to overcome the key integrability obstacle.When designing the first controller,the original system is transformed into a filter system and the integrability obstacle is avoided indirectly.The second controller uses dynamic scaling technique to overcome the integrability obstacle and greatly reduces the dimension of the closed-loop system.The two adaptive pose controllers and an existing certainty equivalent adaptive pose controller are comparatively simulated to verify the effectiveness of the proposed immersion and invariance adaptive pose control strategy.For the lack of spacecraft angular and linear velocities,two dual velocity observers are designed based on immersion and invariance theory and dynamic scaling technique.They both can ensure global exponential convergence of the dual velocity observation error,while the second one has a lower dimension.After replacing the dual velocity in the full state feedback controller with two dual velocity observations,two output feedback pose tracking controllers with an observer-controller structure are obtained.The asymptotic stability of the closed-loop system and the separation principle between the observer and the controller are proved by Lyapunov stability theory.Finally,the two output feedback controllers and the corresponding full state feedback controller are comparatively simulated to verify the effectiveness of the proposed dual velocity observer-based output feedback pose control strategy.