Research On Relative Measurement And Attitude Control For On-orbit Servicing Spacecraft

With the advantages of low-risk, relatively low-cost, potentially high concealment and important military value, on-orbit autonomous servicing has become the new research focus in the future space technology. The new GNC techniques of autonomous rendezvous and docking and attitude control for combined spacecrafts are claimed. Several key problems are studied, and the main results achieved in this dissertation are summarized as follows.An integrated IMU/Vision relative navigation system for the final approach phase of autonomous rendezvous and docking is designed. The inertial measurement unit to measure the motion information of chaser spacecraft, and the method of using relative motion equations to calculate relative motion parameters, are intreducted, overcoming the angles-only output shortcomings including low output frequency and small field of view and improving the system reliability. Based on the C-W rendezvous motion model, the feasibility of applying IMU into relative navigation system is verified, and the integrated IMU/Vision relative navigation algorithm is studied. On-the-ground experimental relative motion model and integrated measurement algorithm are formulated, and on-the-ground validation experiment for integrated IMU/Vision relative navigation system is designed. Analyzing the applicability of the proposed scheme, numerical simulation and on-the-ground experiment show that the system achieves the design goals and satisfies the control precision requirements for autonomous rendezvous and docking.The on-line identification approaches concerning attitude dynamic parameters of on-orbit servicing combined spacecrafts are studied and proposed. Based on the six basic hypotheses, the refueling spacecrafts and equipments for on-orbit refueling missions are simplified, and the mass property time-variation model for the whole refueling process is formulated by using the inertia tensor model conclusions of multi-body spacecraft. The least squares estimate scheme for attitude dynamic parameters of combined spacecrafts is studied, and the theoretical method for nonlinear parameter estimation problem is designed by introducing total least squares principle improving the general least square method. The filter approaches related to attitude dynamic parameters for general on-orbit missions are furtherly studied, and a new nonlinear filter algorithm– Super Iterated Extended Kalman Filter is introduced to solve the strong nonlinear filtering model. The simulations demonstrate that the SIEKF algorithm has rapid convergence rate and high estimation precision for strong nonlinear parameter estimation problem.The multi-sensors united attitude determination approaches for combined spacecraft are studied and proposed. Based on the six minimum attitude measurement systems, three of the filter algorithms are proposed for attitude determination fusing system, specifically the combined Kalman filter algorithm with gyroscope, combined Uncented Kalman filter and combined Nonlinear Predictive Filter without gyroscope, in order to improve the reliability and fault-tolerance of attitude determination system for combined spacecrafts. Considering each local filters having no private state variables, the combined filter algorithms are improved and the compute efficiency is enhanced. From algorithm structure and algorithm principle, the equivalent of both NPF and Kalman filter is demonstrated to establish the theoretical basis of NPF algorithm. The simulations demonstrate the proposed schemes are efficient.The decentralist cooperative attitude control approaches for combined spacecraft are studied and proposed. Based on the active distributed collaboration control to central rigid body and the passive control scheme to flexible components, the attitude control scheme for combined spacecrafts is designed. Aiming at the realization of the control scheme, the basis of command allocation for decentralist cooperative attitude control is studied, and the command allocation criterions for least unloading times are analyzed. The hybrid nonlinear control law of reaction wheel system and the unload control law of magnetic moment are studied. Based on the hybrid algorithms containing input-output nonlinear control and adaptive fuzzy control, the high precision attitude control problem for combined spacecraft including the variety of system dynamic parameter and uncertainty disturbance, and the vibration control problem for flexible accessories, are solved. Compared with the centralized control scheme, the proposed scheme can reduce the configuration requirements of attitude control system for on-orbit servicing spacecraft.On-orbit servicing technology will be one of the most important developing directions for spacecraft technologies, the research in this dissertation can provide scheme references and technique support.