| Detection of gravitational waves opens a new window to explore the universe.Space-borne gravitational wave detectors are capable of detecting the low-frequency signals down to milli hertz,for which they play important roles in fundamental physics researches.TianQin is a space-borne gravitational wave detector proposed by China,which takes three spacecraft to construct a space interferometry and aims to detect gravitational waves by measuring relative displacements between inertial references.The TianQin project has very strict requirements for the inertial reference.In order to ensure the non-gravitational disturbance of the inertial reference to be less than 1×10-15 m/s2/(?),spacecraft must be drag-free controlled.The thesis focuses on the TianQin project,based on which control systems for the spacecraft and the inertial sensor are studied.The main research topics of the thesis are the following:Aiming at the TianQin’s requirement of non-gravitational disturbance rejection and based on the capability of disturbance prediction and compensation of the Embedded Model Control,drag-free control system is designed and validated.Among the design,TianQin’s non-orthogonal sensitive axes are decoupled,constraints on the loop shape from uncertainties are analyzed,and the parameters are tuned through pole placement.Dynamic simulations verify that the decay process of drag-free control under initial conditions is smooth without overshot,the power spectrum density of the stead-state relative displacement of the test mass is confirmed to be less than 4nm/(?).Furthermore,Monte Carlo trials are carried out and prove that the tracking error of the drag-free control can decay under uncertain parameters and initial state of the system,which guarantees the robustness of the control system.The design based on the Embedded Model Control fulfills the TianQin’s requirements.In-orbit performance verification of the inertial sensor and the drag-free control is carried out based on the in-orbit data from TianQin-1 satellite.Among the verification,the closed-loop stability of the inertial sensor is validated by control parameters polling,and the dynamic response is verified by closed-loop stiffness calibration.According to the power spectrum density of the acceleration,the inertial sensor is able to provide the high-accurate measurement of 5 × 10-11 m/s2/(?)acceleration at 0.05 Hz.Drag-free control further compensates the non-gravitational disturbances on the spacecraft,where the non-gravitational acceleration can be suppressed to 2 × 10-11 m/s2/(?)at 4 mHz.Meanwhile,the thrust noise is evaluated to be about 0.2 μN/(?).The in-orbit experiments offer very important support for the future researches.Consider the limits on the redundant degrees of freedom along the non-sensitive axes of the drag-free control,spacecraft attitude control and test mass electrostatic control are realized based on the Embedded Model Control.The attitude control takes the nonlinear dynamics model into consideration,and simulations confirm that the attitude error can be kept below 10 nrad/(?).Different force conditions of the electrostatic control in and off the constellation plane are analyzed,base on which the feedback commands are reconciled with thrusters.Numerical simulator for TianQin control system in science phase is built at last,which prove a reliable test bench for in-orbit experiments.The thesis adequately discusses the design procedure of the Embedded Model Control,and particularly analyze the loop constrains of the control system according to the requirements of TianQin project.The thesis lays the foundations of control system design for the similar missions. |
PDF Full Text Request