Research On The Construction Of The Sensitive Structure And Ground Evaluation Method Of Space Inertial Sensor

In order to keep up with the pace of international frontier scientific research,the Chinese Academy of Sciences proposed China’s own space gravitational wave detection plan-Taiji Project in 2016.The plan is carried out gradually in three stages.The first phase of the mission is to launch an experimental satellite,mainly for Inertial sensing,laser interferometry,drag-free control and other key technologies for on-orbit verification.The core device for inertial sensing technology verification is the space inertial sensor.The sensor is a precision device based on Newton’s second law,which measures the acceleration of the spacecraft or the relative displacement between the test mass and the spacecraft under the action of non-conservative forces.The research content of this paper is based on the first phase experimental satellite "Taiji-1" mission of the Chinese Academy of Sciences Space Taiji Progect.The purpose is to develop a set of engineering prototypes of space inertial sensor sensitive structure with the onorbit capability,and to carry out ground evaluation of inertial sensor performance.Method research,design and build a ground test system for corresponding test evaluation.First,based on the function and composition of the "Taiji-1" inertial sensor,a variable-gap differential capacitive sensor is designed to obtain position and attitude information of the test mass.Combined with the structure of the differential parallel plate capacitor,the static and dynamic models of the test mass under the action of electrostatic force are described.The basic principle of inertial sensor acceleration measurement and the necessity of closed-loop feedback control are obtained.The relationship between single-degree-of-freedom feedback voltages are established.On this basis,the electrode division method and voltage configuration of the inertial sensor are designed in the multi-degree-of-freedom motion state.Secondly,from the perspective of system technical index requirements,based on multi-free electrode division,combined with ground testing and in-orbit working conditions,the key parameters were analyzed in detail,and the inertial sensor sensitive structure was constructed.In the spacecraft’s orbital environment,a quantitative analysis and in-depth study of the main influencing factors such as the orthogonality of the sensitive structure electrode and the area asymmetry are carried out according to the basic equation of acceleration measurement.The contribution of the two to the bias value and acceleration noise is obtained,so as to clarify the degree of influence on the system range and acceleration resolution.On this basis,the manufacturing level requirements of the corresponding key parameters of the sensitive structure are obtained as the constraints for the subsequent development and implementation.Thirdly,based on the detailed design of the sensitive structure,a comprehensive exploration of its forming and assembly process was carried out,and a prototype of the sensitive structure with a coupling error angle better than 5×10-5rad was developed.Aiming at the possible single-point failure risk of the electrode housing structure made of brittle materials during assembly and launching,a further study was conducted using a combination of finite element analysis and experimental verification.The simulation method was used to analyze the stress condition of the electrode plate under different pre-tension moments.A verification experiment based on test pieces and engineering sample was carried out according to the carrying conditions.Comprehensive analysis and comparison of the relative position changes and failures of the structural parts under different conditions.It is obtained that under the conditions of 0.6N m assembly torque and 0.5N m connection torque,the sensitive structure have sufficient reliability and stability under the mechanical conditions of 10 g vibration and 700 g impact,with the ability to enter the orbit safely.Finally,for the purpose of ground performance test and evaluation of inertial sensor,a scale factor calibration method based on suspension wire torsion pendulum is proposed.This method uses local gravity acceleration as a stable input and the factor can be calibrated by an external adjustment mechanism,effectively reduce system complexity Simplify the form of sensitive structure and design a multi-degree-offreedom precision adjustment mechanism based on a spatial two-dimensional flexible structure and a two-level tilt adjustment structure to construct a suspension wire torsion pendulum system.Carry out relevant experimental research on the verification of inertial sensor’s non-sensitive axis and calibration of the scale factor and range.The system’s ability to respond quickly to external stimuli and to stabilize the test mass is verified as well.At the same time,the linearity error of the scale factor obtained by the proposed calibration method is better than 1%.On this basis,the test mass noise level under the current conditions is analyzed in detail,and the system is used to measure the non-sensitive axis acceleration noise measurement experiment.The results show that the resolution of the axial acceleration measurement reaches the level of 9.5×10-7m/s2/Hz1/2 And combined with the experimental parameters to evaluate the performance of the inertial sensor in orbit,it is concluded that the measurement resolution of the non-sensitive axis is expected to be 3.98×10-9m/s2/Hz1/2,which meets the requirements of the "Taiji-1" system.