Research On The Thrust Measurement Method Of Plasma Thrusters Based On The Stress Detection Technology

As an important indicator for evaluating the performance of thrusters,measuring the thrust and analyzing the thrust variation of the thruster is more helpful to understand the relationship between the internal mechanism and external macroscopic characteristics of the thruster,so as to provide technical means for the design and parameter selection of the pulse plasma thruster.In this paper,the pulse plasma thruster was taken as the research object,we proposed a new measuring idea of "low thrust with high stress",and then developed a photoelastic system of cantilever beam structure based on Stokes parameters to measure the thrust,which need no install sensors or other measuring devices directly on the structure.Therefore,this system can reduce the mechanical vibration and disturbance of power supply cable to thrust measurement,and solve the problems of zero drift,unstable balance position,difficult calibration and low precision existing in micro-thrust and micro-impulse measurement devices.The main basis of this measurement system is the photoelasticity of the stress optics law.When the thrust is applied to a cantilever beam made of photoelastic materials,the cantilever beam would be in a state of stress and the stress changes with the thrust,resulting in the polarization state of the light passing through the cantilever beam changing.The Stokes parameter is adopted to characterize the transformation of polarization state.The corresponding experimental equipment is designed and manufactured,including optical excitation module,cantilever loading module,Stokes parameter measurement module,PI swing control module and Ampere force module.The validity of the method was verified by experiments in vacuum,and the average error was less than 5%.At the same time,based on the actual discharge and ablation process of PTFE during the pulsed plasma thruster operation,a numerical simulation of thruster operation process was established considering the energy conversion,phase change of working substance,non-Fourier heat conduction effect and ablation mass accumulation.The reliability of the model is validated by using the experimental data in references,which provides effective guidance for the process analysis of pulse plasma thrusters.