Theoretical And Experimental Investigation On Operation Process And Propellant Modification Of Pulsed Plasma Thruster

Ablative pulsed plasma thruster(APPT)is very suited for attitude control,orbital transfer,resistance compensation,station keeping,formation flying of microsatellite and the main propulsion system of deep space exploration,because of its significant advantages with regard to construction simplicity,high reliability,large range of thrust,high specific impulse,small impulse bit and low development cost.In this paper,modeling and simulation of APPT operation process,theoretical and experimental investigation of influence of plate configuration on APPT performance,non-contact diagnosis of plasma plume in discharge channel and propellant modification were conducted systematically by theoretical analysis,numerical simulation and experimental method.Considering of phase transformation in propellant ablation process,recession of ablation surface and absorption energy of propellant from thermal radiation,a one-dimensional ablation model of polytetrafluoroethylene(PTFE)was established.Considering the increase of ablation mass during discharge process,a novel electromechanical model was established,which is capable of simulating the ablation process of propellant.Selecting LES-6 PPT as the research object,the reliability of the novel electromechanical was verified.By altering structure parameters and electric parameters,the operation process of APPT was simulated for exploring the law how operation parameters influencing the thruster performance.A ground principle prototype which electrodes gap is adjustable was designed and the test-bed for measuring the impulse bit,mass bit and discharge waveform of APPT was built.An electromagnetic damping method used in torsional pendulum was presented and oscillation decay time of the torsional pendulum reduced significantly by using the electromagnetic damping method.Influence of shape and flare angle of electrode on the performance of APPT was investigated by theoretical and experimental methods.Results show that decreasing the width of electrode end and increasing the flare angle of electrode can enhance the inductance gradient of the thruster and improve the upper theoretical limit of APPT efficiency.The mass bit of the thruster employing rectangle or tongue electrode increases at first and then decreases by increasing the flare angle of electrode,but that of the thruster employing trapezoid electrode always decreases.The specific impulse decreases at first and then increases by increasing the flare angle of electrode.When the width of electrode end decreases under a threshold value,the specific impulse always increases by increasing the flare angle of electrode.The time-space resolved spectroscopy and high speed photography test-beds were designed and built,and an ignition system which can be triggered by external trigger signal was designed.Non-contact diagnosis of plasma plume characteristic in discharge channel was conducted by means of time-space resolved spectroscopy and high speed photography.The results indicate that the quantity of plasma is proportional to intensity of discharge current and changes periodically.In the initial phase of operation,thickness of plasmas layer is almost uniform near the ablation surface.As the plasma moves forward,two plasma microspheres appear near the electrodes,and then the two microspheres intersect at some area of discharge channel.In the later period of operation,there is only a filamentous current channel near the ablation surface.Particles in plasma plume in discharge channel mainly consists of CI,CII,CIII,FI,FII,CuI,CuII and CuIII.With the distance is gradually increasing from ablation surface,particle type is almost unchanged and the density of plasma tends to uniform.Plasma temperature increases to the maximum and then decreases with time.In some areas,plasma temperature fluctuates severely due to the collision of different plasma microsphere.The maximum speed of plasma is 45454m/s and 46800m/s measured respectively by time-space resolved spectroscopy and high speed photography.Based on theoretical analysis of ideal propellant characteristics suitable for APPT application,a filling modification scheme was proposed and three type modified propellant and PTFE were manufactured.Ablation surface microstructure of propellant was investigated by scanning electron microscope.The ablation surface of 100%PTFE was smooth,and there was little side ablation and no carbon deposition on ablation surface.The ablation of modified propellant was uneven severely and decreased from anode to cathode.Side ablation was serious and decreased from anode to cathode.The ablation speeds of 100%PTFE and modified propellant were different,so there were many unequal-sized filler particles inlaying on ablation surface.Non-contact diagnosis of plasma plume characteristic in discharge channel for four different types propellant were conducted by time-space resolved spectroscopy and high speed photography.To varying degrees,there was reverse plasma plume in discharge channel of the APPT employing modified propellant.Compared with 100%PTFE,the density of plasma was lower and the time when plasma appeared was later in the discharge channel of the APPT employing modified propellant.With regard to modified propellant,motion direction of plasma was disorganized.Performance parameters of APPTs employing different propellant were measured and computed.Filler can reduce ablation mass and improve degree of ionization and performance efficiently with low discharge energy.But filler of modified propellant increase ablation mass sharply and lower thruster performance with high discharge energy,because there is large difference between the ablation rates of PTFE and filler and propellant was ablated in the form of neutral particles.