Study Of Pulsed Thrust Measurement System Of Attitude-control Rocket Engine

As an important component of modern spacecraft, attitude-control rocket engines have been widely used in satellites, space shuttle and aircrafts. They play a very importance role in attitude adjustment, precision orientation, midcourse correction, docking, rendezvous, separation, braking. The thrust of attitude-control rocket engines is a small pulsed thrust. Accurately measuring the pulsed thrust has important significance to improving engine performance, promoting spacecraft control precision, saving limited fuel carried by small-satellites. The present thrust measurement devices and methods cannot satisfy the requirements of the pulsed thrust.In order to make up for the deficiency of the studies existing, this paper takes the pulsed thrust measurement of attitude-control rocket engines as research object, makes further study on the design and analysis of pulsed thrust measurement system from theoretical simulation to experiment analysis. A pulsed thrust measurement system based on piezoelectric quartz sensors has been developed for attitude-control rocket engine.According to the measurement requirements of the pulsed thrust, the factors which effect dynamic reponse error of the measurement system are studied by analysis of frequency response and transient response. The natural frequency and damping ratio are the main parameters affecting frequency response errors. Transient response errors are related to the product of natural frequency and the rising edge time of the measured thrust. Under low damping conditions, the ralationship curve of the product and the overshoot generates oscillation. The overshoot error of the low damping system can be effectively reduced by adjusting the product near integer within oscillation range. Aiming at the deficiency of the amplitude error of the rising edge affecting the difference between the output and input waveforms, tracking error is used to substitute the amplitude error of the rising edge to determine the dynamic design parameters of the thrust measurement system. According to design requirements of determined natural frequency and damping ratio of the system, piezoelectric quartz force sensors are selected as the force-sensitive element to measure the pulsed thrust of attitude-control rocket engines.The influences of the quantity and type of wafer on the natual frequency, sensitivity and zero drift of piezoelectric sensors are studied, and the quantity and type of wafer of the sensors are determined. An integrated shell is designed, and its stiffness model is established. The parameters of the shell are determined by analyzing its stiffness and natural frequency using stiffness model and finite element method. Two shear-type piezoelectric quartz sensors are symmetrically distributed inside of the elastic rings of the shell. The thrust is transferred by means of friction of fitting surfaces. As the core of the thrust measurement system, the thrust-measuring platform is established. The amplitude-frequency characteristic curve of the system is obtained by hammer experiment. The influences of the additional mass and centroid position on the natural frequency of the system are studied. The static and dynamic calibration systems are established, and calibration experiments are carried out. The natural frequency and static indexes can meet the design requirements, but the output waveforms of the dynamic calibration generate additonal damped oscillation, the amplitude of the output waveform is also less than of the input waveform.The transfer function model of the system is established in order to improving the dynamic measurement performance and eliminating the additional damped oscillation. If the amplitude-frequency and phase-frequency response curves are known, then the transfer function of the system is just related to damping ratios. The transfer function model can be established by determining the damping ratios with half-power method. Based on the model, damping compensation transfer function model of the system is established under the premise of remaining frequency unchanged. The divergence problem of the damping compensation is resolved. The dynamic calibration data is compensated by using damping compensation transfer function model, and the validity of the compensation method is verified. The thrust waveforms before and after damping compensation are evaluated by using tracking error and impulse error. The experimental results indicate that the dynamic measurement error of the system after damping compensation can satisfy the measurement requirements of pulsed thrust of the attitude-control rocket engines.