Study On Low Thrust Vector Measurement

With the rapid development of science and technology, the state launched a variety of spacecrafts into space each year, such as satellites, lunar vehicles, spacecraft and so on. They thrust generated by the small force attitude control engine to adjust their attitude, change tracks, and compensate speed. Therefore, precise control of the engine thrust is very important. Due to precision limitation of manufacturing and installing components, so that the thrust generated by the engine deviates from the ideal value. Therefore, it is required to get the vector parameters of the engine thrust by thrust measurement experiments and evaluate the engine performance.In this paper, using low-thrust vector as the research object. Testing problems for low-thrust vector measurement are the small force and the range ratio in main and lateral directions. In deep analysis of the difficulties of the low-thrust vector measurement from the aspects of test principle, theoretical analysis, simulation and experiment, appropriate solutions are proposed, and a small force value vector force test system is developed at the core of piezoelectric dynamometers.Firstly, in order to solve the test system difficulties of small force, factors of piezoelectric dynamometer resolution and sensitivity are analyzed. From the theoretical and experimental viewpoint, the effect of the piezoelectric dynamometer sensitivity and resolution in the number, the cut type and size of piezoelectric quartz crystal are studied, then optimum design of the above parameters are conduced. Meanwhile, dynamometer preload are studied with experiments, in order to get its effect on sensitivity and a reasonable preload which can increase sensitivity is chosen.Secondly, in terms of the piezoelectric dynamometer structure and calibration of test system, analyzing large range ratio of the thrust measurement, which lead to the cross-interference of main direction to lateral direction. By finite element analysis of the dimensional parameters of the dynamometer cover, getting impact curves of thickness, the central aperture and sensor span to the of cover deformation, and the inter-interference, optimizing the size and selecting the reasonable parameters to reduce interference. Theoretical analysis of loading force deviation is conducted in test calibration to obtain the influence of calibration loading error on test accuracy of vector force. As a guide to the design of calibration load rod connection of the test system, changing it to universal joint connection to reduce inter-calibration interference caused by calibration load deviation.Static calibration and vector measurement simulation experiment of piezoelectric dynamometer and the entire test system show that:the piezoelectric dynamometer is able to measure the desired range of low thrust, its linearity and repeatability indicators are within 2%, and the interference between the piezoelectric dynamometer itself is reduced to less than 4%. After changing the connection mode, the cross-interference between the test system is reduced by more than 37.5%, uncertainty reduced by up 53.9%. The uncertainty of the vector measurement simulation parameters obtained, which the main thrust uncertainty in the nominal value is less than 1%, other vector parameters uncertainty are below 5%. Indicators of piezoelectric dynamometer and test systems have reached the requirements of low-thrust vector testing, it enables accurate measurement of the value of a small force vector force.