Determining the accuracy and repeatability of the solid propellant motor burning rate extraction methods using laboratory static tests in two scales to increase the safety of motor operation

Abstract

In the solid propellant motor, it is vital to specify the maximum burning rate of the propellant and consequently, the motor’s maximum pressure to increase safety in the operation of spacecraft and space thrusters. The burning time extraction method is the most effective parameter in determining the burning rate. The Quality statistical methods for comparing the burning time extraction methods were used because the burning rate was not known before the test. In this research, after selecting the widely used methods in the world's aerospace industries and preparing the software code by performing 26 small-scale static tests, the repeatability of the methods has been extracted, and then in the next step, for the first time, an innovative method to determine the accuracy of burning rate extraction methods was implemented. By designing the motor on a larger scale and performing 10 static tests, Vieille's law coefficient and power were extracted and given as input to a motor gas-dynamics simulation code. Due to the existence of static tests, it is possible to consider the accuracy of the methods in measuring the burning time and, consequently, the average pressure. The statistical results of the smaller motor show that the iterative burning time methods have similar behaviour and the Hessler-Glick and mass balance methods have the lowest coefficient of variation similar to the results of other references. Meanwhile, the reproducibility of the tangential method that is still used is very low. In the investigation of the accuracy in the static tests with different pressures in the larger scale motor, it has been determined that the most repeatable method is not necessarily the most accurate. Also, a difference of about 5 % in Vieille's law coefficient as the input gas-dynamics code parameters can increase the average calculated pressure error from 1 % to 10 %.