Optimization and calibration of thrust stand for micro-pulsed plasma thruster

Abstract

A micro-pulsed plasma thruster is a plasma jet engine used in micro-satellite and nano-satellite to provide attitude control and changes in orbital height. The micro-pulsed plasma thruster will produce impulse bits to achieve its mission. Therefore, it is necessary to accurately measure the impulse bits generated so as to evaluate the performance of the thruster. This leads to the optimization and calibration of thrust stand for the pulsed plasma thruster to measure its impulse bits. In this project, the beam of the thrust stand has been optimally designed so as to reduce the overall weight of the system. Its displacement due to the impulse bits generated by the micro-pulsed plasma thruster will be measured by the laser displacement sensor. First, there is an improved version 3rd prototype in which the beam is made of composite material whereas the earlier 2nd prototype uses aluminium material as the beam structure. However, due to bending effect of beam, the 4th prototype is introduced whereby the beam is symmetrical with respect to the pivot in the centre. Theoretical studies have also been carried out to find out the governing equation of the system which is a 2nd order differential equation for the 3rd prototype. This equation will provide the output response of the system with respect to time. Graphs of the output response with respect to time for the different damping coefficient cases are being plotted to allow better comparison. Thrust stand calibration has also been carried out so as to measure the impulse bits generated by the micro-pulsed plasma thruster when its displacement is known from the laser displacement sensor. There is a series of calibration to be conducted before the pulsed plasma thruster is actually used for the experiment. The purpose of the calibration procedure is to achieve a calibration graph of “Impulse Bits vs Displacement” at the end. First, using electrostatic fins, a graph of electrostatic force versus voltage is achieved. Next, this force will be incorporated with a time interval to produce an impulsive response and used on the thrust stand. This will reveal the variation of the displacement of the beam with impulse bits. With this calibration result, any displacement produced due to the impulse bits of plasma thruster can be checked against it to verify the true value of impulse bits generated.