Characterisation of a Thrust Stand to Assess Micro-Thruster Performance

Abstract

Testing micro-propulsion systems is often a hard and challenging phase in the characterisation process of similar technologies, which are very sensitive to environmental noise and errors due to the human operator. At the Department of Space Engineering of the Delft University of Technology, a thrust bench of the hanging pendulum type is used to assess the performance of the in-house developed micro-resistojets. In order to reduce the influence of external factors and limit the influence of the operator during the testing phase, a calibration process that uses an electromagnetic actuator to find the relation between the pendulum displacement measured by a capacitive sensor and a known exciting force has been developed. The found relations is then used to reconstruct the variation of the thrust over time. However, the numerous wires connected to hardware on the pendulum represents a disturbing effect and seems to affect the results of the measured thrust. This work presents an upgrade version of the pendulum which aims to reduce the unwanted and unpredictable disturbing effects of the wirings through a wireless Bluetooth connection system. Besides that, a new analysis model has been developed to assess the performance of the micro-thrusters, which can be used as a comparison to the calibration method mentioned above. A series of tests has been completed to validate the model. The configuration of the pendulum used in the testing phase has been optimised with respect to the position of the counter mass and displacement sensor position on the thrust stand. The results show an unexpected apparent shift of the pendulum centre of mass. This causes the model to have a higher level of inaccuracy. Further analyses are need in order to understand the causes of this phenomenon. However, it has been possible to located the apparent shift within a specific range. The model has shown promising results, but more tests are needed in order to precisely determine its inaccuracy, mainly due to this unexpected behaviour of the shift of centre of mass.