Closed-Loop Thrust Control for Micropropulsion Systems

Abstract

The growing needs of nano- and pico-satellite missions require several enhancements in micropropulsion capabilities to enable the satellites to perform an increasing variety of orbital maneuvers. This paper presents the design and the implementation of a closed-loop control system for thrust magnitude regulation in micro-resistojets. This is achieved by controlling the propellant mass flow in the microvalve of the feeding system which is designed to make extensive use of off-the-shelf components. The Vaporizing Liquid Micro-resistojet (VLM) is one of the micro-thrusters under development at TU Delft and, for this reason, it is selected for performing the tests. In order to develop appropriate controllers, a non-linear state-space model of the microvalve system is developed analytically and integrated with the analytical model of the complete system. The performance of the analytical model is compared to a multi-domain analysis done with finite element method (FEM) and computational fluid dynamics (CFD). The controllers are designed and tested using the models developed. Finally, the closed-loop control system is implemented in the preliminary hardware design of the micropropulsion system, achieving a resolution of 10 μN in the range of 0-800 μN.