Design, Fabrication and Characterization of MEMS Micro-resistojet Thrusters

Abstract

Small satellites require efficient propulsion systems for attitude and orbit control. This thesis focuses on the development and characterization of two distinct types of micro-resistojet thrusters, namely Vaporizing Liquid Micro-resistojet (VLM) and Low Pressure Micro-resistojet (LPM). Both concepts are developed at TU Delft and are designed to use water as a propellant, conforming to launch-safety, simplicity, and cost-effectiveness criteria.
In VLM, liquid water is vaporized and accelerated through a convergent-divergent nozzle. In contrast, LPM operates by reducing water vapor pressure to below 300 Pa and then accelerating it through expansion slots under a rarefied flow regime. Both types of thrusters are built on Micro-Electro-Mechanical Systems (MEMS) chips to accommodate the size constraints of nano- and pico-satellites.
The thesis introduces refined designs for both VLM and LPM thrusters. Specifically, the VLM design features an optimized nozzle shape and improved inlet flow, while the redesigned LPM assembly is more space-efficient. These modifications increase the thrust-to-size ratio for both thruster types.
The thesis presents a fabrication process for these thrusters, employing an anodic bonded silicon-glass wafer stack with a capped microfluidic channel. Fabrication was executed at the EKL lab, using a simplified manufacturing process that is detailed within the report.
Post-fabrication, the thrusters underwent mechanical and electrical characterization. The results indicate incremental improvements in both design performance and manufacturability. The new VLM design yielded a 15% increase in thrust efficiency, while the new LPM assembly reduced the occupied volume by 30%.