Conception, design and evaluation of a self-pressurizing propulsion storage module for a PocketQube-class satellite using compliant mechanisms

Abstract

The advent of miniaturized satellites has sparked an interest in effective methods of exploiting their capabilities. Potential has been found in propulsion­enabled units, and TU Delft is at the forefront of researching and developing suitable propulsion modules for thrust generation or attitude control of small satellites classified as Cubesats and Pocketqubes for the purpose of technology demonstration, presenting an open platform for students to provide their ideas. Acknowledging the challenges in power budgeting and distribution, the current thesis presents the conception, design and numerical evaluation of a passive, self-­pressurized pro­pellant storage system for use with the in­-house microthrusters. Target components for which the storage must be suitable are the Vaporizing Liquid Microthruster (VLM) and the INKX0511400AA5 VHS Solenoid Lee Valve, an off-­the­shelf component already at the dis­posal of the faculty. Starting from the notion of passive pressurization, an extensive review of literature is used to decide on exploring the idea of compliant mechanisms as a pressuriz­ing method. The scientific output of this work aims to extract productive conclusions on the design and performance level achievable by this concept and open a new design avenue for propellant storage modules. Expanding upon the definition of compliant mechanisms, a considerable amount of design concepts were evaluated under the premise of a two­-stage trade­-off strategy, aiming to balance creativity and practicality. Proclamation of the explored pressurizing mechanism is followed by individual trade­-off procedures for material, shape and configuration of the entire module, leading to a complete preliminary design concept to be evaluated. Traditional and unconventional analytic models are implemented to materialize the design concept, measuring its static and dynamic response in both idle and thrust conditions. They delve into the fields of structural and fluid dynamics and are validated against more advanced and accurate Finite Element (FE) and Computational Fluid Dynamics (CFD) models. Both outputs are compared with the mission, system and subsystem requirements to fully assess the performance levels obtained. Regulated for pressure drops of 500 Pa and 50 Pa from tank to valve, the former is capable of concluding a self-­actuated expulsion within 25 ms in both cases, failing to achieve target values for thrust duration. The conservative design approach has led to a 27.4 gr wet tank mass, with a 2.9 gr propellant capacity. As a first implementation of compliance-based pressurization in propellant storage, the results highlight its viability and the field should be further explored.