Modelling, data analysis and validation of the thermo-fluidic behaviour of the WaterCube water-based resistojet

In the rapidly evolving space sector, cubesats have gained considerable attention due to their versatility and low cost. The introduction of propulsion systems has significantly expanded their operational capabilities, enabling orbit maintenance, collision avoidance, formation flying, and de-orbiting. Among the various propulsion options, water-based resistojets have emerged as a promising alternative due to their use of a green, non-toxic, and cost-effective propellant. Despite this potential, challenges such as high latent heat of vaporization and liquid-vapour separation must be addressed in order to enhance the efficiency and reliability of these systems. The present thesis focuses on the thermal analysis, data post-processing, and model validation of the WaterCube resistojet, a water-based electrothermal thruster under development. The primary objective is to validate a thermo-fluidic model of the first integrated engineering model to better predict its behaviour and performance. In order to achieve this, a comparison has been made between the simulation results and the vacuum chamber test data. Furthermore, an experimental data analysis is conducted to estimate key performance parameters such as thrust and specific impulse, ensuring that the system operates as intended. A thermal model was developed using Matlab, employing the thermal network approach to simulate the temperature distribution and heat transfer dynamics within the vaporization cell and thruster.The simulations considered both steady-state and pulsed operation. In parallel, a Python-based tool was created to process raw data from vacuum chamber tests, including mass flow rate, pressure, and temperature measurements. Performance parameters were estimated using experimental data and predictions obtained through NASA's CEA software. The initial thermal simulations revealed discrepancies of up to 65% compared to experimental results. However, through the refinement and validation of the model, the deviation was reduced to approximately 10%, thereby significantly improving the predictive accuracy. The analysis of test data confirmed the correct operation of the thruster and indicated that its performance aligned with the expected design parameters. This work presents a validated approach to evaluating the thermal behaviour of the WaterCube resistojet, setting the basis for subsequent design iterations and optimisations. The knowledge gained will contribute to the second iteration of the propulsion system, with the aim of supporting its design process.