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.