A recent trend in the Aerospace industry is the miniaturisation of spacecraft. Historically these could not be controlled actively, limiting their operations and lifespan. TU Delft has already committed numerous research towards the development of miniaturised propulsion system using different technologies. This thesis continues work on the Vaporising Liquid Micro-resistojet (VLM) developed by Versteeg. Already three other master students have worked with this thruster and encountered several issues. Water tests had been attempted before but were unsuccessful due to the used feed system. Moreover, the latest experiments showed a significant degradation in terms of nozzle geometry and leak rate, which likely led to a decreased thruster performance. Lastly, the change to the TB-50m thrust bench resulted in unexpected drift behaviour.

This thesis addresses these challenges by implementing changes to the thruster en test set-up. The thruster’s sealing surface has been restored to its original state using a CNC-machine. This was done to counter degradation of the nozzle geometry and reduce the VLM’s leak rate. Additionally, a sealing gasket was developed for the same reason. Unfortunately, its implementation resulted in an undesirable deviation of the nozzle’s geometry and was thus left out. A new water feed system is developed, based on the use of a pressurised tank. This reduced unwanted effects, such as bubble formation, that were encountered with the previously used syringe-based feed system. With the implementation of a liquid mass flow meter, the flow rate can be measured more accurately, thus reducing uncertainty in the VLM’s performance. While these improvements proved to be successful initially, several issues encountered during the work have resulted in a worse overall performance. The nozzle geometry already showed signs of deformation after just two months. Furthermore, a major leak was identified which could not be addressed on time. Despite this, tests were executed with chamber temperatures up to 400 °C using both nitrogen and water as propellants. For nitrogen, the measured thrust varied between 4.1 and 8.6 mN for a throat Reynolds range of 1250 to 3300. The specific impulse increased from 34 to 37 s, while the specific impulse efficiency increased from 0.33 to 0.52. Discharge coefficients between 0.66 and 0.72 were measured. Although the errors are comparable (± 15% at most), this performance is significantly worse compared to earlier results. The water experiments were not successful due to an uncontrollable thruster operation. Regardless of this, the obtained test results showed an equally degraded thruster performance. These were executed at chamber pressures of ∼0.85 bar and at various chamber temperatures. Thrust and specific impulse levels of 4.2 mN and 67 s were achieved, with errors as large as ± 34%. The corresponding specific impulse efficiency and discharge coefficient were 0.56 and 0.39, respectively. The throat Reynolds number decreased from 1550 to 1000. Because of these unsuccessful tests, the VLM performance could not be verified against earlier results, let alone used for validating the developed analytical model. Recommendations are provided to address the encountered issues and improve the thruster’s performance. This should enable successful nitrogen and water tests in the future.