Investigation of a Sublimating Cold Gas Thruster for the CubeSat Platform

Abstract

The large range of propulsion technologies means that the field of CubeSat propulsion has huge potential for future research. This work has taken a high-level design of a sublimating cold gas thruster found in literature and simulated its operation with a low order analytical model of the reservoir and a CFD model of the components downstream of the reservoir. Together, these models provide a holistic understanding of the variables affecting the thruster’s performance and the challenges of modelling microflows through thruster assemblies. The analytical model determined that the propellant sublimation rate can increase to match almost any mass flow rate out of the reservoir by increasing the difference between the reservoir and vapour pressures, even over long open phases. Improvements could be made to the design of the thruster by reducing its size to better fit within the size constraints of a CubeSat, as well as altering the reservoir design to assist in securing the solid propellant in the microgravity environment of orbit. Though the analytical model was calibrated against experimental data from literature, to build confidence in the model it is recommended that an experiment be carried out to verify the results of one of the test cases, in addition to utilising the model to optimise the volume of the reservoir. The CFD modelling of the thruster assembly downstream of the reservoir has found that continuum modelling is insufficient to capture the microflow occurring in the nozzle. Additionally, altering the thermal boundary conditions did not improve the thrust predictions, and it is recommended that a hybrid DSMC/continuum model be used in future works to ensure accurate thrust predictions. Finally, a large deviation in the mass flow rate predictions of the low temperature cases in both the analytical model and CFD model when compared to experimental data from literature has led to the conclusion that solid propellant was being deposited downstream of the reservoir and causing a blockage to the flow. It is recommended that a detailed thermal design be carried out to improve the performance of the thruster and to provide further insights into the accuracy of both models.