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Thermal Behaviour of a Lithium Self-Field Magnetoplasmadynamic Thruster

Abstract

Electric propulsion is the focus of significant research in rocket propulsion due to its high efficiency. However, the high efficiency comes at a cost of low thrust density, and its applications are often limited to low thrust manoeuvres such as station-keeping and attitude control. The magnetoplasmadynamic (MPD) thruster is a form of high power electric propulsion, with the potential to propel heavy-cargo, piloted missions to the Moon and Mars. The Princeton University Electric Propulsion and Plasma Dynamics Laboratory (EPPDyL) is currently collaborating with NASA-JPL to develop lithium MPD thruster technology. This thesis studies the thermal behaviour of the EPPDyL 30 kW MPD thruster, numerically capturing the conductive and radiative heat transfer during the heat-up phase and thruster firing. The motive is to analyse the structural integrity of the thruster under thermal loads, as well as to investigate future possibilities for cost reductions through material adaptation. The thermal model was generated using ANSYS Steady-State Thermal, and experimental validation of the heat-up phase simulation showed broad agreement of 1.3 % to 19.5 % in magnitude at four thermocouple locations. The behaviour of the thruster during firing was also simulated, finding increased temperatures towards the front of the thruster at the anode nozzle, anode plate and cathode plate relative to the heat-up phase. The thruster firing procedure is also discussed in detail through an investigation of the lithium handling process. Techniques were explored to improve the safety of thruster firing due to significant risks from the involvement of lithium. Specifically, this thesis seeks to reliably automate the lithium handling glovebox, which must be maintained at a slight positive internal pressure of argon to prevent lithium from reacting with air. A Proportional-Integral-Derivative (PID) pressure control system was designed, developed and implemented using an Arduino, with a pressure transducer to obtain the state (pressure) and a mechanically integrated motor-valve system to control to input (argon flow rate). PID tuning was conducted to optimise the control system and the setup was experimentally verified through dress rehearsals.