Abstract
The lithium vaporizer for a high-power magnetoplasmadynamic thruster is modeled using a 1-D, thermal-resistive network. We use this model to calculate the required vaporizer length and power as a function of mass flow rate, channel geometry, and material properties. After comparing results predicted by this model with preheat power data for a 200 kW thruster, we investigate performance over a parameter space of interest for the Advanced Lithium-Fed Appled-Field Lorentz Force Accelerator thruster. Heater power sensitivity to cathode tube emissivity, mass flow rate, and vapor superheat are presented. The cold-start heater power for 80 mg/s is found to range from 3.38 to 3.60 kW, corresponding to a vaporizer (axial) length of 18 to 26 cm. The strongest drivers of vaporizer performance are cathode tube emissivity and the conduction heat flow path through the mounting flange. Also, for the baseline case, it is shown that increasing the vapor superheat from 100 to 300 K has the effect of lowering the vaporizer thermal efficiency from 57 to 49%. Finally, the network model results are used to provide boundary conditions for a finite-element thermal model of the cathode assembly. This model is used to calculate a higher resolution temperature distribution throughout the cathode assembly.