Expanded thruster mass model incorporating nested Hall thrusters
A mass and cost model developed to aid in the selection of electric propulsion string sizes has been expanded to include the potential benefits of nesting the discharge channels of Hall thrusters. First, an analytical expression for the thruster specific as a function of the number of nested channels is developed. Three example methodologies for channel nesting are developed, and thruster specific mass values are generated for each. These example methodologies are then applied to the mass model for system powers of 500 kW, 750 kW, 1.0 MW, and 1.25 MW. It is found that for systems with 1 redundant thruster, the nested geometry provides mass savings on the order of 2-10% as compared to the minimum mass of a system of single-channel thrusters, with the savings increasing with increasing system power. It is found in these results that, for the example scaling methodologies studied, nesting more than two or three channels does not provide additional system mass savings. Results are also presented to investigate the effect of requiring additional redundant thrusters. These indicate that the mass savings provided by the nested configuration are decreased with increasing number of redundant thrusters; this is due to the fact that increasing the number of redundant thrusters pushes the mass minimum to a larger number of active thrusters. These results are also presented as a function of the active number of channels, which helps to illustrate that for a given number of active channels - A proxy for system complexity-the nested configuration offers clear mass savings due to its increased packing efficiency. Finally, an argument is made that no modification to the cost portion of the model is required to capture the basic trends of nested thrusters. This then leads to the conclusion that nested thrusters provide a means to shift the system mass minimum to meet the cost minimum.
