Electric thruster mode-pruning strategies for trajectory-propulsion co-optimization

Abstract

Application of idealized constant-specific-impulse, constant-thrust electric thruster performance models or curve-fitted polynomials is quite common for spacecraft trajectory design. However, incorporation of realistic performance models of multi-mode electric thrusters leads to notable challenges, and at the same time, offers unprecedented system-level optimization opportunities. In this paper, a framework is developed for co-optimization of 1) spacecraft trajectory, 2) operation modes of multi-mode propulsion systems, and 3) solar array size. The selection of the most optimal operation modes is in accordance to Pontryagin's minimum principle for solving a payload-mass-maximization problem. The novelty of the work lies in solving a mixed-integer trajectory optimization problem featuring user-defined constraints on the maximum number of operating modes used along the trajectory. Utility of the framework is demonstrated through optimization of a multi-year trajectory from Earth to comet 67P/Churyumov–Gerasimenko using an SPT-140 Hall thruster with 21 operating modes; the results are interesting and of significant practical utility.