Low-Thrust Gravity-Assist Trajectory Design Using Optimal Multimode Propulsion Models

The complexities in using indirect optimization methods get compounded for practical co-optimization problems in the presence of continuous and discrete design variables. In this paper, realistic multimode electric propulsion systems are incorporated within the formulation of gravity-assist, low-thrust trajectory design problems. Electric thrusters operate over a large set of discrete operation modes, and each mode is characterized by specific values for power, thrust, specific impulse, and mass flow rate. Unlike the traditional methods that approximate the aggregate behavior of electric thrusters’ performance (using polynomials fits), a novel construct is proposed to incorporate optimal discrete operating modes within indirect optimization. The capability of the tool and the efficacy of the proposed methodology are demonstrated by solving a multiyear, fuel-optimal trajectory problem from Earth to asteroid Psyche via a Mars gravity-assist maneuver and using a Hall-effect SPT-140 thruster with 21 operating modes. Comparisons with the traditional polynomial-based thruster modeling are presented.