- This paper proposes an overarching trajectory-power-propulsion co-optimization framework by incorporating actual discrete operation modes of electric thrusters within the optimal control formulation of spacecraft trajectory design. An interplanetary trajectory from Earth to comet 67P/Churyu-mov-Gerasimenko is formulated and solved using a spacecraft that is equipped with a thruster with 21 operation modes. It is the first time a systematic methodology is devised to select the most optimal operation modes in accordance with Pontryagin's minimum principle (PMP) to solve a payload-maximization trajectory design problem. It is also shown that there is a possibility to obtain near-optimal solutions with a reduced number of modes and negligible loss of optimality. The maximum payload useful mass solution is shown to have significant advantage over the traditionalfinal-mass-maximization formulation.