Energy Optimal Attitude Control and Task Execution for a Solar-Powered Spacecraft

In this article, we aim to maximize the net energy a solar-powered spacecraft gains when performing a sequence of tasks leading to attitude maneuvers over the spacecraft's orbit, including an eclipse. The net energy can be defined as the integral of the power supplied by the solar panels minus the power used by the payload and satellite systems, including the attitude control system. The energy flow depends on both the power spent on the satellite electronic systems and the power received from the solar panels. Thus, the optimal attitude control problem is formulated so that the attitude of the spacecraft relative to the Sun during the maneuver is included in the calculations in addition to the actuation cost. This article proposes a cost function based on net energy to address this problem, introducing a cost function that incorporates the incoming energy from the solar irradiance and the outgoing energy due to actuation. A function that differentiates between the eclipse's fully and partially shaded regions is added to simulate the solar irradiance in an eclipse. Our approach is demonstrated in a simulation study where the HYPSO-2 Earth observation satellite executes a sequence of imaging, communication, and energy-harvesting tasks. HYPSO-2 is a 6U CubeSat equipped with deployable solar cell arrays, and the optimal control problem is solved using IPOPT in CasADi.