Flight strategy optimization for high-altitude long-endurance solar-powered aircraft based on Gauss pseudo-spectral method

Solar-powered aircraft have attracted great attention owing to their potential for long-endurance flight and wide application prospects. Due to the particularity of energy system, flight strategy optimization is a significant way to enhance the flight performance for solar-powered aircraft. In this study, a flight strategy optimization model for high-altitude long-endurance solar-powered aircraft was proposed. This model consists of three-dimensional kinematic model, aerodynamic model, energy collection model, energy store model and energy loss model. To solve the nonlinear optimal control problem with process constraints and terminal constraints, Gauss pseudo-spectral method was employed to discretize the state equations and constraint equations. Then a typical mission flying from given initial point to given final point within a time interval was considered. Results indicate that proper changes of the attitude angle contribute to increasing the energy gained by photovoltaic cells. Utilization of gravitational potential energy can partly take the role of battery pack. Integrating these two measures, the optimized flight strategy can improve the final state of charge compared with current constant-altitude constant-velocity strategy. The optimized strategy brings more profits on condition of lower sunlight intensity and shorter daytime.