Hybrid multi-objective orbit-raising with operational constraints

Abstract

The optimal design of orbit raising trajectories is formulated within a multi-objective hybrid optimal control framework. The spacecraft can be equipped with chemical, electric or combined chemical-electric propulsion systems. The model incorporates realistic effects of the space environment and complex operational constraints. An automated solution strategy, based on two sequential steps, is proposed for this problem. In the first step, operational constraints are not enforced and the control law of the electric engine is parameterized by a Lyapunov function. A heuristic global search algorithm selects the propulsion system and optimizes the guidance law. Approximate Pareto-optimal solutions are obtained trading off propellant mass, time of flight and solar-cell degradation. In the second step, candidate solutions are deemed as initial guesses to solve the nonlinear programming problem resulting from direct transcription of the operationally constrained problem. The proposed approach is applied to two transfer scenarios to the geostationary orbit. Results show the effectiveness of the methodology to generate not only rapid performance estimates for preliminary trade studies, but also accurate calculations for the detailed design. Additionally, it is identified that the application of operational restrictions causes minor penalties in the objective function.