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Hybrid methods and Q-guidance for rocket performance optimization

Abstract The thrust strategy for extra-atmospheric flight plays a key role in the optimization process for the ascent trajectory of the launch vehicles. In this paper optimization software for the ascent trajectory of the launch vehicles is reported, and the performances, obtained using Q-guidance, proposed by Battin are compared with those obtained solving an optimal control problem via the calculus of variations. The differences with respect to the optimal case are related to the velocity-to-be-gained value. The condition where Q-guidance is a good alternative is defined. The thrust strategies are applied to maximize the payload mass of a four-stage launcher similar to the European launcher Vega. The results are presented in terms of final payload mass and thrust strategies. This comparison is made firstly for the complete trajectory and then only for the last-stage trajectory. In the latter case the performances are compared considering both planar and out-of-plane trajectories.