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Proceedings of GO 2005, pp. 85 – 90.Global Optimization of Low-Thrust Space Missions UsingEvolutionary NeurocontrolBernd DachwaldGerman Aerospace Center (DLR), Institute of Space Simulation, Cologne, Germany,bernd.dachwald@dlr.deAbstractKeywords:Low-thrust space propulsion systems enable flexible high-energy deep space missions, but the designand optimization of the interplanetary transfer trajectory is usually difficult. It involves muchexperience and expert knowledge because the convergence behavior of traditional local trajectoryoptimization methods depends strongly on an adequate initial guess. Within this extended abstract,evolutionary neurocontrol, a method that fuses artificial neural networks and evolutionary algorithms,is proposed as a smart global method for low-thrust trajectory optimization. It does notrequire an initial guess. The implementation of evolutionary neurocontrol is detailed and its performanceis shown for an exemplary mission.Evolutionary Neurocontrol, Spacecraft Trajectory Optimization, Low-Thrust Propulsion.1. Introduction to Low-Thrust MissionsInnovative interplanetary deep space missions require ever larger velocity increments (∆V s)and thus ever more demanding propulsion capabilities. Chemical high-thrust propulsion systems(rocket engines) have a limited ∆V -capability because the chemical energy of the propellantlimits its exhaust velocity. Electric low-thrust propulsion systems can significantlyenhance or even enable high-energy missions by providing much larger exhaust velocitiesthan chemical high-thrust systems. Consequently, they permit significantly larger ∆V s, whileat the same time allowing direct trajectories with simpler mission profiles, flexible launch windows,and mostly even reduced flight times because no gravity assist maneuvers are required.Another innovative low-thrust propulsion system is the solar sail, a large ultra-lightweightreflecting surface made of thin aluminized plastic film. Solar sails utilize solely the freelyavailable solar radiation pressure for propulsion and require therefore no propellant at all.Therefore, their ∆V -capability depends only on their lifetime in the space environment (andtheir distance from the sun). Electric propulsion systems have already been successfully flownin space while solar sails are under development [10].A spacecraft trajectory is, in simple terms, the spacecraft’s path from A (the initial body ororbit) to B (the target body or orbit). In general, the optimality of a trajectory can be definedaccording to several objectives, like transfer time or propellant consumption. Because solarsailcraft does not consume any propellant, trajectories are typically optimized with respectto transfer time alone. Trajectory optimization for electric spacecraft is less straightforwardbecause transfer time minimization and propellant minimization are mostly competing objectives.Spacecraft trajectories can also be classified with respect to the final constraints. If, atarrival, the position r SC and the velocity ṙ SC of the spacecraft must match that of the target, r Tand ṙ T respectively, one has a rendezvous problem. If only the position must match, one hasa flyby problem.