Hybrid methods for interplanetary low-thrust trajectory optimization

Abstract

Hybrid methods for interplanetary low-thrust trajectory optimization are proposed. These methods are combinations of selected, existing methods for trajectory optimization. The focus of this thesis is to obtain solutions to a class of trajectories that are typical to the Mars Sample Return mission. These involve several natural segments such as escape, heliocentric transfer, and capture. A suitable method or combinations thereof is sought for each segment. Both accuracy and sensitivity are the main criteria used to determine the acceptability of the method chosen. Segments of a trajectory are patched together in the transition regions to satisfy continuity conditions. The optimization process is applied to the complete mission instead of each individual segment. Two classes of trajectories are examined: 1) Transfer from specified states in the heliocentric phase to a desired High-Earth Orbit (HEO) and 2) Transfer from Low-Mars Orbit (LMO) to the Low-Earth Orbit (LEO). The proposed hybrid method for the first class of trajectories is a combination of the Collocation and Control Parameterization approaches. The LMO-LEO trajectories are more difficult to solve. A combination of the Edelbaum approximation, control parameterization, and COV methods is proposed for this class of trajectories. Multiple attracting centers have been considered. The solutions obtained using the hybrid methods are compared to those from COV for accuracy as well as ease of computation.