Optimizing low-thrust and gravity assist maneuvers to design interplanetary trajectories

TL;DR

This paper presents a direct finite element method for optimizing interplanetary trajectories that combine gravity assists and low-thrust propulsion, demonstrated through a Mercury mission case study.

Contribution

It introduces a multiphase parametric approach integrating gravity assists modeled with full 3D propagation into trajectory optimization.

Findings

Successful design of Mercury mission trajectories

Comparison of different gravity assist sequences

Effective use of finite element transcription method

Abstract

In this paper a direct method based on a transcription by finite elements in time has been used to design optimal interplanetary trajectories, exploiting a combination of gravity assist maneuvers and low-thrust propulsion. A multiphase parametric approach has been used to introduce swing-bys, treated as coast phases between two thrusted or coasting trajectory arcs. Gravity maneuvers are at first modeled with a linked-conic approximation and then introduced through a full three-dimensional propagation including perturbations by the Sun. The method is successfully applied to the design of a mission to planet Mercury, for which different options corresponding to different sequences of gravity maneuvers or launch opportunities are presented.