Abstract
This paper describes an efficient and robust optimal control algorithm for the design of fuel-optimal low-thrust interplanetary transfers. The solution is obtained with an indirect optimization approach, which has been selected to minimize the number of unknowns and to limit the computational effort. The optimization algorithm can deal with different intermediate conditions, such as flybys, rendezvous, or multiple gravity assists. Moreover, within the formulation adopted, no a priori knowledge of the control structure is required. The application of calculus of variations leads to a Multi-Point Boundary Value Problem (MP-BVP), characterized by complex inner constraints, which has been solved by means of an indirect multiple shooting method. Some effective techniques to increase the robustness of the algorithm and to overcome numerical difficulties are introduced, followed by the presentation of some test cases to assess the overall performances of the software-tool.