Space trajectory design is usually addressed as an optimal control problem. Although it relies on the classic theory of optimal control, this branch possesses some peculiarities that led to the development of ad hoc techniques, which can be grouped into two categories: direct and indirect methods. This paper gives an overview of the principal techniques belonging to the direct methods. The technique known as “direct transcription and collocation” is illustrated by considering Hermite-Simpson, high-order Gauss-Lobatto, and pseudospectral methods. Practical examples are given, and several hints to improve efficiency and robustness are implemented.
F. Topputo. C. Zhang. "Survey of Direct Transcription for Low-Thrust Space Trajectory Optimization with Applications." Abstr. Appl. Anal. 2014 (SI19) 1 - 15, 2014. https://doi.org/10.1155/2014/851720