Trajectory Optimization for Orbit Transfers: Principles, Advances, Case Studies, and Outlook

This review presents an in-depth exploration of trajectory optimization techniques for various orbit transfer applications, focusing on principles, methodologies, and practical case studies. The emphasis is placed on indirect, direct, and data-driven trajectory optimization methods powered by numerical, deterministic, and gradient-based optimization algorithms, and an overview on the basic fundamentals of each method is provided. Applications cover numerous orbit transfer problems, from geocentric and interplanetary transfers to other orbital maneuvers that are applicable to the orbit transfer problem, highlighting critical advancements of trajectory optimization techniques in enabling more efficient and feasible space missions. A minimum-fuel transfer from Earth to Mars is considered as a case study and solved using the indirect, direct, and data-driven methods, respectively, demonstrating an effective primer on the implementation of each method. Finally, we identify open challenges and issues, discuss potential opportunities, and make suggestions for future research directions. By synthesizing current methods and emerging trends, this review provides a comprehensive toolkit for addressing complex challenges in orbit transfers.