This book collects selected papers from the 9th International Conference on Aerospace System Science and Engineering (ICASSE 2025), organized by Shanghai Jiao Tong University and hosted by the National University of Singapore and Technical University of Munich Asia. Held annually since 2017, ICASSE provides a forum for experts in aeronautics and astronautics to exchange new ideas and findings. This book presents high-quality research in aerospace system science and engineering, covering topics such as AI for aerospace, trans-space vehicle design and integration, air and space vehicle systems, near-space vehicles, opto-electronic systems, robotics and unmanned systems, communication, navigation and surveillance, dynamics and control, intelligent sensing and information fusion, aerodynamics and aircraft design, propulsion, avionics, air traffic management, earth observation, deep space exploration, bionic micro-air/spacecraft, flight testing, and aerospace industry development.