Design and Analysis of a Launcher Flight Control System Based on Incremental Nonlinear Dynamic Inversion

This paper investigates the application of Incremental Nonlinear Dynamic Inversion (INDI) for launch vehicle flight control, addressing the limited exploration of nonlinear control architectures and their potential benefits in the context of the current “New Space” era. In this context, this study aims to bridge the gap between the launcher’s traditional linear control practice and nonlinear methods, focusing on INDI, which offers the potential to enhance limits of performance while reducing mission preparation (“missionisation”) efforts. INDI control commands incremental inputs by exploiting feedback acceleration estimates in a feedback-linearised plant in order to reduce model dependency, making it easier to design and resulting in a robust closed loop as compared to nonlinear dynamic inversion. The objective of this paper is therefore to demonstrate INDI’s implementation in a representative industrial launch ascent scenario, evaluate its strengths and limitations relative to industry standards, and promote its adoption within the launcher Guidance, Navigation, and Control (GNC) community. Comparative simulations with traditional scheduled PD controllers, with and without angular acceleration feedback, are highlighted together with several trade-offs. Furthermore, this paper presents a new and practical INDI stability analysis method as applied in the context of aerospace attitude control, as well as an augmentation of the design with an outer control loop for active load relief. Results indicate that while INDI exhibits increased sensitivity to sensor noise and actuator delays as compared to the linear controllers, its advantages in robustness and performance are significant. Notably, INDI’s ability to handle nonlinearities without extensive tuning and gain-scheduling surpasses the capabilities of the traditional linear control counterparts. These results highlight the potential of INDI as a more robust and efficient alternative to state-of-practice launcher control design methodologies.