Responsive tolerant control: An approach to extend adaptability of launch vehicles

This paper reviews the development and state-of-the-art research of attitude control technologies for launch vehicles, as well as the application evaluations of the responsive tolerant control (RTC) technology. First, the control theories and methods related to launch vehicles are classified and surveyed. Although studies in this field are still active, many new methods have not exhibited impressive advantages over a well-tuned gain scheduling-based traditional solution when dealing with a complete rigid–flexible-sloshing model, and few have been adopted for in-flight use. The conservatism in applications stems from the distinctive dynamical characteristics of launch vehicles, which are discussed in detail thereafter. However, as traditional methods also face challenges in meeting the increasing new requirements, an innovative solution, namely RTC, has gradually found its role in robust launch vehicle applications. The RTC differs from the concept of adaptive control in that it has no effect under most conventional operations but responds to certain scenarios in a timely manner, and these scenarios include unmodeled modes, unforeseen disturbances far beyond prescribed limits, and unexpected failures where the fundamental assumptions implied in the feedback control theories or design guidelines are violated. After introducing a practical architecture of RTC, three methods are reviewed and their limitations are analyzed: an adaptive gain and damping adjustment method to deal with unmodeled modes, an angular-acceleration-based active load-relief method to reduce bending moments, and online identification and reconstruction of the command mapping relationship to counter the polarity errors. The RTC introduced in the paper has been validated from an applied and computational domain by flights or simulations with high fidelity, thus effectively improving the robustness and the adaptability of launch vehicles.