Evaluating the stability of NASA's space launch system with adaptive augmenting control

NASA's baseline space launch system (SLS) flight control system (FCS) design includes an adaptive augmenting control (AAC) component that modifies the attitude control system response by augmenting the classical gain-scheduled architecture with additional performance and robustness. The NASA Engineering and Safety Center (NESC) teamed with the SLS Program to perform a comprehensive assessment of the stability and robustness of this FCS with emphasis on the AAC component. Multiple analysis techniques applicable to nonlinear systems were commissioned as part of this assessment, which was conducted in parallel with the program's standard design analysis cycle. The following analyses were included, with each technique adding unique valuable insights: Lyapunov-based stability analysis, classical stability analysis with static AAC gain variations, circle criterion-based analysis of the FCS with a time-varying gain element, time-domain stability margin assessment, Monte Carlo simulations with expanded dispersions, and an extensive set of stressing cases. Several of the completed analyses focused on determining whether the inclusion of AAC introduced risk to the FCS, while others quantified the benefits of the adaptive augmentation.