Physical Modeling and Simulation of Structural Flexibility in Reusable Launch Vehicles for GNC Algorithms Verification and Validation

Abstract

This paper proposes a methodology for the a-causal physical modeling and simulation of structural bending dynamics in launch vehicles. The approach is particularly relevant to Reusable Launch Vehicles (RLVs) due to the increased structural loads in specific mission phases, such as boost-back and landing. Additionally, it has the goal of enhancing the Verification and Validation (V&V) process of Guidance, Navigation and Control (GNC) algorithms, whose robustness against structural deformations is to be proven. To this purpose, the mathematical background and the bending dynamics are illustrated. The related physical model is implemented using Modelica, an object-oriented a-causal modeling language, and integrated into a complete vehicle simulation model. The structural flexibility is considered excited only by the engine with its Thrust Vector Control (TVC) actuation system. As such, the performed analysis focuses on those phases of the mission mostly affected by the TVC actuation, namely boost-back and landing. Numerical results from an end-to-end RLV mission profile are discussed. A comparison between the devised a-causal model and its causal counterpart is provided, highlighting the added fidelity obtained by the chosen approach.