Orion MPCV E-STA Nonlinear Dynamics Uncertainty Factors

Abstract

NASA vibration testing of the European Service Module (ESM) Structural Test Article (E-STA) for the Orion Multi-Purpose Crew Vehicle (MPCV) program demonstrated significant nonlinear behaviors and response deviation from pre-test finite element analysis (FEA). A linear FEA correlation effort, previously performed in 2017, resulted in the creation of two finite element models (FEM) – one correlated to high-load level swept sine responses and one correlated to low-load level swept sine responses. Additional work was required to quantify the uncertainty introduced when applying these linear models to non-sinusoidal flight load cases. To do this, an additional nonlinear dynamics model was developed and correlated with sine sweep test responses for low load level and high load level load cases. Results showed that, when the appropriate linearized model was selected for each specific Coupled Loads Analysis (CLA) loading type (i.e. Liftoff, Transonic, etc…), the linearized models closely matched predicted nonlinear responses with modest error (uncertainty factor). Results of this investigation have established a physics-based nonlinear dynamics approach that uses empirical test data to establish the credibility assumption for usage of linear FEM(s) in CLA. It is anticipated that the methodology employed can be extended for usage in correlation and flight loads analysis of subsequent spacecraft with major joint nonlinearities.