Efficient Loads Analyses of Shuttle-Payloads Using Dynamic Models With Linear Or Nonlinear Interfaces

A technique is presented for conducting efficient loads analyses of Shuttle-payloads systems with linear or nonlinear attachment interfaces. The technique relies on representing the Space Shuttle and the payloads with physical and modal coordinates. Further, by invoking a standard algorithm of numerical integration of equations of motion, the kinematics of the interface degrees of freedom at a given time are determined without calculating the modes of the combined system involving the Space Shuttle and the payload. If the Shuttle-payloads interface coupling induces a linear dynamic model for the loads analysis, the equations of motion of the Shuttle and the payload are integrated separately step-by-step in time. If the dynamic model is nonlinear, the equations of motion of the Shuttle and the payload are again integrated separately. However, in the latter case an iterative procedure is used within a time step to converge to reliable values of the nonlinear terms of the equations of motion. The usefulness of the proposed technique is demonstrated by conducting a loads analysis for the Shuttle abort landing event with the Inertia Upper Stage (IUS) booster carrying a Tracking and Data Relay Satellite (TDRS) in the payload bay. This combined system has at its interface dry friction and hydraulic nonlinear dampers. For the analysis of this system, the discontinuous signum function used traditionally in modeling dry friction is replaced by an expeditious continuous approximation. Because of its efficiency and versatility, the new technique deserves serious consideration for becoming a standard tool for linear or nonlinear analysis of combined systems, in general, and of Shuttle-payloads systems, in particular.