Improved Methodology for Dynamics of Orbiter Payload Bay Doors

The Payload Bay Door Dynamics Simulation (PBDS) computer program simulates the mechanical behavior of the space-shuttle payload bay doors and their latching and driving mechanisms during opening, closing, latching, and unlatching. PBDS was developed to replace an older program that was computationally inefficient and that simulated the door hinges incorrectly. In PBDS, the large system of dynamical equations of the payload-bay-door system is decomposed into smaller systems of dynamical equations at the mechanism level. This decomposition involves decoupling through neglect of the inertial parameters of the driving and latching mechanisms, which are small relative to those of the doors. The equations of motion of the doors, which are flexible, are derived by use of a Cartesian flexible-body formulation. The equations of motion of the mechanisms are derived by use of an efficient recursive formulation. Though decoupled dynamically, the door and the mechanisms are coupled kinematically. In solving the mechanism equations, the responses of the door at points where the door is attached to the mechanisms are fed as inputs to the mechanism equations. The outputs of the mechanism equations are forces and torques, which are fed back to the door equations to complete the computational cycle.