In this paper, stability of a complex spacecraft is studied by the use of two new models. The rst, is a rigid-flexible model, which consists of a rigid body and a deploying flexible beam; while the second, includes a liquid lled rigid body with a deploying flexible beam. In particular, the deploying beam in both models is assumed to have a nite deflection pro le. It has been proved that nonlinear transverse vibrations of a beam are stable when undergoing uniform extension or retrieval