Decentralized control is considered for large space structures composed of a number of subsystems which are connected by springs and dampers. It is assumed that sensors and actuators are collocated. It has been known that the overall system is stable under any perturbations in mass, damping and stiffness if the control law for each subsystem is direct velocity and displacement feedback (DVDFB). In this paper, a condition on interconnections between subsystems is presented under which stability of the overall system is preserved even in case some local controllers fail. Furthermore, it is shown that with appropriately chosen gains, the decentralized DVDFB is optimal for a quadratic cost function.