The focus of this paper is to investigate impact dynamics among space free-floating multibody systems, by developing an extended inertial tensor concept, and to establish the teoretical basis for floating chains collisions. The authors have developed a concept named 'Extended Inversed Inertia Tensor (Ex-IIT)' paying attention to free-floating behavior in space environment. This paper applies the Ex-IIT to impulse minimization arguments. To illustrate the magnitude of the impulses caused by link collisions in various conditions, new concepts of Impulse Index and Impulse Ellipsoid are introduced. By means of these concepts, we discuss the relationship of the impulse with collision directions and link postures, in order to figure out the condition minimizing the impulse.