STEADY RIGID-BODY MOTIONS IN A CENTRAL GRAVITATIONAL-FIELD

In recent work, the exact dynamic equations for the motion of a finite rigid body in a central gravitational field were shown to be of Hamiltonian form with a noncanonical structure. In this paper, the notion of relative equilibrium is introduced based upon this exact model. In relative equilibrium, the orbit of the center of mass of the rigid body is a circle, but the center of attraction may or may not lie at the center of the orbit. This feature is used to classify great-circle and non-great-circle orbits. The existence of non-great-circle relative equilibria for the exact model is proved from various variational principles. While the orbital offset of the non-great-circle solutions is necessarily small, a numerical study reveals that there can be significant changes in orientation away from the classic Lagrange relative equilibria, which are solutions of an approximate model. Accordingly our analysis raises questions concerning the design and control of Earth pointing satellites.