THEMIS Spacecraft Multi-Body Stability Analysis

Stability criteria for a spinning multi-body spacecraft were derived and applied to the THEMIS spacecraft. This paper will discuss a number of aspects of the stability analysis developed and implemented by Swales Aerospace, the spacecraft bus provider. The derivation accommodates a non-axisymmetric central body and arbitrary axial and radial boom locations. Stability criteria expressed in terms of effective inertias, were derived by maximizing the spin axis inertia. Essential details of the derivation and unique plots illustrating the stability criteria were included in this paper. A multi-body time-domain simulation developed to verify dynamic behavior of the THEMIS spacecraft was used to validate the stability criteria for a large number of deployment states. The derived stability criteria capture the affects of the central body, the stabilizing influence of the flexible radial booms, and the destabilizing influence of the flexible axial booms. They were used to determine the optimum lengths of the axial and radial booms given central body mass properties. The stability criteria presented in this paper can be readily applied to other axisymmetric or non-axisymmetric spinning spacecraft with axial and radial booms to ensure sufficient stability margins exist for all deployment configurations