Computer-aided stability analysis of spinning spacecraft with on-board liquids

Abstract

A new computer algorithm identifies the dynamic equilibrium states of spinning spacecraft that contain liquids in complex, arbitrarily shaped tank configurations. This algorithm has been implemented in a computer program that determines whether liquid shifts can relocate, reorient, or destabilize a spacecraft's nominal spin axis. The program determines whether the desired spin axis is dynamically stable, estimates the extent of the stable region, and locates other possible stable states (energy traps). The algorithm is described, its theoretical basis is discussed, and a numerical example is given for a spacecraft with manifolded propellant tanks. The numerical results manifest the wobble-amplification effect described by McIntyre and others, in which a rigid-body dynamic imbalance causes the spin axis to tilt further than would be expected from simple rigid body considerations. The computer analyses generally agree with published theoretical results. Some differences, however, are identified and explained.