Resonance capture in unbalanced dual-spin spacecraft

Abstract

Abstract : This study examines the spinup dynamics of dual-spin spacecraft having an imbalanced rotor. Of particular interest is a phenomenon called 'resonance capture' during which the spinup motor torque induces uncontrolled growth of nutation. A captured spacecraft tumbles end-over-end, while an escaped spacecraft experiences little nutation growth. The conditions which lead to both state are analyzed. A set of criteria based on the spacecraft's kinetic energy at the of spinup is used to determine whether or not it has been captured. To calculate the final energies against which these criteria are compared, a set of nondimensional equations of motion are numerically integrated. Using computer simulations, magnitude of the motor torque is shown to affect the probability of capture. For prolate spinup, larger torques are desirable, whereas for oblate spinup, smaller torques are preferred. This probability is also influenced by the initial spin configuration and is determine here as a function of the initial energies. For a given motor torque, some initial energies lead to guaranteed capture and others to guaranteed escape. This information is combined to form a 'map' which allows designers to find the best initial spinup conditions for a given spacecraft.