Influence of electromagnetic stiffness on coupled dynamic performance of flexible load driven by solar array drive assembly

The micro-vibrations inherent to the functions of higher precision spacecraft is a crucial consideration and these must be mitigated effectively in order to achieve extremely high pointing accuracy and communication frequency. A particular spacecraft component relevant to this is Solar Array Drive Assembly (SADA), which rotates the array to obtain maximum solar power in full-orbit circle. The drive assembly, characterized by rigid - flexible and electromechanical coupling, generates broadband and low amplitude micro disturbances that become one of the major barriers for improving performance accuracy. Based on motion pattern of solar array, this work presents disturbance dynamics of different SADA configurations driving flexible system (along spin axis) and analyses the influence of electromagnetic stiffness and electronic frequencies on coupled disturbance behavior. SADA employed for research is a step motor with four beats, subcategorized to hybrid bi-phase with every full step angle micro-stepped to 32 subdivisions (SDs). Initially, mechatronics model for electromagnetic torque of SADA is simplified and linearized to obtain its equivalent structural dynamic model and formulation for input excitation torque. Keeping in view amplitude of current, number of rotor teeth, SDs and beats, the mathematical equation for frequency of electronic vibration is formulated and corresponding active disturbance behavior is analyzed through experimental tests. Analytical dynamic model for flexible load operated by SADA is developed next by approximating the assembly to mass moment of inertia, torsional spring system and Eigen values of the mechanical configuration are obtained. Taking four degrees of freedom dynamic model as study object the simulation method of mechanical assembly is illustrated. Results obtained from analytical model are validated through disturbance dynamics identified from simulations and coupled disruption influence on system vibration parameters is analyzed. It is observed that vibration response of SADA driving flexible system consists of electromagnetic frequencies, natural frequencies of mechanism and electronic vibrations of drive. In addition, disturbance amplitude and coupled dynamics is directly influenced by variation in hybrid motor parameters. The study can be utilized in designing of drive circuits for active decoupling vibration to control disturbances and understanding of SADA dynamics when it is driving real solar array during space operation.