Micro vibrations behavior investigation of Solar Array Drive Assembly operating under different subdivisions and loadings

Solar Array Drive Assembly (SADA) can dramatically restrict scientific space missions as it generates micro-vibrations that can significantly alter position precision and reduce pointing accuracy of satellite. The main disturbance causing factors are structural and electromagnetic coupling between Solar Array Drive Assembly and its operated load. The present study analyses these disturbances when SADA is operating dead (no load) and rigid load. Drive assembly under investigation consists of fifty rotor teeth, four beats and is a two-phase hybrid stepper motor operated in 32 and 64 subdivisions. The formulations for impact induced active vibration disturbance, electromagnetic stiffness coupling and no load SADA vibrations are developed first. A rigid force / moment micro vibrations test bed is used to acquire amplitude of disturbance moments produced by different subdivisions SADA operated without load. Research is extended to determine micro vibrations generated by SADA when it is driving a rigid load through flexible transmission shaft. The stiffness of shaft is varied to study the coupled disturbance phenomenon of 32 & 64 subdivisions SADA. The dynamic vibration function, for SADA coupled to rigid load, is obtained by transforming the system to motor torsional spring moment of inertia system. The developed analytical model contains information about stiffness of electromagnetic spring, stiffness of transmission shaft, moment of inertia of rigid load and SADA rotor. Attempts are made to validate the frequency response by comparing the results with simulations conducted in Matlab/Simulink. It is verified that increase in subdivisions number causes reduction in micro vibrations generated by SADA. Moreover, an improvement in stiffness of transmission shaft reduces the chances of active and structural natural frequencies to coincide and helps in avoiding resonance particularly in low frequency domain. The study lays a firm foundation for study on vibration damping, applicability for design of drive circuit and analysis of SADA disturbance during in orbit operation.