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An electromechanical dynamic model of the solar array drive system (SADS) was proposed to analyze the disturbance characteristics, and verified by the experiment study in the laboratory. The factors which directly cause the SADS’s disturbance were differentiated based on the idea of reductionism, and corresponding disturbance characteristics were investigated. The other kinds of factors which do not cause disturbances but affect the disturbance characteristics of SADS, as well as their influence rules, were also analyzed. The results of the proposed model agree well with the experimental data, with an error of less than 10%. Disturbances of SADS occur when the rotational-motion acceleration and structural-vibration acceleration are not both equal to zero. The current subdivision of the drive controller, nonlinear magnetic field of the stepping motor, and the varying meshing parameters of the gear reducer can directly cause disturbances, which vary periodically and occur near excitation frequencies and high-order harmonic frequencies. The amplitude of the disturbance increases with a decrease in the number of current subdivisions, an increase in electromagnetic excitation and the fluctuation margin of gear-meshing parameters. The closed-loop current control, nonlinear friction between the brush and slip ring, the bending-torsional coupling of the solar array, and the gear clearance of the gear reducer do not cause the SADS’s disturbances but can affect their profile and spectrum distribution from different aspects, even introducing disturbance components in the non-driving directions.

An equivalent modal analysis method that considers the influence of the drive control is presented for operational spacecraft tracking-drive flexible systems (STFS). The proposed method is verified by simulations and laboratory experiments using a spacecraft model with fixed connections. The effects of the parameters of the drive control, such as the drive speed and control gains of the current loop, on the system’s dynamic characteristics are determined. The results indicate that the drive mechanism with the influence of drive control can be regarded as a torsional spring-dashpot boundary. The drive control causes a decrease in the equivalent stiffness of the drive mechanism but does not affect the equivalent damping. In general, the decrease in the equivalent stiffness is positively correlated with the drive speed and negatively correlated with the control gains. The drive control of the STFS has relatively low influence at low drive speeds but has a significant influence on the system’s dynamic characteristics at high drive speeds. The torsion-mode natural frequencies of the STFS are directly proportional to the control gains and inversely proportional to the drive speed. The relationships between the parameters of the drive control and the torsion-mode modal damping ratios, however, do not conform to a uniform pattern and require further study.