Characterization of sadm induced disturbances and their effects on spacecraft pointing errors

This paper presents the modeling and analysis of the induced oscillations due to the Solar Array Drive Mechanism (SADM) on the pointing performances of a generic Earth observation spacecraft. First the SDT (Satellite Dynamics Toolbox) is used to obtain a Linear Parameter Varying model of the spacecraft fitted with a flexible solar panel parameterized according to its angular configuration. Then a detailed model of the SADM including the stepper motor and the gear box is included using the TITOP (Two-Input Two-Output Ports) approach. Such an approach allows to build the dynamic model of the structure just by assembling the sub-structure models. TITOP models consider the 6 d.o.f. (degrees of freedom) to take into account all the geometrical, kinematic and dynamic couplings required to capture the propagation of the perturbations inside the overall flexible structure. Moreover these models allows the user to evaluate the pointing errors on the 3 axes. Parametric robustness analysis tools are then used to isolate the worst harmonics of the various SADM imperfections and the solar array angular configuration from the pointing performance point of view.