  Modern and future observation Space missions face increasingly more demanding
pointing performance requirements. This is accompanied with the development of
larger lightweight flexible structures. This paper outlines a methodology for
modeling a generic multi-body flexible spacecraft in an end-to-end fashion
within the Two-Inputs Two-Outputs Port framework: from disturbance all the way
to pointing performance by tacking into account all the uncertainties of each
sub-system. A particular focus is dedicated to a novel generic model for Solar
Drive Array Mechanisms and its harmonic disturbances produced by the
micro-stepping driver and the gearbox imperfections. The proposed model is
validated with the on-board telemetries of a European spacecraft. Moreover this
paper shows how the proposed model-based approach can be easily used for
control design and closed-loop robust performance analysis. Worst-case
scenarios of mechanical parameters combination are investigated to provide
robust performance certificate of the reference study case. A Linear
Parameter-Varying observer, scheduled by the solar array rotor angle, is
finally proposed in order to estimate the disturbance torques induced by the
gearbox imperfections just using the measurements coming from a classical
attitude control system: a star tracker and a gyrometer.
