Design and Validation of a Flexible Spacecraft Model for Attitude Control Applications.

The purpose of this thesis is the assessment of a comparison between a flexible spacecraft model, studied during previous theses and scientific articles, and the implementation of the same spacecraft in the software MSC Adams, aiming at validating the model. Thanks to this innovative tool it is possible to evaluate several features the user could desire to have available, conducting a non-linear multi-body analysis, that allows to provide more realistic data sets. The Picard satellite of the French Space Agency (CNES) is used as the main body of the spacecraft and its dynamics is expressed with Euler equations for a rigid body. The configuration, in terms of locations and dimensions, of the solar panels and the reaction wheels has been modified with respect to Picard in order to have advantages during the construction of the spacecraft in MSC Adams and to have a more general type of satellite. In particular, four symmetrical solar panels and a system of three reaction wheels located at the center of mass of the spacecraft are considered. The most important aspect of the work is the flexible part of the satellite, represented by the four solar panels. A Finite Element Method (FEM) analysis with MSC Patran/MSC Nastran is conducted to obtain the natural modes and frequencies necessary for the model and a coupling matrix between rigid and flexible part is also evaluated. The second part of the thesis is about the spacecraft design implementation in MSC Adams View and the simulation phases, which are made through both MSC Adams and MATLAB/Simulink environment. A simple Proportional-Derivative (PD) controller is implemented for the attitude control during a manoeuvre, with the purpose of achieving the desired Euler angles, aiming at simulating a command for a new pointing direction towards a particular objective. The comparison between the two models is done in order to understand better the influence of the flexibility of the solar panels and the possible differences between the more complex analysis in MSC Adams and the linearized, more approximated one through the mathematical model. The attitude control in case of failure of three solar panels is also assessed. The PD controller ensures good performance and a stable response during the manoeuvre, despite of the external (only the gravity gradient is taken into consideration) and internal (vibrations of the solar panels) disturbances acting on the system. Nevertheless, this basic controller has some problems in case of failure of the panels.