Attitude control of the airborne telescope SOFIA: μ-synthesis for a large scaled flexible structure

The airborne observatory SOFIA is in development with the intent to provide astronomers access to infrared wavelength unavailable from the ground. The operation of the telescope under the harsh environmental conditions in the aircraft makes the quality image stability a crucial issue. To evaluate the limits of performance that can be reached by the attitude control, a μ-synthesis optimization of the control loop is investigated during the conceptual design. A finite element model offers the most precise description of the structural dynamics of the telescope structure in this design phase and is chosen as basis for the controller design. The paper focuses on the practical aspects of robust controller design such as plant and controller reduction, weighting function selection and uncertainty modelling for flexible structures