Experience with wind-excited mirror vibrations

For the performance of Extreme Large Telescopes the control of wind excited vibrations of the mirror segments may be an issue. There exits some experience with wind excitations of airborne telescopes. At the moment, the 2.7m airborne observatory SOFIA is under construction, where aircraft and aero-acoustic excitations are the design driver for the mirror supporting system. The planning and execution of the first test flights is coming up in the next 12 month. The paper explains the related vibration isolation and compensation features of SOFIA. The experience with the design and end-to-end simulation, the results of the on-ground tests, and the plans how to verify them in-flight, will be presented. This experience may give some hints for the design of the alignment systems for the mirror segments of Extreme Large Telescopes. The paper will present some ideas, comments and recommendations of the SOFIA system engineer for control systems of mirror segments.