ISBN 9783843947428

978-3-8439-4742-8, Reihe Raumfahrt

Friederike Graf
Image jitter reduction and vibration compensation for large optical systems at the example of the airborne SOFIA telescope

205 Seiten, Dissertation Universität Stuttgart (2020), Softcover, A5

Zusammenfassung / Abstract

Large optical structures such as telescopes, antennas, science instruments or free-space optical communication systems share stringent stability requirements. Often, sophisticated compensation techniques for structurally induced motion of the light beam are necessary to ensure a stable signal. This dissertation introduces strategies for minimizing the fast image motion due to vibrations in an optical system at the example of the Stratospheric Observatory for Infrared Astronomy (SOFIA).

SOFIA enables infrared astronomy aboard a modified Boeing 747SP at altitudes of up to 45 kft. At the beginning of this work, the telescope was considered diffraction-limited in the far-infrared wavelengths beyond 50 μm. A study of the different sources of blur revealed that the reduction of the fast image motion, the image jitter, is necessary to reach SOFIA’s image size goals. During flight, the telescope is exposed to a continuously changing excitation environment, leading to deformation of its flexible structure in a wide range of frequencies. In the framework of this thesis, the different vibration sources and the impact of the changing flight conditions were evaluated and improvements throughout the control system were identified and implemented. During full operations, these efforts led to an image jitter reduction of 40%.

While the fast image motion was considerably reduced, further upgrades are necessary to reach SOFIA’s image jitter requirement. Therefore, an image motion estimator was developed by determining the motion of the light beam due to relative movement of the optical elements. This was achieved with 13 additional accelerometers at the mirrors of the telescope and a polynomial Multiple Input Single Output model that fuses data from several sensors. This estimator is able to reproduce the image jitter with very high accuracy and its implementation will enable SOFIA to reach the demanding image quality goal of diffraction-limited imaging beyond wavelengths of 25 μm.