Modal analysis of the DOBSON SPACE TELESCOPE
- Paper number
IAC-06-C2.P.1.01
- Author
Mrs. Kerstin Kracht, Technical University of Berlin, Germany
- Year
2006
- Abstract
This paper gives an overview about the results of modal analysis (mechanical vibrations) for the deployment structure of the Dobson Space Telescope. This work was done in cooperation between the ‘Institut für Luft- und Raumfahrt’ (ILR) (Institute of Aeronautics and Astronautics) supported by the ‘Institut für Mechatronische Maschinendynamik’ (Institute of Mechatronical Dynamics of Machines) from the Technical University of Berlin, Germany (TU-Berlin), in the framework of the diploma thesis of the author. The DOBSON SPACE TELESCOPE is a research project of the ILR. Aim of the project is to develop a new type deployable telescope. It makes use of the fact that a telescope is mainly empty space between the optical elements. This space is needed only for observation but not during launch. If the telescope is folded down during launch and unfolded after the satellite reached its orbit, much larger telescopes would fit in a given mass and volume budget. This concept makes the DOBSON SPACE TELESCOPE very valuable for the limited space given by cost effective micro satellites. There are two basic questions referring to mechanical vibrations. First, what is the behaviour of the folded structure during launch? Damage due to launcher vibration must be avoided by any mean. Thereto in the first part of the diploma thesis the folded down telescope is excited by a shaker with a NASA frequency spectrum to simulate the launch. The measurement data of the satellites vibration response are logged by contact less measuring technique. Second, how does the deployed telescope vibrate during continuous working? Are the vibration amplitudes in the range of the optical instruments displacement tolerance, so that the camera is able to produce high quality photos? For understanding and answering these questions the following facts have to be considered. Telescopes are very sensitive to displacement of their optical elements. The tolerance is only a few micrometer in each direction. The Dobson Space Telescope uses a Cassegrain design whereas needed distance between primary and secondary mirror generated via a deployable structure. Due to this fact the foldable boom is the most likeable source of in orbit deformations. Its behaviour to mechanical vibrations is of highest interest. The highest vibration amplitudes result from resonance. If the value of excitation frequency is the same as one of the various natural frequencies of a vibratory body, resonance would occur. The most important excitation of the satellite results from the unbalance of the reaction wheels which change the position of the satellite to execute the various operation modes of the telescope. The wheels’ velocity is in a range from -3000 to 3000 RPM. That means the satellite structure is excited with frequencies in the range from 0 to 50 Hz. So the examination of the Booms natural frequencies is the subject of the second part of the diploma thesis because the knowledge about these frequencies is the supposition to avoid resonance with suitable design features e.g. vibration isolation, vibration extinction. Therefore analytical, numerical and experimental modal analyses are executed. The metrological examination is also realised by a Shaker and contact less measuring technique.
- Abstract document
- Manuscript document
IAC-06-C2.P.1.01.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.