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Proceedings Paper

Modeling of the SOFIA secondary mirror controller
Author(s): Andreas Reinacher; Hans-Peter Roeser
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Paper Abstract

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5m infrared telescope built into a Boeing 747SP. During observations the telescope will not only be subject to aircraft vibrations and maneuver loads - by opening a large door to give the observatory an unhindered view of the sky, there will also be aerodynamic and aeroacoustic disturbances. A critical factor in the overall telescope performance is the SOFIA Secondary Mirror Assembly (SMA). The 35cm silicon carbide mirror is mounted on the Secondary Mirror Mechanism (SMM), which has five degrees-offreedom and consists of two parts: The slow moving base for focusing and centering, and on top of that the Tilt Chop Mechanism (TCM) for chopping with a frequency of up to 20Hz and a chop throw of up to 10arcmin. The development of the controller that is used to meet the stringent performance requirements relys heavily on a state space model of the system. A pole-placement controller is compared to an optimal LQG control approach which makes use of the model to calculate all required system states in real-time. The paper explains the modeling of the TCM with linear differential equations and the optimization via a grey-box model approach with system identification data. Simulated data is then compared to measurements taken on ground and in flight.

Paper Details

Date Published: 10 November 2011
PDF: 10 pages
Proc. SPIE 8336, Integrated Modeling of Complex Optomechanical Systems, 83360S (10 November 2011); doi: 10.1117/12.915590
Show Author Affiliations
Andreas Reinacher, Univ. of Stuttgart (Germany)
NASA Dryden Flight Research Ctr. (United States)
Hans-Peter Roeser, Univ. of Stuttgart (Germany)

Published in SPIE Proceedings Vol. 8336:
Integrated Modeling of Complex Optomechanical Systems
Torben Andersen; Anita Enmark, Editor(s)

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