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Proceedings Paper

A new test environment for the SOFIA secondary mirror assembly to reduce the required time for in-flight testing
Author(s): Yannick Lammen; Andreas Reinacher; Rick Brewster; Benjamin Greiner; Friederike Graf; Alfred Krabbe
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Paper Abstract

The Stratospheric Observatory For Infrared Astronomy (SOFIA) reached its full operational capability in 2014 and takes off from the NASA Armstrong Flight Research Center to explore the universe about three times a week. Maximizing the program's scientific output naturally leaves very little flight time for implementation and test of improved soft- and hardware. Consequently, it is very important to have a comparable test environment and infrastructure to perform troubleshooting, verifications and improvements on ground without interfering with science missions. SOFIA's Secondary Mirror Mechanism is one of the most complex systems of the observatory. In 2012 a first simple laboratory mockup of the mechanism was built to perform basic controller tests in the lower frequency band of up to 50Hz. This was a first step to relocate required engineering tests from the active observatory into the laboratory. However, to test and include accurate filters and damping methods as well as to evaluate hardware modifications a more precise mockup is required that represents the system characteristics over a much larger frequency range. Therefore the mockup has been improved in several steps to a full test environment representing the system dynamics with high accuracy. This new ground equipment allows moving almost the entire secondary mirror test activities away from the observatory. As fast actuator in the optical path, the SMM also plays a major role in SOFIA's pointing stabilization concept. To increase the steering bandwidth, hardware changes are required that ultimately need to be evaluated using the telescope optics. One interesting concept presented in this contribution is the in- stallation of piezo stack actuators between the mirror and the chopping mechanism. First successful baseline tests are presented. An outlook is given about upcoming performance tests of the actively controlled piezo stage with local metrology and optical feedback. To minimize the impact on science time, the laboratory test setup will be expanded with an optical measurement system so that it can be used for the vast majority of testing.

Paper Details

Date Published: 27 July 2016
PDF: 12 pages
Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99064T (27 July 2016); doi: 10.1117/12.2232152
Show Author Affiliations
Yannick Lammen, Deutsches SOFIA Institut, Univ. Stuttgart (Germany)
NASA Armstrong Flight Research Ctr. (United States)
Andreas Reinacher, Deutsches SOFIA Institut, Univ. Stuttgart (Germany)
NASA Armstrong Flight Research Ctr. (United States)
Rick Brewster, SOFIA Science Ctr., NASA Ames Research Ctr. (United States)
Benjamin Greiner, Deutsches SOFIA Institut, Univ. Stuttgart (Germany)
Friederike Graf, Deutsches SOFIA Institut, Univ. Stuttgart (Germany)
SOFIA Science Ctr., NASA Ames Research Ctr. (United States)
Alfred Krabbe, Deutsches SOFIA Institut, Univ. Stuttgart (Germany)

Published in SPIE Proceedings Vol. 9906:
Ground-based and Airborne Telescopes VI
Helen J. Hall; Roberto Gilmozzi; Heather K. Marshall, Editor(s)

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