27 July 2016 A new test environment for the SOFIA secondary mirror assembly to reduce the required time for in-flight testing
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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.
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Yannick Lammen, Yannick Lammen, Andreas Reinacher, Andreas Reinacher, Rick Brewster, Rick Brewster, Benjamin Greiner, Benjamin Greiner, Friederike Graf, Friederike Graf, Alfred Krabbe, Alfred Krabbe, } "A new test environment for the SOFIA secondary mirror assembly to reduce the required time for in-flight testing", Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99064T (27 July 2016); doi: 10.1117/12.2232152; https://doi.org/10.1117/12.2232152
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