Mr. Yannick Lammen Profile

Yannick Lammen

Development Engineer at European Southern Observatory

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Author

Publications (8)

Proceedings Article | 29 August 2022 Presentation + Paper

The design and development of the M2, M3 and M5 cells for the European Extremely Large Telescope

A. Tomàs, J. A. Andion, M. Canchado, J. M. Casalta, O. Casamor, O. Ramos, M. Redondo, F. Grañena, G. Olivella, M. Mueller, Y. Lammen, J. F. Pirard, P. Zuluaga

Proceedings Volume 12188, 121880K (2022) https://doi.org/10.1117/12.2629427

KEYWORDS: Mirrors, Actuators, Telescopes, Sensors, Interfaces, Manufacturing, Optical alignment

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Proceedings Article | 25 August 2022 Presentation + Paper

ESO ELT: vibration performance and budget verification: measured equipment data as input to telescope model

B. Sedghi, P. Zuluaga Ramirez, D. Pilbauer, S. Leveratto, U. Lampater, M. Müller, G. Jakob, M. Haug, M. Accardo, Y. Lammen, J. Abad-Pastor, J. C. González-Herrera

Proceedings Volume 12187, 1218714 (2022) https://doi.org/10.1117/12.2628907

KEYWORDS: Telescopes, Mirrors, Wavefronts, Actuators, Control systems, Adaptive optics, Vibrational characterization, Modeling and simulation, Vibration isolation, Active vibration damping

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Proceedings Article | 6 July 2018 Paper

An end-to-end simulation to predict the in-flight performance improvement of a modified SOFIA secondary mirror mechanism

Yannick Lammen, Andreas Reinacher, Alfred Krabbe

Proceedings Volume 10700, 107001F (2018) https://doi.org/10.1117/12.2309802

KEYWORDS: Mirrors, Kinematics, Device simulation, Finite element methods, Data modeling, Actuators, Sensors, Silicon carbide, Linear filtering, Structural dynamics, Structural analysis, Structural engineering, Vibration control, Vibration isolation

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Proceedings Article | 14 September 2016 Presentation + Paper

SOFIA pointing and chopping: performance and prospect

Andreas Reinacher, Yannick Lammen, Friederike Graf, Holger Jakob

Proceedings Volume 9973, 99730L (2016) https://doi.org/10.1117/12.2237789

KEYWORDS: Infrared telescopes, Shape memory alloys, Telescopes, Cameras, Actuators, Mirrors, Motion estimation, Position sensors, Control systems, Sensors

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Proceedings Article | 9 August 2016 Paper

SOFIA's secondary mirror assembly: in-flight performance and control approach

Andreas Reinacher, Yannick Lammen, Hans-Peter Roeser

Proceedings Volume 9908, 99082V (2016) https://doi.org/10.1117/12.2232851

KEYWORDS: Mirrors, Space telescopes, Telescopes, Actuators, Position sensors, Sensors, Filtering (signal processing), Linear filtering, Data modeling, Amplifiers

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5m infrared telescope built into a Boeing 747 SP. In 2014 SOFIA reached its Full Operational Capability milestone and nowadays takes off about three times a week to observe the infrared sky from altitudes above most of the atmosphere’s water vapor content. An actively controlled 352mm SiC secondary mirror is used for infrared chopping with peak-to-peak amplitudes of up to 10 arcmin and chop frequencies of up to 20Hz and also as actuator for fast pointing corrections. The Swiss-made Secondary Mirror Mechanism (SMM) is a complex, highly integrated and compact flexure based mechanism that has been performing with remarkable reliability during recent years. Above mentioned capabilities are provided by the Tilt Chopper Mechanism (TCM) which is one of the two stages of the SMM. In addition the SMM is also used to establish a collimated telescope and to adjust the telescope focus depending on the structure’s temperature which ranges from about 40°C at takeoff in Palmdale, CA to about −40◦C in the stratosphere. This is achieved with the Focus Center Mechanism (FCM) which is the base stage of the SMM on which the TCM is situated. Initially the TCM was affected by strong vibrations at about 300 Hz which led to unacceptable image smearing. After some adjustments to the PID-type controller it was finally decided to develop a completely new control algorithm in state space. This pole placement controller matches the closed loop system poles to those of a Bessel filter with a corner frequency of 120 Hz for optimal square wave behavior. To reduce noise present on the position and current sensors and to estimate the velocity a static gain Kalman Filter was designed and implemented. A system inherent delay is incorporated in the Kalman filter design and measures were applied to counteract the actuators’ hysteresis. For better performance over the full operational temperature range and to represent an amplitude dependent non-linearity the underlying model of the Kalman filter adapts in real-time to those two parameters. This highly specialized controller was developed over the course of years and only the final design is introduced here. The main intention of this contribution is to present the currently achieved performance of the SOFIA chopper over the full amplitude, frequency, and temperature range. Therefore a range of data gathered during in-flight tests aboard SOFIA is displayed and explained. The SMM’s three main performance parameters are the transition time between two chop positions, the stability of the Secondary Mirror when exposed to the low pressures, low temperatures, aerodynamic, and aeroacoustic excitations present when the SOFIA observatory operates in the stratosphere at speeds of up to 850 km/h, and finally the closed-loop bandwidth available for fast pointing corrections.

Proceedings Article | 27 July 2016 Paper

Characterization of the mechanical properties of the SOFIA secondary mirror mechanism in a multi-stage approach

Benjamin Greiner, Yannick Lammen, Andreas Reinacher, Alfred Krabbe, Jörg Wagner

Proceedings Volume 9906, 99063R (2016) https://doi.org/10.1117/12.2231648

KEYWORDS: Mirrors, Finite element methods, Observatories, Telescopes, Infrared astronomy, Hardware testing, Sensors, Data modeling, Motion models, Actuators

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Proceedings Article | 27 July 2016 Paper

A new test environment for the SOFIA secondary mirror assembly to reduce the required time for in-flight testing

Yannick Lammen, Andreas Reinacher, Rick Brewster, Benjamin Greiner, Friederike Graf, Alfred Krabbe

Proceedings Volume 9906, 99064T (2016) https://doi.org/10.1117/12.2232152

KEYWORDS: Actuators, Mirrors, Observatories, Cameras, Telescopes, Shape memory alloys, Sensors, Position sensors, Aluminum, Manufacturing

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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.

Proceedings Article | 27 July 2016 Paper

SOFIA secondary mirror mechanism heavy maintenance and improvements

Yannick Lammen, Andreas Reinacher, Ivar Kjelberg, Serge Droz, Holger Jakob, Friederike Graf, Michael Lachenmann, Alfred Krabbe

Proceedings Volume 9906, 99061R (2016) https://doi.org/10.1117/12.2231352

KEYWORDS: Mirrors, Calibration, Temperature metrology, Observatories, Autocollimators, Telescopes, Sensors, Shape memory alloys, Sensor calibration, Position sensors

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The Stratospheric Observatory For Infrared Astronomy (SOFIA) reached its full operational capability in 2014 and completed hundreds of observation flights. Since its installation in 2002, the Secondary Mirror Mechanism was subject to thousands of operating hours equivalent to millions of load cycles. During the aircraft heavy maintenance in fall 2014, a four month time window enabled the removal of the mechanism from the telescope structure for service and improvements. Next to visual corrosion- and crack-inspection of the flexures, critical electronic components (in particular the set of three eddy current position sensors that determine the mirror tilt) were replaced. Moreover, a detailed temperature dependent position calibration of the system was performed in a cold chamber to improve the pointing accuracy. Until then, a simple temperature independent linear gain was used to translate the sensor output voltage into a position. For accurate positioning across the whole temperature range, a temperature dependent correction function had to be developed. This calibration would have cost hours of observing time when performed in flight which made it an essential goal for completion during the maintenance period. An autocollimator was used as optical reference camera to measure the tip-tilt position of the secondary mirror in the cold chamber. Using this calibration setup, a pattern of many mirror positions in the tip-tilt domain was approached at several temperature points to provide a high resolution data set for the new multidimensional calibration function. Follow-up in-flight verification measurements confirmed a large improvement in pointing accuracy as soon as the temperature measurements were included into the position correction. Improvements of up to a factor of 10 were especially noticed in the lower temperature range. This contribution provides an insight into the work performed during the SOFIA - Secondary Mirror Mechanism maintenance with the focus on the temperature dependent position calibration.

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