Dr. Ole Singelstad Profile

Dr. Ole Singelstad

at Steward Observatory

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Proceedings Article | 25 July 2024 Poster + Paper

Optimizing thermal control of the MMTO primary mirror

J. Duane Gibson, Will Goble, Dallan Porter, Maya Williams, Charlie Goldberg, Thomas Ole Singlestad

Proceedings Volume 13101, 1310121 (2024) https://doi.org/10.1117/12.3013551

KEYWORDS: Air temperature, Mirrors, Telescopes, Control systems, Wavefront sensors, Sensors

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Thermal control of the MMT Observatory (MMTO) primary mirror (M1) has been optimized to reduce M1 thermal anomalies and mirror seeing while enhancing overall imaging quality. These refinements include 1) increased use of temperatures from outside, chamber, M1 glass, and U.S. National Weather Service sources for thermal control, 2) expanded monitoring and analysis of the M1 glass temperatures, 3) integration of multiple feedback-based PID (proportional-integral-derivative) controllers in M1 thermal control, and 4) extensive data analysis of thermal anomalies and trends within the M1 mirror and surrounding telescope enclosure. The newly deployed control strategy uses the minimum temperature from different sources (i.e., outside, chamber, and forecast) to regulate the temperature of the conditioned air used to cool the M1 mirror. The controlling temperature source commonly changes during the night. Before this current work, thermal control of the M1 ventilation system used a linear regression model to determine the setpoint of the main glycol chillers. This simple approach has been replaced by a combination of open-loop and closed-loop, feedback-based PID servo controllers that regulate the chillers and coolant valves along the M1 ventilation air path. Different feedback temperatures for the various PID servos are considered, allowing for more detailed and responsive conditioning of air within the M1 ventilation system. Comparison of M1 glass-air temperature contrasts to wavefront-sensor (WFS) seeing values define optimal performance conditions. This work has led to recommendations for operational changes that aim to improve thermal conditions for the M1 mirror and telescope chamber, including during the transition from daytime to nighttime activities.

Proceedings Article | 4 October 2023 Presentation + Paper

Focus diverse phase retrieval testbed development of continuous wavefront sensing for space telescope applications

Hyukmo Kang, Kyle Van Gorkom, Jess Johnson, Ole Singelstad, Aaron Goldtooth, Daewook Kim, Ewan Douglas

Proceedings Volume 12677, 126770G (2023) https://doi.org/10.1117/12.2677900

KEYWORDS: Signal to noise ratio, Phase retrieval, Point spread functions, Monochromatic aberrations, Wavefront sensors, Wavefront errors, Interferometers, Space telescopes, Telescopes

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Continuous wavefront sensing on future space telescopes allows relaxation of stability requirements while still allowing on-orbit diffraction-limited optical performance. We consider the suitability of phase retrieval to continuously reconstruct the phase of a wavefront from on-orbit irradiance measurements or point spread function (PSF) images. As phase retrieval algorithms do not require reference optics or complicated calibrations, it is a preferable technique for space observatories, such as the Hubble Space Telescope or the James Webb Space Telescope. To increase the robustness and dynamic range of the phase retrieval algorithm, multiple PSF images with known amount of defocus can be utilized. In this study, we describe a recently constructed testbed including a 97 actuator deformable mirror, changeable entrance pupil stops, and a light source. The aligned system wavefront error is below ≈ 30 nm. We applied various methods to generate a known wavefront error, such as defocus and/or other aberrations, and found the accuracy and precision of the root mean squared error of the reconstructed wavefronts to be less than ≈ 10 nm and ≈ 2 nm, respectively. Further, we discuss the signal-to-noise ratios required for continuous dynamic wavefront sensing. We also simulate the case of spacecraft drifting and verify the performance of the phase retrieval algorithm for continuous wavefront sensing in the presence of realistic disturbances.

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