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PI Active Optics in Astronomical Telescopes |
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Keck I and Keck II observatories and NASA Infrared Telescope Facility (IRTF) (silver dome), Mauna Kea, Hawaii. Photo: Karl Spanner. |
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During the last decade, PI has designed several large-aperture tip/tilt systems for image stabilization. Resolution in large earthbound telescopes is limited by atmospheric turbulence and vibrations which cause image shifting. Piezo-electrically driven active secondary mirrors significantly improve telescope resolution, up to 1000% during long integrations, by correcting for these image shifts in real time.
Momentum Compensation Due to the inertia of the large mirrors and the high accelera- |
tions required to correct for image fluctuations, significant forces can be induced in the telescope structure, causing unwanted vibrations.
To cancel these forces before they excite vibrations in the structure, PI has developed momentum compensation systems integrated into the tip/tilt platforms. Any vibration caused by the motion of the mirror is canceled with an efficiency of up to 95% by the internal, piezoelectrically driven momentum-compensation mechanism. |
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The Horsehead Nebula. Photo: Brian Lula. |
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Active tip/tilt mirror for Subaru Telescope (Mauna Kea, Hawaii). Mirror diameter: 150 mm Tip/Tilt range: ±600 µrad Resonant frequency: 610 H |
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Telescope, rear view Active secondary tip/tilt mirror for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, with Hexapod 6-degree-of-freedom align-ment system (for information on Hexapod systems see the “Micropositioners” section, see here ff) Mirror diameter: 244 mm Tip/Tilt range: ±250 µrad Resonant frequency: 490 Hz |
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Telescope structure with active secondary mirror (from “Progress Report on DISCO: A Project for Image Stabilization at the 2.2 m Telescope,” F. Maaswinkel, S. D’Odorico and G. Huster, ESO, F. Bortoletto, Istituto di Astronomia, University of Padova, Italy) |
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Active tip/tilt mirror for Subaru Telescope, rear view |
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Active secondary tip/tilt mirror for the United Kingdom Infra-Red Telescope (UKIRT) on Mauna Kea, Hawaii, with Hexapod 6-degree-of-freedom alignment system (for information on Hexapod systems see the “Micropositioners” section, see here ff.). Mirror diameter: 314 mm Tip/Tilt range: ±500 µrad Resonant frequency: 280 Hz |
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Active secondary tip/tilt mirror for ESO’s (European Southern Observatory) 2.2 m telescope in La Silla, Chile.
Mirror diameter: 100 mm
Tip/Tilt range: ±400 µrad
Resonant frequency: 900 Hz |
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Tip/tilt steering mirror units for the Keck Outrigger tele-scope in Hawaii. The units are controlled by a high-per-formance digital controller with a fiber optic interface (not shown)
Mirror diameter: 250 mm
Tip/Tilt range: ±150 µrad
Resolution: nanorad realm
Feedback: capacitive sensors |
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