Adaptive secondary mirror for the 6.5-m MMT

Todd K. Barrett; Donald G. Bruns; Timothy J. Brinkley; David G. Sandler; Bruce C. Fitz-Patrick; Troy A. Rhoadarmer

doi:10.1117/12.321623

11 September 1998 Adaptive secondary mirror for the 6.5-m MMT

Todd K. Barrett, Donald G. Bruns, Timothy J. Brinkley, David G. Sandler, Bruce C. Fitz-Patrick, Troy A. Rhoadarmer

Proceedings Volume 3353, Adaptive Optical System Technologies; (1998) https://doi.org/10.1117/12.321623
Event: Astronomical Telescopes and Instrumentation, 1998, Kona, HI, United States

Abstract

We report the latest progress on the design, fabrication and testing of the adaptive secondary mirror to be used in the adaptive optics system to for the 6.5m upgrade to the Steward Observatory's MMT. The adaptive secondary will use electromagnetic force actuators is conjunction with a rigid reference structure to deform a thin and flexible glass facesheet. The facesheet is fabricated with figure accuracy comparable to the surface of a traditional static secondary mirror. The flexible facesheet can however, be deformed by the actuators to conjugate the changing atmospheric aberration. Capacitive position sensor are placed at each actuators and are used to rapidly measure the position of the glass facesheet relative to the rigid reference structure. These measurements are used as feedback in a servo control-loop which maintains the desired figure of the adaptive secondary facesheet. In the proposed design the mechanical interface between the facesheet and the reference structure is limited to a small hub in the center of the facesheet. Due to heat dissipation in the electromagnetic voice-coils a temperature control system is required to maintain the facesheet of the adaptive secondary near the ambient temperature of the atmosphere. We report on laboratory test of a nearly full size 60 actuator adaptive secondary prototype. We include test of actuator stroke and position accuracy, control-loop stability, and closed-loop bandwidth.

Citation Download Citation

Todd K. Barrett, Donald G. Bruns, Timothy J. Brinkley, David G. Sandler, Bruce C. Fitz-Patrick, and Troy A. Rhoadarmer "Adaptive secondary mirror for the 6.5-m MMT", Proc. SPIE 3353, Adaptive Optical System Technologies, (11 September 1998); https://doi.org/10.1117/12.321623

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KEYWORDS

Actuators

Mirrors

Prototyping

Sensors

Glasses

Control systems

Servomechanisms

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