Adaptive secondary mirror for the 6.5-m MMT

Todd K. Barrett, Donald G. Bruns, Timothy J. Brinkley, David G. Sandler, Bruce C. FitzPatrick, James Roger P. Angel, Troy A. Rhoadarmer

Research output: Contribution to journalConference articlepeer-review

4 Scopus citations


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 in conjunction with a rigid reference structure to deformed a thin and flexible glass facesheet. The facesheet is fabricate 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 sensors are placed at each actuator 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.

Original languageEnglish (US)
Pages (from-to)754-763
Number of pages10
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 1998
EventAdaptive Optical System Technologies - Kona, HI, United States
Duration: Mar 23 1998Mar 23 1998

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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