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TMT’s lead Optics, Adaptive Optics and Systems Engineering with the ADOPTICA team during the Adaptive Secondary Mirror Conceptual Design Review, on September 25, 2018, at the TMT Project Office in Pasadena, CA. Image Credit: TMT International Observatory

TMT Adaptive Secondary Mirror Passes Conceptual Design

Pasadena, CA - Sept. 25, 2018 – The TMT Project Office recently held a conceptual design review to evaluate the design study for the TMT’s Adaptive Secondary Mirror (AM2) system.

The main goals of the study were to:

  • Develop a conceptual design that meets the TMT requirements, including a preliminary analysis of the system reliability and maintainability. One of the main challenges of the TMT secondary mirror is that it is large (~3.2m) and convex.
  • Identify the challenges of the design, the technical risks and potential showstoppers.
  • Develop a project plan, including cost and schedule to complete the design, manufacture and test of such a system.

The AM2 design study was executed by the ADOPTICA Italian consortium, which is composed of Microgate Engineering and A.D.S. international. ADOPTICA has successfully deployed several adaptive secondary mirrors for very large astronomical facilities, such as MMT, LBT, and ESO VLT, and is currently manufacturing the large 2.4m flat M4 deformable mirror for the ESO E-ELT.

The ADOPTICA AM2 design consists of a ~3.2m convex deformable mirror assembly mounted on a positioning system, which includes a segmented thin shell mirror controlled by 3,828 contactless voice coil actuators, a reference body and the deformable mirror cell. The mirror thin shell layout is composed of seven segments: six petals arranged around a central hexagonal segment.

The AM2 Conceptual Design review (CoDR) was successfully completed; no showstoppers were identified, making it possible to mature the current concept as part of a potential future preliminary design study phase.

The AM2S and the TMT conventional Secondary Mirror System (M2S) are designed to be interchangeable. While the M2S is a passive mirror, the current AM2 design is a deformable mirror dedicated to correct for relatively low order modes of wavefront aberrations caused by atmospheric turbulences.

Adaptive optics systems work by rapidly deforming mirrors in real-time, precisely counteracting the effect of the distortion produced by the passage of light through the Earth’s atmosphere. Specifically, an adaptive secondary mirror for the TMT will correct the turbulences located within the lower layers of the Earth’s atmosphere (commonly named the “ground layers”), improving the image quality for instruments that would otherwise return seeing-limited images.

“We are pleased by the outstanding work done by ADOPTICA on the very advanced conceptual design of the adaptive secondary mirror system,” said Corinne Boyer, TMT Adaptive Optics group leader. “TMT’s adaptive secondary system is a technological challenging system, but it will undeniably provide some real benefits to the TMT science programs.”

The AM2 mounted on the TMT telescope top end.

The AM2 mounted on the TMT telescope top end.

The AM2 layout showing the mirror thin shell, the reference body, a subset of the actuators, the mirror and reference body cell, and the positioner.

The AM2 layout showing the mirror thin shell, the reference body, a subset of the actuators, the mirror and reference body cell, and the positioner.


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