Design of the fast steering secondary mirror assembly for the Giant Magellan Telescope

Abstract

The Fast-Steering secondary mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1m diameter segments with effective diameter of 3.2m. Each of the seven segments is held by three axial supports and a central lateral support with a vacuum system to mirror gravity compensations. The mirror assembly has a tip-tilt feature capable of guiding to attenuate telescope wind shake and mount control jitter. Both on-axis and off-axis mirror segments were optimized under various design considerations using finite element analyses and optical performance analyses. An integrated model of the mirror cell assembly was developed including sub-assembly parts consisting of axial supports, lateral support, breakaway mechanism, seismic restraints, and pressure seal. In this paper for the optimized FSM mirror and mirror cell assembly, the design considerations are addressed, and performance prediction results are discussed in detail with respect to the specifications.

Development status of the fast-steering secondary mirror of GMT

“…To evaluate the safety level for the mirrors, Von-Mises stress of the flexure and shear and peel off stress of the bonding have been calculated as well. Detailed results are presented in Cho et al (2018) [10] from which one can find the stress level is well below than the level of possible handling stress. Also this FE model has been used for sensitivity analyses in the development of error budget, such as mis-positioning of the lateral flexure from the CG location of the mirror, residual error of the vacuum pressure control, and pressing force on the mirror by the vacuum sealing.…”

“…In this section, we summarize the main design features which have been improved through the dPDR study. More details on the FSM design are described in our separate papers by Cho et al (2018) [10] and Jeong et al (2018) [11] .…”

“…The axia breakaway sy which limit th an earthquake experimental results indica lengths shoul operation has and from the is far below th n in Figure 8 existing teles line thickness d to determine ermal effects, (2018) [10] . sm, called the oaded springs rror in case o n as well as an 8) [12] .…”

Non-Rotationally Symmetric Field Mapping for Back-Scanned Step/Stare Imaging System

“…The third-generation IRST systems utilize the FPAs with step/stare imaging to achieve wide area coverage. The new IRST achieves greater performances than the previous generation thanks to their staring nature, i.e., to longer integration times (milliseconds rather than microseconds) [3][4][5][6][7][8].…”

“…They also suffer from more false alarms [2].The third-generation IRST systems utilize the FPAs with step/stare imaging to achieve wide area coverage. The new IRST achieves greater performances than the previous generation thanks to their staring nature, i.e., to longer integration times (milliseconds rather than microseconds) [3][4][5][6][7][8].In step/stare imaging applications, a high-resolution narrow FOV sensor is rapidly stepped or indexed across an area of interest, stopping at intervals to stare and collect imagery. Then the images at each location are stitched together to form a large but high-resolution image.…”