22 July 2016 Advanced structural design for precision radial velocity instruments
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Abstract
The GMT-Consortium Large Earth Finder (G-CLEF) is an echelle spectrograph with precision radial velocity (PRV) capability that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF has a PRV precision goal of 40 cm/sec (10 cm/s for multiple measurements) to enable detection of Earth-like exoplanets in the habitable zones of sun-like stars1. This precision is a primary driver of G-CLEF’s structural design. Extreme stability is necessary to minimize image motions at the CCD detectors. Minute changes in temperature, pressure, and acceleration environments cause structural deformations, inducing image motions which degrade PRV precision. The instrument’s structural design will ensure that the PRV goal is achieved under the environments G-CLEF will be subjected to as installed on the GMT azimuth platform, including:
    Millikelvin (0.001 °K) thermal soaks and gradients
    10 millibar changes in ambient pressure
    Changes in acceleration due to instrument tip/tilt and telescope slewing
Carbon fiber/cyanate composite was selected for the optical bench structure in order to meet performance goals. Low coefficient of thermal expansion (CTE) and high stiffness-to-weight are key features of the composite optical bench design. Manufacturability and serviceability of the instrument are also drivers of the design.

In this paper, we discuss analyses leading to technical choices made to minimize G-CLEF’s sensitivity to changing environments. Finite element analysis (FEA) and image motion sensitivity studies were conducted to determine PRV performance under operational environments. We discuss the design of the optical bench structure to optimize stiffness-to-weight and minimize deformations due to inertial and pressure effects. We also discuss quasi-kinematic mounting of optical elements and assemblies, and optimization of these to ensure minimal image motion under thermal, pressure, and inertial loads expected during PRV observations.
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Dan Baldwin, Dan Baldwin, Andrew Szentgyorgyi, Andrew Szentgyorgyi, Stuart Barnes, Stuart Barnes, Jacob Bean, Jacob Bean, Sagi Ben-Ami, Sagi Ben-Ami, Patricia Brennan, Patricia Brennan, Jamie Budynkiewicz, Jamie Budynkiewicz, Moo-Young Chun, Moo-Young Chun, Charlie Conroy, Charlie Conroy, Jeffrey D. Crane, Jeffrey D. Crane, Harland Epps, Harland Epps, Ian Evans, Ian Evans, Janet Evans, Janet Evans, Jeff Foster, Jeff Foster, Anna Frebel, Anna Frebel, Thomas Gauron, Thomas Gauron, Dani Guzman, Dani Guzman, Tyson Hare, Tyson Hare, Bi-Ho Jang, Bi-Ho Jang, Jeong-Gyun Jang, Jeong-Gyun Jang, Andres Jordan, Andres Jordan, Jihun Kim, Jihun Kim, Kang-Min Kim, Kang-Min Kim, Claudia Mendes de Oliveira, Claudia Mendes de Oliveira, Mercedes Lopez-Morales, Mercedes Lopez-Morales, Kenneth McCracken, Kenneth McCracken, Stuart McMuldroch, Stuart McMuldroch, Joseph Miller, Joseph Miller, Mark Mueller, Mark Mueller, Jae Sok Oh, Jae Sok Oh, Mark Ordway, Mark Ordway, Byeong-Gon Park, Byeong-Gon Park, Chan Park, Chan Park, Sung-Joon Park, Sung-Joon Park, Charles Paxson, Charles Paxson, David Phillips, David Phillips, David Plummer, David Plummer, William Podgorski, William Podgorski, Andreas Seifahrt, Andreas Seifahrt, Daniel Stark, Daniel Stark, Joao Steiner, Joao Steiner, Alan Uomoto, Alan Uomoto, Ronald Walsworth, Ronald Walsworth, Young-Sam Yu, Young-Sam Yu, } "Advanced structural design for precision radial velocity instruments", Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99123I (22 July 2016); doi: 10.1117/12.2235250; https://doi.org/10.1117/12.2235250
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