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Proceedings Paper

A conceptual design for a Cassegrain-mounted high-resolution optical spectrograph for large-aperture telescopes
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Paper Abstract

We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320–1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.

Paper Details

Date Published: 18 September 2013
PDF: 12 pages
Proc. SPIE 8836, Optomechanical Engineering 2013, 88360Y (18 September 2013); doi: 10.1117/12.2024056
Show Author Affiliations
Cynthia S. Froning, Univ. of Colorado at Boulder (United States)
Steven Osterman, Univ. of Colorado at Boulder (United States)
Eric Burgh, SOFIA / USRA (United States)
Matthew Beasley, Planetary Resources, Inc. (United States)
Paul Scowen, Arizona State Univ. (United States)
Todd Veach, NASA Goddard Space Flight Ctr. (United States)
Steven Jordan, Ball Aerospace & Technologies Corp. (United States)
Dennis Ebbets, Ball Aerospace & Technologies Corp. (United States)
Michael Lieber, Ball Aerospace & Technologies Corp. (United States)
James deCino, Ball Aerospace & Technologies Corp. (United States)
Bruno Vaz Castilho, Lab. Nacional de Astrofísica (Brazil)
Clemens Gneiding, Lab. Nacional de Astrofísica (Brazil)
Antonio César de Oliveira, Lab. Nacional de Astrofísica (Brazil)

Published in SPIE Proceedings Vol. 8836:
Optomechanical Engineering 2013
Alson E. Hatheway, Editor(s)

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