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Proceedings Paper

The prime focus imaging spectrograph for the Southern African Large Telescope: structural and mechanical design and commissioning
Author(s): Michael P. Smith; Kenneth H. Nordsieck; Eric B. Burgh; Jeffrey W. Percival; T. B Williams; Darragh O'Donohue; James O'Connor; J. Alan Schier
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Paper Abstract

The Prime Focus Imaging Spectrograph (PFIS) is a first light instrument for the Southern African Large Telescope (SALT). PFIS is a versatile instrument designed to operate in a number of scientific modes by utilizing volume phase holographic gratings, Fabry-Perot etalons, and polarimetric optics, which are manipulated in and out of the beam using various placement mechanisms. The instrument is mounted at the prime focus 15m above the primary mirror and tilted at 37°. This remote placement and the need for 240° of rotation about the optical axis raises important design issues with mass, flexure and access. The instrument structure provides the interface to the telescope Prime Focus Instrument Platform (PFIP) as well as support points for all the optics, mechanisms and electrical equipment. The structure is a welded open truss of hollow, square-section Invar beams. The open truss provides the highest stiffness to weight ratio and minimizes the effect of wind loading, while the use of Invar negates the effects of thermal expansion. It has been designed using finite element analysis in conjunction with an optical tolerance analysis of the optics nodes to minimize effective image motion under the varying gravity load. The fundamentals of the design of the structure to minimize the flexure and its effect on image motion, the motivation for using the open Invar truss structure, and the design of the remotely operated mechanisms are discussed. In 2005 PFIS was installed and commissioned on SALT in South Africa. Included in this text are some of the results and experiences of taking PFIS into operation.

Paper Details

Date Published: 29 June 2006
PDF: 13 pages
Proc. SPIE 6269, Ground-based and Airborne Instrumentation for Astronomy, 62692A (29 June 2006); doi: 10.1117/12.672415
Show Author Affiliations
Michael P. Smith, McDonald Observatory, Univ. of Texas, Austin (United States)
Kenneth H. Nordsieck, Space Astronomy Lab., Univ. of Wisconsin, Madison (United States)
Eric B. Burgh, Space Astronomy Lab., Univ. of Wisconsin, Madison (United States)
Jeffrey W. Percival, Space Astronomy Lab., Univ. of Wisconsin, Madison (United States)
T. B Williams, Rutgers Univ. (United States)
Darragh O'Donohue, South African Astronomical Observatory (South Africa)
James O'Connor, South African Astronomical Observatory (South Africa)
J. Alan Schier, The Pilot Group (United States)

Published in SPIE Proceedings Vol. 6269:
Ground-based and Airborne Instrumentation for Astronomy
Ian S. McLean; Masanori Iye, Editor(s)

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