The Hobby-Eberly Telescope Dark Energy Experiment ( at the University of Texas McDonald Observatory will deploy the Visible Integral-Field Replicable Unit Spectrograph (VIRUS) to survey large areas of sky. VIRUS consists of up to 192 spectrographs deployed as 96 units. VIRUS units are fiber-fed and are housed in four enclosures making up the VIRUS Support Structure (VSS). Initial design studies established an optimal array size and an upper and lower bound on their placement relative to the existing telescope structure. Tradeoffs considering IFU (optical fiber) length, support structure mass, and ease of maintenance have resulted in placement of four 3x8 arrays of spectrograph pairs, about mid-point in elevation relative to the fixed HET structure. Because of the desire to minimize impact on the modal performance of the HET, the VSS is required to be an independent, self-supporting structure and will only be coupled at the base of the telescope. Analysis shows that it is possible to utilize the existing azimuth drives of the telescope, through this coupling, which will greatly simplify the design and reduce cost. Each array is contained in an insulated enclosure that will control thermal load by means of heat exchangers and use of facility coolant supply.

Access for installation and maintenance on the top, front, and rear of the enclosures must be provided. The design and analysis, discussed in the

paper, “Integration of VIRUS Spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment,” coauthored by James Heisler, Nick Mollison, Ian Soukup, and Richard Hayes (UTCEM) and Gary Hill, John Good, Rich Savage, and Brian Vattiat (UT McDonald Observatory) and presented at the SPIE Astronomical Telescopes and Instrumentation 2010, San Diego, California, 27 June-2 July 2010, must provide an optimum balance in meeting the stringent requirements for science and facility constraints such as cost, weight, access, and safety.

For more information please contact James Heisler

The current VSS concept with the tracking package removed for clarity

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