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The grating turret is one of many parts of the Gemini near infrared spectrograph (GNIRS)1'2 being designed for the Gemini8-rn telescope project. It provides four gratings and one flat mirror mount, with each one able to tilt in discrete 1/4° stepsover a full +1-7.5° range while maintaining a 1/10 pixel or 2.7iim position stability. There are distinct design featuressatisfying space, weight, and performance limitations. We use 2 motors, one to control the grating selection, and one forgrating tilt. These motors are located outside the vacuum/cryogenic environment for easy access. We employ a proventechnique using rubbing plates to provide thermal contact for effective cooling. 3-D modeling was used extensively tooptimize weight and structural stiffness for the mechanism.Keywords: grating mechanism, novelty design, cryogenic environment, high repeatability, physically compact, large beamsize 1. REQUIREMENTS AND SPECIFICATIONS It is beyond the scope of this paper to discuss the entire GNIRS design specifications3. Requirements relevant to the gratingturret design are summarized here in five categories. First are the optics, which drives the entire design process. Second arethe stability requirements defming the structural stiffness of the grating turret structure as well as the structure in which thegrating turret mechanism is mounted4. Third is the concern of available space, compelling a vigorous 3-D modeling effort to |
