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9 July 2008 Integrated modeling for the GPi flexure sensitive structure
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The Gemini Planet Imager (GPi) is comprised of three main opto-mechanical systems: the Adaptive Optics (AO) system, the Calibration (CAL) system, and the Integral Field Spectrograph (IFS). Each of these subsystems are built and aligned independently, and then integrated into the final instrument. A truss framework called the Flexure Sensitive Structure (FSS) has been designed to locate each optical subsystem within the instrument, utilizing kinematic bipods to eliminate distortion due to flexure and thermal changes. Due to the distributed nature of the optical system, an end-to-end opto-mechanical modeling approach is taken using the NRC Integrated Model (NRCIM). This set of numerical tools was originally developed to support the Canadian VLOT and TMT telescope studies. The instrument structural response is calculated using a commercial finite element package; and the 6 degree-of-freedom rigid body motions of the optical elements are then passed to an optical model. Ray-tracing is performed to determine the line-of-sight errors at numerous critical focal planes and pupil planes. Disturbances to the system include gravity induced flexure and thermal distortions. Optical compensation using a combination of closedloop feedback and open-loop models are then applied using steering mirrors to improve the line-of-sight figures of merit. Finally, these figures of merit are compared against the system optical error budget to assess the overall performance of the opto-mechanical system.
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Darren Erickson, Scott Roberts, John S. Pazder, and J. Murray Fletcher "Integrated modeling for the GPi flexure sensitive structure", Proc. SPIE 7017, Modeling, Systems Engineering, and Project Management for Astronomy III, 701711 (9 July 2008);

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