We discuss the field retermination of high-fiber count MTP fiber connectors used with the APOGEE spectrograph at Apache Point Observatory (APO) in 2021. We address lessons-learned, wear-analysis of removed MTPs, and throughput of the fiber train with the newly terminated fibers in SDSS-V. For the past decade the spectrograph at APO, as part of multiple incarnations of the Sloan Digital Sky Survey (SDSS), has relied upon rapid changes of ten MTP connectors, each containing 30 terminated fibers, and all contained within a custom gang connector system. These rapid changes enable the iterative plugging of the gang connector into multiple cartridges with different plug plates to observe various survey fields throughout the night. While robotic Focal Plane Systems have been developed for SDSS-V to replace plug plates, which will minimize the fiber connector cycles, we nonetheless reterminated the most heavily used MTP connectors. The connector cycles had far exceeded manufacturer lifetimes and the overall system throughput was degrading.
We present the on-sky performance of the new wide field corrector for the fifth generation of the Sloan Digital Sky Survey (SDSS-V). This new three-element corrector was designed to replace the previous two-element design, which had an aspherical focal surface and was not optimized for the infrared (H-band). The purpose of the new corrector is to improve the imaging performance required for a new robotic Fiber Positioning System (FPS). For commissioning, a Focal Surface Camera (FSC) was developed and used to determine the focal surface location relative to the telescope interface, and to verify imaging performance across the 3-degree field of view of the corrector. This paper discusses the commissioning process in detail, describes how the imaging data were processed, and presents the measured image quality across the field.
We describe the on-sky performance of the robotic Focal Plane System (FPS) units that replace the fiber plug-plate systems at the Sloan and duPont telescopes for the SDSS-V survey. The first FPS was arrived at Apache Point in December 2021, and the second unit will be delivered to Las Campanas in spring 2022. Each FPS carries 500 zonal fiber positioners carrying three fibers: two science fibers for the BOSS and APOGEE spectrographs and a back-illuminated metrology fiber. The FPS enables the SDSS-V Milky Way and Black Hole Mapper surveys that will begin survey operations in 2022.
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