SDSS-V focal plane system high-precision metrology

Abstract

The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The robotic Focal Plane System (FPS) carries 500 robotic fiber positioners, 60 stationary Fiber-Illuminated Fiducials (FIFs), and 6 Guide, Focus, and Acquisition cameras (GFAs). The GFAs find and use guide stars to compute target positions for the robots. The FIFs provide a reference basis against which precise measurements of the robot positions can be made using the Fiber Viewing Camera (FVC). Once imaged by the FVC, closed loop control allows the robots to reach their commanded positions to within 12 microns of precision. This paper discusses the metrology process for the FIFs and GFAs, thus allowing for accurate robot moves and reliable FVC measurements.