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This paper will focus on the testing, validation and performance of the ongoing SDSS-V fiber positioners production. The tested critical parameters include positioning accuracy calibration and validation, fiber misalignment control as well as lifetime test and thermal reliability check over the large temperature scale encountered in the telescopes. The presented results give a good overview on the general design performance and on the general reliability the complete robotic positioning system will achieve.

This paper presents the design and performance of an easily scalable Theta/Phi fiber positioner for Multi-subject Spectrographs. It has been developed by Ecole Polytechnique Federale de Lausanne (EPFL) together with the Swiss manufacturer of miniature microsystems MPS Microsystems. The positioner has been designed with the purpose of adapting readily to the requirements of any Multi-Object Spectrograph, which requires precise positioning of optical fibers. Whether MOONS, COBRA, MEGARA, or DESI, each project has so far developed its own fiber positioner from scratch, with all of the risks linked to such a complete new development. The positioner presented in the current paper intends to significantly reduce the development time, costs, and eliminate unforeseen risks. The design is easily scalable in size, length, and shape. For validation, we built eight prototypes with a diameter of 9.5mm which are capable to reach any target within five micrometers with just two correction moves.

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.1 This paper describes the design of the theta/phi fiber positioner robots that are being produced to be integrated in the Focal Plane System (FPS) of the SDSS-V telescopes. For each installation, 500 robots are being manufactured, more than 800 units have already been received from the manufacturer and validated. Mechanical, electronic and firmware designs are presented in the current paper in detail. We will expose the different iterations of the prototypes that were developed, built and tested and ultimately allowed to achieve the end version that meets the requested science requirements. The fiber positioner robot is carrying 3 optical fibers integrated into a single snowflake ferrule. Two of the fibers are science fibers connected to two different spectrographs, and the third fiber is used for metrology. The robot is capable of positioning the fibers with a planar accuracy better than 50 microns with a first blind move within its workspace of a diameter of 44.8mm. With a complementary fiber viewing camera (FVC) and the backlighted metrology fiber to perform a few small corrections moves, the positioner can reach a sub 5-micron precision on the fiber position.

One of the big research topics in modern cosmology is the mystery of dark Energy. To unveil the secret, cosmologists want to measure precisely the evolution of large scale structures in the universe. One way of doing so is to measure the 3D location of a high number of galaxies. By measuring the redshift of a galaxy, it is possible to find its distance. In order to measure a high number of galaxies in a practical amount of time, we need to observe multiple objects in parallel. Instead of a spectrograph, thousands of optical fibres are placed in the focal plane of a telescope. They will transmit the light of many objects to a spectrograph. Each fibre has to be positioned to several μm precision in the focal plane of a telescope for each exposure. Each fibre is positioned by a 2-axis fibre positioner. In this paper such a fibre positioner with 24-mm diameter is presented. It is driven by two brushless DC motors in combination with a backlash free gearbox. The positioner has an optimal central fibre path and improved angular alignment. The fibre runs through the centre of the positioner and is only bent at the top to reach its target position. In this way, the flexion and torsion of the fibre are minimal. In addition to the high positioning accuracy, the design is optimized to allow a minimal tilt error of the fibre. This is demonstrated using a novel optical tilt measurement system.

The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of more than 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. SDSS-V presents significant innovations in both hardware and software, chiefly due to the introduction of a robotic Focal Plane System (FPS) that replaces plug-plate operations. This new mode of operations introduces new challenges with respect to target scheduling, fibre robot positioner reconfiguration optimisation, telescope guiding, observer interfaces, and observatory operations. During normal operations SDSS-V will observe a new field every 15 minutes. For each field requiring a new telescope pointing the FPS will reconfigure 500 robotic fibre positioners with feedback from an external Field Viewing Camera (FVC) in less than two minutes. Six CCD cameras mounted on the FPS will be used to automatically acquire the field and maintain the necessary guiding accuracy. These strict requirements highlight the need for streamlined operations software and procedures to minimise the time spent during FPS reconfigurations. We describe the overall design and implementation of the SDSS-V survey operations, with special emphasis on software development, conventions, and observing procedures. While specific to SDSS-V, the solutions we describe can be readily applied to other astronomical surveys and are of special interest given the rapid increase in projects employing robotic fibre positioners.