MOSAIC at ELT: Design and First Prototyping of Novel Robotic Optical-Relay Positioners
Abstract
The Extremely Large Telescope (ELT) is, to date, the most ambitious ground-based telescope under construction. MOSAIC is a multi-objects spectrograph (MOS) that aims to make full use of the largest telescope in the world. At its heart, about 300 robotic positioners will pick-off skylight from the focal surface of the ELT to feed it to its Near Infrared (NIR) and visible (VIS) spectrographs. The gigantic scale of the ELT presents three main challenges for MOSAIC positioners: (1) the light beams on the focal surface cannot be focused in a single fiber, similarly to other MOS instruments, involving a design with relay mirrors patrolling the field of view, and reimaging the sub-field on 2 fixed fiber bundles located 600 mm behind the ELT focal plane (2) The positioner needs to adapt to the local telecentricity, which means it has to point at the ELT pupil center located 37.868 m away from the focal plane (3) The Atmospheric Dispersion Corrector (ADC) needed to cover the whole focal surface of the ELT is impossible to build to this scale; hence each positioner needs its own ADC. EPFL is responsible for designing and supervising the mass manufacturing of the positioners. This paper aims to present its initial design and prototypes.
Versions
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BibTeX
@misc{rombach2026mosaic,
title = {{MOSAIC at ELT: Design and First Prototyping of Novel Robotic Optical-Relay Positioners}},
author = {Maxime Rombach and Markus Thurneysen and Lucas Ortolani and Jurgen Schmoll and Diane Chapuis and Malak Galal and Sebastien Pernecker and Alec York and Ellen Schallig and Ian Lewis and Louis Gabarra and Cassio Berni and Ojonugwa Adukwu and Gavin Dalton and Fabio Fialho and Michaela Hirschmann and Thomas Augustejin and Kacem El Hadi and Marisa Garcia-Vargas and Marie Larrieu and Alessandro Meoli and Tim Morris and Roser Pello and Mathieu Puech and Myriam Rodrigues and Ruben Sanchez-Janssen and Alondra Sola and Jay Stephan and Christian Surace and Jean-Paul Kneib},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.20194},
eprint = {2606.20194},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.20194},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - MOSAIC at ELT: Design and First Prototyping of Novel Robotic Optical-Relay Positioners
AU - Maxime Rombach
AU - Markus Thurneysen
AU - Lucas Ortolani
AU - Jurgen Schmoll
AU - Diane Chapuis
AU - Malak Galal
AU - Sebastien Pernecker
AU - Alec York
AU - Ellen Schallig
AU - Ian Lewis
AU - Louis Gabarra
AU - Cassio Berni
AU - Ojonugwa Adukwu
AU - Gavin Dalton
AU - Fabio Fialho
AU - Michaela Hirschmann
AU - Thomas Augustejin
AU - Kacem El Hadi
AU - Marisa Garcia-Vargas
AU - Marie Larrieu
AU - Alessandro Meoli
AU - Tim Morris
AU - Roser Pello
AU - Mathieu Puech
AU - Myriam Rodrigues
AU - Ruben Sanchez-Janssen
AU - Alondra Sola
AU - Jay Stephan
AU - Christian Surace
AU - Jean-Paul Kneib
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2606.20194
UR - https://arxiv.org/abs/2606.20194
AB - The Extremely Large Telescope (ELT) is, to date, the most ambitious ground-based telescope under construction. MOSAIC is a multi-objects spectrograph (MOS) that aims to make full use of the largest telescope in the world. At its heart, about 300 robotic positioners will pick-off skylight from the focal surface of the ELT to feed it to its Near Infrared (NIR) and visible (VIS) spectrographs. The gigantic scale of the ELT presents three main challenges for MOSAIC positioners: (1) the light beams on the focal surface cannot be focused in a single fiber, similarly to other MOS instruments, involving a design with relay mirrors patrolling the field of view, and reimaging the sub-field on 2 fixed fiber bundles located 600 mm behind the ELT focal plane (2) The positioner needs to adapt to the local telecentricity, which means it has to point at the ELT pupil center located 37.868 m away from the focal plane (3) The Atmospheric Dispersion Corrector (ADC) needed to cover the whole focal surface of the ELT is impossible to build to this scale; hence each positioner needs its own ADC. EPFL is responsible for designing and supervising the mass manufacturing of the positioners. This paper aims to present its initial design and prototypes.
ER -