M1 handling tool’s major failure at Paranal Observatory: A review

During the M1 re-coatings leading up to 2022 at the VLT, the M1 Handling Tool located at the Mirror Maintenance Building (MMB) displayed erratic behavior during operation, which ended with the tool on a locked state whilst holding an M1 in the air. This high risk situation triggered an investigation on the tool and how to recover it. Furthermore, the next coating process involved the handling of UT2’s primary mirror, which holds a large manufacturing defect on its underside. Given the high stakes, additional analyses were performed to ensure the mirror’s integrity in worst-case scenarios. This paper reviews the different techniques used and the positive results obtained from the performed work, as well as the lessons learned regarding M1 integrity and future improvements to be made to the M1HT itself.