Gemini North Telescope (GN) primary mirror (M1) suffered damage due to a collision with its wash cart during uncontrolled descent onto the cart in preparation for stripping and coating in October 2022. Gemini M1 is an 8.1 m aperture ULE thin meniscus mirror. The damage consisted in two stress-induced conchoidal fractures located on the outer perimeter and the underside of the M1, one approximately 300 by 200 mm and the other approximately 100 x 50 mm. In addition to mitigating the glass damage, the repairs required relocation and modification of one of the lateral pads of the M1 support system. A multidisciplinary team was assembled to repair the GN M1, led by NOIRLab Engineering Services. The repairs were successfully accomplished without affecting the optical performance of the Telescope. This paper describes the damage assessment, the mitigation strategy, the team and resources involved, the preparatory work and tests done prior to start of the repairs, the repairs and modifications performed, the techniques employed, post-repair assessment, and the engineering analysis and experiments performed to verify long-term safety and performance of the repaired M1. After successful completion of the repairs and recoating of the M1, Gemini North telescope returned to normal science operations in June 2023. No noticeable decrease in optical or mechanical performance of the mirror has been detected.
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