Gemini North primary mirror glass repair after fracture incident

In October 2022, there was an accident with the Gemini North Primary Mirror (M1) during routine mirror movements that caused it to come in contact with its washcart. The M1 came into contact with an earthquake restraint on the washcart as it was being moved in preparation for stripping and recoating activities. After the incident, analyses were conducted to determine the extent of the damage and the necessary steps to restore the telescope to normal operations. The extent of the fracture was determined by through visual inspection, and by observing stress polarization within the glass. Due to damage occurring along one of the lateral supports on the M1, it was first necessary to determine a safe method for removal. Grinding and polishing work of the damaged areas was then necessary to secure the glass and remove any stress. It was then necessary to bond a new lateral support to the M1 to prevent higher order aberrations from the asymmetrical support. Since a small change in the location of the support was necessary, a finite element analysis was performed to determine how its new location would affect optical aberrations on the M1. Test samples were produced to verify the performance of the new bond. This paper provides detailed explanations how the Gemini North telescope was returned to normal operations.