After gathering spectrophotometer data from the 6.5m primary mirror at the MMT Observatory (MMT) for over ten years, the MMT has developed a soap and water wash procedure that effectively removes contaminates from the surface of the mirror without damaging the bare aluminum coating. While the in-situ soap and water wash requires a small amount of telescope downtime, these washes are still scheduled to take place every six months. The frequency of the washing was selected to keep the mirror performance as close to a fresh coating as possible throughout the year and to extend the recoating interval without allowing the reflectivity degrading more than 3% from a fresh coating. After being in service for almost two years, the spectrophotometer measurements indicate the 2016 primary mirror coating is on-track to maintain the specified reflectance for five years. This paper outlines the soap and water wash procedure developed for the MMT primary mirror and presents spectrophotometer data throughout the life of the 2005 and the 2016 mirror coatings.

© 2018 COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Ricardo Ortiz, Joseph T. Williams, and William Goble, "Lessons learned from wet washing the 6.5m MMT primary mirror in-situ," Proc. SPIE 10700, Ground-based and Airborne Telescopes VII, 1070004 (Presented at SPIE Astronomical Telescopes + Instrumentation: June 10, 2018; Published: 6 July 2018); https://doi.org/10.1117/12.2314348.