Design of the Automated CO2 Optics Cleaning System for the Thirty Meter Telescope

Thirty Meter Telescope (TMT) plans to incorporate fully automatic CO2 snow cleaning in-situ process for its segmented primary mirror. Due to the size of the primary mirror, usual single hand-held narrow coverage CO2 snow cleaning wands are no longer feasible option, though existing 2 and 4 inch wide models provided design insight. A new, extra-wide linear coverage CO2 snow horn/nozzle arrangement has been successfully developed along with appropriate liquid CO2 bulk delivery system. Challenges of such design include large CO2 flow rates at pressures providing liquid state all the way to the spray nozzles, ensuring stable and uniform transition of liquid to solids, bulk CO2 storage in the facility and coordination of the cleaning process with other telescope daytime activities. Additionally, automated rotating cleaning arms inspired by the Subaru telescope have been designed to expeditiously cover area of the TMT primary mirror at controlled speeds and reasonable time. Results of the study optimizing the cleaning parameters and test of various hardware options and combinations with respect to optics cleaning efficiency are also described.