Realuminizing Subaru's Primary Mirror
December 31, 2006
This year, we conducted a three-week maintenance of the telescope including the realuminization of the primary mirror, and this was a major downtime in three years. As long as the weather allows, the telescope is in business every night throughout the year. During the daytime, instrument exchange, troubleshoot and other engineering or maintenance programs take place. The primary mirror is cleaned twice a month in situ (i.e. without being dismounted), but still the dust piles up. It is time to take a break from continuous operation since August of 2003 not just for the mirror but other critical equipment for long-term use.
Aluminization process of the primary mirror consists of three major steps: mechanical works for disassembly/reassembly, removal of the old coating, and apply fresh aluminum coating on the glass surface. Among other critical maintenance/upgrade works, dollies for the 2200-ton enclosure were readjusted and lubricated. This task requires a few days per set of dolly, with 4 or more personnel. Works like this cannot be done while observations are done every night. The three-week process was a break for the telescope, but it was a very busy period for staffs at Subaru Telescope.
Aluminizing of the primary mirror is the fifth time since its arrival on site in 1998. For the details of the aluminization procedure at Subaru Telescope, please look at the report of the realuminization in 2001. As we repeat this campaign, the procedure has been refined and staffs gain experiences and confidence. There was almost a year of preparation, and the heavy equipment was finely adjusted, dry runs repeated. Placing the primary mirror back to the mirror cell is difficult still and all of us were nervous again this time. There was a big relief when the mirror was safely remounted. The washing process went quite well. Figuring out a way to dry the glass surface faster is our next task.
The improvement that were made from the previous aluminizing process:
- The efficiency of preparing tungsten filaments pre-wetted with aluminum was improved thanks to the new clips developed locally.
- We were able to pursue several large-scale works in parallel, with caution, thanks to the staffs' improved skills.
- Safer approach and close communication, interaction among staffs, reveals the proficiency of summit operation.
For further development of the telescope, new adaptive optics has been applied. Above all, equipment transportation, installation, and adjustment for the laser guide star system were a large-scale project. Moreover, for the new observation equipment to be mounted on the telescope, we laid an optical fiber cable along the telescope truss. Subaru telescope is still growing!