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Goals:To remove loose dust and material from the SAC mirrors.Equipment and Conditions Required:- Relative humidity < 80%- 8 bottles of liquid CO2 (for both SAC and main mirror) - Short CO2 cleaning wand, jacketed hose and safety strap - 3 people, JLG driver, CO2 operator, ground support - JLG with either small or large basket - JLG safety harnesses for two people - Hearing protection for JLG personnel - Gloves for CO2 operator and ground support - Safety glasses for CO2 operator - Radios for all personnel - Tracker tie-down strap - HRS lower pellicle cover - Tie-wraps Frequency:Monthly, immediately before the main mirror is cleaned (See Primary Mirror CO2 Cleaning procedure)Time Required:Approximately one hour.Responsible Party:Optical TechProcedure:Put the short cleaning wand in the JLG basket and secure with a safety strap. String the hose along the boom, and tape the tygon tubing to the JLG boom. There should be one tube for each boom, and one each in the middle and at the bottom of the lower boom. The hose should run freely through the tubing.Connect the hose to the CO2 bottle. Verify that the CO2 snow/gas comes out of the wand. Position the structure facing south, the rho ring at -90 degrees, and the slide in position 3. This configuration provides access for installing the HRS lower pellicle cover from the JLG basket. Drive the JLG to the tracker and secure with tie-down strap. Drive the JLG alongside of the tracker and install the lower pellicle cover on the housing for the HRS pellicle. Drive the JLG basket to a position underneath the PFIP. Rotate the rho ring to 0 degrees. Climb up and unzip the light baffle for M-4 and M-5. Remove tie-wraps as needed to gain access to the mirrors. Clean both mirrors with a left/right as well as an up/down pattern. Zip up the baffle and install new tie-wraps. Remove the lower HRS pellicle cover. Climb down and unzip the light baffle for M-2 and M-3. Remove tie-wraps as needed to gain access to the mirrors. Clean both mirrors with a left/right as well as an up/down pattern. Zip up the baffle and install new tie-wraps. Remove the tracker tie-down strap and drive the JLG to the floor. The ground support person should change bottles whenever the wand no longer shoots liquid. Typically this procedure takes less than one bottle to clean the SAC; however, sometimes a bottle is low on gas or the access tube is damaged and another bottle is required. Upon completion of cleaning, the short CO2 wand should be removed, and the long CO2 wand should be installed in preparation for cleaning the main mirror. Safety Precautions:- All personnel shall observe HET safety precautions as described in the HET Safety Document.- The cleaning wand and regulator will get quite cold as the CO2 expands. The CO2 operator and the ground support person should wear gloves to protect hands from cold burns. - The CO2 operator should wear hearing protection. The JLG operator may wear hearing protection; however, at least one person must be monitoring the radio. - The CO2 operator should wear eye protection. - The high velocity, dry CO2 will cause a static charge to build up on the CO2 wand. The CO2 operator should be aware that a strong static-electric shock is possible. - The CO2 wand will develop freezing condensation on humid days. Avoid dripping water or ice on the SAC mirrors. - Avoid striking the SAC mirrors with the wand. Notes:- The SAC shall be CO2 snow cleaned before the main mirror, so any particles that fall onto the main mirror will be cleaned off.- The SAC should be reflectivity tested immediately after being cleaned (e.g. the same day) in order to monitor the condition of the mirrors. See the SAC Mirror Reflectivity Measurement procedure for details. History:This procedure was first written up on 22 October 2002 by Richard Schuler.Return to Policy & Procedures |
Created: 2-May-2002 Send comments to: webmaster@het.as.utexas.edu |