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Primary Mirror CO2 Cleaning

Goals:

To remove loose dust and material from the primary mirror segments

Equipment and Conditions Required:

  • 6-8 bottles of liquid CO2
  • CO2 cleaning wand, jacketed hose, and safety strap
  • 3 people, JLG driver, CO2 operator, ground support
  • relative humidity < 80%
  • JLG small basket
  • JLG safety harnesses for two people
  • hearing protection for JLG personnel
  • gloves for CO2 operator and ground support
  • radios for all personnel

Frequency:

Monthly

Time Required:

Approximately 2-3 hours

Responsible Party:

Optical Tech

Procedure:

The JLG should have the small basket attached so that you can enter the structure.

The CO2 bottles should be staged by the garage door inside the enclosure. Put the cleaning wand in the JLG basket and attach it to the basket with a safety strap. String the hose along the boom. 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 one of the CO2 bottles.

Verify that CO2 snow/gas comes out of the wand.

Using the JLG, the driver and operator should enter the structure and head for the top of the array. The ground support person should rotate the structure as required to allow entry and travel. Starting with segment 86, clean each segment with a left/right as well as an up/down pattern. It is easiest to clean the right side of the array first, then move the structure to allow cleaning of the left side.

The ground support person should change bottles when ever the wand no longer shoots liquid. Typically this procedure requires six bottles to clean the array, however, sometimes a bottle is low on gas or the access tube is damaged and more bottles may be required.

Upon completion of the cleaning, the CO2 hose/wand should be removed from the JLG and put back in storage. The empty CO2 bottles should be placed in the Empty Bottle Rack outside the spectrograph room. Full bottles should be returned to the Full Bottle Rack. The empty bottles should be returned to the supplier and new bottles ordered.

Safety Precautions:

  • All personnel shall observe HET safety precautions as described in the HET Safety Document.
  • The cleaning wand and the 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 driver may wear hearing protection however at least one person needs to be monitoring the radio.
  • The high velocity, dry CO2 will cause 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 dropping water or ice on the segments.
  • Avoid striking the segment surface with the wand.

Notes:

In the future the CO2 wand should have a ground wire inside the wand to aid in static charge dissipation.

Keck actually heats their bottles to increase the pressure and to create more liquid.

An eight bottle manifold with a permanent hose through the JLG cable wrap would allow easier operation for the ground support person as well as provide improved bottle security.

Reflectivity measurements should be taken before and after cleaning so that you can quantify the change. See the procedure ???? for details.

History:

This procedure was first written up on 17 Sept 2002 by Jim Fowler.

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Created:   2-May-2002
Last updated: 01-Oct-2003

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