How to handle and install DEIMOS slitmasks

Procedure and Components

De Clarke, UCO/Lick, Jan 2002

[picture of a person holding a DEIMOS slitmask]

You'll find the inventory of DEIMOS slitmasks in [where the heck will people find this inventory, how is it organized?]

DEIMOS slitmasks are large. They are milled out of 15 to 20 thou aluminium stock. Being fairly thin they are suceptible to damage by bending and twisting. The "hot dog cutout" on the spine of the mask in particular should be protected from distortion and damage, since it's essential to proper engagement with the insertion mechanism.

DEIMOS slitmasks are labelled with a permanent barcode label. [picture of barcode label on mask]

This label is made of 3 thou aluminium and affixed with a special adhesive rated for orbital applications. Do not attempt to remove this label. If a label is damaged, there are workarounds for using the mask; a replacement mask should be ordered ASAP rather than attempting to relabel an existing mask.

Slitmasks are also labelled with a human-readable name which is engraved into the surface. [picture of engraved mask name]. This name provides confirmation of the mask's identity, and should match the name provided by the observer in the desired configuration data from the CARA web server. If you find there is a disagreement between the name and barcode shown on the desired configuration page, and the barcode for the mask of that name found in the mask inventory, immediately report this discrepancy to the observer, the mask mill operator, and the database custodian (email addresses will be found below).

DEIMOS slitmasks are loaded into an 11-slot cassette. It was originally a 13-slot cassette, but slots 1 and 13 have proven unreliable and are now disabled. Do not attempt to load masks into these two slots. [picture of cassette mechanism showing slot numbers]

To access the slit mask cassette, rotate the instrument to about [fill in approx PA here] and open the Mask Access Hatch which you will find on the right side of the instrument looking from the rear (i.e. from a vantage point standing on the deck). Push the button which sends the cassette transport mechanism to the Unload position [photo of pushbutton controls].

Now remove the two tethered thumbscrews and lower the slit mask cassette door. [photos of door in closed and open positions]

You can now insert and remove masks. Be careful about getting the slot numbers right -- parallax error plus darkness and confusing reflections off neighbouring masks can make it tricky. Be careful about "cross-threading" masks, i.e. starting out in one slot but having the mask bend into a neighbouring slot during insertion. An LED headlamp may help by giving you a good light source while leaving both hands free to manipulate the mask.

It doesn't matter which slot which mask goes in, but of course it matters which slots you remove masks from to make room for new ones. When you have swapped or installed masks according to the observer's desired configuration list, close the slitmask cassette door. It should seat firmly, and all mask spines should settle into the bronze [brass? ask Vern] comb. Visually inspect masks to make sure they are all straight, untensioned, and settled properly into the comb. A comb misalignment can lock out operation of the cassette mechanism.

Important Note: Inspect the mask barcode labels as you install masks. If you must install a mask with a damaged or missing label, this is a serious problem and will cause the auto-mask scan operation (below) to fail. Therefore, if you notice a damaged or missing label, you can either skip the mask-scan operation and work around it manually, or if the damage seems slight you can give it a try but later check the results very carefully.

Once you are satisfied with the mask loading operation, close the access hatch. You can now scan the command code "SCAN-MASKS" on the laminated barcode sheet using the bargun. This will initiate a process which lasts about 4 minutes. During this 4 minutes you can rotate the instrument freely, and this may be a good time to reload the filter wheel or change a grating. During this 4 minutes you cannot use dremel to scan other barcodes, but you can get all set up to do more scanning as soon as the mask scanning activity is done.

When the mask scan is successful, the annunciator will sound a "success" tone. Success in this case is indicated by one short buzz. Two buzzes indicate a failure of some kind. If no sound at all is heard within about 5 minutes, something's wrong and you will have to resort to the Troubleshooting Guide.

Once the mask scan is complete, no more action on your part is required for mask configuration, unless you had to install a mask with a missing or damaged bar code label. If this happened, the automatic mask scanning method will not work and you will have to resort to the Workarounds documentation.
De Clarke