DEIMOS masks can occasionally jam or get cross threaded and
someone needs to manually set things right. There are multiple
ways things can go wrong here. The description below is for the
case of cross threaded masks. Certain other problems may pose a
danger so proceed carefully and consult with the support
astronomer as you go.
- Have the support astronomer move the grabber arm out of
the way (if possible) by hitting the RETRACT button
on the slitmask subpanel.
- Rotate the instrument remotely to -90° from the DEIMOS dashboard rotator
subpanel. Alternatively, use the hand paddle: set the
paddle to manual, select mode 2, select position 4, and push
and release either the FWD or REV button.
- The slit mask access door should now be on the same side
as the hand paddle (right side when viewing from back of
instrument, looking toward telescope).
- Safety first! Set the band brake. See figure 1.
- Open the access door with a flat blade screwdriver,
pulling the handle out and pushing door down. Screwdriver
should be on tether beside the handpaddle.
- Figure 2 shows the slit mask
mechanism. Undo the two red knobs (captured) and flip the
little slit mask door down.
- Pause for a moment. Is the grabber arm all the way to
one side allowing any or all masks to be removed? If not, it
could move suddenly. Be careful.
- You should now be able to look down the lengths of the
masks and see if any are cross threaded such that two share
the same slot in the back.
- You may be facing a problem other than a simple cross
thread. Describe what you see to the support astronomer. If
it is a simple cross thread, pull the offending mask out a bit
and try to wiggle it into its correct slot in the back.
- If the grabber arm is stuck somewhere other than all the
way to one side so that masks can be pulled out do not proceed
further without instructions. If an attempt is to be made to
free the grabber arm, instrument air should be released for
safety reasons. See air
pressure reset procedure.
- If for some reason a bent mask is suspected you may be
asked to remove one or more masks and examine them. If so,
the best way to proceed is to look at one mask at a time.
Pull it out, look at it, put it back in its original slot.
- After closing the access panel, release band brake and
return hand paddle to computer mode.
Figure 1. DEIMOS band brake
Band brake. Push lever down to engage. Pull up to release.
Figure 2. Slitmask mechanism
Door to release for slitmask removal.