MDM Trouble Report for 2015 Nov 16

Telescope: 2.4m
Observer(s): Frank (OSU)
Instrument: OSMOS

Problem(s) Encountered:
Encountered 3 major problems, solved them or found a work-around, 
so I could continue but under non-optimal conditions.

1. At the beginning of the night, the dome did not follow the 
   telescope properly.
   It failed to reach its designed location four times by getting
   stuck somewhere in between. The final positions when stuck were twice
   each at 65 degrees and 285 degrees AZ.
    When I noticed that pattern, I climbed a ladder to see whether
    there were any obstructions, but culd not find anything
    obvious.
    Twice the dome continued just running around in circles, despite
    the telescope being clearly NOT close to the zenith.

    In all cases, I moved the dome manually back to home,
    and then set the dome azimuth to 320.
    
    Rest of night, the dome worked properly.

2. Severe loss of pointing.
   First three targets (and a couple of bright test stars) 
   come up right where expected, but at slewing to the fourth
   target (hour angle of about -2 hrs) the pointing got off.
   I tried to restore it with the usual tilt-meter routine,
   but completely failed to locate a nearby bright star after that 
   exercise.
   Repeating the zenith-storing three times with the same negative
   result, I then began  jogging around  to eventual find the 
   supposedly nearby bright star.
   Luckily, OSMOS has such a wide field of view : the target was
   >25 arcmin (!) from anticipated position.
   
   Resetting the RA/DEC encounters to this new position then
   fixed the problem -- for ONLY the next object, basically.
   Any time that there was a larger slew of the telescope involved, 
   this would happen again.
  
   Bringing back the telescope from those faulty positions to a spot
   close to the zenith via the TCS (and not just manually), 
   I noticed that the supposed zenith position (given to TCS 
    and executed as a move) were far off target, according to 
   the tilt-meters (in one case, the tilt meters read +0.67 and 
    +0.38, when the TCS showed that it actually was right at zenith.

    Obviously EXTREMELY tedious to have to hunt for a bright 
    star to get the telescope to know where it is, but at least
    OSMOS' field of view allowed for that exercise.

    I also noticed, as mentioned in the afternoon already, that despite 
    drives and track off, the tilt meters kept changing values
     over a range of +-0.1 !

    When once the xtcs had to re-initialise due to a crash, I made 
    sure to have the correct tracking rate for RA set (15.06).

3. The most severe problem was the guider and guide probe failing
    or malfunctioning.

   Apart from generally not providing accurate positions
   for possible guide stars via Jskycalc (which may have to do
   with the pointing problem), the guide probe showed some erratic
   behaviour.

   At one point during a routine procedure to put the object into 
   the slit, the guide probe would not move when given the
    dy  command in the MIS window.
   dx moves, and moves of the telescope apparently worked fine
   (as I could see a guide star moving appropriately when
   dx commands were issued, or the hand paddel was used in 
   any direction, including y).

   In addition, the guide probe did not move to y positions
   issued either by Jskycalc or in the xMis window --
   that window would INDICATE that a move in y had been made, but 
   looking at the screen, one could clearly see that 
   nothing had happened (star stayed in exactly the same position).

   Furthermore, the guiding itself went fairly poorly, as
   positional errors would not be dampened, but rather 
   increased rapidly -- despite having the recommmended settings
   for X and Y speed.

   In order to get objects into the slit, I manually jogged them 
   in their after having calculated have far to move. A bit cumbersome,
   yet not critically destructive.
   The biggest problem, however, is that the guiding fails ! 
   For longer exposures, that it obviously a huge problem -
   I basically reverted to the old fashioned  put a box around
   a guide star, and keep it manually in there  procedure,
   but given the rapidity of it marching out of the box,
   this is very cumbersome.

 

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Submitted on 2015 Nov 17 [5:34:19]