MDM Trouble Report for 2012 Jan 19

Telescope: 1.3m
Observer(s): Stoll and Adams (OSU)
Instrument: CCDS

Problem(s) Encountered:
At UT 06:06, the telescope suddenly started to slowly slide 
north.  We saw this by streaks on the slit viewer and by 
losing guiding.  Judging by the length of the streak and the 
size of the field, the slide rate was about 1' every 15 
seconds.  We stopped guiding and read out the science image 
before its scheduled end time while we attempted to diagnose 
the problem.  Although given the direction of movement it was 
clearly not a tracking problem, we toggled the tracking on and 
off because the rate seemed similar.  We then slewed back to 
the target, and watched it slide away again.  Although the 
Prospero status window indicated TC was up, +TCSLink, and 
+ICtoTCS, our next step was going to be to restart the TCS.  
Suddenly, though, at UT 06:12, the problem stopped and we saw 
round, stationary stars on the slit viewer.  We slewed back to 
the target location and reacquired.  During reacquisition (and 
indeed, during the initial acquisition) we noticed that hand 
paddle commands in the N and S direction were producing much 
smaller moves than requested (10.0 produced about 2, 30.0 
about 5).  The HA when this problem occurred was about -02:40, 
and the Dec of the target is +16:15.  Total time lost to this 
issue was about ten minutes, counting reacquisition, or 27 
minutes, if the truncated seventeen-minute long exposure turns 
out to be unusable for the program.

The troubling part of this is that we don't know why it 
happened nor how to fix it should it happen again.  Our best 
theory, though it is only a theory, is that perhaps the 
telescope is slightly out of balance in a way that interacted  
badly with the Dec drives at that particular position for some 
reason.


Later, TCS link went down twice, at around UT 07:20 and at 
around UT 07:55.  Lost about five minutes each time.  Would 
have been less, except the first time, it was new to us, and 
the second time, we were also recovering from a pointing error 
left over from our recovery from the first time.  

Prospero TCS link lost one more time later in the night, and we 
recovered near-instantly by simply running telinit and startup 
in Prospero.  The link going down appears to be correlated 
with attempting to move the guide stage while the telescope is 
slewing.  A false efficiency; don't try it.

The TCS link problems were minor.  We think we know how to 
avoid them, and we certainly know how to fix them should they 
happen again.  The fix is well documented in the AGN12 manual.

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Submitted on 2012 Jan 20 [6:43:43]