Date: Mon, 14 Jun 1999 07:13:51 -0600 (MDT)
From: hayes@apo.nmsu.edu
Subject: 2.5 m obslog 990613 (MJD 51344)
			Sunday June 13, 1999
                   Apache Point Observatory SDSS 2.5m
                           Observing Log
Observing Team:
		Jeffrey Hayes (APO)
		Ellyne Kinney (APO)
                Connie Rockosi (UC)
		Arrone Merelli (CMU) (apologies from last night)
                Adrian Pope (CMU)
                Bob Nichol (CMU)
Weather:  Cloudy, raining and windy with gusts to 45 mph.
Low dust (~500).  At about 9:30 the humidity went up to 90% and
we had a dew point depression of under 2.2 C, while the clouds
disappeared.
We managed to get the building off at 7 pm and: 1) take the engineering
camera off; 2) take the corrector lens off cartridge 2 and put it on the
engineering camera, and 3) put the mosaic camera on the telescope for
possible pumping down.  All this was done in about an hour.  The engineering
camera and the corrector were left in the shed on the cart.  The safety
bolts for the corrector are on the toolbox in the building were Dan noted
them last night.
*We report that the West door of the building did not stop at its maximum
height and went quite a bit above it.  This was during the time we
opened at about 7 pm.  We did get it to move down at that time, and it did
go down when we closed up, but it is now probably unreliable at this time
and may get stuck there if not careful. We also noted that the north end
of the door actually seemed to sag, and when the door was coming down
it made a awful racket.*
We did perform a series of AZ motions to test the repeatability of the
fiducial settings once we were inside the building.  We did this by
disabling the same interlocks as listed on the 22 April 1999 log.
For the record, the telescope can be safely slewed in the building
from 113 degrees to 127 degrees.  We found that the MCP seems to "forget"
where it is if left untouched for a while.  When we started, we crossed
the AZ valid fiducial (33) in a CCW direction (as viewed by an observer at the
laptop) and it was at 120:47:01:358.  When we came at the same fiducial from
the CW direction, it read 120:45:46:845.  Note that this is not setting the
fiducial, but just reporting where 33 is.  We used the j and k commands for
moving the telescope (we did not record the velocities).  On setting the
fiducial, we had:
120:52:00:362 before, and 120:50:43:947 after.
We then did a series of sweeps between the limits available to us in the
building and recorded the various readings for fiducial 33 as we went by
it (and the direction of motion: velocity was 10000 cts):
120:45:46:831 (CW)
120:45:45:093 (CCW)
120:45:47:097 (CW)
Here the variation is on the order of a few arc-seconds.
We then left the MCP for 1 hour to see if there was a drift due to time.
We came back at 8:30 pm and tried the experiment of using the d command and
slewing the telescope from 113 to 127 degrees at a velocity of 120000 cts
(slew speed) through 10 complete sweeps.  We then used the d command to
place the telescope at roughly instrument change positions and set the fiducial.
The results are:
Commanded stow position: 120:30:00:000 (30948773 in encoder counts)
Actual stow position:    120:30:00:001 (30948773 in encoder counts)
After setting fiducial:  120:29:59:918 (30948768 in encoder counts)
There does not seem to be an accumulated error when slewing in AZ, but we
were limited to only 14 degrees of range and only read the one fiducial.
We recommend that the same tests be done with the telescope out of the
building and it be slewed through a number of fiducial marks as a
check of this result.
At about 11 pm we tried the same experiment again, and again, we obtained
results to very good accuracy.  The numbers are:
Commanded stow position: 120:30:00:000
Actual stow position:    120:29:59:988
After setting fiducial:  120:30:00:086
Connie then went down in the hole to watch the motion of the encoder roller
as we passed through the 14 degrees of motion we had in steps of 2.33 degrees,
from 113 to 127 degrees, and saw nothing unusual.  She did note that there
were the remains of some moths on the encoder, but *not* on the crown,
which was almost perfectly clean, and therefore should not have been affected
by these remains.  We suggest that, weather permitting and before the roller
is cleaned, the reported AZ problems be reproduced if possible.
At 11:45 pm, we noted there was a brown-out but the backup generator did not
come on.
The telescope was left with all the interlocks back in place (i.e. reactivated).
We waited for the weather to inprove -- it being either too windy or too
humid to open.   At about 12:30 am we decided to pump the mosaic camera and
by 3:00 am decided to call it a night.
Jeffrey and Ellyne