MDM Trouble Report for 2003 Dec 29

Telescope: 2.4m
Observer(s): Brogt, Halpern (Columbia)
Instrument: 8K

Problem(s) Encountered:
Mirror covers failed to open at the beginning of the night.
Halpern has seen this particular failure mode at least three
times, and was able to pry the mirror covers open.  Since this
particular failure and solution are not described in the 2.4m
manual, Halpern is rewriting section 9.4 concerning failure
of the mirror covers to open or close. The following text is
to be included, and is open for comments and/or corrections.
Tonight's problem is referred to below as  the most common
reason for the mirror covers failing to open. 

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The mirror covers consist of four petals that have to open and
close in a particular order.  They open in the order south, north,
west, east, and they close in the reverse order.
If only one cover fails to open or close, manually slew the telescope
using the hand paddle in the dome so that the desired motion of the
cover is aided by gravity.  For example, if the east cover fails to
open, slew the telescope east.  If the east cover fails to close, slew
the telescope west.  Sometimes a petal will get stuck on the central
baffle, with which it has very tight clearance, and can be freed
by pulling on the cover, or pushing on the baffle with long pole.

The most common reason for the mirror covers failing to
open at all is that the west cover has overlapped the edge of the
south one when they were last closed, preventing the south cover
from opening first.  If all of the mirror covers fail to open, go out into
the dome and use the hand paddle to tilt the telescope way over
to the west.  Then very carefully take the tall ladder and climb 
up to where you can reach the edge of the west petal and pry it off the top
of the south one.  When you set up the ladder, make sure that it,
as well as your head, will not be hit when the west petal finally opens.
Have another person assisting you if possible.
If this is in fact the problem, fixing it is a 
DANGEROUS OPERATION because the mirror covers are
very heavy and move quickly.  In particular, if you don't remove
your hand INSTANTLY after the south cover is free, it will be crushed
painfully, because the west cover that you are holding will promptly 
slam back to its closed position.


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Submitted on 2003 Dec 29 [6:16:53]