Subject: APO 3.5m Shutdown Extension/Mirror Cover damage

From: Ed Turner

Submitted: Wed, 21 Jul 2004 22:54:06 -0400 (EDT)

Message number: 800 (previous: 794, next: 801 up: Index)

An unfortunate mechanical accident has damaged the primary mirror covers 
of the APO 3.5-meter; repairs will require an extension of the in-progress 
shutdown through August 25 (science operations to resume on the night of 
August 26).  Contingent and regularly scheduled science programs for the 
nights of August 7-25, inclusive, are thus canceled.  Details follow:

During an attempt to close the mirror covers under manual control, either 
incorrect sequencing of shutters or some other undetermined problem 
stressed the structure to the point that two rivets were popped loose and 
numerous others were damaged and greatly weakened.  There was also some 
damage to the metal surrounding some of the rivets.

The good news is that there was no apparent damage to the glass or any 
other components of the telescope and that repair is expected to be 
reasonably straightforward and simple, though laborious.  The bad news is 
that these repairs will require removal of the primary and tertiary 
mirrors, quite substantial and time consuming tasks.  Moreover, the very 
limited number of personel available at APO to work on the shutdown and 
the necessity for some of them continuing to concentrate on other tasks 
(including some associated with the SDSS) limit the rate at which the 
repair work can be carried out.

It is not entirely clear yet, but there is also a good chance that it will 
be necessary to go back into operation without an operational NS2 guider.

After careful construction of a detailed plan for the repair effort, it is 
our best ESTIMATE that the telescope will be next available for scheduled 
science operations on the night of August 26.  Of course, many 
eventualities (slips in the schedule, discovery of additional problems, 
weather delays in on-sky recommisioning etc) could affect this date.  
Updates will be posted here, of course.

Aside from the accident with the mirror cover mechanism, I am happy to 
report that the planned shutdown engineering projects have gone well and 
are essential on-schedule and successful.

Ed Turner

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