Subject: DIS Refurbishment, Plan 1
From: au@jhu.edu
Submitted: Tue, 23 Jul 1996 13:06:51 +0000
Message number: 21
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DIS REFURBISHMENT PLAN 1
Comments I received from some of you are incorporated here. The
changes are that baffling is added as an important task and the
computer for the slit viewer and the replacement detectors have
been deferred.
I know I might be offending some of you with criticisms of
equipment and software. If so, I apologize. (Nobody's complained,
but I know I might be miffed.) I want to be clear that DIS is an
excellent example of the quality of instrumentation this
observatory needs and that many of the complaints are really new
requirements imposed by observing strategies and science
interests that could not have been anticipated. Everyone
providing input understands this and I'm confident that objective
decisions will provide the optimum instrument.
I have had recent conversations or correspondence with K.
Anderson, J. Burns, J. Holtzman (NMSU), B. Gillespie (APO), L.
Rebull (UC), J. Gunn, G. Pauls, and Michael Strauss (PU). I have
also read past apo35m-dis postings, which I should have done
before. Details of the correspondence and new (to me) input are
at the end.
PLAN 0, PLAN 1 DIFFERENCES
Salaries are separated from the tasks. By adding baffles we are a
bit short staffed even if we don't do the new detectors. The
impact is that more work will be done by APO staff, probably
extending the timeline a bit.
The slit viewer upgrade is split into two parts: the camera
replacement and the new computing system. A high speed camera
would provide the real-time setup capability that some of us find
essential. The new computing system would allow easy integration
into the observatory control system and give us the ability to
use the slit viewer data for more than just looking (guiding,
point-to-center setups, fast remote slit viewing, etc.). The
camera replacement is in this plan, the new computer is deferred.
The total cost is higher because of the baffles, a better
estimate of the UV coatings, and travel, which was not included
before. I would be surprised if the numbers come out lower, not
surprised if they were 20-30% higher. If we work hard, $65K can
be encumbered by December 1996 (doing all of the first group
except 2 and part of 3, which require DIS downtime in 1997, and
half the travel cost).
Baffling should be top priority even if it isn't fixed on the DIS
structure. Items 2-8 should not be prioritized except to remove
tasks that can be deferred (it does not make sense to separate 2
and 3, though). Assigning priorities to these can make for
inefficient use of people time. Decisions on both the slit viewer
computer and the new detectors (items 11 and 12) are deferred
until, say, after the UV throughput is repaired.
BUDGET
======================================================
1. Baffling (maybe done on the telescope) $ 5K
2. UV throughput repair $12K
3. Overall throughput analysis & repair $ 9K
4. Remove noise from CCD readouts $ 2K
5. Fast slit viewer camera $ 8K
6. Reflecting air gap slits $ 5K
7. New (different dispersion) gratings $14K
8. Automatic calibration lamp control $ 2K
9. Salaries for above $20K
10. Travel and incidentals $10K
SUBTOTAL $ 87K
DEFERRED ITEMS
11. New slit viewer computing system $13K
12. New detectors $12K
13. New detector salary $ 8K
TOTAL $120K
======================================================
SCHEDULE AND DOWNTIME
Except for 2 and 3, the first 8 items can probably be done
without significant DIS downtime, although we would like the
instrument not to be scheduled for a few contiguous days
occasionally. These tasks each take a month or two of clock time
and all could probably be finished within a 1-year time frame.
Items 2 and 3 require that DIS be removed from service for a few
months.
Alan Uomoto
July 23, 1996
---------------------------------------------------------------
SUMMARIES OF COMMUNICATIONS
EMAIL FROM LUISA REBULL - ROTATOR ANGLE DEPENDENT FLATS
Luisa Rebull pointed out the rotation dependent flat fields
(http://astro.uchicago.edu/home/web/rebull/research/rotation/).
The effect is large and is probably caused by DIS seeing stray
light from the telescope structure or enclosure.
We might revisit the schedule for baffle installation on the
telescope and consider temporary baffles on DIS or the Naysmith
port if the proper fix is difficult or long-range. A shot in the
dark price for parts is $5K. This might not be a proper fix (it
might vignette DIS, invade the telescope beam, etc.) but it would
get us decent flats.
NMSU CONCERNS - THROUGHPUT and NEW GRATINGS
Most important, I think, were improving throughput and new
intermediate dispersion gratings. Kurt Anderson found that we
have four spare DIS grating holders, so new gratings would
require little effort. Replacing detectors and new slit viewer
capabilities had lower priority.
BRUCE BALICK'S POST ON APO35M-DIS
1. Pixel binning besides 2x2 should be available (2x1 and 3x1,
for example). This might be a software enhancement (?).
2. Subraster readouts. This may not possible without major
modifications to the readout electronics (?), at least if the
reason is to save time.
3. New slits. New air slits are on the list of improvements and
Steve Knapp has already made new quartz slit masks.
4. Spectrum undersampling. With not-so-narrow slits, spectral
features are undersampled. Changing this would require a new
camera and/or detector, both expensive options.
JIM GUNN ON COATINGS
Jim is confident that the UV throughput problem resides in three
dielectric coatings: a fold mirror and the two reflections in the
blue camera. Each location requires that a cemented joint be
separated. The plan 0 estimate for fixing this ($4K) becomes
3x$4K=$12K.
While we're at it, we should coat the back of the beamsplitter to
eliminate the blue ghost.
MICHAEL STRAUSS QUESTIONS
Michael asked me to note that many tasks can be done without
removing DIS from service for long periods. Michael also asked
about the residual charge problem, and others have suggested
separate red and blue channel shutters to reduce this problem.
This problem should probably be attacked only if we decide not to
replace the detectors, since replacing the detectors might make
it go away. And finally, Michael asked about remote slit viewing:
yes, it would be possible with the new slit viewer computing
system, but the computer is a deferred item now.
APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO
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