Subject: DIS Refurbishment, plan 0
From: au@jhu.edu
Submitted: Thu, 18 Jul 1996 11:29:50 +0000
Message number: 19
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DIS REFURBISHMENT & UPGRADES
Here is an outline of how we might refurbish DIS. The costs are
estimates. In some cases, problems are not precisely identified
but inferred from rumor and incomplete measurements. The
solutions, therefore, are similarly imprecise. We should
consider this a starting point for discussions rather than a
firm plan since I have made no attempt to optimize the dollars.
The total cost of all repairs and improvements is around $90K,
although inflation to $100K or more is possible depending on
options chosen (and we don't have to do everything on the list,
either). Travel, phone, and incidental costs are not included.
I have commitments from two people at JHU: a research scientist,
David Golimowski, who is developing the JHU HST Advanced Camera
CCD calibration facility, and Christy Tremonti, a first-year,
and one of our best, graduate students who wants to spend a year
in instrumentation research. David is available half time for
three months beginning in October. Christy should start in
September. Both will need salary support (this has been included
in the costs below). We may be able to negotiate longer terms if
needed.
We will also need assistance from APO staff and the NSO machine
shop.
I would like to proceed this way: Get David and Christy on board
as soon as possible to start work on the throughput analysis. It
is important to identify correctly the things to fix, and doing
so will take some time because test equipment needs to be
gathered. In parallel, I will work on the smaller tasks with the
help of APO staff (CCD noise, calibration lamps, etc.). The
users committee will help by setting priorities and schedules
based on user feedback.
List of DIS improvements:
1. Remove noise from CCD readouts
2. Reflecting air gap slits
3. New (different dispersion) gratings
4. Automatic calibration lamp control
5. Fast readout, integrating slitviewer
6. Overall throughput analysis & repair
7. UV throughput repair
8. New detectors
REMOVING NOISE FROM READOUTS
The nearly periodic noise superposed on the CCD readouts is
probably due to 60 Hz pickup. The solution may be as simple as
replacing a cable run with fiber optics, costing $1-2K. This
might not be correct, but it's the first thing to investigate.
REFLECTIVE AIR GAP SLITS
Air gap slits will improve throughput over the aluminized quartz
plates. These will probably cost about $1500 each. Three would
cost $4.5K.
NEW GRATINGS
For "off the shelf" gratings, typical replication costs might be
around $5K. Add to that the cost of the blank, around $2K,
polished, so each new grating would be around $7K. We would
probably want two (one red, one blue) for a cost of $14K.
AUTOMATIC CALIBRATION LAMP CONTROL
This means closing the mirror covers and turning on the lights
without going to the dome and using Remark or the science
workstation to do this. Probably $2K for cabling, a
microprocessor, relays, sensors, etc.
FAST READOUT, INTEGRATING SLITVIEWER
This will allow faster, more accurate object setup. New software
lets you pick an object and drive the telescope to it.
A commercial CCD camera ($5K) can be used. Machine work to
incorporate it will be around $3K. $8K here.
For easy, accurate setup a new computer ($3K) running LynxOS (a
real-time Unix clone; $4K) will be used to acquire the imaging
data and present guider signals to the TCC if needed. LynxOS,
being Unix, communicates naturally with the science workstation
so the slitviewer is easily integrated with user software
(remember that a software overhaul is also a desired item).
Labor: About 1 month software development time ($6K). This data
acquisition system is a step towards an integrated software
system for the observer. Additional cost: $13K.
OVERALL THROUGHPUT ANALYSIS & REPAIR
System throughput for DIS spectroscopy is unexpectedly low. Some
of the problem is in degraded telescope mirror coatings, but
this does not explain the entire problem. The task here is to
measure individual component efficiency, identifying items
needing repair.
Measuring equipment needs to be purchased or built: about $1K
for a calibrated photodiode, $3K for readout electronics and
computer upgrades, and about $3K for machined parts. Labor: 6
months graduate student time ($12K). Repairs will be in the form
of new coatings or optical elements costing from $1K to $5K
each. This operation requires DIS downtime. $21K if we assume
$3K of optical repairs.
UV THROUGHPUT REPAIR
It is possible that the poor UV throughput is due to a bad
coating on the blue camera. This coating is embedded in a
cemented surface so its repair requires breaking the glue joint,
posing a risk to the camera. Because DIS is likely to be the
only UV spectrograph for quite some time (the proposed JHU
spectrograph does not run blueward of about 3700 Angstroms) it
is probably worth the risk if UV sensitivity is a priority (is
it?).
Cost might be $2K for disassembly and inspection, $1K for
recoating, and $1K for re-assembly. Most of the previous item
(throughput analysis) should be completed before this can be
done. This operation requires DIS downtime. $4K.
NEW DETECTORS
Both DIS detectors are old. Replacing one or both will improve
throughput. The "overall throughput analysis" should be done
before we take action on this, and we will need to decide
whether the improvements are worth the cost. Here are some
options:
1. Replace the blue chip with a WFPC2 blue sensitive chip that
is idle at JHU (800x800, 15 micron pixels). This is attractive
because we can simply clone the red side electronics and drop
in the new detector. It's inexpensive but we do not know if
the chip is up to the job. Maybe $5K for new electronics plus
$8K for labor.
2. Replace the blue chip with an HST Advanced Camera blue
sensitive 1024x1024 chip. These have excellent UV sensitivity
and 21 micron pixels. In this case, we would clone the SDSS
readout electronics and integrate data acquisition with the
LynxOS data system described for the slitviewer. A ballpark
estimate would be $20K for electronics and labor, not
including the LynxOS system. This is the preferred option (of
the three) because the improvement is large and the cost is
reasonable.
3. Purchase an appropriate CCD for the blue and/or channel. This
is the same as option 2 plus the cost of the new CCDs.
Alan Uomoto
July 17, 1996
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