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 APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 19 in the apo35-dis archive. 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