The major activity during this quarter was preparation for, and hosting the PDR. By the end of the quarter we had received formal comments from the chairman of the PDR Committee, Dan Fabricant.
A report of 244 pages plus appendices was prepared for the PDR. Copies are available on request. The PDR meeting went well, with approximately 50 people attending. The meeting revealed no basic flaws with the instrument concept or preliminary design, and lots of good advice was obtained. The committee agreed with our intent of buying the optical glass following the PDR and starting optical fabrication as soon as possible. However they disagreed with purchasing the Laser Cutter early, and the consequences of this recommendation are currently being investigated. The comments of the PDR Committee, and our response are attached as appendices to this report.
Following the PDR, the process of completing the Error Budget for the instrument was started. Sandy Faber, Jack Osborn and Eric James are the primary people involved, and they expect to complete a budget by the end of January. Obviously this budget will change as the instrument development proceeds, but it gives a good foundation on which the detailed design can start.
On reviewing the camera after the PDR, Harland Epps has decided to re-look at the design. The effect on the schedule is to push the optical fabrication of the lenses onto the critical path to a completion in July 1998. Under the revised schedule, fabrication of the lenses would start six months later than planned, which would be in September 1995. The revised schedule calls for the glass to be ordered in April 1995.
A new optical generator, a Strasbaugh 18AS Spherometer, and a Zygo f/.65 Transmission Sphere have been ordered for the Optical Lab. These items are needed for the fabrication of the camera lenses and represent about half the dollar value of items identified in the budget for the Optical Lab.
2. Status of Risk Items
The following are specific risk items mentioned in the PDR.
2.1 Flexure Control System
The PDR report deals with this subject in some detail. The PDR Committee was intrigued with the idea but thought we needed first to give careful attention to the native stiffness of the instrument. They recommended that a structural consultant be brought into the project. Making the instrument as stiff as possible is certainly endorsed by our design team, and has been from the beginning. Work has started to identify a consultant to work with the DEIMOS team on the structure of the instrument.
The attached response to the PDR outlines other possible contributions to fringing in the detectors other than lack of wavelength stability. However it is still assumed that active flexure control will be necessary to meet the instrument specification. The instrument design is assuming that the tent mirrors need to be active in the direction parallel to dispersion and that the Camera/Detector group will need to be active in the direction perpendicular to dispersion.
2.2 Optics Fabrication
The PDR Committee agreed that Lick could fabricate the proposed optics.
2.3 Slit Mask Handler
The PDR Committee had considerable concern about the complexity of this mechanism and recommended that the spectrograph be moved back from the nominal focal plane to accommodate a simpler design. The PIs have agreed that we can move the instrument back between 4 and 10 inches without seriously affecting the optical quality. This will allow a simpler slit mask handler. See the PDR response for further details.
Jack Osborne will start design of the new handler early this year. Preliminary investigations have the handler either being similar to the LRIS design or in a carousel arrangement. Either way, the insertion motion is a simple uni-directional slide-in from the side.
On a related issue, the design of the slit mask will likely be changed to have the mask in a cylindrical shape, rather than trying to conform to the spherical focal plane precisely. Eric James completed a draft report on fitting both a cylinder and a cone to the focal plane, and Harland is going to review the conclusions of the report. Eric's draft recommends a cylindrical shape for the slit mask.
2.4 Detector Mosaic
The PDR review indicated several concerns about the complexity of the preliminary concept for aligning the CCD chips into a mosaic, and alternatives will be investigated as part of the detailed design. A simpler solution to the one originally proposed is desired.
Lick is developing a new testing facility to measure CCD flatness. The test is similar to a Hartmann test and uses a laser to measure device flatness. This capability will probably prove to be useful in simplifying some alignment aspects of the CCD mosaic assembly and may aid in designing a simpler mosaic mounting structure.
2.5 CCD Data Handling
Steve Allen has begun collecting information on multi-screen windowing extensions for use in displaying 8K x 8K images. So far, one commercial product and one public-domain product has been identified. We are now considering equipment requirements for testing evaluation copies of these products.
Bob Kibrick has been in contact with Leach regarding an Sbus interface to the Leach system, which might significantly simplify the CCD data handling effort. Leach currently has this board in development, and more details should be available this Spring.
2.6 Total Sofware Burden
In response to a request by the PDR committee to identify possible areas that might be reduced or eliminated should significant budget overruns occur, an estimate of possible budgetary savings that might accrue from simplification of the software requirements was reviewed, and is included in the response to the committee's report. Related reductions which would also reduce the total software burden include using only one readout amplifier per CCD chip.
2.7 Slit Mask Cutter
The PDR Committee recommended that we not purchase the cutter until after the CDR, and we have agreed with this recommendation. A revision of the schedule has been made, and the effect is detailed in the following section on Electronics.
2.8 Total Budget Overrun
The budget section of this report deals with the contingency fund and what has been committed against the original allocation.
3. Reports on Specific Areas
3.1 Optics