Previous Article Next Article Table of Contents
WIYN Project Summary (1Jun95) (from KPNO, NOAO Newsletter No. 42, June 1995) WIYN activity is concentrating in three main areas: analyzing and correcting telescope performance issues identified during telescope commissioning; instrument commissioning; and completion of the Instrument Adaptor Subsystem (IAS). By mid-February of this year, it had become clear that telescope performance needs further work in three main areas. First, the all-sky pointing accuracy was limited to 15"-20" RMS. Analysis of pointing data suggested that this problem was related to both systematic and random encoder errors. Second, when the telescope was pointed into the wind, significant wind shake (approximately 0.2" RMS) would begin at wind speeds of 10 m/s and increase with increasing wind speed. Preliminary analysis suggested that this problem was related to main axis servo performance or mechanical vibration of the truss structure that supports the secondary cage. Third, when the wind speeds reached sustained speeds of 16 m/s, with gusts above 20 m/s, the wind torque would exceed the available motor torque and blow the telescope off target. Investigation of project archival documentation by Dan Blanco, the Project Engineer, revealed that this problem arose from a series of specification mistakes (e.g., typographical errors incurred when transferring numbers from one document to another) and under-conservative design decisions. In other words, the as-built main axis motors and their power supplies deliver exactly the specified torque with a little overhead, but the specification was wrong. The Project is now working with Kitt Peak Engineering to investigate these problems in more detail, and to develop plans to correct them. The friction-driven incremental encoder system is being "wrung out" by KPNO Engineering both mechanically and electronically. At this writing (late April), suspicions center on how the encoders are mechanically mounted. Electronically, the encoders seem to be performing correctly. The wind shake investigation is concentrating on understanding the servo disturbance rejection algorithm in the hopes of tuning it to a higher bandwidth. How successful this will be is questionable since the current bandwidth is 6 Hz and the first fundamental resonance of the telescope is at 8 Hz. Reducing wind shake further may involve using a more sophisticated rejection algorithm or reducing the wind buffeting mechanically (e.g., with a wind screen). There are two obvious solutions for increasing motor torque: (1) increase the power delivered to the current motors, if that is safe to do; or (2) install new motors that can handle more delivered power. Both options are being evaluated. As this second phase of telescope commissioning continues, night-time activity is dominated by instrument commissioning. Hydra commissioning is going very well. Multi-FOPS and gripper TV closed-loop guiding both work well. Astrometric solutions derived from photographic plates acquired as described in NOAO Newsletter No. 41 have been folded into the fiber position algorithm. While some fine tuning of the placement algorithm is needed, fibers have been successfully placed on stars under computer control. A number of minor performance issues have been uncovered and solutions are being developed. There are still many things to check out in both Hydra and the Bench Spectrograph, but progress to date has been encouraging. Training of support personnel is scheduled to begin in May. If MOS/Hydra commissioning continues smoothly, MOS/Hydra may be ready for science operations on 1 July (plus or minus two weeks). Progress on commissioning the CCD imager has been hampered by a number of minor hardware problems and non-photometric weather. The Filter Shutter Assembly (FSA) built by Indiana University has been interfaced into the Arcon/IRAF observing software so that the observer can be prompted for the filter when taking an exposure and the filter can be changed if desired. A shutter timing problem was identified and corrected. Focusing the imager is currently very inefficient, but an improved IRAF/Arcon "focus" utility and a calibration of telescope focus as a function of telescope temperature should greatly improve matters. Software is being developed to implement these two features soon. The complete set of WIYN 4 X 4 filters has been received, but two of the Ha filters were returned for replacement. One had a bad red-leak, and the other showed signs of poor mechanical sealing. Unless some unanticipated problem develops, the Imager/FSA package should be ready for science operations by 1 June. Mechanical work on the baseline Instrument Adaptor Subsystem (the WIYN guiding and acquisition system) was essentially completed in mid-February. The internal wiring harness is now being installed while the low-level control software is written. Wiring progress has been excellent and wiring should be completed by mid-May. At that time, the full-up low-level control software will be installed and tested. If all goes well, the IAS should be shipped to WIYN during the first week of June. Nominally, IAS commissioning would begin at that point. Unfortunately, the interface between the main Telescope Control System (TCS) and the low-level IAS control system, originally scheduled for development in Madison, has unexpectedly become the responsibility of the Project. Completing the unanticipated control system task will take several months, slipping the completion of IAS commissioning by an equivalent amount of time. In the interim, it seems likely that imaging observations will begin using the "substitute" IAS constructed by Indiana University. Use of the substitute IAS will result in lower efficiency imager operations primarily because the substitute IAS guide probe samples a very small and specific area of the telescope field and because the higher level software needed for efficient guide star acquisition, focus control, and wavefront measurement cannot be implemented until the IAS/TCS interface is completed. Responsibility for the operation, maintenance, and further development of the WIYN control system has been completely transferred from the University of Wisconsin Controls Group (UWCG) to the WIYN operations staff at KPNO. A variety of control system loose ends remained after the transition, the most significant being the IAS/TCS interface discussed above. The operations staff is working to tie up these loose ends, consulting with the UWCG as necessary. The median WIYN Delivered Image Quality (DIQ) for June 1994 through March 1995 slipped to 0.8" FWHM, somewhat larger than reported in NOAO Newsletter No. 41. Since the delivered wavefront continues to be excellent (often within 120 nm RMS or smaller of the ideal wavefront), this suggests that the site seeing was not as good during this period. This conclusion is not surprising given the unstable weather conditions during most of February and March; for example, WIYN was forced to remain closed during roughly 50% of its scheduled nights in February due to inclement conditions. Nevertheless, WIYN continues to have the best median DIQ on Kitt Peak. Science Operations are currently scheduled to begin on 15 July 1995, roughly the same time as the deadline for the September 1995 NOAO Newsletter. We anticipate that the next Project report will focus on a smooth transition to shared risk science operations. Dave Silva, WIYN Project Manager
Previous Article Next Article Table of Contents