Minutes to APO 3.5m User's Committee Phone Conference, October 9, 1995 Attending: Julie Lutz, Rene Walterbos, Bruce Gillespie, Ed Turner, Michael Strauss, Don York, Chris Stubbs, Lew Hobbs, Rich Kron Agenda: 1. Update from Bruce Gillespie. 2. Recent engineering activities and results 3. Scheduling issues. 4. Preparation of budget for Board of Governors in November (we will get copies of this, distributed by Aspasia). Let Bruce know of any specific suggestions. Bruce Gillespie: Things are working so well, there is not much to say. Highlights of this past month: The amount of uptime has been much better than previous months due to good weather and fewer hardware problems. 80% of scheduled time was used for science or scheduled engineering. 17% of the time was lost to weather, only 3% to instrument problems. Quite respectable. The seeing has also been better. r0 as measured by the seeing monitor has gone up from 6 cm to 10 cm over the last month. Impression has been that the telescope has been delivering better seeing. Close to 1.3" average over the past few weeks. (0.9" last night!). Does this just reflect that the weather patterns have changed, or is it due to improvements at the telescope? 70-75% of all runs are remote observing. The networks have not been as noise-free as we would like. A test has been run every hour to test how well the network is working. A series of packets is sent to each ARC site, and number of packets returned and time for return are monitored. Success rate is 70-100%; round-trip time 50-300 seconds. Looking about speeding up transmission using compression. Also looking into alternative routing (APO to UW requires 23 hops!). Chris Stubbs also looking into alternative routing which can reduce this number to 7, using an NASA backbone. We definitely need to monitor and improve the network connections, as well as backup (telephone) connections if the Internet is down. An alternative is to develop specific ftp-like transfer software optimized for the problem at hand; potential speed up of transfer time of images by a factor of 10. Average rate of data transfer during observing is ~10% of T1. We pay $14K for T1. T3 would probably cost around $100K. Stubbs: tasks to interrogate RA and Dec from telescope through DSC brings telescope to its knees. Information transfer is somehow screwed up; the protocols that DSC uses are different from that of the other instruments. Kron: Fermilab group is out there right now working on the DA for DSC, Monitor telescope; presumably working on this problem. Stubbs: DSC has some electronic problems with CCD that need some clean-up, UW wants to bring the instrument to Seattle to work on this and have TIm McKay come out as well. Instruments all behaving themselves reasonably well. John Brinkman is on-board. Will be deciding what to do with instruments during down-time; let him know any suggestions you might have, Engineering (Gillespie): Telescope collimation: A problem with secondary actuators appeared; mostly repaired, but we're not convinced that we can return reliably to collimation over day-long timescales. Are actuators missing steps? The secondary is rezeroed every day in an attempt to get around this. 20 Hz resonance: By moving frequency of servo motors to 25 Hz much diminishes this, but image motion at other frequencies goes up. Total power unchanged, unfortunately. Tension of diagonal struts holding secondary cage is not to spec (too low by factor of 4), putting resonances at too low frequency. Tightening these rods is non-trivial (getting close to failure mode). The altitude drive servo has limited dynamic range; if we reduce the gain by a factor of several, the least significant pulse will be much smaller, cutting down on induced vibration in the telescope. Will slow down altitude slew speed by the same factor, but this is rarely the limiting factor in speed of slew. Stubbs: Plan to trail images across DSC with power off during a night of good seeing to see how much of the seeing is due to the optical figure, and how much is due to these various resonances. CHAOS measured 0.4" images in 1-2 sec exposures at 6000A. Wow! Corrections he has to put in are in agreement with known figure errors in secondary. Full-blown Hartmann screen with 44 holes will be done tonight (unless the weather doesn't cooperate; a possibility to take science time for this project in the next few nights if it can't be done tonight). This will characterize overall optical performance of the system, although it doesn't tell you unambiguously which piece of optics is responsible for the errors that are seen. Strong suspicion that the secondary is the culprit. One test would be to redo the test with the secondary rotated 90 or 180 degrees; it might be doable reasonably straightforwardly with minor work on the secondary support structure. How about the tertiary? Very difficult to rotate this? Stubbs: what about a prime focus Hartman test? This would be absolutely unambiguous. Not easy however; you have to get a camera up there which could take this very fast beam. Could this be done during this fall engineering run? Probably not. Could the Rodier technique be used to measure the wave front at prime focus more easily since it utilizes out-of-focus images? Enclosure wheels: redesigned wheel is on order; expected in 2 weeks from L&F. Cracks are continuing to spread. A real problem if this wheel is delayed; we may have to delay the start of the month-long engineering shut-down by one week, by shuffling science programs. We'll make a decision in 7-10 days. There is a reserve fund of $60K for catastrophic failures, such as this problem with the wheel. The whole project cost of replacing all four wheels is $25K. Exact weight of the enclosure is not known, thus complicating the wheel problem. Guider: lots of engineering being done. Guider definitely works to 0.2" closed loop on bright (8th mag) guide star. To do: Characterize guiding ability as function of brightness of star. Characterize guiding ability close to zenith. Implement a calculation of rotator angle which gives you a bright star in the guider. Hope to get something out for use by scientists in the next week. Remark should be able to operate the guider soon, but not yet; right now, you have to have the night assistant do it. For longer term, there are plans to put a 512x512 chip into the camera, while the current 1024x1024 chip is sent back to Spectrasource to reduce read noise. Another improvement will be to put in a field reducer to get a larger field of view (pixel size is 0.1"). Another possibility is starting over with a new camera. Throughput testing: DSC data by Chris; not yet reduced. A long integration PSF to get wings would be very useful, best to use DSC. Scattered light is probably from the secondary? dirtiness of the optics; baffling might also be an issue. Planning for upcoming shutdown going well. A list of 40 tasks lies ahead. Enough to keep us busy for six months. The 4-week shutdown will concentrate on mechanical aspects. Bruce will distribute this list of tasks soon. This task list includes a number of goals, such as, at the end of six months: 1. Have the amount of uptime available to do science >= 90% 2. Telescope points, guides, tracks to within a factor of 2 of spec 3. Images of 1.2" median, and a best seeing of 0.6". (and so on). Scheduling: A new model, following ROSAT: Each institution decides on some fraction of the proposals making up 50% (70%?) of its time allocation to be of high priority, to be scheduled exactly has requested. An additional 100% (60%?) of the time would be proposals (perhaps in a rank-ordered list), which can be scheduled according to what fits best into the remaining schedule. This requires a new level of commitment for insitutional schedulers to make sure that people don't get rejected many quarters in a row. Either people will get closer to what they requested, or they won't get anything at all. Also requires that people be very specific as to what the minimum time is that they require to do their science. Next year's budget will be discussed at the Board of Governor's meeting next month. Possible major new items include: 1. Money for a secondary mirror ($250K? A blank exists, polishing is straightforward; the testing is the most involved process. May take up to two years). 2. Add a software engineer or systems administrator for APO (a goal of software self-sufficiency on the site in 1.5 years). 3. A new camera for the guider (see above). 4. Infrastructure for people on the site: test equiptment, basic electronic components, spare chips, and test devices (oscilloscopes). Gillespie: observing support from site staff. We do not do service observing, whereby observatory does all the observing for you. However, staff would like opportunity to be involved in scientific collaborations; they could actually carry out some of the observations of some such collaborative project. Of course, Bruce has to be kept informed, and this takes lower priority than their regular duties. Turner et al.'s QSO gravitational lensing program has been done in collaboration with Long and Bergeron. People should be aware of this, and take advantage of it where it is appropriate. Ideally the site staff would be involved in scientific process (i.e., not just carrying out flat fields in the afternoon). We have to guard against it being abused, which would cause much ill-will. It is not part of the duty of the site staff to take part in these collaborations; participation in projects would be up to the individuals involved, assuming that it doesn't take up too much of their time. Next meeting Monday, November 13, 1995 at noon. -Michael Strauss ------- end ------- APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 19 in the apo35-general archive. You can find APO the archive on http://astro.princeton.edu:82/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO