An extensive set of engineering projects intended to improve the performance of the APO 3.5m and its instrumentation to levels which are generally competitive with the best other 4m class telescopes and which are uniquely powerful in some respects is now well underway. These include both those upgrades described in the "Three Year Plan" and remediation of some problems discovered since its adoption. A later message from Chris Stubbs will summarize the results to date. Fast progress in this effort is being given very high priority, and the necessary shutdowns of the telescope are being accepted as an unavoidable cost. We are continuing to try to optimize the procedures by which we simultaneously use the telescope for science while this engineering campaign is in progress. The difficulties with the schedule for the planned 3Q1997 engineering shutdown of the 3.5m which were discussed in two preceding messages are not unique. In fact, we have encountered quite similar problems with the three previous major engineering shutdowns: namely, the June shutdown for installation of the new guider, the April shutdown for installation of a new support system for the primary, and the Dec-Jan shutdown for replacement of the enclosure rotation wheels and re-aluminization of the optics. There are two basic problems: 1) Despite our best efforts, it has proven impossible to accurately predict, months in advance, the date on which all necessary preparations for a particular shutdown will be completed. These include receiving parts, preliminary work not requiring telescope shutdown and scheduling of critical personnel to work on the shutdown. Often the completion of such preparations is affected by matters entirely beyond the control of the Observatory and/or which are inherently unpredictable. In practise, since things always take longer than one expects, we have never been fully ready at the beginning of a major shutdown. This results in less efficient use of the shutdown time and thus ultimately reduces available science time. 2) Despite often heroic efforts by those working on a shutdown, it usually has proven impossible to complete all planned engineering tasks within the scheduled duration of the shutdown. This is partly due to problem #1, not being fully ready to start. However, it is also due to other factors such as absence of a detailed understanding of the tasks involved months in advance, growth in the scope of planned work as time passes, discovery of unanticipated problems in the course of the shutdown work, need for clear skies for some tasks (typically as the telescope is being returned to service) and so forth. This results in both disappointment for users scheduled to use the telescope immediately following the shutdown and in enormous stress on those working on the engineering tasks as they strive to meet what may well be an unrealistic goal. Based on experience and such considerations, all those immediately concerned have concluded that the present system of scheduling extended shutdowns (EN00 time) is not working in an acceptable way. We will therefore try one or more different systems in future quarters. A specific proposal is described below. The Users Committee will discuss it on July 14 and perhaps in subsequent meetings. Please give your comments and suggestions to your institutional UC representative and/or email them to me. The proposed new system for dealing with EN00 time is as follows: 1) No EN00 time will be explicitly scheduled in each quarter; only EN01 time will be scheduled specifically (EN01 is typically a single night set aside for routine engineering tasks on a regular basis, e.g., pointing models, and usually amounts to about 7% of all available time). 2) When *all* preparations for a given major engineering task requiring extended (more than one night) shutdown of the telescope are *complete*, those planning to carry out the work will request a shutdown of some specific duration, based on their best estimate of how long it will take. 3) The shutdown will then be scheduled and announced at least, but very often no more than, two weeks in the future (2 weeks notice) and will simply pre-empt whatever science programs are scheduled for that period. 4) From the Observatory point-of-view, time lost in this way will be like that lost to bad weather or equipment problems in that there will be no attempt to provide compensating time. (Of course, institutions may arrange such compensation internally if they wish.) Of course, pre-empted time will be accounted as engineering time and not charged to the affected institutions; in this respect, it is not like time lost to weather or equipment problems. 5) In scheduling such pre-emptory engineering time, account may be taken of programs that are of particularly high priority (as determined by institutional TACs) or which would produce data not easily obtainable at other times (e.g., occultations, observations coordinated with other observatories or spacecraft). Programs which are believed to merit such special protection should be explicitly identified in the proposals and institutional scheduling requests. However, it should be understood that no program can be certainly exempted (i.e., no promises) from cancellation due to EN00 engineering shutdowns. This system should solve the first problem described above and somewhat alleviate the second (which probably cannot be entirely avoided). Although it will doubtless produce inconvenience and disappointment for those whose observing time is canceled with as little as two weeks notice, this should be viewed in perspective with the fact that observing time is often lost with much less (even zero) notice to weather and equipment problems. The overall gain in total science time available (due to more effective use of shutdown time) and in telescope/instrument performance (due to the engineering improvements themselves) should also help to ease the blow. Many other ways of dealing with this scheduling problem are certainly possible, and several of them have been proposed and discussed. However, the one described above seems to me to be the simplest and most effective. I look forward to receiving your comments on it. Ed Turner APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 151 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/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