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07 Dec. 2006 -- Observing efficiency -- Meeting notes


  • Quick intro on the NGAO and background info for this meeting
  • Introduce WBS for Observing Efficiency and Uptime
  • Review quickly current experience from Keck, Lick and Palomar
  • Propose and discuss definitions for these terms and establish work scope
  • Open the attached notes and guideline for the meeting (ppt)

Attendees: Randy Campbell, Jason Chin, Jim Lyke, Marshall Perrin, Ellie Gates, Erik Johansson and David Le Mignant. Antonin Bouchez and Rich Dekany were excused as they were in the middle of an observing run at Palomar. No news from James.

Meeting minutes: (see ppt presentation above)

  • Overall: great participation from everyone, good inputs and good discussion. The meeting lasted longer than expected (1h 30min instead of one hour). We went through the topics included from the presentation.
  • Background info on NGAO: Most participants to this meeting knew little about NGAO and have not yet read the NGAO proposal. Most promise they will. It was clear to all that this is a work in its earliest phase: the system design.
  • Our tasks: Both WBS 3.1.111 and resp. 12 describe our task as "to determine what will be required to meet the Observing Efficiency (resp Uptime) Requirements. At this point and to our knowledge, we do not know whether these requirements have been documented anywhere. We anticipate we will work with the science teams to define the requirements. In order to define the observing efficiency requirements, we have drafted a generic observing scenario (see link somewhere above in this page).
  • Looking into our current Observing Efficiency and Uptime budgets: The WBS recommends looking into current operations. The Keck guys gave a quick overview of the Keck observing efficiency and uptime. Ellie talked about the Lick operations where the main overhead is acquiring the laser and long dither legs (beyond FAA restrictions). For both observatories, the main limitations for observing efficiency in good weather conditions are the target acquisition and the serial (vs parallel) communication between telescope/AO-laser during the observing sequence. Note that IRCAL at Lick writes to the disk while the telescopes moves, and that the greater level of automation at Keck has permitted to reduce some of the overhead (e.g., laser acquisition). Keck downtime is mainly attributed to catastrophic failures (WFC crashes, dye comtamination and laser burns). Keck also reports a very acute weakness in pointing confidence (<0.1arcsec) on OSIRIS for very faint galaxy.
  • Defining the wording: The discussion on the definitions of Observing Efficiency and Uptime and the subtle differences between these two over-used terms kept going for a while and was very insightful. We all agreed are current definitions (see slides) are ill-defined and should be adjusted for NG AO: current definitions may fit the observatories' needs but they don't take into account the point-of-view of the observers (for the science: it's all time losses, no matter what). Below are some notes, that will be used in writing the final report.
    • Observing Efficiency: The Observing Efficiency is the open shutter time during dark time when the instrument runs at the performance level where it is designed to operate, for the given observing conditions. It also means that understanding observing efficiency for NGAO may require tagging the various sets of data (science, calibrations, etc). Marshall pointed out the need for facility calibrations and the notion of efficiency per brain cell (the best use of everyone's time by not having to re-invent the wheel over and over).
    • Uptime:
      • Uptime is the opposite of downtime! Bad weather may be included in downtime budget (TBD). The instrument is considered not to be in an uptime state if the performance is degraded (again, w/ respect to design requirements for the observing conditions) or/and there is an instrument failure.
      • Except for downtimes caused by weather, space command or aircraft laser shuttering, and laser collisions with other observatories, downtime will be due either to degraded performance or some sort of system failure (these are preventable failures). While it is insightful to look at current uptime statistics for general trends, the amount of downtime we can expect in the NGAO due to preventable failures will be directly related to the resources used in achieving a robust design and implementation and in establishing a rigorous post-integration periodic maintenance program, not in some sort of extrapolation of current AO system statistics to NGAO. It is possible to design a system that will have no downtime due to preventable failures, but it may very well be unaffordable. The key to establishing a valid uptime performance budget will be in understanding what constitutes an acceptable level of downtime for each observing scenario (i.e., uptime requirements), and then determining how these uptime requirements can be distributed throughout the main system components in order to achieve the overall desired level of uptime.
    • Following this discussion, we thought it would be necessary to add new parameters in the generic Observing Scenario Sheet such as performance range to achieve successful science. Also, it would be important to include concrete example in the report for Observing Efficiency and Uptime. It is clear that whichever exact definition we use, they go hand-in-hand.
  • Formulating a budget: From the observing scenario at the Keck telescope, we may be able to estimate some overhead such as slew time, minimum dither time, etc. Yet some more critical items such as centering and acquisition will be difficult to estimate (assuming current system, it would sure look ugly!). We will try to propose various methods and estimate overhead for each. We will also have to play with various science operations models. Dito for uptime budget; we will work with the science teams and understand the requirements for mean-time between any faults. From there we will try to promote various cases with 1% 2% and 5% downtime (TBD). Note that given the complexity of a systems that includes n independent system variables, each system variable will likely need to be at 99.999% reliable (even for a 5% downtime). Again, here the impact on science from downtime and catastrophic failure in particular, will depend on the science operation model: whether there is a compelling (TAC-ranked) back-up science program with the same or different instrument and whether spares are readily available.
  • Closing remarks and best-effort actions items:
    • DLM to write the minutes. Other to review and send comments
    • EJ and DLM to meet and report to EC on grouping or not teh two WBS
    • Most will read the proposal
    • Most will review the Observing Scenario Sheet and provide comments/suggestions to DLM. how do we get more feedback from science teams for the uptime budget??
    • DLM and EJ to write the work scope sheet for these two WBS and submit to EC
    • DLM and others? to look into current hard limitations:
      • min time for telescope slew
      • min time for dither slew
      • min time for pointing/centering with 1arcsec precision
      • more ideas? Jason and others?
  • That's it folks! Next meeting sometime within two weeks, to be scheduled. Everyone is invited to come back and provide information/suggestions in the meantime. Let DLM know if you'd like not to participate. And thank you all for this good meeting!

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