Keck NGAO Opto-mechanical meeting minutes, Nov. 27, 2007 Telecon. Attendees: Don Gavel, Reni Kupke, Viswa Velur, Anna Moore, Jim Bell, Sean Adkins, Brian Bauman, Peter Wizinowich Discussion of progress on specifying Functional Requirements ------------------------------------------------------------ Some discussion on what "requirements" are, and enumerated some example requirements, e.g.: * Optical - Field of view - f/# - optical quality - field-dependent aberration to science instrument - field-dependent aberration to LOWFS - field-dependent aberration to HOWFS (LGS) - Choice of dichroics - definition of bands Note: current "definitions" are to be found in the error budget spreadsheet. ***ACTION*** (Sean): Sean will collect these definitions, determine if they are appropriate for science goals and science instruments, and document final definitions in a KAON * Mechanical - Stability - Vibration Three types of vibration spec, one an "input", one and "output", and one "internal": 1) The system will work within spec when it is subject to a vibration spectrum/enviroment of XXX (microG's/Hz or whatever) 2) The system will not cause vibration of more than XXX (microG's/Hz) transmitted to the rest of the telescope system, as measured at location YYY 3) There is an error budget allocation for vibration effect on wavefront sensing, which will flow down to a requirement on AO system's vibration sources not shaking the WFS more than XXX - Athermalization. Lots of discussion about this topic. Decided that the best nominal approach is: AO optical system will work "just as well" (within spec) in all "dimensions of requirements" other than emmissivity, within the range 0 to -20 degrees Celsius - Tolerances ***ACTION*** (Reni): Would like to have nominal tolerances derived from the current optical design. - Motorized stages Need a spreadsheet of moving stages, accuracy of motion, whether moving during observation. ***ACTION*** (Don & Chris): Draft such a spreadsheet * Enclosure - Must enclose all AO optics, mounts, and allow for service access and possible upgrade/expansion (need to better define the later). - After some discussion with Sean and Jim, it seems prudent that the enclosure include all science instruments except OSIRIS. Sean mentioned d-NIRI & on-axis Visible and IR imagers. What about the narrow field IFU spectrograph (super OSIRIS)? - There will be no additional windows between AO relay and instruements, other than the windows into dewars of the instruments (driven by emmissivity requirements and surface counts) - Enclosure will maintain -20 degrees C operation. ***ACTION*** (Jim) Need to calculate/estimate total mass and time to cycle. - Humidity must be controlled so water does not condense on optics Optical design issues --------------------- * ***ACTION*** (Reni) - remaining from last meeting: Distrubute the optical design without the LGS WFS corrector plate. Also, analyze zenith and field dependent aberrations of the LGS without the plate and comment on the required dynamic range of the WFS * ***ACTION*** (Reni) - We made some nominal decisions about the 150 arcsec field of view 2 meetings ago. We need to document this decision, in particular, how far out can we point LGS as a function of zenith angle without vignetting their beams? how oversized should the K-mirror derotator be to accomodate the wide field cases and allow for flat-mirror polishing roll-off? Document in a memo or KAON. * Not clear why the single-level layout has packaging problem (K-mirror and 1st dichroic clearance), when the existing AO system does not. ***ACTION*** (Peter) - Post the current AO system Zemax description on the Twiki. * ***ACTION*** (Reni) - Reni will lead a discussion on a telecon this Friday. Topic will be walk-through of the single-layer optical design. Attendees: Reni, Viswa, Peter * ***ACTION*** (Don) - Write a Pro/Con list for choice of single-layer vs 2-layer optical layouts. Use this as input to a decision to be made at next Tuesday's meeting as to what optical design to carry forward Inputs needed from the Science Teams ------------------------------------ * Clarification on requirements that will drive LOWFS and NGS WFS to have to move during exposure (or exposure sets): - pupil-fixed mode - probably used in high-contrast on-axis imaging science. requires pupil fixed so TT stars will rotate on LOWFS field. how long and exposure, how accurate - non-siderial tracking - used in planet and asteroid imaging/spectroscopy. again, TT stars will rotate on LOWFS field. in NGS mode, the NGS will move with respect to the tracked science target. ***ACTION*** (Don) - field question to Claire, who will ask for feedback from the science team (most likely affecting Macintosh, Liu, Marchis). also, David LeMignant may have some comment. - interface issues: pupil-fixed and non-siderial will affect the architecure of the laser projection system. make sure that team is producing consistent requriements as well.