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NFIRAOS Facility AO for the Thirty Meter Telescope

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NFIRAOS Facility AO for the Thirty Meter Telescope

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    1. TMT.AOS.PRE.05.047.REL03 1 NFIRAOS Facility AO for the Thirty Meter Telescope TMT Week Presentation September 2005 Glen Herriota et al. aNRC-HIA

    2. TMT.AOS.PRE.05.047.REL03 2 NFIRAOS side view

    3. TMT.AOS.PRE.05.047.REL03 3 Outline of Talk a. Requirements b. Design description c. Trade studies, options, technical issues, plan for resolution d. Performance of design e. Work plan and schedule to CoDR (May 2006) and Cost Review (Sept 2006) f. Cost targets discussion

    4. TMT.AOS.PRE.05.047.REL03 4 NEFARIOUS purposes NFIRAOS is pronounced “nefarious” Narrrow-field, InfraRed Adaptive Optics System SRD REQUIREMENTS: Facility Laser Guide star AO system feeding three near infrared instruments 0.8 – 5 mm (goal 0.6 – 5 mm) 50% sky coverage at galactic pole 133 nm rms wavefront error over 30 arcsecond field 95% throughput NFIRAOS must increase background < 15% vs sky + telescope Part of larger TMT AO program. cf Ellerbroek presentation.

    5. TMT.AOS.PRE.05.047.REL03 5 NFIRAOS feeds three Instruments IRIS Integral Field Unit Near IR Spectrograph 1.0 – 2.5 µm, specified to have 2” IFU and 10”x10” imager NIRES Near infrared Echelle Spectrograph 1 – 5 µm, high spectral resolution, narrow field. WIRC Wide field ( 30”) infrared camera, 1 – 5 µm

    6. TMT.AOS.PRE.05.047.REL03 6 NFIRAOS on Nasmyth

    7. TMT.AOS.PRE.05.047.REL03 7

    8. TMT.AOS.PRE.05.047.REL03 8 Baseline & Upgrade At first light, 133 nm wavefront error over a 30 arcsecond field is judged to be too ambitious and risky. Baseline NFIRAOS has 60x60 actuators on each of 2 DMs, 5 mm pitch, 9 micron stroke, correcting a 10 arcsecond field of view, with relaxed error budget. NFIRAOS will later be upgraded with More actuators on DM conjugate to 0 km (120x120) 2.5 mm pitch, but reduced stroke. 4x More subapertures on LGS WFS 4x Laser power vs. ~100 - 150 W baseline (2 or 3 lasers) Adaptive Secondary mirror as “woofer” giving more stroke.

    9. TMT.AOS.PRE.05.047.REL03 9 Baseline configuration

    10. TMT.AOS.PRE.05.047.REL03 10 Upgrade configuration

    11. TMT.AOS.PRE.05.047.REL03 11 Risk avoidance NFIRAOS will minimize dependence on unproven AO component technologies. It will operate with currently demonstrated laser pulse formats. Piezo stack deformable mirrors with actuator stroke and density similar to existing mirrors NGS and LGS detectors that are minimal extrapolations from current technology in terms of read noise, number of pixels and read rates. Plan to use radial format CCD with 4x16 pixel subarrays aligned with each subaperture’s elongated spot.

    12. TMT.AOS.PRE.05.047.REL03 12 Subsystem Decomposition

    13. TMT.AOS.PRE.05.047.REL03 13 Subsystem Decomposition Bench Cold Enclosure “Table” Optomechanics Components Control Electronics Software Electrical Enclosure Tip/Tilt Platform Deformable Mirrors Mirrors Drive Electronics & Power Supplies

    14. TMT.AOS.PRE.05.047.REL03 14 Science Optics Path

    15. TMT.AOS.PRE.05.047.REL03 15 NFIRAOS on Nasmyth

    16. TMT.AOS.PRE.05.047.REL03 16 Interfaces to Instruments Interface is mounting surface for Instrument’s rotary bearing ~ 1 meter back focal distance for each Identical optical feed & mechanical interface on all three ports Two vertical-axis ports for IRIS, NIRES Constant gravity environment One horizontal-axis port for WIRC External Rotation bearing or internal rotating pupil relay Instruments responsible for NGS tip/tilt/focus sensing Field derotation bearings (if any) Atmospheric dispersion compensation (if any) Cable wraps (if instrument rotates)

    17. TMT.AOS.PRE.05.047.REL03 17 Back Focal Dist (BFD) All 3 ports same 500 mm [past mounting face] (all 3 ports) 250-500 mm “snouts” may be allowed on all ports 1 m total

    18. TMT.AOS.PRE.05.047.REL03 18 Lower Instrument in hole on Nasmyth

    19. TMT.AOS.PRE.05.047.REL03 19 Volume: 8.2 x 4.2 x 2.5 meters Incoming optic axis 2 m above Nasmyth Outgoing optic axis (downward) Focuses at Nasmyth elevation Mass: (very preliminary estimates) NFIRAOS: 10 – 15 tonnes WIRC: 10 tonnes IRIS: 4 tonnes NIRES: 8 tonnes

    20. TMT.AOS.PRE.05.047.REL03 20 Natural Guide Star IR WFSs in instruments All client instruments will have choice of Near-Infrared Natural star WFSs Either 3 tip/tilt NIR sensors (likely best performance, but less convenient) Or a single 2x2 tip/tilt/focus/astigmatism sensor (may confuse variable Sodium Altitude with plate scale) Fed by a 2 arcminute “technical field”, image sharpened by MCAO operation giving Strehl > 0.1 over technical field.

    21. TMT.AOS.PRE.05.047.REL03 21 Instrument interface trades studies Feeding instruments via large positive back focal distance Reducing footprint on Nasmyth (hole in floor) Field Rotation Reducing emissivity (K mirror studies.) Constant gravity vector for >1 instrument Truth WFS and Acquisition camera in NFIRAOS not instruments. NGS TTF sensors ok on-axis. IR NGS WFS in instrument vs. visible TT WFSs in NFIRAOS Horizontal vs vertical Bench Trolleys

    22. TMT.AOS.PRE.05.047.REL03 22

    23. TMT.AOS.PRE.05.047.REL03 23 High Order Error Budget

    24. TMT.AOS.PRE.05.047.REL03 24 Error Budget summaries: telescope residual = SRD spec or RFP spec

    25. TMT.AOS.PRE.05.047.REL03 25 Tip – Tilt Error budget

    26. TMT.AOS.PRE.05.047.REL03 26 Error Budget Supporting work uncorrectable telescope aberrations LGS asterism selection tip/tilt correction Range to the Na Layer LGS WFS linearity, bias, and sensitivity to noise NCPA calibration (non-common-path aberration) Altitude of conjugation trade study ? DM @ h= 12 km Note that the tip/tilt error budgets are based upon sky coverage simulations

    27. TMT.AOS.PRE.05.047.REL03 27 Sky Coverage Calculated by Richard Clare, TMT. Includes servo lag (sample rate and tip-tilt mirror performance), photon noise, read noise, windshake, turbulence Spagna sky model, J-band stellar density image sharpened IR NGS WFS Still to include: tradeoff with Na altitude focusing.

    28. TMT.AOS.PRE.05.047.REL03 28 Defeating Windshake with DM/TT woofer-tweeter

    29. TMT.AOS.PRE.05.047.REL03 29 Sodium Range Focusing Temporal Errors Time History of Sodium Altitude, and power spectrum. Residual WFE ~46 nm rms = f(Natural GS sky coverage) Wide variability among 3 nights’ data so far.

    30. TMT.AOS.PRE.05.047.REL03 30 Non-Common-Path (NCP) Error Budget

    31. TMT.AOS.PRE.05.047.REL03 31

    32. TMT.AOS.PRE.05.047.REL03 32 Optical Design of LGS WFS

    33. TMT.AOS.PRE.05.047.REL03 33 Radial CCD Pixel Geometry for Laser Guidestars

    34. TMT.AOS.PRE.05.047.REL03 34 LGS Spot Elongation mitigation Luc Gilles’ matched filter simulations. Right figure is systematic error using “Old” sodium layer profile, with respect to a perfectly linear transfer function between Wavefront Tilt and Measurement.

    35. TMT.AOS.PRE.05.047.REL03 35 LGS WFS simulation parameters include 0.5 arc second pixels, 0 or 5 read noise electrons, 1000 photodetection events per subaperture a 30 cm laser beam projected from a 50 cm launch telescope, 50 cm LGS WFS subapertures.

    36. TMT.AOS.PRE.05.047.REL03 36 Number of LGSs

    37. TMT.AOS.PRE.05.047.REL03 37 Emissivity & Throughput Top Level Science requirement on added background. NFIRAOS must increase background < 15% compared with sky and bare 3-mirror TMT telescope, assumed to be at 0 Celsius. Given the estimated emissivity of NFIRAOS optics and entrance window.. NFIRAOS temperature must be about -33 Celsius.

    38. TMT.AOS.PRE.05.047.REL03 38

    39. TMT.AOS.PRE.05.047.REL03 39 Intimate connections with Observatory Control ensure observing efficiency

    40. TMT.AOS.PRE.05.047.REL03 40 AO Sequencer Diagrams Corrine Boyer’s sequence of events to make it all run smoothly

    41. TMT.AOS.PRE.05.047.REL03 41 Important Dates TMT “TMT Week:” September 26-30, 2005 Conceptual Design Review: May 8-12, 2006 NFIRAOS Study May 26, 2005 Kickoff meeting July 15, 2005 Draft Initial OCDD and FPRD Aug 02, 2005 Interim Review Aug 26, 2005 Interim Review Response Sept 23, 2005 Initial OCDD and FPRD Oct 18, 2005 Conceptual Design Report Outline Nov 9, 2005 Mid-Course Review Feb 1, 2006 Conceptual Design Report and Management Plan Mar 1, 2006 Conceptual Design Review Apr 14, 2006 Revised Design Report and Management Plan

    42. TMT.AOS.PRE.05.047.REL03 42

    43. TMT.AOS.PRE.05.047.REL03 43 Workscope Schedule Optomech, Interfaces, S/W, Modeling

    44. TMT.AOS.PRE.05.047.REL03 44 Cost Targets by WBS – construction phase. WBS cost targets $K Does not include Preliminary Design during DDP Preliminary design burn rate estimated at 3 FTE for 1.6 years ~$500K

    45. TMT.AOS.PRE.05.047.REL03 45 Key Tasks During PDR phase: 1.  Detailing interfaces with the Nasmyth platform, instruments, and control systems 2.  Detailing interfaces and requirements for components including LGS WFS detectors, deformable mirrors, and the RTC 3.  Design and analysis of key components/aspects of the system where cost/technical risk remain, including:  the LGS WFS, coatings, FEA analysis of flexure and thermal effects, etc. 4.  A more typical PDR level of design for the remainder of NFIRAOS—finding the right balance will be important.

    46. TMT.AOS.PRE.05.047.REL03 46 Outstanding TMT-wide issues impacting NFIRAOS Quantitative SRD requirement for “near diffraction limited performance” for 50% sky coverage needed. Need SRD requirements for NFIRAOS NGS WFS mode (e.g. guide star wavelength, sky coverage probability, image quality) Need observatory Operational Concepts document OCDD Need Defined standards for TMT environmental conditions Wavelength, flat field and spectral line calibrators More detailed Telescope wavefront error budget (especially temporal & spatial power spectra of dephasing, pointing, focusing) … in particular, a credible windshake model is vital

    47. TMT.AOS.PRE.05.047.REL03 47 Outstanding Issues Print-through of mirror supports, and edge discontinuities aliasing into WFS. Much more data needed on temporal variability of sodium layer structure, altitude, density. Much more data needed on winds aloft, (temporal frequencies of turbulence.) SRD throughput requirement is nearly impossible (95% spec. vs expected 79%) Space on Nasmyth needed by NFIRAOS approaches elevation axis ( David C.’s layout omits instrument supports and service access)

    48. TMT.AOS.PRE.05.047.REL03 48 The Bottom Line The first-light baseline NFIRAOS will get diffraction limited images, and do the Astronomy envisaged by the Science Requirements Document, but just take a little more integration time.

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