Keck NGAO Proposal: Technical Overview Presenters: Adkins, Dekany, Gavel, Wizinowich Other Contributors: Bauman, Bell, Bouchez, Flicker, Macintosh, Neyman, Velur SSC Meeting June 21, 2006 1 Presentation Sequence 1. Introduction (PW, 5 min) • • 2. 3. 4. 5. 6. 7. System Design Process Requirements Flow Down Point Design Overview (PW, 10 min) Performance Budgets (RD, 30 min) Point Design Feasibility (DG, 15 min) Point Design Product Structure (PW, 10 min) Point Design Instruments (SA, 10 min) Summary (PW, 1 min) 2 PW 1. Introduction: System Design Process • Starting point needed to support development of science cases & requirements • One pass made through the system design process loop to provide this starting point: Science Requirements Technical Implications Initial Concept Performance Assessment Repeat as required while making improvements & balancing trade offs • Resulted in an initial architecture or “point design” 3 PW 1. Introduction: Science Requirements Flow Down • Primary functions to meet science requirements: • • • • • • • Wavelength coverage from ~0.6 to 5.3 mm Near diffraction-limited correction in near-IR Modest Strehl in visible (0.6-1.0 mm) High sky coverage Multiplex observations over 2 arcmin field of regard High throughput & low thermal near-IR background Calibration & control of AO systematic effects 4 PW 2. Point Design Overview • • • • Architecture LGS Asterism Opto-mechanical Layout Real-time System 5 PW 2. Point Design: Architecture • This is only a starting point to demonstrate feasibility of meeting the requirements (& for initial cost estimation purposes) • Design will evolve during the system design phase 6 PW 2. Point Design: Elements Components/features needed to fulfill requirements: • Multiple LGS (Strehl & sky coverage) • Measurement of 3-D turbulence structure (Sky coverage, Strehl, calibration) • Multiple AO corrector elements (Strehl, sky coverage) • ~ 1000 actuator (Strehl) • 2 arcmin field of regard (Sky coverage) • Multiple near-IR low-order NGS wavefront sensors with AO correction (Sky coverage) • Minimize number of optics (SNR, emissivity) • Cooling of AO system (emissivity) 7 PW 2. Point Design: LGS Asterism • 5 LGS (cone effect) • ~ 30W each • variable radius (high on-axis Strehl vs wider field correction) • 3 corrected tip-tilt stars for good sky coverage • Wavefront sensors • LGS: Shack-Hartman • NGS: MOAO correction with MEMS, near-IR, pyramid WFS for tip/tilt/focus/astig • NGS: Slow S-H WFS for LGS calibration 8 PW 2. Point Design: Optical Layout Cooled AO Enclosure (-15 C) Basic AO Relay (MOAO or MCAO) 1.5 m Nasmyth Platform Outline 9 PW 2. Point Design: Opto-Mechanical Layout 10 PW 2. Point Design: Dichroic Switchyard Demonstrates a Feasible Switchyard Point Design 11 PW 2. Point Design: Real-time Architecture • Massively Parallel Processing pipeline architecture Wavefront Wavefront Sensors Wavefront Sensors Wavefront Sensors Sensors Image Image Processors Image Processors Image Processors Processors Tomography Unit Centroid algorithm Cn2 profile r0, guidstar brightness, Guidestar position Wavefront Wavefront Wavefront Sensors DM Sensors Sensors Projection DM conjugate altitude Image Image Processors Image Processors DM Processors Fit Image Image Processors Image Processors Deformable Processors Mirrors Actuator influence function • Power & space requirements are reasonable • 10-20 boards with 50-100 FPGA chips, <2 kW total power estimated 12 PW 3. Performance Budgets • • • • Wavefront Error (WFE) Budget Emissivity Companion Sensitivity (high contrast performance) The following performance budgets will not be presented: • • • • • • • Throughput Point Source Sensitivity Photometry Astrometry Polarization Observing Efficiency Up-time 13 RD 3. Wavefront Error Budget Wavefront error budgets developed for several scenarios using measured Mauna Kea site conditions • LGS • KBO Astrometry – Narrow field • Galactic Center – Low elevation • GOODS-N - Sky coverage • “Best possible” Narrow-field • Current Keck II LGS – Cross check • NGS • Io – Bright object NGAO point design does all this science! • This iterative approach will continue during the system design phase 14 RD NGAO Performance Summary by Observing Scenario Keck II LGS System delivers 360 nm 15 RD NGAO Error Budget High-Order Errors 121 nm Atmosphere 93 nm Based on Lick, Palomar & Keck experience Systematics 0.71 mas (9 nm) Atmosphere 3.81 mas (50 nm) 0 nm 20 nm 28 nm Tilt Measurement Tilt Bandwidth Tilt Anisoplanatism Res. Centroid Anisoplanatism Res. Atmospheric Dispersion Res. Telescope Pointing Jitter 45 nm Atmospheric Fitting 59 nm Bandwidth 33 nm High-order Measurement 41 nm LGS Tomography 29 nm Asterism Deformation 22 nm Multispectral 25 nm Science Scintillation 15 nm WFS Scintillation 10 nm Angular Aniosplanatism Tip-Tilt Errors 3.88 mas (51 nm) Calibration 76 nm 50 nm KBO imaging scenario Total Equivalent WFE 131 nm Science Inst. Mechanical Drift Long-Exposure Field Rotation Go-to Control 0 nm Res. Na Layer Focus High-Order Aliasing 3 nm 20 nm 2.39 mas 1.68 mas 0.00 mas 1.99 mas 0.95 mas 1.05 mas 0.50 mas 0.50 mas 17 nm DM Finite Stroke Hysteresis Drive Digitization Static WFS Zero-point Calibration Dynamic WFS Zero-point Calibration Unc. AO Sys. Aberrations Unc. Instrument Aberrations DM-to-Lenslet Misregistration Unc. Static Telescope Aberrations Unc. Dynamic Telescope Aberrations 25 nm 13 nm 3 nm 25 nm 15 nm 20 nm 25 nm 13 nm 44 nm 23 nm 16 RD NGAO Error Budget Example: KBO imaging scenario Engineering Tool Key: green = allocation All others supported by detailed calculations 17 Error Budget PSFs (Narrow field) V R I J H K 135 nm + 8 mas + 15 mas + 25 mas Used by Science Teams for Simulations 18 RD NGAO Error Budget (Narrow-field) NGAO point design Narrow-field science target performance 1.00 H-band Strehl ratio 0.90 0.80 0.70 1% sky fraction 0.60 10% sky fraction 0.50 30% sky fraction 0.40 99% sky fraction 0.30 0.20 0.10 0.00 10 12 14 16 18 20 Science target brightness (mH) Almost every 2MASS object can be observed with high Strehl by NGAO! 19 RD NGAO KII LGS NGAO H-band Strehl improved by 5x in median conditions Strehl > 40% for seeing < 1” rms Wavefront Error (nm) NGAO Improves Performance over Wide Range of Conditions 20 RD Variable LGS Asterism Size supports Good Sky Coverage Use of sharpened tip-tilt stars is key to sky coverage Tip-tilt sensor patrol field is a driver for good performance over large sky fraction Up to 4-5’ may be beneficial Cannot be done with current AO system (field = 2’) 21 RD Cooled AO System (-15 C) Lowers Background Below Sky in K-band Sky + Tel background Component Emissivity Temp. 0.00075 273 0.02 258 Rotator mirrors (3) 0.03 x 3 “ OAPs (2) 0.03 x 2 “ 0.03 “ 0.0005 “ 0.05 “ 0.0015 x 2 “ 0.02 x 2 “ IR dichroic (reflection) 0.05 “ Camera CaF2 window 0.0005 “ CaF2 window (bulk) CaF2 window (surface) AO background K-band DM IR/vis dichroic (bulk) IF/vis dichroic (surface) IR ADC (bulk) IR ADC (surface) Total = L-band 0.37 M-band 22 RD 3. Companion Sensitivity: NGAO can achieve 10 mag contrast at 0.5” • High-contrast sensitivity goes up rapidly with high Strehl • Limited by AO + atmosphere, plus static internal & external wavefront errors NGAO can exceed current AO contrast by an order of magnitude 23 RD 4. Point Design Feasibility: Technology NGAO wavefront control presents a significant increase in the level of technical challenge over the present AO system: • Multiple laser beacons • Multiple wavefront sensors: LGS & NIR Tip-Tilt • Tomographic reconstruction of a 3-D volume of turbulence, rather than just one 2-D phase • Multiple Deformable mirrors, in series (woofer-tweeter) & parallel (MOAO) • Higher bandwidth – need to keep up with the atmosphere 24 DG 4. Point Design Feasibility: Unique architecture (mix of MCAO & MOAO) Laser Beacons Key Enabling Technologies MEMS DMs Dichroic Deformable Mirror Science Instruments & NIR Tip-tilt Sensors Tomography Computer MEMS DMs LGS Wavefront Sensors 25 DG 4. Point Design Feasibility: Lasers Laser situation much improved in last few years Demonstrated options include: • LM/CT 14W mode-locked CW laser delivered to Gemini • 50 W Gemini-S laser is our notional point design choice • SOR 50W mode-locked CW laser Potential future options include: • Fiber Raman laser (ESO) • Fiber sum frequency laser (LLNL) • Waveguide sum frequency laser with programmable pulse format (LM/CT) • Mode locked sum frequency crystal (Palomar) • Coherent DFB semiconductor laser (Telaris) Note: Required power depends on sodium coupling efficiency 26 DG 4. Feasibility: MEMS Deformable Mirrors • MEMS deformable mirrors: • For IR tip-tilt correction; in deployable IFUs • Working beautifully in UCSC lab (1000 actuators) • Funded by a consortium (up through 4000 actuators) • Sky demonstration at Lick within the year LGS, astro & NGS light • Open-loop AO: • For deployable IFUs • Already demonstrated in field tests along several-km horizontal path • Tests in progress at Lab for Adaptive Optics; working well Wavefront Sensor MEMS AO (NGS+IFU) 27 DG 4. Necessary MEMS Technology Available Point Design MEMS Test Beam Beam Splitter Reference Beam Hartmann Sensor Camera Interferometer Camera Far Field Camera Point Diffraction Interferometer measures to 200pm rms 32x32 actuator MEMS DM (Boston Micromachines Corp) Top mirror surface Membrane Electrode MEMS electrostatic actuator 28 DG 4. Technical risk reduction effort will use lab and sky test results • Tomography: • In lab: Lab for AO + 3 others (past, present) • Gemini-S MCAO (next year) • Solar MCAO (in progress now at two different telescopes) • VLT Advanced AO Demonstrator (next year) • Palomar & MMT with multiple wavefront sensors (in progress now) • Visible-wavelength AO: • Demonstrated: Air Force & Mt. Wilson • Planned: Palomar, Lick 29 DG 5. Point Design Product Structure • • • • AO system Laser system Operations tools Science Instruments 30 PW 5. Point Design: AO System 31 PW 5. Point Design: AO System Subsystem Key Features Motion Control Discussion 5 Shack-Hartmann WFSs Motion to register lenslets. 62x62 offers a graceful fallback from 48x48. 31x31 for low sodium return case 48x48 subaperture baseline 62x62 & 31x31 subaperture option LGS Wavefront Sensors (WFS) 4x4 pixels/subaperture 256x256 pixel CCD with 1e read-noise at 1 kHz readout rate Center WFS located on-axis Four WFS translate radially from 1050". Also need z-adjustment for field curvature. x,y control for 5 lenslets for DM registration & changing lenslets x,y control for assembly Tracking to stay conjugate to Na layer CCID-56 under development 4 10 2 1 For dispersion correction 32 PW 5. Point Design: Trade Studies Sample Key Trade Studies: • Alternate optical relay designs • MOAO versus MCAO (e.g., crowded fields) • Iteration of science field of regard & IFU multiplexing • Performance impact/mitigation of Rayleigh scatter • High contrast performance requirements & performance • Upgrade of current system to NGAO • Background requirement & how to achieve • Best way to support interferometer operations 42 technical trade studies documented to date (24 high priority) Science Requirements Technical Implications Initial Concept Performance Assessment Repeat as required while making improvements & balancing trade offs 33 PW 5. Point Design: Laser System 34 PW 5. Point Design: Operations Tools 35 PW 6. NGAO Notional Instrumentation • Large parameter space, specialized instruments • • • • • Simpler instruments Emphasize diffraction limited image quality Imaging Spectroscopy Nasmyth platform operation • • Single axis of rotation Up looking or down looking 36 SA 6. NGAO Instrumentation • Design notions: • Simple imagers and IFU spectroscopy • Optical and thermal considerations define coverage breakpoints • Available detectors or evolutionary developments • Hawaii 2RG -> Hawaii 4RG • LBNL 2k x 4k -> 4k x 4k • Heritage software (OSIRIS/MOSFIRE) closely integrated with AO system • Emphasize observing efficiency 37 SA 6. NGAO Instrument Priorities • Science case priorities: • Convolved with first light needs, development timelines: 38 SA 6. NGAO Instrumentation 1.0 H 0.9 Ca II IRT 0.8 H K } Deployable near-IR IFU Near-IR imager Single object near-IR IFU 0.7 Strehl ratio J NGAO 0.6 Visible IFU Deployable near-IR IFU Near-IR imager imager Single object near-IR IFU 0.5 0.4 0.3 0.2 IFU Visible imager 0.1 0.0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Wavelength, nm 39 6. Imagers Instrument Wavelength coverage (µm) FOV Sampling Visible Imager 0.6 to 1.1 20” x 20” Nyquist (6 mas) Near-IR Imager 1.0 to 2.45 20” x 20” Nyquist (10 mas) Thermal near-IR Imager (L & M-band Imager) 3 to 5.3 25” x 25” Nyquist (25 mas) • Filter wheels • Coronagraph (near-IR) • Possibly grisms for R ~100 to 400 spectroscopy • Polarimeters (visible and near-IR) 40 6. Spectrometers Instrument Near-IR deployable IFU (6 units) Wavelength coverage (µm) 1.0 to 2.45 Sampling (Spaxels) Spectral Resolution R ~4,000 30 x 34 Near-IR single object IFU 1.0 to 2.45 80 x 50 Visible single object IFU 0.6 to 1.1 60 x 60 R ~4,000 R ~3,000 • Near-IR deployable IFU 100 mas spaxel scale • Single object IFUs may have additional spaxel scales • Single object IFUs may have broad band and narrow band modes • We will study the possibility that OSIRIS might meet many of the needs for the near-IR single object IFU 41 Technical Summary • NGAO point design demonstrates feasibility of meeting science requirements • Next technical steps understood • Ready to proceed to system design phase 42 PW 43 1. Requirements: Observatory (Existing infrastructure influences design) • Facility • Location – Keck II left Nasmyth • Pupil – entire Keck pupil • Secondary mirror – Use existing f/15 • Instruments • OSIRIS & NIRC2 • Interferometer • OHANA • Operational • • • • • • Facility-class Operations transition review AO downtime - < 6 months? Telescope downtime - < 5 days? Mauna Kea laser projection requirements Operate under normal environmental conditions 44 CN 2. Point Design: Architecture Optimized for high Strehl on-axis and wide field (lower Strehl) • 5 LGS atmospheric tomography • Variable radius • Basic AO relay • Image derotator • Pair of OAPs with pupil conjugate to DM (dact = 0.177 m) • Option to use OAP1 as 2nd DM in a MCAO system (conjugate to 9 km) • Window to cooled AO enclosure acts as a field lens • Dichroic switchyard to divide light amongst: • LGS mode: • 5x LGS Shack-Hartmann (S-H) wavefront sensors (WFS) (ds = 0.25 m) • 3x NGS IR tip/tilt/focus/astigmatism pyramid sensors with 32x32 MEMs • 1x NGS visible slow S-H WFS for LGS calibration • NGS mode: 1x visible S-H WFS • Science instruments (near-IR & visible) 45 PW 2. Point Design: Subapertures & Actuators Actuator spacing chosen to minimize segment errors. Subaperture size chosen to balance measurement error with laser power. Risk: Lenslets not registered to actuators. Fallback is a lenslet array matching actuator spacing. 46 PW 3. Mauna Kea Site Conditions Median seeing conditions at = 0.5 mm: • r0 = 18 cm. = 3 cm. L0 = 75 m. • 0 = 2.5 arcsec • fG = 39 Hz • L0 = 75 m • Cn2 profile: Median sodium density = 4E9 atoms/cm2 Altitude (km) Fractional Cn2 Wind Speed (m/s) 0.0 0.471 6.7 2.1 0.184 13.9 4.1 0.107 20.8 6.5 0.085 29.0 9.0 0.038 29.0 12.0 0.093 29.0 14.8 0.023 29.0 47 RD 3. Input Assumption - Site Data Mauna Kea median seeing conditions at = 0.5 mm: • r0 = 18 cm. = 3 cm. L0 = 75 m. • 0 = 2.5 arcsec • fG = 39 Hz • L0 = 75 m • Cn2 profile from data Altitude (km) Fractional Cn2 Wind Speed (m/s) 0.0 0.471 6.7 2.1 0.184 13.9 4.1 0.107 20.8 6.5 0.085 29.0 9.0 0.038 29.0 12.0 0.093 29.0 14.8 0.023 29.0 Sodium column density Median sodium density = 4E9 atoms/cm2 48 RD NGAO Error Budget Io Scenario 49 Color key: blue/green = allocation NGAO Error Budget Galactic Center Scenario 50 Color key: blue/green = allocation NGAO Error Budget GOODS-N Scenario 51 Color key: blue/green = allocation NGAO Error Budget “Best Possible” Narrow-Field Scenario 52 Color key: blue/green = allocation Keck II LGS Error Budget Narrow-Field Scenario (1% Sky Fraction) 53 Color key: blue/green = allocation Keck II LGS Error Budget Narrow-Field Scenario (20% Sky Fraction) (Requires acquisition of tip/tilt star at angular offset of 49” from science target) 54 Color key: blue/green = allocation Current Keck II LGS Error Budget (target-guiding scenario) Current Keck LGS (Guiding on science target, TT from STRAP) 0.25 K-Strehl 0.20 0.15 r0 = 18cm, w = 10 m/s r0 = 25cm, w = 5 m/s 0.10 0.05 0.00 10 12 14 16 18 20 22 24 Strap TT guide star magnitude Assumes: tip/tilt information from target itself, b=30, Na laser power = 20W LP spigot, Na = 4e9 atoms/cm2, exposure time = 10 sec, 20x20 SH EEV39 HOWFS, STRAP tip/tilt sensor, optimal HO and LO WFS integration times 55 NGAO Improves Stability over Wide Range of Conditions Time Evolution of NGAO and Keck II LGS performance for 20% sky fraction 0.90 Mean = 0.65 /Mean = 16% 0.80 H-band Strehl Ratio 0.70 0.60 0.50 NGAO Keck II LGS 0.40 0.30 0.20 Mean = 0.12 /Mean = 67% 0.10 507 488 468 449 429 410 390 371 351 332 312 293 273 254 234 215 195 176 156 137 117 97. 78 58. 39 19. 0 0.00 Time (minutes) Performance estimate of NGAO and Keck II LGS based on actual MASS/DIMM measurements (from Palomar) scaled to median r0 = 18cm 56 NGAO Error Budget (GOODS-N spectroscopy scenario) 57 RD D-IFU has Excellent Encircled Energy & Sky Coverage 58 RD Variable Asterism Radius Improves NGAO Performance With fixed 30” radius quincunx Mean = 0.43 Sigma = 0.19 With variable (optimized) quincunx Mean = 0.48 Sigma = 0.20 Performance Histograms from Statistical Model (r0 (log-normal, mean=18cm, sigma=4cm), tip/tilt brightness (Gauss, mean = 18, sigma = 4), tip/tilt dist (Gauss, mean = 45, sigma = 15) In all cases LGS and tip/tilt integration times are optimized for each realization. 59 RD NGAO Point Source Sensitivity Estimates Point source limiting magnitude (5 in 1 hr of integration) Zero-point (magnitudes) Sky (mag. arcsec-2) 105 nm 140 nm 195nm 330nm V 27.09 21.3 29.9 28.7 27.6 27.6 R 27.10 20.4 29.9 29.0 27.1 27.1 I 26.98 19.3 29.6 29.0 27.7 26.5 J 25.47 16.1 27.3 27.0 26.5 24.4 H 25.51 13.8 26.0 25.8 25.6 24.4 K’ 24.84 13.5 25.3 25.2 25.0 24.4 L’ 23.60 4.31 19.5 19.5 19.4 19.2 Ms 21.42 1.10 16.6 16.6 16.5 16.4 Filter The measured performance of LRIS and NIRC2 are faithfully used as the basis of these calculations, with only the pixel scale varied to sample the diffraction limit at each wavelength. The expected transmission and thermal background of the NGAO system (cooled to 258K) are included, as is the effect of varying optimum photometric aperture from diffraction-limited to seeing-limited in the low Strehl limit. 60 3. Throughput • Throughput requirement to science instrument (telescope + AO) • ≥ 70% at 0.6-5.5 mm • Point design -> 77% w/o IR ADC • Point design -> 51% w/ IR ADC • ≥ 60% at 5.5-14 mm 61 RD 3. Emissivity Sky background AO background NGAO cooled to 258 K (red) compared to that due to the sky plus telescope (black), assuming a total telescope emissivity of 0.10 63 RD 3. Companion Sensitivity: careful consideration of telescope effects essential Can be mitigated by advanced wavefront sensing & coronagraph or improved segment figure (warping & dimples) 64 RD Point Source Limiting Magnitude (5 sigma in 1 hr) 3. Point Source Sensitivities Filter Zeropoint mag Sky (mag*arc sec-2) V R I J H K’ L’ Ms 27.09 27.1 26.98 25.47 25.51 24.84 23.6 21.42 21.3 20.4 19.3 16.1 13.8 13.5 4.31 1.1 Point source limiting magnitude (5 in 1 hr of integration) 105 nm 140 nm 195nm 330nm 28.7 27.6 29.9 27.6 29 27.1 29.9 27.1 29 27.7 29.6 26.5 27 26.5 27.3 24.4 25.8 25.6 26 24.4 25.2 25 25.3 24.4 19.5 19.4 19.5 19.2 16.6 16.5 16.6 16.4 30 Sky (mag*arcsec-2) 105 nm 28 140 nm 195 nm 26 330 nm 24 22 20 18 16 0.5 1.5 2.5 3.5 Wavelength (microns) 4.5 65 RD 3. Photometry Photometric accuracy requirement: • 0.01 mag 0.7-2.5 mm for <5” from H<16 NGS • 0.02 mag 0.7-3.5 mm for <10” from H<16 NGS • 0.05 mag at 0.9-2.5 mm for < 20” off-axis & 20% sky coverage • 0.1 mag at 0.7-2.5 mm for < 20” off-axis & 20% sky coverage • Not yet evaluated • Appropriate PSFs with field dependence produced • Next step: evaluate sample science images, produced with PSFs, to determine accuracy 66 PW 3. Astrometry Astrometric accuracy requirement: • 0.1 mas for Galactic Center • 10 mas at 0.7-3.5 mm for 30% sky coverage • 50 mas at 0.7-3.5 mm for 50% sky coverage • Not yet evaluated • Appropriate PSFs with field dependence produced • Next step: evaluate sample science images, produced with PSFs, to determine accuracy • GC: Keck II LGS AO approaching 0.25 mas • Astrometric accuracy ~ FWHM/SNR • Strehl improvement from 30 to 75% at K 2.5x improvement • Many issues could prevent astrometry at these levels (e.g., field dependent stability) 67 PW 4. Feasibility: Low Noise Wavefront Sensing CCD • Project spearheaded by Sean Adkins, Jerry Nelson, Jim Beletic, in collaboration with MIT Lincoln Labs and Lick Observatory CCD lab • Recent lab measurements: < 1 e- read noise • Radial pixel layout design accommodates elongated LGS spot Wavefront sensor subapertures shown with respect to telescope primary mirror Sodium Layer LGS spot Serial Register LGS spots in each subaperture Video output Pixel array for corresponding LGS spot Clock Lines Centrally Projected Laser 68 DG 4. Today’s FPGA Technology Meets Realtime Processing Requirements Wavefront Wavefront Sensors Wavefront Sensors Wavefront Sensors Sensors Image Image Processors Image Processors Image Processors Processors Tomography Unit Centroid algorithm Cn2 profile r0, guidstar brightness, Guidestar position Wavefront Wavefront Wavefront Sensors DM Sensors Sensors Projection DM conjugate altitude Image Image Processors Image Processors DM Processors Fit Image Image Processors Image Processors Deformable Processors Mirrors Actuator influence function • Very fast – can keep up with real-time reconstructor requirements (1kHz frame rate) • Implemented with massive parallel processing • All the algorithms are “parallelizable” • Today’s FPGA technology can do it with margin • Power and space requirements are reasonable • 10-20 boards with 50-100 FPGA chips, <2 kW total power estimated 69 DG MEMS Flattening: < 1 nm rms Before • • After RMS WFE RMS WFE in control band Lowpass Before 148.1 nm 144.1 nm After 12.8 nm 0.54 nm 70 DG Correction of Kolmogorov Test Plate With spatially filtered Hartmann WFS Power Spectrum 71 DG MEMS Open-Loop Control Plate, membrane, and capacitor model predicts forces and displacements of the top mirror surface Open loop control to 30 nm wavefront has been demonstrated in the lab. We expect to get better than this with calibration refinement. 72 DG Difficulties upgrading Keck II LGS to NGAO • General • Large majority of NGAO requires new subsystems (lasers, wavefront sensors, real-time software, control software, etc.) • Sum of • A major retrofit to c. 1995 components imposes many interface constraints and limits component choices • Component aging • Optical bench • Imposes limit on sky coverage • Passes only 2 arc min; NGAO would prefer 4-5’ • Insufficient space for multiple wavefront sensors (LGS or NGS) • Integration & Testing • NGAO will require significant lab testing and characterization • Operations impact • Upgrade would significantly interrupt science operations 73 6. System Design Technical Approach • Coordination between science requirements & AO development • Key personnel: Project manager & Project scientist • Builds on existing science & technical teams from NGAO proposal • Facilitates rapid iteration of design • Track overall performance metrics • • • • • • Sky coverage wavefront error photometry astrometry emissivity imaging & spectroscopic sensitivities • Define & control interfaces between AO, instruments & facility 74 PW 6. System Design Technical Approach • Key Trade studies: • Evaluate the performance impact of Rayleigh scatter on NGAO performance & consider various mitigation methods such as a pulsed laser. • Determine the relative cost versus benefits of an adaptive secondary mirror implementation • Consider the cost/benefits of stand-alone tip/tilt mirror as opposed to mounting another necessary optic on the tip/tilt stage • Consider cost/benefits of different options for achieving the NGAO science goals in the K through M-Bands. • Determine the best way to support Keck-Keck interferometer operations when NGAO is operational. 75 PW