MCAO System Overview Brent Ellerbroek

MCAO May 24-25, 2001MCAO Preliminary Design Review2 Presentation Outline Primary subsystems and their characteristics –Laser System (LS) –Beam Transfer Optics (BTO) and Laser Launch Telescope (LLT) –Adaptive Optics Module (AOM) –MCAO Control System (MCAO CS) –Safe Aircraft Localization and Satellite Acquisition System (SALSA) System performance summary –Strehl –Strehl variability –Transmittance and Emissivity –Availability and Reliabilty

MCAO May 24-25, 2001MCAO Preliminary Design Review3 System Block Diagram LS SALSA LLT BTO AOM TCS/SCS/OCS/DHS OI WFS Science Inst. Laser/LGS NGS Science field (Boresight Calibration) Real-Time Control Functional Control MCAO CS Emergency halt Safety status Telescope pointing Observing sequences Data logging M2/M1 offloads Commands Status Fast tip/tilt Diagnostics Beam alignment WFS data DM/TTM commands Close/open loops Calibration functions

MCAO May 24-25, 2001MCAO Preliminary Design Review4 Laser and LGS Parameters Number of LGS5 LGS locations in Field(0,0) and (+/-30,+/-30) arc sec LGS signal at WFS125 PDE’s/cm 2 /sec (80 with regrets) LLT/BTO transmittance0.72/0.54 (laser on/off telescope) Laser power per LGS6-15 Watts Transmitted beam quality1.5 time diffraction limited RMS 1-axis beam jitter0.05 arc sec 1/e 2 beam diameter0.3 m LLT diameter, location0.45 m, behind secondary

MCAO May 24-25, 2001MCAO Preliminary Design Review5 BTO and LLT Schematic BS Pointing Array (PA) Top-End Ring Mirror KM LLT Center Section Top End Relay BDS Centering mirror (CM) Fast Steering Array Pointing mirror (PM) Centering Array (CA) X-Shaping Mirrors Periscope PM, CM PAC PA, CA PAC PA, CA PAC Pre Alignment Beam position & tilt LGS WFS Offload to KM, PM, CM PA, CA MCAO CS Closed-loop Alignment Control CC Shutter Boresight Calibration PS LLT cover Near- and far-field beam profiles /4 Plate Beam Dump Mirror /4 Plate Safety Shutter(SALSA) Miscellaneous Features

MCAO May 24-25, 2001MCAO Preliminary Design Review6 Science Path OAP1 OAP2 DM9 DM0 TTM DM4.5 SCIBS ADC NGS WFS Path OAP3 WFS WFSBS ADC LGS WFS Path Zoom Focus Lens LGS WFS Other Stuff Source Simulators Diagnostic WFS and Imaging Camera f/33.4 output Focal- and pupil plane locations preserved Standard optical bench design with space frame support In-plane packaging with adequate room for electronics Adaptive Optics Module

MCAO May 24-25, 2001MCAO Preliminary Design Review7 Baseline AO Component Parameters Number of DM’s3 DM conjugate ranges0.0, 4.5, 9.0 km Actuator pitchD/16, D/16, D/8 Number of WFS5 (LGS)3 (NGS) WFS order16 by 16Tip/tilt Pixels/subaperture4 by 4 (2 by 2 used)2 by 2 WFS pixel subtense1.0 arc sec0.5 arc sec WFS read noise6 electronsNone AOM throughput Detector QE WFS sampling rate800 Hz

MCAO May 24-25, 2001MCAO Preliminary Design Review8 Higher- order wave front control Tip/tilt (tt) and tilt aniso- Planatism (ta) control Real Time Control Block Diagram DM’s Null uncon- trolled modes TTM BTO tip/tilt LGS WFS’s NGS WFS’s + Integrator OIWFS Focus OIWFS Tip/tilt Focus adjustment Boresight adjustment M2 Offload M1/M2 Offload Tip/tilt Higher order tt ta

MCAO May 24-25, 2001MCAO Preliminary Design Review9 MCAO Control System Instrument Sequencer 1 Real Time Controller 3 AOM Component Controller 2 BTO/LLT Component Controller 4 SALSA Controller 5 Laser Controller 6 Laser hardware SALSA hardware BTO/LLT devices AOM devices AOM WFS/DM/TTM OCS commandOCS command status BTO Fast TT NGS probe offset DWFS Detector Controller 7 Controller commands/status commands/status WFS data/DM commands Pupil Alignment Observing data TCS pointing Oiwfs data M2 data M1 data seeing (CR angle Offset) CR angle TCS pointing

MCAO May 24-25, 2001MCAO Preliminary Design Review10 SALSA Elements Boresighted IR aircraft camera All-sky aircraft cameras Laser traffic control arbitration with local observatories Available radar feeds from air traffic control agencies (TBD) US Laser Clearinghouse interface (TBD)

MCAO May 24-25, 2001MCAO Preliminary Design Review11 Strehl Ratio Summary Zenith30 Degrees45 Degrees 0.85 microns microns microns microns Median Cerro Pachon seeing Mean Strehls over 1 arc minute square field Delivered Strehls at the detector Bright NGS Detailed error budgets in system modeling presentation

MCAO May 24-25, 2001MCAO Preliminary Design Review12 Performance with an Interim Laser Complement Initial MCAO laser configuration may be reduced for reasons of schedule or cost Growth path to the full laser system should be maintained One possible interim laser configuration: –60% nominal laser power, split into –1 full power and 4 half power laser guide stars Strehl Ratio Reduction Spectral band Center FoVEdge FoVCorner FoV J H K Expends Margin Sodium column density Laser power and beam quality

MCAO May 24-25, 2001MCAO Preliminary Design Review13 RMS Relative Strehl Nonuniformity LGS SignalWavelengthZenith30 Degrees45 Degrees 125 PDE’s/ cm 2 /sec 1.25  m  m  m PDE’s/ cm 2 /sec 1.25  m  m  m square arc min field, median Cerro Pachon seeing, bright NGS CoDR results Linear modeling Neglect effects of diffraction, 3-d LGS, DM-to-WFS misregisration, and other implementation error sources Initial simulation results including these effects see no significant change

MCAO May 24-25, 2001MCAO Preliminary Design Review14 Science Path Transmittance and Emissivity Wavelength1.00  m1.65  m2.20  m (emissivity) Per reflection Per air-glass I/F Beamsplitter (net) Overall, 9 reflections Overall, no ADC ADC air/glass I/F Overall, with ADC

MCAO May 24-25, 2001MCAO Preliminary Design Review15 System Availability Total Unavailable Time Laser Pulse Format Overhead ScenarioSatellite Loss PulsedCW (MCAO) Full setup + astrometry12.9%30%38% Partial setup + astrometry11.8%29%37% Partial setup, no astrometry9.1%27%35% Dwell on fixed object43.0%54%59% Astrometry adds extra setup time for plate scale determination CW laser penalty is due to LGS interference with thin cirrus Conventional LGS AO still feasible Includes system downtime of 10% Met with laser MTBF of 48 hours

MCAO May 24-25, 2001MCAO Preliminary Design Review16Summary Overall system architecture equivalent to conventional LGS AO Significant subsystem design progress since CoDR Delivered H-band Strehl of –Median CP seeing, zenith, bright NGS, average for a square 1 arc min field Useful performance for an interim laser system with 60% power –Strehl ratio reduction factors of to RMS relative Strehl nonuniformity of 0.04 in H Science path throughput of in H band, emissivity of in K System availability of 62-73% with queue scheduling

MCAO May 24-25, 2001MCAO Preliminary Design Review17 PDR Agenda Thursday, 5/ Welcome 0805 Project overview 0830 Science case 0930 Break 0945 System overview 1015 System modeling 1100 AO Module optics 1145 Lunch 1245 AO Module mechanics 1340 AO Module electronics 1400 Break 1415 Beam Transfer Optics 1510 Laser Launch Telescope 1545 Closed committee session 1800 Adjourn