mcao system overview brent ellerbroek. mcao may 24-25, 2001mcao preliminary design review2...

MCAOMCAO

System OverviewSystem Overview

Brent Ellerbroek

May 24-25, 2001 MCAO Preliminary Design Review

2

MCAOMCAO

Presentation OutlinePresentation 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


3

MCAOMCAO

System Block DiagramSystem Block Diagram

LS

SALSA

LLT

BTO

AOM

TCS/SCS/OCS/DHS

OIWFS

ScienceInst.

Laser/LGSNGS

Science field

(BoresightCalibration)

Real-TimeControl

FunctionalControl

MCAO CS

Emergencyhalt

Safety status

Telescope pointing

Observing sequences

Data logging

M2/M1offloads

CommandsStatus

Fast tip/tilt

Diagnostics

Beamalignment

WFS data

DM/TTMcommands

Close/open loops

Calibration functions


4

MCAOMCAO

Laser and LGS ParametersLaser and LGS Parameters

Number of LGS 5

LGS locations in Field (0,0) and (+/-30,+/-30) arc sec

LGS signal at WFS 125 PDE’s/cm2/sec (80 with regrets)

LLT/BTO transmittance 0.72/0.54 (laser on/off telescope)

Laser power per LGS 6-15 Watts

Transmitted beam quality

1.5 time diffraction limited

RMS 1-axis beam jitter 0.05 arc sec

1/e2 beam diameter 0.3 m

LLT diameter, location 0.45 m, behind secondary


5

MCAOMCAOBTO andBTO andLLT LLT SchematicSchematic

BS

Pointing Array (PA)

Top-End Ring Mirror

KM

LLT

CenterSection

TopEnd

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

PreAlignment

Beam position & tilt

LGS WFS

Offload to KM, PM, CM

PA, CA

MCAOCS

MCAOCS

Closed-loopAlignmentControl

CCShutter

BoresightCalibration

PS

LLT cover

Near- and far-field beam profiles

/4 Plate

Beam Dump Mirror

/4 Plate

Safety Shutter(SALSA)

MiscellaneousFeatures


6

MCAOMCAO

Science Path

OAP1 OAP2

DM9DM0

TTMDM4.5

SCIBS ADC

NGS WFS Path

OAP3WFS

WFSBS

ADC

LGS WFS Path

Zoom FocusLens

LGS WFS

Other Stuff

SourceSimulators

DiagnosticWFS andImagingCamera

• 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 ModuleAdaptive Optics Module


7

MCAOMCAOBaseline AO Component Baseline AO Component ParametersParameters

Number of DM’s 3

DM conjugate ranges

0.0, 4.5, 9.0 km

Actuator pitch D/16, D/16, D/8

Number of WFS 5 (LGS) 3 (NGS)

WFS order 16 by 16 Tip/tilt

Pixels/subaperture 4 by 4 (2 by 2 used)

2 by 2

WFS pixel subtense 1.0 arc sec 0.5 arc sec

WFS read noise 6 electrons None

AOM throughput 0.65 0.6

Detector QE 0.95 0.60

WFS sampling rate 800 Hz


8

MCAOMCAO

Higher-order wavefront control

Tip/tilt (tt) and tilt aniso-

Planatism (ta) control

Real Time Control Block Real Time Control Block DiagramDiagram

DM’s

Null uncon-trolled modes

TTM

BTO tip/tilt

LGS WFS’s

NGS WFS’s

+

Integrator

IntegratorOIWFSFocus

OIWFSTip/tilt

Focusadjustment

Boresightadjustment

M2Offload

M1/M2Offload

Tip/tilt

Higher order

tt

ta


9

MCAOMCAO

MCAO Control SystemMCAO Control System

Instrument Sequencer

1

Real TimeController

3

AOM Component Controller

2

BTO/LLTComponent Controller

4

SALSAController

5

LaserController

6

Laser hardware

SALSA hardware

BTO/LLT devices

AOM devices

AOM WFS/DM/TTM

OCS command OCS command status

BTOFast TT

NGSprobe offset

DWFSDetector

Controller7

Controller commands/status

commands/status commands/statuscommands/status commands/statusWFS data/DM commands

PupilAlignment

Observing data

TCS pointing

Oiwfs data

M2 data

M1 data

seeing

(CR angleOffset)

CR angle

TCS pointing


10

MCAOMCAO

SALSA ElementsSALSA 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)


11

MCAOMCAO

Strehl Ratio SummaryStrehl Ratio Summary

Zenith 30 Degrees 45 Degrees

0.85 microns

0.031 0.010 0.002

1.25 microns

0.201 0.121 0.052

1.65 microns

0.398 0.298 0.184

2.20 microns

0.596 0.506 0.386

• 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


12

MCAOMCAOPerformance with an Interim Performance with an Interim Laser ComplementLaser 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

0.9300.9450.976H

Strehl Ratio Reduction

Corner FoV

Edge FoVCenter FoV

Spectral band

0.8880.9100.959J

0.9580.9680.985K

Expends Margin• Sodium column density• Laser power and beam quality


13

MCAOMCAORMS Relative Strehl RMS Relative Strehl NonuniformityNonuniformity

LGS Signal Wavelength

Zenith 30 Degrees

45 Degrees

125 PDE’s/cm2/sec

1.25 m 0.068 0.098 0.181

1.65 m 0.040 0.058 0.106

2.20 m 0.023 0.033 0.060

80 PDE’s/cm2/sec

1.25 m 0.071 0.101 0.186

1.65 m 0.042 0.060 0.110

2.20 m 0.025 0.035 0.064• 1 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


14

MCAOMCAOScience Path Transmittance Science Path Transmittance and Emissivityand Emissivity

Wavelength 1.00 m 1.65 m 2.20 m 2.20 m(emissivity

)

Per reflection 0.979 0.986 0.987 0.013

Per air-glass I/F 0.991 0.987 0.989 0.011

Beamsplitter (net) 0.930 0.960 0.965 0.022

Overall, 9 reflections

0.826 0.881 0.889 0.117

Overall, no ADC 0.768 0.845 0.858 0.139

4 ADC air/glass I/F 0.965 0.949 0.957 0.044

Overall, with ADC 0.742 0.802 0.821 0.183


15

MCAOMCAO

System AvailabilitySystem Availability

Total Unavailable Time

Laser Pulse Format

Overhead Scenario Satellite Loss

Pulsed CW (MCAO)

Full setup + astrometry 12.9% 30% 38%

Partial setup + astrometry 11.8% 29% 37%

Partial setup, no astrometry

9.1% 27% 35%

Dwell on fixed object 43.0% 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


16

MCAOMCAO

SummarySummary

• Overall system architecture equivalent to conventional LGS AO

• Significant subsystem design progress since CoDR• Delivered H-band Strehl of 0.398

– 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 0.888 to 0.985

• RMS relative Strehl nonuniformity of 0.04 in H• Science path throughput of 0.80-0.85 in H band,

emissivity of 0.14-0.18 in K• System availability of 62-73% with queue

scheduling


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MCAOMCAO

PDR AgendaPDR Agenda

Thursday, 5/240800 Welcome 0805 Project overview 0830 Science case0930 Break0945 System overview1015 System modeling1100 AO Module optics1145 Lunch

1245 AO Module mechanics1340 AO Module electronics1400 Break1415 Beam Transfer Optics1510 Laser Launch

Telescope1545 Closed committee

session1800 Adjourn

mcao system overview brent ellerbroek. mcao may 24-25, 2001mcao preliminary design review2...

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