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MCAO
System Overview
Brent Ellerbroek
Presentation Outline
MCAO
• 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
May 24-25, 2001
MCAO Preliminary Design Review
2
MCAO
System Block Diagram
(Boresight
Calibration)
LLT
Emergency
halt
BTO
Fast
tip/tilt
Beam
alignment
Diagnostics
LS
SALSA
MCAO CS
Status
Commands
Safety status
WFS
data
Close/open loops
Functional
Control
Telescope
pointing
NGS
Laser/LGS
Science field
May 24-25, 2001
Real-Time
Control
DM/TTM
commands
Observing
sequences
AOM
OI
WFS
Science
Inst.
Calibration
functions
Data
logging
M2/M1
offloads
TCS/SCS/OCS/DHS
MCAO Preliminary Design Review
3
Laser and LGS Parameters
MCAO
Number of LGS
5
LGS locations in Field
LGS signal at WFS
(0,0) and (+/-30,+/-30) arc sec
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
May 24-25, 2001
0.45 m, behind secondary
MCAO Preliminary Design Review
4
BTO and
LLT Schematic
MCAO
Near- and far-field beam profiles
Beam position & tilt
PA, CA
Miscellaneous
Closed-loop
Boresight
Periscope
Pre
Alignment
Calibration
Features
X-Shaping
Control
Mirrors
BS
PA, CA
CC
Top-End
Ring Mirror
Top
End
Center
Section
PAC
PAC
Relay
Pointing
Array (PA)
PA, CA
MCAO
CS
BDS
Centering
mirror (CM)
Beam Dump
Mirror
Shutter
LGS WFS
KM
Pointing
mirror (PM)
Fast Steering Array
Offload to KM, PM, CM
l/4
Plate
LLT
cover
MCAO
CS
PAC
Centering Array (CA)
l/4 Plate
Safety Shutter(SALSA)
May 24-25, 2001
PS
MCAO Preliminary Design Review
LLT
PM, CM
5
MCAO
Adaptive Optics Module
Science
Path
NGS
WFS
Path
LGS
Other
WFS
Stuff
Path
DM0
DM9
SCIBS
ADC
Source
Simulators
• f/33.4 output
• Focal- and pupil plane
WFSBS OAP1
locations preserved
TTM
• Standard
optical bench
DM4.5
design with space frame
support
• In-plane packaging with
adequate room ADC
for
WFS
electronics
May 24-25, 2001
OAP2
Diagnostic
WFS and
Imaging
Camera
Zoom Focus
OAP3
Lens
LGS WFS
MCAO Preliminary Design Review
6
Baseline AO Component
Parameters
MCAO
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
4 by 4 (2 by 2 used)
2 by 2
1.0 arc sec
0.5 arc sec
6 electrons
None
AOM throughput
0.65
0.6
Detector QE
0.95
0.60
Pixels/subaperture
WFS pixel subtense
WFS read noise
WFS sampling rate
May 24-25, 2001
800 Hz
MCAO Preliminary Design Review
7
Real Time Control Block Diagram
MCAO
BTO tip/tilt
OIWFS
Focus
Integrator
M1/M2
Offload
Focus
adjustment
Higherorder wave
front control
LGS WFS’s
OIWFS
Tip/tilt
+
Null uncontrolled modes
Integrator
Boresight
adjustment
NGS WFS’s
Tip/tilt (tt) and
tilt anisoPlanatism (ta)
control
Higher order
ta
tt
TTM
M2
Offload
Tip/tilt
May 24-25, 2001
DM’s
MCAO Preliminary Design Review
8
MCAO
MCAO Control System
OCS command
Controller commands/status
CR angle
Observing
data
M1 data
Oiwfs
data
AOM
Component
Controller
2
(CR angle
Offset)
Pupil
Alignment
NGS
probe
offset
Real Time
Controller
3
BTO
Fast TT
commands/status
WFS data/DM commands
AOM
devices
AOM
WFS/DM/TTM
May 24-25, 2001
DWFS
Detector
Controller
7
Instrument
Sequencer
1
TCS pointing
seeing
M2 data
TCS pointing
OCS command status
BTO/LLT
Component
Controller
4
commands/status
BTO/LLT
devices
MCAO Preliminary Design Review
SALSA
Controller
Laser
Controller
5
6
commands/status
SALSA
hardware
commands/status
Laser
hardware
9
SALSA Elements
MCAO
• 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)
May 24-25, 2001
MCAO Preliminary Design Review
10
MCAO
Strehl Ratio Summary
0.85 microns
1.25 microns
1.65 microns
2.20 microns
•
•
•
•
•
Zenith
30 Degrees 45 Degrees
0.031
0.010
0.002
0.201
0.121
0.052
0.398
0.596
0.298
0.506
0.184
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
May 24-25, 2001
MCAO Preliminary Design Review
11
Performance with an Interim
Laser Complement
MCAO
• 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 FoV
Edge FoV
Corner FoV
J
0.959
0.910
0.888
H
0.976
0.945
0.930
K
0.985
0.968
0.958
May 24-25, 2001
MCAO Preliminary Design Review
Expends Margin
• Sodium column
density
• Laser power
and beam
quality
12
MCAO
RMS Relative Strehl Nonuniformity
LGS Signal
Wavelength
125 PDE’s/
cm2/sec
1.25 mm
0.068
0.098
0.181
1.65 mm
0.040
0.058
0.106
2.20 mm
0.023
0.033
0.060
1.25 mm
0.071
0.101
0.186
1.65 mm
0.042
0.060
0.110
2.20 mm
0.025
0.035
0.064
80 PDE’s/
cm2/sec
Zenith
30 Degrees 45 Degrees
• 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
May 24-25, 2001
MCAO Preliminary Design Review
13
Science Path Transmittance and
Emissivity
Wavelength
1.00 mm
1.65 mm
MCAO
2.20 mm
2.20 mm
(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
May 24-25, 2001
MCAO Preliminary Design Review
14
MCAO
System 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%
9.1%
27%
35%
43.0%
54%
59%
Partial setup, no astrometry
Dwell on fixed object
• 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
May 24-25, 2001
MCAO Preliminary Design Review
15
MCAO
Summary
• 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
May 24-25, 2001
MCAO Preliminary Design Review
16
MCAO
PDR Agenda
Thursday, 5/24
0800 Welcome
0805 Project overview
0830 Science case
0930 Break
0945 System overview
1015 System modeling
1100 AO Module optics
1145 Lunch
May 24-25, 2001
1245 AO Module mechanics
1340 AO Module electronics
1400 Break
1415 Beam Transfer Optics
1510 Laser Launch Telescope
1545 Closed committee session
1800 Adjourn
MCAO Preliminary Design Review
17
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