MCAO
Adaptive Optics Module
Mechanical Design
Eric James
Major Design Issues
MCAO
•Packaging
•Weight and balance
•Volume
•Access to components
•Structural
•ISS interface
•Flexure/vibrations
•Thermal expansion
•Performance
•Minimize surfaces
•Minimize reflection angles
May 24-25, 2001
MCAO Preliminary Design Review
2
8 meter
Primary
Mirror
MCAO
AOM Location
Cassegrain
Rotator
Instrument
support
structure
AO Module
May 24-25, 2001
MCAO Preliminary Design Review
3
MCAO
May 24-25, 2001
MCAO Preliminary Design Review
4
MCAO
Optical Paths
Science path
Beam splitters
LGS focus
NGS focus
LGS path
NGS path
May 24-25, 2001
MCAO Preliminary Design Review
Science focus
5
Optical Bench
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
6
Bench Support
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
7
Electronics Enclosures
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
9U 19”rack mount
chasses (12 total)
8
Electronics Bay Open
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
9
Thermal Management
MCAO
Heat exchanger
100 mm foam insulation
at optics bay
50 mm foam insulation
elsewhere
Calculated heat loss to dome: 35 –85 Watts
May 24-25, 2001
MCAO Preliminary Design Review
10
Finite Element Analysis
MCAO
• Static (Gravity Induced) Flexure Analysis
• Telescope at zenith
• Zenith angle = 45º
• Zenith angle = 60º
• Dynamic (Vibration Induced) Flexure Analysis
• Natural frequency
• Vibration Amplitude
• Seismic (Earthquake Induced) Stress Analysis
May 24-25, 2001
MCAO Preliminary Design Review
11
Static Analysis
at Zenith
MCAO
Telescope at Zenith:
Maximum deflection
~50 mm
Gravity
May 24-25, 2001
MCAO Preliminary Design Review
12
MCAO
Static Analysis at
60º from Zenith
Telescope at 60º from
Zenith:
Maximum deflection
~200 mm
Gravity
May 24-25, 2001
MCAO Preliminary Design Review
13
Dynamic Analysis
MCAO
Dynamic Analysis
Mode 1: “fishtailing”
motion
Lowest natural
frequency: 39 Hz
May 24-25, 2001
MCAO Preliminary Design Review
14
Seismic
Analysis
Seismic
Analysis
MCAO
Maximum Stress:
~ 8 x 106 Pascals
May 24-25, 2001
MCAO Preliminary Design Review
15
MCAO
Alignment
• Initial Alignment (acquire image)
– Align elements within major components to datum surface.
• Done by vendor at vendor facility.
– Align components and single elements to the optical bench.
– Align optical bench to the telescope.
• Done by Gemini on the telescope at Gemini south.
• Final Alignment (optimize image)
– Wave front analysis using source simulators and wave front
sensors.
– Image analysis using stars and science detector.
May 24-25, 2001
MCAO Preliminary Design Review
16
AO Module Sensitivity Analysis
MCAO
• Optical fabrication and alignment sensitivities
computed
• Modeling accounts for partial compensation of
errors by the AO control loops
– Initial alignment in the lab
– Flexure/thermal errors during closed-loop operation
• Sensitivities computed for
–
–
–
–
Higher order wave front errors (science, NGS, LGS paths)
Pupil alignment/distortion (science, LGS paths)
Boresight (tip/tilt) errors (science, LGS paths)
DM adjustments to compensate errors
May 24-25, 2001
MCAO Preliminary Design Review
17
Error Budget chart
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
18
MCAO
Sensors and compensators for final
alignment in the lab
Astronomer
Distortion map
Mean tip/tilt and
higher order correction
(3 x 35 Zernikes)
Source
simulator
DMs
Diagnostic
WFS
Science
Instrument
NGS WFS
Tip/tilt/focus
adjustment
LGS WFS
•Tip/tilt/focus adjustments
•Pupil alignment
Non-common path calibration
Influence function measurements
May 24-25, 2001
MCAO Preliminary Design Review
19
Sensors and compensators for closed•M2 focus
loop AO
MCAO
•Telescope pointing
On-axis
Tip/tilt/focus
Telescope
DMs
OIWFS
3 by 35
Zernikes
•LGS WFS focus
Least-squares
fit
3 x tip/tilt
•NGS WFS boresight
NGS WFS
Pupil mirror
5 by 35 Zernikes
LGS WFS
5 x tip/tilt
(tilt removed)
LGS pointing
May 24-25, 2001
MCAO Preliminary Design Review
20
MCAO
Wave front error budget results
Error budget study results summary
Line
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Error
Optical
Category
Path
Wave front error Science
"
"
"
"
"
"
"
"
"
"
"
Laser GS
"
"
"
"
"
"
"
"
"
"
"
Natural GS
"
"
"
"
Pupil Variables Science
"
"
"
Laser GS
"
"
"
"
DM adjustments
DM0
DM4.5
DM9.0
Description
Tilt removed
"
"
RMS 2-axis tip/tilt
"
"
Tilt removed
"
"
RMS 2-axis tip/tilt
"
"
Tilt removed
"
"
20-Apr-01
Zenith
Angle
Pupil Motion
Pupil Mag
RMS 2-axis Pupil Motion
Induced LGS motion
RMS Pupil distortion
0
45
60
0
45
60
0
45
60
0
45
60
0
45
60
Dsgn res.
1.294E+01
1.294E+01
1.294E+01
Calibrated
Calibrated
Calibrated
3.528E+01
3.528E+01
3.528E+01
Calibrated
Calibrated
Calibrated
4.558E+01
4.558E+01
4.558E+01
Fabric.
4.150E+01
4.150E+01
4.150E+01
Calibrated
Calibrated
Calibrated
5.840E+01
5.840E+01
5.840E+01
Calibrated
Calibrated
Calibrated
4.810E+01
4.810E+01
4.810E+01
Error Source
Init. Align Flex/therm
7.700E-03 4.050E+01
7.700E-03 7.960E+01
7.700E-03 8.560E+01
Calibrated
1.160E-02
Calibrated
3.500E-02
Calibrated
3.800E-02
7.540E+01 4.410E-01
7.540E+01 1.290E+00
7.540E+01 1.440E+00
Calibrated
5.040E-01
Calibrated
9.030E-01
Calibrated
1.015E+00
6.540E+01 5.380E+01
6.540E+01 7.590E+01
6.540E+01 8.400E+01
45
45
45
45
45
8.600E-03
1.600E-02
1.130E-04
1.164E-03
1.722E-03
2.000E-02
2.000E-02
0.000E+00
0.000E+00
2.600E-03
1.090E-03
1.680E-02
0.000E+00
0.000E+00
2.260E-03
45 2.760E+01 1.200E+02 3.500E+01
45 3.840E+01 1.200E+02 5.670E+00
45 2.920E+01 1.200E+02 1.330E+01
Legend
Allocation
Includes 20 nm allocation for LGS WFS spot relay lens
May 24-25, 2001
MCAO Preliminary Design Review
4.110E-04
4.460E-03
3.500E-02
3.605E-01
1.180E-03
Rad/index
1.210E-01
1.210E-01
1.210E-01
1.309E-05
1.309E-05
1.309E-05
3.430E-05
3.430E-05
3.430E-05
4.580E-04
4.580E-04
4.580E-04
5.800E-02
5.800E-02
5.800E-02
8.740E-04
2.140E-05
3.110E-05
3.203E-04
3.050E-06
1.780E+01 4.434E+00
2.630E+01 4.434E+00
6.150E+01 4.434E+00
Overall
(RSS)
5.941E+01
9.070E+01
9.601E+01
1.160E-02
3.500E-02
3.800E-02
1.017E+02
1.017E+02
1.017E+02
5.040E-01
9.030E-01
1.015E+00
1.075E+02
1.201E+02
1.254E+02
units
nm
"
"
arc sec
"
"
nm
"
"
arc sec
"
"
nm
"
"
2.182E-02 beam diam
3.095E-02
"
3.500E-02
"
3.605E-01 arc sec
4.028E-03 beam diam
1.293E+02 nm OPD
1.289E+02
"
1.387E+02
"
Red numbers indicate the value is
over budget or at least of some
concern
21
Error Budget points of interest
MCAO
•Most areas meet goals. All goals are met at the zenith
position.
•Flexure at 45º and 60º are about 50% over the goals. This
suggests special design effort at a few areas.
•Science path tip/tilt errors must be carefully calibrated out.
•Within goals for:
•LGS pupil displacement (input to simulations)
•LGS WFS boresight errors (input to simulations)
•LGS RMS pupil distortion (input to simulations)
•RMS wave front errors in LGS and NGS paths
•DM adjustments
May 24-25, 2001
MCAO Preliminary Design Review
22
Active Components
MCAO
•Source simulators
•Science ADC
•DM0 aperture stop
•Beam splitter changer
•Diagnostic wave front sensor
•Shutters
•NGS wave front sensor
•NGS ADC
•LGS zoom corrector
•LGS wave front sensor
May 24-25, 2001
MCAO Preliminary Design Review
23
LGS wave front sensor
MCAO
Active lenses
Commercial
tip/tilt mirrors
CCD detectors
5 beam paths – 2 omitted for clarity
May 24-25, 2001
MCAO Preliminary Design Review
24
MCAO
NGS Wave front sensor
Probe arms
NGS path
NGS path
X-Z translation stages
May 24-25, 2001
MCAO Preliminary Design Review
25
MCAO
Diagnostic WFS/Source simulators
•LGS Source
•5-star constellation
•LEDs at ~.589 microns
•NGS Source
•5x5 array of 4 micron
diameter fiber sources
•8 200 micron diameter
sources at ~ 1 arc minute
radius
NGS Source
LGS Source
CCD detector
Video camera
(not shown)
Diagnostic WFS
May 24-25, 2001
MCAO Preliminary Design Review
26
MCAO
LGS Zoom Corrector
LGS wave front
sensor
Fixed elements
May 24-25, 2001
MCAO Preliminary Design Review
27
MCAO
Beam splitter changer
Rotation to change beam splitters
Science path
To Science
instrument
Science path
From DMs
Science ADC
LGS/NGS path
May 24-25, 2001
MCAO Preliminary Design Review
28
Misc. Active components
MCAO
• Science ADC
• Counter-rotating prisms
• Retractable
• Calcium fluoride and silica prisms
• NGS ADC
• Counter-rotating prisms
• Flint and crown prisms
• Shutters
• Baseline same as Altair
• Aperture stop
• Normally retracted, used only with source simulator to
overfill DM0 for flattening.
May 24-25, 2001
MCAO Preliminary Design Review
29
Mass and Center of Gravity
MCAO
Goal center of mass
900kg 970kg (estimated)
May 24-25, 2001
MCAO Preliminary Design Review
30
Procurement strategy 5 work packages:
1.
AO Bench (including
enclosures and most
electronics)
2.
Deformable mirrors
3.
Diagnostic WFS &
source simulators
4.
LGS wave front sensor
5.
NGS wave front sensor
May 24-25, 2001
MCAO Preliminary Design Review
MCAO
31
Procurement Strategy –
Acceptance testing & Integration
Vendor
facilities:
Pre-ship
tests
AO Bench
DMs
LGS WFS
NGS WFS
MCAO
DWFS/ Sources
Hilo: Acceptance
tests, integration,
& closed-loop AO
Cerro Pachon:
reassembly,
realignment, &
commissioning
May 24-25, 2001
MCAO Preliminary Design Review
32
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
33