Gemini AO Program
The Gemini Adaptive Optics Program
MCAO for Gemini-South
Gemini Adaptive Optics Team
B. Ellerbroek and F.Rigaut
October 21, 1999
Gemini Science Committee
1
Gemini AO Program
Top Level Perf. Requirement #2
“ Image quality of better than 0.1 arcsec with AO:
Achievement of outstanding image quality will have
the highest scientific priority for the project […]”
• The proposed evolution of the program at CP will
enable unique NGST-class science 4 years ahead of
NGST launch. It will keep Gemini competitive during
the NGST era.
October 21, 1999
Gemini Science Committee
2
Gemini AO Program
AO and Science
AO is a rather new domain...
– First AO instrument for astro. -> Come-on, ESO 1990
– UH curvature system, Mauna Kea 1992
– 1994-1998: Exponential progression of # of systems
…but science is already flowing:
– Number of Astro paper is growing exponentially
– Total of 70+ refereed papers (lost count). Highlights:
Discovery of an asteroid satellite, wrap of  Pic disk,
Surface and orbital parameters of solar system bodies,
YSO disks and outflows (e.g. HL and GG Tau), Stellar
motions in GC, Stellar multiplicity surveys, Structure in
AGNs, Galaxy dynamic (e.g. CFHT AOSIS), etc...
October 21, 1999
Gemini Science Committee
3
Gemini AO Program
A short history of astronomical AO
• 1989: First AO images w/ Come-On (OHP & ESO) 110mas
• 1992: First Curvature system (UH) 70mas
• 1996: First Facility system (CFHT AOB)
October 21, 1999
Gemini Science Committee
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Gemini AO Program
CFHT Pueo
1996
Galactic Center
2.2 m
FWHM
130 mas
October 21, 1999
Gemini Science Committee
5
Gemini AO Program
A short history of astronomical AO
• 1989: First AO images w/ Come-On (OHP & ESO) 110mas
• 1992: First Curvature system (UH) 70mas
• 1996: First Facility system (CFHT AOB)
•
•
•
•
1996: First compensation in the visible (Mt Wilson) 58mas
1996: First LGS systems
1998: LGS systems getting closing expectations
1999: First h.order system on a large telescope (Keck) 40mas
October 21, 1999
Gemini Science Committee
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Gemini AO Program
Keck AO System
1999
Vesta 1.5 m
FWHM
<40 mas
October 21, 1999
1’’
Gemini Science Committee
7
Gemini AO Program
Gemini’s Dedication
Courtesy C.Roddier, UH-IfA
October 21, 1999
Gemini Science Committee
8
Gemini AO Program
ALFA AO Results
(18 Modes, 0.9-1.0’’ seeing, K band)
Open loop
Loop closed
with LGS AO
• 4 W dye laser
NGS AO
• 0.23 Strehl
• 0.42 Strehl
• FWHM diffraction limited.
• 0.53 predicted
October 21, 1999
Gemini Science Committee
9
Gemini AO Program
Where is AO standing ?
• AO technology for astronomy is maturing rapidly
– Well designed and calibrated NGS AO systems (CFHT Pueo,
Hokupa’a, MIT/Lincoln Laboratory, SOR) now closely
approach their performance predictions.
– Rayleigh beacon LGS AO programs (MIT/LL, SOR) have
been technically successful
– Astronomical sodium beacon LGS AO systems have
progressed from Strehls of 0.03 to 0.30 in two years
– Sodium layer variability has been well characterized by
numerous LIDAR campaigns
October 21, 1999
Gemini Science Committee
10
Gemini AO Program
Proposed Baseline AO Program
NORTH
1999
Altair
10W LGS
Hokupa’a
SOUTH
CP AOS/LGS
CP Hokupa’a
2000
36
Keck
2001
2002
2003
2004
85
Subaru
VLT
VLT-LGS
85
2W LGS
October 21, 1999
Gemini Science Committee
11
Gemini AO Program
Baseline Program: Altair
NORTH
1999
2000
2001
2002
2003
2004
Altair
10W
LGS well (CDR 02/99)
•Progresses
36 for Altair
85 LGS upgrade nearly ready
Hokupa’a
•Statement of work
SOUTH
CP AOS/LGS
CP Hokupa’a
Keck
Subaru
VLT
VLT-LGS
85
2W LGS
October 21, 1999
Gemini Science Committee
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Gemini AO Program
Baseline Program: 10W LGS
NORTH
1999
2000
2001
2002
2003
2004
10W LGS
10W
•10 W LGS
Laser RFP to go out early October
36 vary from857 to 23W depending on laser pulse
Hokupa’a
•Power requirements
format
Keck
Subaru
•Design of the LLT and BTO underway
SOUTH
CP AOS/LGS
CP Hokupa’a
VLT
VLT-LGS
85
2W LGS
October 21, 1999
Gemini Science Committee
13
Gemini AO Program
Baseline Program: MK-Hokupa’a
NORTH
1999
Hokupa’a
2000
36
2001
2002
2003
2004
85
•Hokupa’a-36
10W
LGS installed on the telescope early June this year
•Images fully compatible
with85
expectations (seeing ok but not
36
Hokupa’a
exceptional), near diffraction limit in K band w/ Strehl ~ 15-30%.
Keck
Subaru
Great tool for telescope engineering
SOUTH
•85 Actuators upgrade to be done next year
team on
VLT by UH
VLT-LGS
internal funds. Small transferred field (30’’)
CPUH/NSF
AOS/LGS
Performance w/ NGS (AO only) (285
fold vs 36 actuators):
CP Hokupa’a
Seeing
Strehl(J)
Strehl(K)
2W LGS
0.45’’
50%
80%
0.65’’
25%
62%
October 21, 1999
Gemini Science Committee
14
Gemini AO Program
Cerro Pachon-AOS/LGS Forum
April 1999, Review Panel Recommendations
1
2
3
4
5
The IGPO should develop a strategy for its overall adaptive optics program which satisfies the
Gemini community. Timing of the program, staff resources, and cost must be addressed. The
RP also notes that the experience gained with the Altair AO and Hokupa'a teams are valuable to
the overall program and should be folded into the planning.
The Project should conduct a significant but time-limited study of a multiconjugate adaptive
optics system for Cerro Pachon. This would provide an exciting advancement in capabilities but
implementing the system should be conditional on "filling" the AO gap on Gemini-South and
addressing the requirements of the coronagraphic imager. The study should address the
theoretical analysis, science drivers, technical challenges, systems engineering, and
programmatics of such an AO system. With the development of a plan, the RP recommends
that Gemini adopt as aggressive a schedule as possible to bring this capability to the
community.
The IGPO should lead the conceptual design program of the Gemini-South AO system,
including defining the allocation of subsystems across the Gemini Community
In light of the proposals presented for turn-key laser systems, the RP recommends that the
IGPO explore with LiteCycles the manufacture of a Sum Frequency laser. To reduce cost and
risk for the laser, procurement through a consortium should be explored, including Keck, and
possibly other groups if they can participate on timescales which are consistent with Gemini's
schedule for laser deployment.
The project should avoid relying on major technological developments such as MEMs, liquid
crystals, and other 'advanced' DMs for the CP AOS
October 21, 1999
Gemini Science Committee
15
Gemini AO Program
Baseline Program: CP-Hokupa’a
SOUTH
1999
CP Hokupa’a
2000
2001
2002
2003
2004
85
2W LGS
36 MK upgrade
85 of Hokupa’a to 85 actuators. UH AO
Hokupa’a
• AO: Duplicate of the
Team. Proposal submitted
NSF 08/99. Optomechanical upgrades
Keck to
Subaru
(FoV 60’’) + LGS compatible
SOUTH
Performance w/ NGS (AO only):
VLT
VLT-LGS
Strehl(K)
CP Seeing
AOS/LGSStrehl(J)
80%
85
CP 0.45’’
Hokupa’a 50%
0.65’’
25%
62%
2W
LGS
• LGS: Off-the-shelf 2W CW laser. Coherent/Spectra physics CW 10W
pump laser + ring dye laser (demonstrated in lab)
• IR Imager: ABU
October 21, 1999
Gemini Science Committee
16
Gemini AO Program
Baseline Program: CP-Hokupa’a
SOUTH
1999
2000
2001
CP Hokupa’a
2002
2003
2004
85
2W LGS
Hokupa’a
Rationale:
36
85
• Gives us a 2+ yearKeck
window Subaru
of unchallenged AO+LGS capability in the
SOUTH
southern hemisphere (comp. NAOS) w/ Adequate JHK performance.
VLT
VLT-LGS
• Build expertise on LGS by stepping up gradually (Laser Launch
CP
AOS/LGS
Telescope + Beam Transfer Optics)
85
CP
Hokupa’a
• Getting
AO on CP as soon as possible relieves
pressure, allowing us to
avoid LGS
the rush and do a better job on the final CP system
2W
October 21, 1999
Gemini Science Committee
17
Gemini AO Program
Baseline Program: Facility CP AOS
SOUTH
1999
2000
2001
2002
2003
2004
CP AOS/LGS
10W
LGS
Context:
36
85
Hokupa’a
• Simplest case = duplicate Altair -> No AO facility until late 2002.
KeckhaveSubaru
• Other observatories
very capable AOSs in the north (Keck 1999)
SOUTH
and in the south (VLT-NAOS 2001) -> Competitiveness issue
VLT
VLT-LGS
Rationale:
(Why?)
CP
AOS/LGS
• Provide the Gemini community with NGST-like
capabilities (spatial res.
85
CP
Hokupa’a
and field), matching the Gemini science goals and instrumentation
2W
LGS
• Sets
up Gemini to be a lead ground-based facility in the NGST era
with matching resolution and similar field of view
• Future ELTs require “wide” field of view AO
October 21, 1999
Gemini Science Committee
18
Gemini AO Program
Baseline Program: Facility CP AOS
SOUTH
1999
2000
2001
2002
2003
2004
CP AOS/LGS
10W
LGS(What?)
Proposal:
36
85
• Build a high performance,
2 arcminutes
field of view AOS with
Hokupa’a
homogeneous PSF Keck
quality over
the entire field of view, with very high
Subaru
sky coverage
SOUTH
VLT
VLT-LGS
How ?
CP
AOS/LGS
• Using
Multi-Conjugate AO, i.e. 4-5 LGSs and wavefront sensors to
85
measure
the turbulence in 3D and 2-3 deformable
mirrors to correct it
CP
Hokupa’a
• ThisLGS
uses currently available technology. NO hardware development
2W
required other than lasers (same as MK-LGS)
October 21, 1999
Gemini Science Committee
19
Gemini AO Program
What is Tomography ?
90 km
1. Cone effect
October 21, 1999
Gemini Science Committee
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Gemini AO Program
What is tomography ?
90 km
2. Multiple guide star and tomography
October 21, 1999
Gemini Science Committee
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Gemini AO Program
What is multiconjugate?
October 21, 1999
Gemini Science Committee
22
Gemini AO Program
What is multiconjugate?
October 21, 1999
Gemini Science Committee
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Gemini AO Program
What is multiconjugate?
Turb. Layers
#1
Telescope
#2
WFS
DM1
DM2
Atmosphere
UP
October 21, 1999
Gemini Science Committee
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Gemini AO Program
Baseline Program: Facility CP AOS
SOUTH
1999
2000
2001
2002
2003
2004
CP AOS/LGS
10W
What LGS
does MCAO do that another system wouldn’t ?
36 increased85(50-500x) w/ respect to a NGS system
Hokupa’a
• Sky coverage (50%)
• Increased performance
axis w/ respect to a LGS system because
Keck on
Subaru
the cone effect is taken care of
SOUTH
• Increased field of view (well matched toVLT
IRMOS)VLT-LGS
CP
AOS/LGS
• Uniform PSF across the FoV -> Easier and more accurate Data Reduc.
85
CP Hokupa’a
2W LGS
October 21, 1999
Gemini Science Committee
25
Gemini AO Program
MCAO Performance Summary
Early NGS results, MK Profile
No AO
320 stars / K band / 0.7’’ seeing
October 21, 1999
Classical AO
MCAO
1 DM / 1 NGS
2 DMs / 5 NGS
165’’
Gemini Science Committee
Stars magnified for clarity
26
Gemini AO Program
MCAO Performance Summary
Early NGS results, MK Profile
MCAO
Classical AO
Guide star location
October 21, 1999
Gemini Science Committee
27
Gemini AO Program
Baseline Program: Facility CP AOS
1999
SOUTH
2000
2001
2002
2003
2004
CP AOS/LGS
10W
LGS
Performance
Hokupa’a
Mode
NGS
SOUTH
LGS
MCAO
CP AOS/LGS
36
%Sky3
Keck
1%
17%
34%
85
SR
J(0’’) SRJ(48’’)
Subaru
0.55
0.04
0.47
0.04 VLT
0.54
0.35
CP Hokupa’a
1 50% Strehl ratio attenuation
FOV
Hardware
30’’ 1 1DM
1
32’’ VLT-LGS
1DM/1LGS
2’ 2
3DM/5LGS
85
limited by the AO-Fold aperture
2W LGS
3
2
Sky coverage at galactic pole
October 21, 1999
Gemini Science Committee
28
Gemini AO Program
Baseline Program: Facility CP AOS
SOUTH
1999
2000
2001
2002
2003
2004
CP AOS/LGS
10W
LGS
Where
are we?
36
85
Hokupa’a
• Feasibility study progressing, including:
Subaru
•First pass on Keck
the science
drivers
SOUTH
•Theoretical analysis of MCAO control/numerical
VLT
VLT-LGS
simulations/Performance assessment
CP AOS/LGS
•A proof-of-concept optical and mechanical layout
85
CP Hokupa’a
•Assessment of the need in computing issues
2W •Management
LGS
plan including schedule and resource needs
October 21, 1999
Gemini Science Committee
29
Gemini AO Program
MCAO for Gemini-South
Performance, Feasibility, and Schedule
•
•
•
A multi-conjugate AO system for Gemini-south can
theoretically provide highly uniform turbulence compensation
over a 1-2’ diameter field-of-view
System can be implemented with largely existing hardware and
technology
– Fully acceptable deformable mirrors, tip/tilt mirrors, and
wave front reconstructs have been demonstrated
– Most recent high-speed 1282 CD's meet wave front sensor
requirements with margin
– Significant improvements still required in sodium laser
power and reliability
• Comparable with conventional LGS AO on a per beacon
basis
Estimated schedule for science handover is spring 2004
October 21, 1999
Gemini Science Committee
30
Gemini AO Program
NGS, LGS, and Multi-conjugate AO
Performance Characteristics
NGS AO
LGS AO
MCAO
Sky coverage
Poor (0.1-2%)
Good (~17% at
galactic pole,
SR=0.6 in H)
Further improved
(~34% at galactic
pole)
Compensated
field-of-view
20-40”
(Nonuniform)
20-40”
(Nonuniform)
1-2’
(Nearly uniform)
Fundamental
limits
• Guide star
brightness
• Common
anisoplanatism
•T/T guide star
brightness (relaxed)
• Tilt anisoplanatism
• Cone effect
•T/T guide star
brightness (relaxed)
• TBD (new inverse
problem)
• Sky coverage and field-of-view are for J, H, K bands with 0.5 arc
second seeing
October 21, 1999
Gemini Science Committee
32
Gemini AO Program
Analysis and Simulation Models
•
•
•
Two approaches available for more detailed modeling of MCAO
– Upgraded simulation
– Statistical analysis based opon turbulence statistics,
MCAO system parameters
Both approaches treat laser- and natural guide stars, WFS/DM
geometries, CP turbulence profiles
– Analysis derives “optimal” wave front reconstructors
– Simulation more efficient for standard least-squares
approach
Both approaches extendable to model WFS noise, servo lag,
telescope/instrument aberrations
– Simulation can potentially model wave optics effects in
wave front sensors and the atmosphere
October 21, 1999
Gemini Science Committee
33
Gemini AO Program
MCAO Parameters for Gemini-CP
• 4 or 5 laser guide stars
– 30 to 60” (48”) offset from optical axis
– 10 to 20 Watts CW equivalent power, 1.5 XDL
• 4 or 5 LGS wave front sensors
– 12 by 12 or 16 by 16 subapertures
– 80 by 80 to 128 by 128 pixels
– 5 to 10 read noise electrons, 500 to 1000 Hz sampling
• 2 or 3 deformable mirrors
– 13 or 17 actuators across beamprint
– Conjugate ranges of 0, 4-4.5, 8-9 km
• 3-4 T/T or T/T/F natural guide stars, 1 T/T mirror
(Parameters Used for Following Sample Results) (Parameters not Yet Modeled)
October 21, 1999
Gemini Science Committee
34
Gemini AO Program
Sample Numerical Results
0 degree zenith
• 50% seeing
• 12 by 12 NGS (black)
• 12 by 12 MCAO (red)
• 16 by 16 MCAO (blue)
• I, J, H, and K bands
•
K
H
J
I
October 21, 1999
Gemini Science Committee
35
Gemini AO Program
Sample Numerical Results
Variation with Seeing and Zenith Angle
0 Degree Zenith
45 Degree Zenith
12 by 12 NGS (black), 12 by 12 MCAO (red), and 16 by 16 MCAO (blue)
• I, J, H, and K spectral bands
•
October 21, 1999
Gemini Science Committee
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Gemini AO Program
Sample Results
Slit Coupling Efficiency at 0 Degrees Zenith
•16 by 16 MCAO, I, J, H, and K spectral bands
• Horizontal and vertical 0.1 arc second slits
October 21, 1999
Gemini Science Committee
37
Gemini AO Program
Why Multiple Tip/Tilt NGS’s?
– Consider a turbulence profile
with a focus aberrations at
two ranges (blue)
– LGS measurements (yellow)
cannot determine range of the
aberration
• Tip/tilt information lost
• Equal focus measurement
from each LGS,
regardless of aberration
range
– Tip/tilt NGS measurements
can determine range from the
differential tilt between stars
– Three tip/tilt NGS’s needed
for all three quadratic modes
– Alternate approaches:
Rayleigh LGS’s, or a solution
to the LGS tilt indeterminacy
problem
October 21, 1999
Gemini Science Committee
f(r)=a(cr+d)2
=ac2r2+2acdr+ad2
~ ac2r2
After tilt removal
f(r)=ar2
38
Gemini AO Program
MCAO Sky Coverage with
Multiple Tip/Tilt NGS
• Quantitative sky coverage calculations more complex than for
conventional AO, but some initial estimates are possible
– Only one NGS need be sufficiently bright for correction of
high-bandwidth, wind-shake induced tip/tilt jitter
– The atmospheric modes corrected by remaining reference
stars are lower frequency, allowing lower control
bandwidths and dimmer stars (e.g. 30Hz sampling rate)
– Preliminary calculation for the galactic pole:
• LGS AO sky coverage for 60% Strehl in H: 17%
• MCAO coverage with 1 m=18 star and 2 m=20 stars
within 1’ radius: 34%
October 21, 1999
Gemini Science Committee
39
Gemini AO Program
MCAO Implementation-
Feasibility study conclusions:
• Optics and optics bench
– Mass, volume similar to Altair
• Wave front sensor camera
– Goal of a single camera for all laser guide stars
– 80 by 80 to 128 by 128 pixels, 5 to 10 read noise electrons
• Deformable mirrors and tip/tilt mirror
– Number of actuators, other parameters demonstrated
• Wave front reconstruction electronics
– Frame rate, number of inputs/outputs demonstrated
• Tip/tilt sensors, laser transfer optics and launch telescope
– Appear straightforward, feasibility designs in progress
– 2-3 T/T sensors + 1 more provided by OIWFS
• Laser(s): Technology and engineering development required
October 21, 1999
Gemini Science Committee
40
Gemini AO Program
MCAO Science Optical Path
•3 DM’s at R=0, 4, and 8 km
•13 actuators across beamprint
•4 folds, 2 off-axis parabolas,
1 dichroic beamsplitter (not shown)
- Near-minimum number of surfaces for
facility MCAO
• f/30 output focus
October 21, 1999
Gemini Science Committee
41
Gemini AO Program
MCAO LGS Optical Path
• Outgoing: Single launch telescope for all guide stars
• Return: One WFS camera for all guide stars
ZEMAX optical schematic
October 21, 1999
4 LGS’s sensed with 1 WFS CCD
Gemini Science Committee
42
Gemini AO Program
WFS Camera Options
Pixels
Requirement
EEV CCD
MIT/LL CCD
80 by 80
to
128 by 128
80 by 80
128 by 128
Read
noise
electrons
5-10
5
6-10
Frame
rate, Hz
Comments
5001000
1000
1-2 Cameras
for 4-5 LGS,
12 by 12 SA
1000+
Supports
5 LGS,
16 by 16 SA
• MIT/LL read noise level is new information since feasibility study
October 21, 1999
Gemini Science Committee
43
Gemini AO Program
Approach to Multiple Tip/Tilt
NGS WFS’s
200mm
To APDs
Focal plane
XX stage
stage
Y stage
• Fiber-fed
APD quadrant
detectors
•2 or 3 T/T
WFS’s in AO
instrument
package
• One
additional
T/T/F WFS
in each
facility
instrument,
for a total of
3-4 sensors
October 21, 1999
Gemini Science Committee
44
Gemini AO Program
Laser Issues
• Power requirement:
– Equivalent to conventional LGS AO on a per beacon basis
– 20-40 Watts per LGS, 80-200 Watts total for short pulse,
flashlamp+Nd:YAG-pumped dye lasers (LLNL)
• ~20 Watts demonstrated
• Scaling a cost/engineering issue (electrical power, heat
dissipation, flammable dye)
– 7-12 Watts per LGS, 28-60 Watts total for diode-pumped,
Nd:YAG sum frequency lasers (MIT/LL and others)
• ~5 Watts demonstrated
• Scaling a technical issue (Nd:YAG beam quality and sum
frequency feasibility at higher powers)
October 21, 1999
Gemini Science Committee
45
Gemini AO Program
Baseline Schedule
2000
2001
2002
2003
2004
Duration O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M
1632 days
ID Task Name
1 CP LGS M CAO System
2
Conceptu al Design
632 days
• Conceptual design
review: 3/00
3
CP Sight Characterization
4
Science and System Implimentation Review
5
CoD Forum
6
Review Forum
7
System Concept Development
8
System Requirements Review (Gemini Board)
• Preliminary design
reviews: 12/00
9
System Conceptual Design
10
Conceptual Design Review
11
Subsystem Requirements and Interface Description
12
261 days
65 days
1 day
22 days
AO Instru m ent Package
152 days
1 day
87 days
0 days
799 days
13
Prelim inary Design Phase
141 days
14
Preliminary Design
140 days
• Critical design
reviews: 12/01
15
Lab Demo
140 days
16
Integration and Test Planning
120 days
17
Preliminary Design Review (s)
18
Detailed Design Phase
1 day
Subsystem Detailed Design
257 days
20
Integration and test planning
160 days
• Subsystems
complete: 6/03
21
Critical Des ign Review (s)
• System integration
and test: 10/03
27
• Science handover:
3/04
October 21, 1999
Fabricatio n Phase
1 day
Fabrication of Subsystems
300 days
24
I, T, & C Pr oceedures
200 days
25
Operational Softw are Implementation
300 days
26
Integration and Test
100 days
799 days
28
Prelim inary Design Phase
141 days
29
Preliminary Design
140 days
30
Integration and Test Planning
140 days
31
Preliminary Design Review (s)
32
Detailed Design Phase
1 day
Subsystem Detailed Design
257 days
34
Risk Reduc tion Prototyping
257 days
35
Integration and Test Planning
160 days
36
Critical Des ign Review (s)
Fabricatio n Phase
12/14
258 days
33
37
12/11
400 days
23
Laser Sys tem
12/14
258 days
19
22
3/31
44 days
1 day
12/11
400 days
38
Fabrication of Subsystems
300 days
39
I, T, & C Pr oceedures
200 days
40
Operational Softw are Implementation
300 days
41
Integration and Test
100 days
42
System In tegration Phase
201 days
43
System Integration and Test
100 days
44
Commissioning
100 days
45
Science Handover
1 day
Gemini Science Committee
46
Gemini AO Program
Gemini AO Program:
Division of Work within Partnership
Gemini AO program ambitious, but IGPO is not proceeding alone
•
•
Partnership Workload (including vendors):
– Hokupa’a-85 for Gemini-North: UH
– Hokupa’a-85 for Gemini-South:
• WFS and DM: UH
• Commercially supplied dye laser
– Altair: HIA
– Altair LGS:
• WFS upgrades: HIA
• Laser source: Contract
– Coronograph AO: Instrument supplier
Common infrastructure (IGPO): LGS transfer optics, launch telescope,
and safety system
• MCAO is the focus of IGPO efforts. Outsourcing of work
expected after CoDR.
October 21, 1999
Gemini Science Committee
47