Transcript MAGIQ Overview - Caltech Optical Observatories

NGAO System Design Phase
Update
Peter Wizinowich, Rich Dekany, Don Gavel, Claire Max
for NGAO Team
SSC Meeting
January 24, 2007
Presentation Sequence
• SSC Co-Chair Questions
• Management Update
A.
B.
C.
D.
E.
Management Structure
Systems Engineering Management Plan
Documentation & Coordination
Instruments Working Group
Project Report #1
• Technical Update
– Science Requirements
– Performance Budgets
– Trade Studies
• Summary
2
SSC Co-Chair Questions
All of the following questions are addressed in the Systems Engineering
Management Plan (summarized in the following Management update
slides):
1. What is the product of this study phase?
•
Following Keck development process (see System Design phase
deliverables on slide 6). Includes conceptual design (with options), initial
cost estimate & management plan for remaining project. Instrument
concepts developed to proposal level (precursor to their System Design
phase).
2. Are any intermediate reviews planned?
•
Frequent internal product reviews, including cost reviews in Aug & Dec.
SDR at end of this phase (3/31/08). Project reports provided prior to each
SSC meeting.
3. Who is doing what, and what % of time is each person devoting to
NGAO?
•
Details in project plan. High level summary of key personnel on slide 10.
4. What are the major goals/milestones of this phase?
•
See milestones on slide 9.
3
SSC Co-Chair Questions
5. What are the big issues and how are they being addressed?
•
•
Big picture: Cost, schedule & performance + structuring the program to suit the
funding. Science & engineering team working closely with management to produce
a compelling & realistic vision.
Near term: Science community input & team ramp-up. Engaging scientists in
science case requirements & performance budgets. Freeing personnel from other
responsibilities.
6. What is the timescale for this phase and when can the SSC expect a full
report?
•
See schedule on slide 15.
7. What is the relationship between the NGAO team and the AOWG
–
–
–
–
AOWG – Bouchez, Dekany, Koo, Larkin, Liu (co-chair), Macintosh, Marchis,
Matthews, Max (co-chair) + Ellis (rotating on)
The AOWG was a very active participant in the NGAO proposal.
Max, Liu & Marchis are leading the science case requirements
AOWG last met 8/06.
8. Comparison of NGAO versus planned AO performance of current generation.
Why should we believe new models?
–
Addressed in the performance budgets section.
4
A. Management Structure
•
•
Proposal approved at Jun/06 SSC & Board meetings
WMKO, UCO & COO Directors subsequently established
an Executive Committee (EC) to manage System Design
phase:
Wizinowich-WMKO (chair), Dekany-Caltech, Gavel-UCSC, MaxUCSC, CFAO (project scientist)
5
B. Systems Engineering Management Plan
(SEMP)
•
SEMP submitted to Directors at end of Sept/06
–
–
•
System design started Oct/06
–
•
Verbal approval received to proceed
Budget approval being finalized
Completion planned for mid-FY08
Products of this study phase (Q1) - System design phase
deliverables
–
–
–
–
System Requirements Document - Science & Observatory
requirements & flow down to system requirements
System Design Manual – Performance budgets, functional
requirements, system & subsystem architectures
SEMP – For remaining NGAO phases
System Design Report – Summary for System Design Review
6
B. SEMP: Approach
Science
Requirements
1.
2.
3.
4.
Initial
Concept
Performance
Assessment
Initial focus on requirements & performance budgets to ensure that we
understand largest levers on the design
Initial attempt at defining the AO system architecture & the functional
requirements for the major systems
In parallel with 1 & 2 perform trade studies to better understand the
appropriate design choices
A process of iteration and refinement will lead to the final version of the
AO architecture & major systems requirements
•
5.
Technical
Implications
Includes continued development of performance budgets & functional
requirements
Develop cost estimates & plans for remainder of NGAO project
7
B. SEMP: Budget
Cost ($k)
WBS
Name
FY07
FY08
Total
1
Management
74
49
123
2
System Requirements
119
3
122
3
System Design
560
90
650
4
Systems Engineering Management Plan
5
79
84
Travel/Procurements
40
20
60
Contingency (part of overall Observatory
contingency)
10
94
104
808
335
1143
Total ($k) =
Work (hours)
Institute
FY07
FY08
Total
COO
2836
702
3589
UCSC
2991
845
3926
WMKO
5355
1852
7360
Students
1850
0
1850
Total =
13032
3399
16725
$163k increase in cost of labor since
proposal, due to distributed project
nature
Total work same as in original proposal
8
B. SEMP:
Milestones
MILESTONE
DATE
DESCRIPTION
SD SEMP Approved
10/9/06
Approval of plan by Directors
SD phase contracts in place
10/27/06
Contracts issued to Caltech & UCSC
for the system design phase
Science Requirements Summary v1.0
10/27/06
Initial Release of Science
Requirements as input to trade
studies & performance budgeting
System Requirements Document v1.0
12/8/06
Initial release with emphasis on the
science requirements
Performance Budgets Summary v1.0
2/27/07
1st round of all performance budgets
complete & documented
System Requirements Doc v2.0
3/22/07
2nd release
Trade Studies Complete
5/25/07
All trade studies complete &
documented (as a series of KAONs)
System Requirements Doc v3.0
7/12/07
3rd release of System Requirements
System Design Manual v1.0
8/31/07
1st release of System Design Manual
Technical Risk Analysis v1.0
11/13/07
1st round of project risk analysis
complete & documented
Cost Review Complete
11/30/07
Project cost estimates complete,
documented & internally reviewed
System Design Manual v2.0
1/8/07
2nd release
System Design Review Package Distributed
3/4/08
SDR documents sent to reviewers
System Design Review
3/31/08
SDR meeting
SDR Report & Project Planning
Presentation at SSC meeting
4/14/08
Final SD phase report including
9
results of SDR & project plans
B. SEMP: Team
Name
Institute
%
NGAO-relevant Expertise
Bouchez
COO
11
AO systems & science
Dekany
COO
33
EC; AO systems & mgmt
Moore
COO
31
Instruments
Velur
COO
38
Lasers & wavefront sensors (mechanical)
Bauman
UCSC
21
Optics
Gavel
UCSC
33
EC; AO systems & mgmt
Max
UCSC
22
EC Science Team chair
Postdoc
UCSC
46
AO science
Adkins
WMKO
15
Instruments & Project Mgmt
Chin
WMKO
18
Electronics
Flicker
WMKO
38
AO Modeling
Johansson
WMKO
18
AO Control (software & electronics)
Le Mignant
WMKO
15
AO science operations
Meguro
WMKO
13
Mechanical
Neyman
WMKO
67
AO systems
Wizinowich
WMKO
36
EC chair; AO systems & mgmt
Represents 84% of the work force.
10
C. Documentation & Coordination
•
•
NGAO Twiki site at http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/WebHome
Includes collections for
–
Team meetings
•
–
Executive committee
•
•
–
Table of WBS elements, planning sheets & products
Performance budgets
•
–
Planning & tracking documents
EC weekly meeting minutes
Work packages
•
–
Agendas & documents posted in advance; action items posted &
followed up
Meeting summaries & products
Science team
11
D. Instruments Working Group
• Instruments Working Group (IWG) being formed for NGAO System
Design Phase
– Focused on instrumentation related matters
• Instrument specialist perspective for NGAO
• Resource for AO system design team on instrumentation issues
– Organization (6 to 8 members)
• 3 to 4 funded from current NGAO plan
–
–
–
–
Responsible for most of technical work related to NGAO instrumentation WBS
Sean Adkins (IWG chair, overall systems, detectors, electronics & interfaces)
Anna Moore (instrument generalist, optical & mechanical)
James Larkin/UCLA IR Lab staff members (instrument design, optical &
mechanical, cryogenics experience)
– TBD software engineer
• 3 to 4 TBD volunteers from NGAO science team
– Primary contacts with science team for instrument related science requirements
• Regular meetings will be held involving the entire group
• Additional assistance & advice will be sought from the diverse base of
the collective instrumentation & technical resources at UC & CIT
12
E. Project Report #1
•
•
Directors’ requested written project reports prior to each
SSC meeting
1st report submitted to Directors on Jan. 19
http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/SystemDesignPhasePlanning
•
•
•
Good progress made on initiating NGAO System Design
phase & on building up an effective team
Emphasis to date, as planned, on understanding the major
design drivers through a process of iteratively developing
the science case requirements & the performance budgets
Work has begun on a number of trade studies in support of
the performance budgets & the future design choices
13
E. Project Report #1
#
MILESTONE
DATE
DESCRIPTION
1
SD SEMP Approved
10/9/06
2
SD phase contracts in place
10/27/06
Contracts issued to Caltech & UCSC
for the system design phase.
$50k initial contracts
issued on 12/20
3
Science Case Requirements
Summary v1.0 Release
10/27/06
Initial Release as input to trade
studies & performance
budgeting
V1.0 to be completed in
Jan/07
4
System Requirements
Document v1.0 Release
12/8/06
Initial release of System
Requirements with emphasis on
science requirements
5
Performance Budgets
Summary v1.0 Release
2/27/07
1st round of all performance budgets
complete & documented
Good progress
6
System Requirements Doc
v2.0 Release
3/22/07
2nd release of System Requirements
Document
Not started yet
7
Trade Studies Complete
5/25/07
All trade studies complete (Keck
Adaptive Optics Notes)
Good progress
Approval of this plan by the
Directors. SEMP released to
Directors on 9/29/06.
STATUS
Verbal approval received.
Written approval
requested
V1.0 to be completed in
Jan/07
14
E. Project Report #1
15
E. Project Report #1
Budget
•
•
$772k budgeted for FY07 in 5-year plan
$110k spent in 1st quarter
–
–
Low due to slower than planned ramp up of personnel
Average of 4.3 FTEs
Summary
•
Good technical progress as you will see in the following slides
•
Team and management processes now largely in place
•
Expect the teams rate of progress to be close to the rate in the plan
during the 2nd quarter
16
Science Case Requirements
& System Requirements
Max, Ghez, Law, Liu, Lu, Macintosh, Marchis, Steidel
Neyman, Wizinowich
Science Requirements Process
• Approach:
– Start from significant science case development in proposal
– Analyze limited set of these key science cases in order to
understand and document the requirements on NGAO +
Instruments
– Begin with cases that stress AO design the most in multiple
directions
– Progress to include more science cases
– Iterate 4 times with AO & instrument requirements
• For each case, discuss
– Science goals, proposed observations, AO performance
requirements, instrument requirements
19
Science
Requirements &
Performance
Budget Process
20
Science Case Requirements Document
Release 1 Contents
• JWST and ALMA capabilities
• Future AO capabilities of other observatories
• Key science cases and what they stress most:
– Multiplicity, size, shape of minor planets
• High contrast, wavefront error, visible light performance
– Planetary & brown dwarf companions to low mass stars
• High contrast
– General relativistic effects in the Galactic Center
• Astrometry and radial velocity accuracy
– Assembly and star formation history of high z galaxies
• Lower backgrounds, multiple deployable IFUs, sky coverage
21
JWST capabilities
•
•
•
Cryogenic 6.5-m space telescope, launch in
2013
Higher faint-source sensitivity than Keck
NGAO, due to low backgrounds
Not diffraction limited below K band
–
–
•
Primary mirror spec
NIRCAM px scale 0.035”, NIRSpec px scale
0.1”
Areas where Keck NGAO would complement
JWST
1. Spectroscopy @ spatial resolution better than
0.1”,  = 0.6 - 2 μm
2. Imaging @ spatial resolution better than 0.07”,
 = 0.6 - 2 μm
3. Multi-IFU spectroscopy
22
Key science requirements:
Multiplicity, size, shape of minor planets
• Minor planet formation history and interiors by
accurate measurements of size, shape,
companions
• Small, on-axis imaging field ( ≤ 3 arc sec)
• Relative photometry to 5%, astrometry ≤ 5 mas,
wavefront error ≤ 170 nm, contrast H  5.5 at
0.5 arc sec
• Instruments:
– Imaging: visible and near-IR
– Near IR IFU spectroscopy: 1.5 arc sec field; still
need to specify spectral resolution
• Observing modes: non-sidereal tracking,
<10 minute overhead switching between
targets, consider queue or flexible scheduling
Asteroid Sylvia
and moons
23
Key Science Requirements:
Planetary & brown dwarf companions to low mass stars
• Faintness of low-mass stars, brown dwarfs,
and the youngest stars make them
excellent NGAO targets
• Small imaging field ≤ 5 arc sec
• Relative photometry to 5%, astrometry to
PSF FWHM/10, contrast H = 13 at 1 arc
sec
• Instruments:
– Imaging 0.9 - 2.4 microns
– Single near IR IFU spectroscopy, still need
to specify spectral resolution
• Observing modes: coronagraph needed
24
Key Science Requirements:
General relativistic effects in the Galactic Center
• Measure General Relativistic
prograde precession of stellar
orbits in Galactic Center
• Requires astrometric precision of
100 as (now 250 as) and radial
velocity precision to 10 km/sec
(now 20 km/sec)
• K band, wavefront error ≤ 170 nm
• Imaging field 10 x 10 arc sec
• Near IR IFU spectra, R ≥ 4000,
FOV ≥ 1” x 1”, need IR ADC
Need to evaluate optimal
spectral resolution
25
Key Science Requirements:
Assembly and star formation history of high z galaxies
• Redshifts 1.5 ≤ z ≤ 2.5: most active
star formation, form bulges & disks
– Optical lines such as H are shifted
into near IR
• Density 2 - 20 / sq arc sec 
6 to 12 IFUs in field of regard
• J, H, K bands
• IFU fields ~ 1 x 3 arc sec for sky
subtraction, 50 mas spaxels, R = 3000
- 4000, EE > 50% within 50 mas for
optimal tip-tilt stars
• Low backgrounds: AO system
Need to evaluate which high-z
< 10-20% of (sky + telescope)
science could be done with
higher backgrounds
26
Science requirements summary to date
• Wavefront error 170 nm or better
– Need sensitivity study to see how science would fare if wavefront
error were 200 nm
• Relative photometry to 5%
• Contrast H  5.5 at 0.5 arc sec, H  13 at 1 arc sec
• Astrometry: companions to 5 mas, Galactic Center to
100 as. Need near-IR ADC.
• K-band backgrounds: AO system + IFU < 10-20% of (sky
+ telescope)
– Need sensitivity study to see how high-z science would fare at
higher background levels
• Not yet found a compelling science case for a large
contiguous field (i.e., MCAO)
27
Instruments & observing mode requirements,
to date
• Instruments:
– Refining the requirements developed for the proposal
– On-axis near-IR imager, field ~ 10 x 10 arc sec, coronagraph
– On-axis visible imager (to 0.6 or 0.7 m), field ~ 3 x 3 arc sec,
coronagraph?
– Near IR deployable IFU:
•
•
•
•
6 - 12 channels, field of regard TBD
Field of view ~ 1 x 3 arc sec
50 mas spaxels, EE > 50% within 50 mas for optimal tip-tilt stars
Still need to evaluate optimum spectral resolution
• Observing modes:
– Non-sidereal tracking, <10 minute overhead switching between
targets, consider queue or flexible scheduling
28
NGAO Performance Budget Development
Dekany, Ghez, Marchis, Max, Liu, Gavel, Flicker, Wizinowich,
Cameron, Lu, Britton, Macintosh, Neyman, Ireland, Olsen,
Bouchez, Law, Bauman, Le Mignant, Johansson, Chin
Developing Science-based Performance Budgets
• Systems engineering will consider all of the following
budgets
–
–
–
–
–
–
–
–
–
–
Model assumptions
Model/tool validation
Wavefront error vs. sky coverage
for 5-7 science cases
Photometric precision
in crowded and sparse stellar fields
Astrometric accuracy
at the GC and in sparse fields
High-contrast for diffuse debris disks and compact companions
Polarimetric precision
for high-contrast observations
Transmission/background/SNR
for several science cases
Observing efficiency
Observing uptime
30
Performance Budget Development Goals
• Produce a technical report
– Describing the major drivers, including experimentally supportive
information, quantitative background, and potential simulation
results
• Produce a numerical engineering tool to support future
design iterations
– Emphasizing abstracted quantitative scaling laws and
interdependencies
• Support science requirements development
– Capturing the experience of the science team and reflecting
quantitative underpinning to current limitations
31
Wavefront Error and Encircled Energy
• Science Cases
– Maintain all cases from the June ‘06 NGAO proposal
• Key Drivers for initial budget
– Uncertainty in tomographic reconstruction error
– Uncertainty in sodium laser photoreturn from the mesosphere
• Per delivered Watt, as a function of different pulse formats
• Requires 50W class lasers to investigate non-linear optical pumping effects
– Uncertainty in multi-NGS tilt tomography efficacy
• Not included in original budget development
– Uncertainty in tip/tilt control efficacy with large tip/tilt mirrors
32
Wavefront error budgets
Keck Wavefront Error Budget Summary
Band (microns)
V
R
I
J
H
K
m 0.55 0.70 0.91 1.25 1.65 2.20
m 16% 31% 17% 30% 24% 22%
/D (mas) 11.3 14.4 18.8 25.8 34.0 45.4
• For observations of
–
–
–
–
–
–
TNO multiplicity
Galactic Center
Field galaxies
Io
Nearby AGN
Gravitational Lenses
Wavefront
Error (rms)
High-order Errors (LGS Mode)
Atmospheric Fitting Error
Bandwidth Error
High-order Measurement Error
LGS Tomography Error
Asterism Def ormation Error
Multispectral Error
Scintillation Error
WFS Scintillation Error
nm
nm
nm
nm
nm
nm
nm
nm
43
15
20
10
0
1
16
13
18
4
20
25
15
nm
nm
nm
nm
nm
nm
nm
nm
nm
nm
nm
nm
nm
44
74
150
5
0.50
30
0.37
Alloc
Subaps
Hz
W
beacon(s)
m LLT
zenith angle, H band
Scint index, H-band
Strehl Ratios
0.67
0.72
0.64
0.62
0.94
1.00
0.97
0.99
0.78
0.81
0.76
0.75
0.96
1.00
0.98
0.99
0.87
0.89
0.85
0.84
0.98
1.00
0.99
1.00
0.93
0.94
0.92
0.91
0.99
1.00
0.99
1.00
0.96
0.96
0.95
0.95
0.99
1.00
1.00
1.00
0.98
0.98
0.97
0.97
1.00
1.00
1.00
1.00
0.79
0.97
0.95
0.99
1.00
1.00
1.00
0.98
0.96
1.00
0.95
0.92
0.97
0.86
0.98
0.97
0.99
1.00
1.00
1.00
0.99
0.97
1.00
0.97
0.95
0.98
0.92
0.99
0.98
1.00
1.00
1.00
1.00
0.99
0.98
1.00
0.98
0.97
0.99
0.95
0.99
0.99
1.00
1.00
1.00
1.00
1.00
0.99
1.00
0.99
0.98
0.99
0.97
1.00
0.99
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.99
0.99
1.00
0.99
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.99
1.00
1.00
1.00
1.00
1.00
1.00
1.00
118 nm
Uncorrectable Static Telescope Aberrations
Uncorrectable Dy namic Telescope Aberrations
Static WFS Zero-point Calibration Error
Dy namic WFS Zero-point Calibration Error
Go-to Control Errors
Residual Na Lay er Focus Change
DM Finite Stroke Error
DM Hy steresis
High-Order Aliasing Error
DM Driv e Digitization
Uncorrectable AO Sy stem Aberrations
Uncorrectable Instrument Aberrations
DM-to-lenslet Misregistration (all sources)
64 Acts
Dekens Ph.D
Alloc
Alloc
Alloc
30 m/s Na lay er v el
4.0 um P-P stroke
f rom TMT
44 Subaps
10 bits
Alloc
Alloc
Alloc
68 nm
Angular Anisoplanatism Error
0 nm
Total High Order Wavefront Error
• During requirements
flowdown & initial
design, all performance
budgets will be used
for rapid reevaluation
of performance
cost/benefit
55
50
58
60
22
25
15
10
Parameter
136 nm
Angular
Error (rms)
Tip/Tilt Errors
Tilt Measurement Error (one-axis):
Tilt Bandwidth Error (one-axis)
Tilt Anisoplanatism Error (one-axis)
Residual Centroid Anisoplanatism
Residual Atmospheric Dispersion
Science Instrument Mechanical Drif t
Long Exposure Field Rotation Errors
Residual Telescope Pointing Jitter (one-axis)
5.18
0.63
5.99
1.99
1.06
0.50
0.50
4.85
Total Tip/Tilt Error (one-axis)
mas
mas
mas
mas
mas
mas
mas
mas
9.61 mas
Total Effective Wavefront Error
Sky Coverage
Galactic Lat.
0 arcsec
High Order Strehl
0.10 0.24 0.43 0.64 0.77 0.86
Parameter
Strehl ratios
Equivalent
WFE (rms)
63
8
73
24
13
6
6
59
nm
nm
nm
nm
nm
nm
nm
nm
17.8
61.0
40.2
5
20
Alloc
Alloc
29
mag (mV)
Hz
arcsec
x reduction
x reduction
(0.2 mas)
(0.2 mas)
Hz input disturbance
0.49
0.98
0.42
0.87
0.39
0.99
0.99
0.53
0.61
0.99
0.54
0.91
0.44
1.00
1.00
0.64
0.73
0.99
0.67
0.95
0.84
1.00
1.00
0.75
0.83
1.00
0.79
0.97
0.96
1.00
1.00
0.85
0.90
1.00
0.87
0.98
1.00
1.00
1.00
0.91
0.94
1.00
0.92
0.99
1.00
1.00
1.00
0.95
116 nm
Tip/Tilt Strehl
0.22 0.31 0.44 0.59 0.72 0.82
179 nm
Total Strehl
0.02 0.08 0.19 0.38 0.55 0.71
30 deg
Corresponding Sky Coverage
5.0%
This f raction of sky can be corrected to the Total Ef f ectiv e WFE shown
Assumptions / Parameters
r0
Theta0_ef f
Sodium Abund.
Science Target:
LOWFS Star(s):
0.165 m
at this zenith
1.98 arcsec at this zenith
4 x 109 atoms/cm2
SCAO
MOAO
2 TT
star(s) &
Wind Speed
Outer Scale
LGS Ast. Rad.
13.67 m/s
75 m
0.08 arcmin
0 TTFA
star(s)
Zenith Angle
HO WFS Rate
HO WFS Noise
HOWFS anti-aliasing
LO WFS rate
LO WFS Noise
30 deg
1114 Hz
1.7 e- rms
NO
915 Hz
4.5 e- rms
SH
using
CCD
SH
using
SNAP
Example for LGS observation of TNO using two galactic M-dwarfs as tip/tilt stars
33
Improving Performance Predictions
• Performance versus Blue Book
– Delivered system & science instrument didn’t achieve some
requirements
– Environment different than some assumptions
• Why will NGAO performance estimates be better
– Experience at Palomar, Lick & Keck
– Better understanding of Keck environment
– Performance estimation tools more complete & anchored to actual
performance
• For effects such as multi-guide star tomography for which we don’t
have real-world experience:
– Based on modeling and detailed simulations
• Comparing & validating these tools (TMT, Gemini, COO, Keck, UCO)
– Aided by lab experiments (e.g. LAO)
– Undoubtedly there will be “real-world” effects that we are not yet taking
into account
34
Keck LGS AO Wavefront Error Budget
LGS (10th mag)
Explanations
Blue Book Measured NGAO tool
Atmospheric fitting
123
128
102
Telescope fitting
105
60
70
Camera
35
113
113
NIRC2 aberrations
DM bandwidth
36
157
143
Lower bandwidth
DM measurement
98
142
135
Lower laser power
TT bandwidth
34
109
30
Vibrations - will be added to NGAO tool
TT measurement
34
23
4
LGS focus error
35
36
25
Focal anisoplanatism
127
175
151
Different atmosphere
LGS high-order error
0
80
80
Centroid anisoplanatism
0
0
21
Atmospheric dispersion
0
0
81
Miscellaneous
0
0
0
Dyn calibs, tel, poorly sensed, atmos disp
Miscellaneous (NGAO)
0
0
53
Seven ~20 nm terms
Calibrations
30
0
40
Total wavefront error
243
358
330
K-band Strehl
0.62
0.35
0.41
Percentile Seeing
50%
75%
65%
35
NGAO Trade Studies
Dekany
To date: Bauman, Clare, Gavel, Flicker, Kellner, Neyman, Velur
Design Trade Studies
• Trade studies were initiated at the start of System Design phase
• We have completed or nearly completed:
–
–
–
–
–
–
Methods of mitigating laser Rayleigh backscatter
Laser guide star asterism & geometry
Multi-Object (MOAO) & Multi-Conjugate (MCAO) architectures
Variable vs fixed laser asterism on the sky
Fast tip/tilt opto-mechanical implementation options
Low order wavefront sensor type & number
• Additional design studies now underway include:
–
–
–
–
–
LGS wavefront sensor architecture & type
Science instrument re-use
Telescope static & dynamic errors
Interferometer support
Sodium return versus laser format
37
Mitigating Laser Rayleigh Backscatter
• Evaluate impact of unwanted Rayleigh backscatter on
NGAO system performance
• Status:
– Evaluated the intensity of the Rayleigh as well as aerosol and
cirrus backscatter as seen at the Keck focal plane
– Surveyed the available lasers and pulse formats
– Surveyed methods of blocking Rayleigh
– Interim results at NGAO meeting 3 (12/13/06)
• Best rejection choice: appropriately pulsed laser which
can have a gated return so that almost no Rayleigh
background is encountered
• However, most powerful & promising lasers in terms of
sodium return per Watt, are CW
38
LGS Asterism & Geometry
• Find the simplest LGS
asterism geometry meeting
the performance budget
goals
– Number of guidestars
– Constellation configuration
– Constellation size
• Conclusions
– Simulations of tomography
generally validate the
theoretical scaling laws
– 5 LGS constellation works
ok on 20 arcsec field
– 7-9 LGS will be needed on
90 arcsec field
• KAON 429
39
Multi-Object vs Multi-Conjugate AO
•
Understand potential risks, technical challenges, limitations, advantages &
room for improvement with Multi-Object (MOAO) & Multi-Conjugate (MCAO)
MCAO
Laser
Beams
Laser
Beams
MOAO
Hybrid
Laser
Beams
LGS
Wavefront
Sensors
Dichroic
Tomography
Computer
Dichroic
Science
Instruments
LGS Wavefront
Sensors
•
•
Dichroic
Deformable
Mirrors
Tomography
Computer
DM
Science
Detector
DM
Science
Instruments
Science
Detector
LGS Wavefront
Sensors
Deformable
Mirrors
Tomography
Computer
Calculated performance for 1, 2 & 3 DM MCAO systems & compared to
small sub-field IFU or imager arms, each with a DM
Conclusions:
– MCAO offers a contiguous field for imaging, but a large error term. “Generalized
anisoplanatism” dominates in wide-field cases
– MOAO greatly reduces anisoplanatic error at cost of non-contiguous field
•
KAON 452
40
Summary
• Management update:
– Systems Engineering Management Plan in place
– Executive Committee working well together
– Ramp up slower than planned, but team & processes now in
place
– Good technical progress is being made
• Technical update:
– Iterations between science requirements & performance budgets
are achieving our goals of understanding what is really needed
– Learning what we need to from architecture trade studies
– Building base for design choices & cost/benefit trades
We now have the management structure, plan & enthusiastic
team to produce an excellent NGAO System Design.
41