NGAO System Design Phase
Update
Peter Wizinowich, Rich Dekany, Don Gavel, Claire Max
for NGAO Team
(with input from Sean Adkins, Matthew Britton, Ralf Flicker, Chris Neyman)
SSC Meeting
June 20, 2007
Presentation Sequence
• Project Report #3
• Science & System Requirements
• System Engineering
– Performance Budgets
– Trade Studies
– System Architecture
• Keck Science Meeting
• Summary
2
Project Report #3
Project Report #3
•
3rd report submitted to Directors on June 18
http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/SystemDesignPhasePlanning
•
Emphasis during this report period has been on:
–
Scheduled mid-year replan
•
–
Science case & system requirements
•
•
–
Good progress on system requirements & significant work remains
Postdoc, Elizabeth McGrath, has started on a part-time basis
Performance budgets & trade studies
•
•
•
–
Replan complete & being tracked
Astrometry & wavefront error reports issued
Good progress on companion sensitivity
9 trade studies complete
The definition and start of the system architecture phase
•
Priority task for this summer
4
Replan
•
Replan documents (v26) posted at
http://www.oir.caltech.edu/twiki_oir/pub/Keck/NGAO/SystemDesignPhasePlanning/
– KAON 481 System Design Phase Mid-FY07 Replan
– MS Project plan
– Excel spreadsheet which records the changes
•
•
Purpose to accomplish what we need for the system design phase within
remaining budget & schedule.
Endeavored to utilize lessons learned from the 1st 6 months.
–
–
–
–
•
Descoped some activities not critical to system design
Added some new activities that have been identified from our studies
More encompassing system architecture phase introduced prior to subsystem
designs
Different management approach selected - using a small dedicated team with
weekly telecons, for the 3 month system architecture phase. This phase will act as
a test of this approach.
In addition we will need to actively work with the team to bring tasks to closure
5
Project Report
#3 – Status of
New Milestone
Dates
#
MILESTONE
DATE
STATUS
1
SD SEMP Approved
10/9/06
Complete
2
SD phase contracts in place
10/27/06
Complete
3
Science Requirements Summary v1.0
Release
10/27/06
Complete
4
System Requirements Document
(SRD) v1.0 Release
12/8/06
Complete
5
Performance Budgets Summary v1.0
Release
6/15/07
25% complete
6
SRD v2.0 Release
5/22/07
Good progress
7
Trade Studies Complete
6/22/07
15 of 18 complete
8
SRD
v3.0 Release
9/7/07
9
System Design Manual (SDM)
v1.0 Release
9/21/07
10
Technical Risk Analysis
V1.0 Release
11
Cost Review Complete
12/7/07
12
SDM
v2.0 Release
2/12/08
13
System Design Review
Package Distributed
3/4/08
14
System Design Review
3/31/08
15
SDR Report & Project Planning
Presentation at SSC meeting
9/21/07
4/14/08
Some work as part of
system architecture
Some work as part of
system architecture
Some work as part of
system architecture
9
Project Report #3
Schedule: 38% of System Design Phase activities complete through May
Budget: $427.5k spent through May.
–
–
52% of the FY07 budget (versus plan of ~67%)
41% of the System Design Phase budget, excluding contingency
10
Project Report #3
•
Products since last report include the following KAONs:
–
303 Mauna Kea Atmospheric Parameters
–
471 Wavefront Error Budget
–
474 Photometry for NGAO
–
475 Tomography Codes Comparison and Validation for NGAO
–
476 Observing Models Trade Study
–
480 Astrometry for NGAO
–
481 System Design Phase Mid-FY07 Replan
–
482 Keck Telescope Wavefront Error Trade Study
–
483 Keck Interferometer Support Trade Study
–
485 Adaptive Secondary Mirror Trade Study
–
487 LOWFS Architecture Trade Study
–
490 Rayleigh Rejection Trade Study
–
492 Null-mode & Quadratic Mode Tomography Error
–
493 Science Instrument Reuse Trade Study
–
494 NGAO Project Report #3
All KAONs at http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/NewKAONs
11
Science Case Requirements
+ Science Instruments
Science Case Requirements
• Review of the science requirements section of the System
Requirements Document (SRD) raised issues
– Need to complete science requirements for each science case
– Need to document flow down to performance requirements
– Science Case Requirements Document (SCRD) v1 missing several
science cases
– Need to better document science operations requirements & flow down
• Next steps
– Complete identification of performance requirements for AO & instruments
– Work on “TBD” parameters identified in SRD
– Complete science operations requirements section with identification of
AO & instrument requirements
– Complete SRD v2 with goal values for performance requirements & initial
sections for implementation & design requirements
13
Science Requirements: Improved Methodology
• Cleaner separation between science-based requirements and derived
requirements for AO + instruments
• Example: Spectroscopy of galaxies lensed by galaxies (3 of 17 rows)
• Better basis for evaluating AO trades (in process)
1
2
3
Science Performance
Requirement
SNR ≥ 10 for a z = 1–2
galaxy in an integration
time ≤ 3 hrs for a
Gaussian width 20
km/sec (50 km/sec
FWHM) with a spatial
resolution of 50 mas
Target sample size of ≥
50
galaxies,
with
density on the sky of 10
per square degree.
Survey time ~ 3 years.
Required
observing
wavelengths J, H and K
(to 2.4 µm). Emphasis
is on J and H. Would
use z and I bands if
available.
AO Derived
Requirements
Wavefront error and tip-tilt
coverage such that 50%
enclosed energy fraction is
< 50 mas over at least 33%
of the sky.
Instrument Requirements
Spectral resolution needed
to achieve 20 km/sec sigma
on these targets. Spatial
sampling at least 0.025 arc
sec.
Number of IFUs: one for
the lensed galaxy, plus one
to monitor the PSF and one
to monitor the sky. The
extra two IFUs could be
dispensed with if there were
other ways to monitor the
PSF
and
the
sky
background.
Implies
a
maximum Coverage from I band to
wavefront error in order to 2.4 microns
achieve performance in
item 1 for J band
14
Science cases have been re-worked
using new approach
• “Science” parts of science requirements are clear
• Flow-down to AO & instrument requirements in process
• To date, no science case requires corrected fields larger
than 15 - 20 arc sec
• However, analysis of an additional science case is
needed: resolved stellar populations
– Trade-off between lower Strehl ratio over larger contiguous area
(MCAO), vs. higher Strehl over multiple smaller areas (MOAO)
• Until this is resolved, the system architecture study is
carrying along one MCAO option
15
Science Case Requirements
• The cases with initial science requirements tables include:
–
–
–
–
–
–
–
–
–
Asteroid companions survey and orbit determination
Moons of the giant planets
Shape and size of asteroids
Galactic Center astrometry and radial velocities
Planets around low mass stars
High redshift galaxies
Nearby AGNs
Gravitational lensing
QSO host galaxies
• Galactic Center Nature of Sgr A*: 3-5 µm color & 2 µm polarimetry was
descoped as lower priority in the replan.
• The science cases still requiring initial requirements tables include:
– Debris disks, protostellar envelopes and outflows: contrast and polarimetry
– Resolved stellar populations in crowded fields
V1.10 of SRD:
http://www.oir.caltech.edu/twiki_oir/pub/Keck/NGAO/WorkProducts/KAON456_NGAO_SRD_v1.10.doc
16
Science Instruments (IWG)
• Working on initial flow down from science requirements
• Draft of “Summary Descriptions of NGAO Instruments” in progress
• Next step is review of instrument function allocations and
descriptions with science team
17
NGAO System Engineering:
Performance Budgets
Trade Studies
System Architecture
Wavefront Error Budget Predictions
Scenario
HO GS
TT GS
Io
Kuiper Belt
Exo Jupiter
Ext. Groth
Gal. Ctr.
Sci. Target
6 x LGS
6 x LGS
6 x LGS
6 x LGS
Sci. Target
Field star
Sci. Target
Field star
IRS 7
Sky Cov. Exp. Time
n/a
10.00%
n/a
30.00%
n/a
10 sec
300 sec
300 sec
1800 sec
30 sec
HO Error
97 nm
172 nm
129 nm
162 nm
268 nm
TT Error 1.65 um
Strehl
6.2 mas
5.7 mas
3.4 mas
18.3 mas
2.0 mas
73.00%
56.00%
74.00%
36.00%
36.00%
Assumes a typical Mauna Kea turbulence profile
with a Greenwood Frequency of 41 Hz
Optimum system configuration depends on
observing scenario
Frame rates up to 2.5 kHz
 Asterism diameters up to 1.6 arcmin

Astrometric Precision Recommendations
Astrometric accuracy/precision limited by imperfect PSF, optical distortion
knowledge & refraction effects. Several tools could improve astrometry:
•
Cn2 measurement on minute timescales
–
–
–
•
Auxiliary PSF camera
–
–
•
Example: a well-machined pin hole slit mask far upstream in the optical path
Need to rotate & translate to solve for positions & optical distortions
Atmospheric dispersion corrector (ADC)
–
•
•
To provide simultaneous OTF for use in post-processing
Nyquist sampled & deployable to find a PSF
Ability to solve for & monitor optical distortion in AO & instrument
–
–
•
Baseline to understand stability expectations
Aid to target selection & observing strategy decisions
Profiles in post-processing algorithms for improving astrometry
Could make identifying & correcting residual atmospheric refraction more difficult
Provide plate scale stability at level of current Keck AO (<10−4 over a night)
Provide an adequate wavefront error
–
Preliminary: 140 nm required to achieve < 0.1 mas
20
Trade Studies
• The following studies have been completed since the last meeting:
–
–
–
–
–
–
–
–
–
MOAO & MCAO
Adaptive secondary mirror option
Keck Interferometer support
Science instrument re-use
Telescope wavefront errors
Observing model
Rayleigh rejection
LGS wavefront sensor number and type
Low order wavefront sensor architecture
• Remaining studies:
– Optical relay & field rotation strategy
– D-IFU & LOWFS AO & object selection (new)
– Uplink compensation (new)
21
LOWFS architecture Trade Study
• Main conclusions:
– Benefit from doing LOWFS in the NIR &
combining J+H band
• Consistent with KAON 470
– Pyramid overall performance better than
Shack-Hartman (not significantly for tip-tilt)
– NGS image sharpening is a performance
driver:
• Strongly suggests internal MEMS correction
• Consider dedicated LGS for NGS sharpening
• Tentative architecture recommendation:
– Two near-IR tip/tilt WFS
– One 2x2 pyramid WFS (tip/tilt, focus,
astimatism)
– All three have internal MEMS DMs
22
System Architecture
•
•
•
Focused “core” team (6 members)
Builds on work to date (requirements, performance budgets & trade studies)
1st define 2-3 candidates for each of the key subsystems:
– LGS production & control, optical relay, LGS & NGS wavefront sensing, acquisition
– Example - LGS WFS evaluation includes: radial & conventional Shack-Hartman WFS
& Pyramid WFS
•
•
2nd evaluate these options for performance, risk & cost
July 9-13 UCSC meeting will focus on:
– Candidate architectures as combinations of top ranked subsystems
– Architecture system-level cost estimation
– Initial subsystem functional requirements
•
http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/SystemArchitecture
23
Keck Science Meeting
• We would like to request part of the Keck Strategic
Planning Meeting for NGAO
– Entire morning or afternoon if possible
• Goal
– Broader community exposure, input & engagement
• Suggested Topics
–
–
–
–
Science cases & requirements
System design overview
Operational models
Science instruments
24
Summary
• Management:
– Scheduled mid-year replan completed
– Keeping on schedule will need close attention
– Intention continues to be to deliver the system design within
budget & schedule
• Technical:
– Good progress made on requirements, performance budgets &
trade studies
– System architecture phase begun
25