Trade Study Report:
NGAO versus Keck AO Upgrade
NGAO Meeting #5
Peter Wizinowich
March 7, 2007
Presentation Sequence
•
•
•
•
Dictionary Definition & Status
Performance Budgets versus Requirements
Potential Upgrade Plan
Summary
2
WBS Dictionary Definition & Status
•
Definition: Consider the feasibility of upgrading one of the existing Keck AO systems
incrementally to meet the NGAO science requirements. Consider opto-mechanical
constraints & upgradeability of embedded & supervisory control systems. Consider
impact on science operations during NGAO commissioning. Complete when option
assessment documented.
•
Status:
– Work scope planning sheet approved
http://www.oir.caltech.edu/twiki_oir/pub/Keck/NGAO/WorkProducts/3.1.2.1.2_NGAOvsKeckAOUpgrades.doc
– KAON 461 Wavefront error budget predictions complete (need to check NGAO
results) http://www.oir.caltech.edu/twiki_oir/pub/Keck/NGAO/WorkProducts/KAON461_Keck_AO_Error_Budget.doc
– KAON 462 Trade study report contains comparison of upgrade to performance
budgets (needs more work) & a potential upgrade plan
http://www.oir.caltech.edu/twiki_oir/pub/Keck/NGAO/WorkProducts/KAON462_Keck_AO_Upgrade.doc
•
Remaining
– More work on performance budgets
– Discussion of opto-mechanical constraints & upgradeability of embedded &
supervisory control systems
– Discussion of impact on science operations
3
Wavefront Error Budget (KAON 461)
1st step: anchor the NGAO excel tool to measured Keck AO performance
Atmospheric fitting
Telescope fitting
Camera
DM bandwidth
DM measurement
TT bandwidth
TT measurement
LGS focus error
Focal anisoplanatism
LGS high-order error
Miscellaneous
Miscellaneous (NGAO)
Calibrations
Total wavefront error
K-band Strehl
Percentile Seeing
NGS bright star
Blue Meas- NGAO
Book
ured
tool
123
139
110
105
60
66
35
113
110
36
103
115
0
17
16
34
75
91
0
9
5
0
0
0
0
0
0
0
0
0
0
120
0
0
0
106
30
0
30
175
258
250
0.78
0.58
0.57
50%
75%
65%
LGS (10th mag)
Blue Meas- NGAO
Book
ured
tool
123
128
110
105
60
66
35
113
110
36
157
146
98
142
150
34
109
94
34
23
11
35
36
36
127
175
208
0
80
80
0
120
0
0
0
72
30
0
30
243
378
372
0.62
0.31
0.30
50%
75%
65%
LGS (18th)
Meas- NGAO
ured
tool
128
110
60
66
113
110
157
146
142
150
300
243
300
349
36
91
175
208
80
80
120
0
0
72
0
30
557
563
0.15
0.08
75%
65%
4
Wavefront Error Budget (KAON 461)
2nd step: Define a series of upgrades:
• NGWFC
• K1 LGS
• CCID56
• 2x DM
• Science Instrument
• Simplified Tomography
• Vibration Reduction
• 50W Laser
• For reference the NGAO case was also evaluated
3rd step: Evaluate the wavefront error budget using the NGAO tool
• 3 cases considered
– NGS AO with an 8th mag NGS
– LGS AO with a 10th mag NGS
– LGS AO with an 18th mag NGS
5
Wavefront
Error
Budget
LGS (10th mag) case:
• Upgrade achieves 229
nm vs 155 nm for
NGAO
• Next upgrade step
would be multiple LGS
(need to look at
feasibility)
• Relevant requirements:
155 nm for 1% sky
coverage
205 nm for 20% sky
coverage
6
Wavefront
Error
Budget
LGS (18th mag) case:
• Upgrade achieves
419 nm vs 158 nm
for NGAO
• NGAO estimate
likely incorrect
• Next upgrade step
would be multiple
NIR tilt sensors
• Relevant
requirements:
205 nm for 20% sky
coverage
240 nm for 80% sky
coverage
7
Wavefront
Error
Budget
NGS (8th mag) case:
• Upgrade achieves
149 nm
• No significant
difference between
Upgrade & NGAO
• Relevant
requirements:
155 nm for 1% sky
coverage
8
Companion Sensitivity
•
Galactic Center Requirement
Contrast versus Radius
≥ 4 mags at 0.055” at 1-2.5µm
≥ 10 mags at 0.5” at 0.7-3.5µm
for 30% sky coverage & ≤ 20”
object diameter
•
Conclusions
– GC requirement can be met
with Upgrade
– General requirement can be
met at H & K with Upgrade
– NGAO only ~ 0.4 mag better
at H & K than Upgrade,
increasing to 1.5 mag at 1 µm
•
Question
– Are these the right
requirements?
K1 LGS (1.25um)
-2.00
General Requirement
K1 LGS (1.65um)
-3.00
K1 LGS (2.2 um)
-4.00
Contrast (magnitudes)
•
K1 LGS (1.0um)
Upgrade (1.0um)
-5.00
Upgrade (1.25um)
-6.00
Upgrade(1.65um)
Upgrade 2.2um)
-7.00
NGAO (1.0um)
-8.00
NGAO (1.25um)
-9.00
NGAO (1.65um)
NGAO (2.2um)
-10.00
-11.00
-12.00
-13.00
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Radius (arcsec)
9
Other Performance Budgets
• Upgrade likely to meet
–
–
–
–
–
–
–
Throughput requirements
Galactic Center astrometry requirement (barely)
Other astrometric requirements (may already be met)
Observing efficiency
Observing uptime
Compatibility with new science instruments (designed for Keck AO)
Interferometer support
• Upgrade not likely to meet
– Emissivity requirement
• Uncertain
– Photometric requirements
– Polarimetric requirements
10
Potential Upgrade Plan
11
Summary
•
A Keck AO upgrade path is worth further consideration
– This could be an incremental or a few-shot approach
•
Pros:
– Lower cost
– If an incremental approach is taken:
• Performance improved as funds available
• Performance improvements sooner
– Don’t take all or nothing risk (this can be mitigated some for NGAO)
– Interferometer addressed
•
Cons:
– Lower performance than NGAO
– If an incremental approach is taken
• Periodic shutdowns for upgrades
• Risk to operations of a system always under development
• Risk to development team schedule from supporting operational system
– Only two science instruments (possibly 3) at any one time (unless also upgrade
other telescope)
12