Trade Study Report:Trade Study Report:NGAO versus Keck AO UpgradeNGAO versus Keck AO Upgrade

NGAO Meeting #5NGAO Meeting #5Peter WizinowichPeter Wizinowich

March 7, 2007March 7, 2007

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Presentation Sequence

• Dictionary Definition & Status• Performance Budgets versus Requirements• Potential Upgrade Plan• Summary

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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

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Wavefront Error Budget (KAON 461)

Blue Book

Meas-ured

NGAO tool

Blue Book

Meas-ured

NGAO tool

Meas-ured

NGAO tool

Atmospheric fitting 123 139 110 123 128 110 128 110Telescope fitting 105 60 66 105 60 66 60 66Camera 35 113 110 35 113 110 113 110DM bandwidth 36 103 115 36 157 146 157 146DM measurement 0 17 16 98 142 150 142 150TT bandwidth 34 75 91 34 109 94 300 243TT measurement 0 9 5 34 23 11 300 349LGS focus error 0 0 0 35 36 36 36 91Focal anisoplanatism 0 0 0 127 175 208 175 208LGS high-order error 0 0 0 0 80 80 80 80Miscellaneous 0 120 0 0 120 0 120 0Miscellaneous (NGAO) 0 0 106 0 0 72 0 72Calibrations 30 0 30 30 0 30 0 30Total wavefront error 175 258 250 243 378 372 557 563K-band Strehl 0.78 0.58 0.57 0.62 0.31 0.30 0.15 0.08Percentile Seeing 50% 75% 65% 50% 75% 65% 75% 65%

LGS (10th mag) LGS (18th)NGS bright star

1st step: anchor the NGAO excel tool to measured Keck AO performance

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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

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Wavefront Error

BudgetLGS (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

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Wavefront Error

BudgetLGS (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

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Wavefront Error

BudgetNGS (8th mag) case:

• Upgrade achieves 149 nm

• No significant difference between Upgrade & NGAO

• Relevant requirements:

155 nm for 1% sky coverage

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Companion Sensitivity• Galactic Center Requirement

≥ 4 mags at 0.055” at 1-2.5µm

• General Requirement≥ 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?

Contrast versus Radius

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Radius (arcsec)

Co

ntr

ast

(mag

nit

ud

es)

K1 LGS (1.0um)

K1 LGS (1.25um)

K1 LGS (1.65um)

K1 LGS (2.2 um)

Upgrade (1.0um)

Upgrade (1.25um)

Upgrade(1.65um)

Upgrade 2.2um)

NGAO (1.0um)

NGAO (1.25um)

NGAO (1.65um)

NGAO (2.2um)

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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

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Potential Upgrade Plan

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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)