ngao systems engineering status

NGAO Systems Engineering StatusNGAO Systems Engineering Status

Team Meeting #3 (Video)Team Meeting #3 (Video)R. DekanyR. Dekany

13 December 200613 December 2006

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Outline

• Systems Engineering Overview – WBS 3.1 - Systems Engineering Work Products

– SD Phase Milestones

• IPT progress– Wavefront Error and Encircled Energy

– Photometric Precision

– Astrometric Precision

– High-Contrast

– Background and Throughput (SNR)

– Observing Efficiency and System Uptime



WBS 3.1 Systems Engineering - Work Products• Performance Budgets

– Model Assumptions, Model/Tool Validation– Performance/Efficiency Budgets

• Throughput, Background, WFE, Encircled Energy, Photometric Accuracy, Astrometric Accuracy, Polarimetric Accuracy, Companion Sensitivity, Observing Efficiency, & System Uptime

• Each produces a technical report and numerical tool

– Performance Budgets Summary– Science Products

• e.g. All-in Simulations, Point Source Sensitivities, PSF Uniformity & Stability

• Trade Studies– System Architecture TS Reports– AO System TS Reports– Laser Facility TS Reports

• System Architecture– System Architecture Document– Functional Requirements Documents

• AO, Laser, & Science Ops Functional Requirements, Science Instrument Functional Allocation

– Technology Driver Summary– Technical Risk Analysis



WBS 3.1 - Milestones

• Initial Performance Budgets - 1/22/07 (Team Meeting #4) • Performance Budgets Summary Document - 2/27/07• Trade Studies Complete - 5/25/07• System Architecture Document

– Version 1: 4/18/07

– Version 2: 8/17/07

• Technical Risk Analysis 11/13/07

• I believe we need an ROM cost exercise in Mar/Apr ‘07 on the major architecture options– Current cost estimation (WBS 4.1.2) occurs late in 2007, upon substantial

development of the baseline AO system design



Initial architecture choice timeline

• Initial architecture choices in Mar/Apr 2007– All performance budgets tools in hand– ~60% of the way through all the trade studies

• 95% through system architecture studies

• We need a period of review from the SSC on the high-level architecture choices for NGAO

– e.g. Nasmyth relay, AM2, interferometer support issues, wide-field d-IFU, overall complexity and cost

• Should AO and Laser system architecture development await this SSC input? – Should they precede it?

• March 2007 SD Phase replan may be too close to mid-April to wait and discuss it then

Photometric Precision IPT Status

Matthew Britton (IPT Lead) Richard Dekany, Ralf Flicker, Knut Olsen



Photometric Precision

• Science cases– Photometry in disks and bulges of high-z galaxies

» Claire to provide Observing Scenario for TM #3

– Stellar populations in crowded fields» Knut to provide Observing Scenario for TM #3

• Key Drivers for initial Budget– Crowding

» Knut to parameterize

– Sky background– Photon noise

» Rich to parameterize

• Both cases are limited by imperfect knowledge of the system PSF» Claire to comment on the relevant time scales for PSF estimation



Determining the PSF• A number of techniques aimed at estimating the guide star PSF from Shack-

Hartmann telemetry data are being developed and tested, yielding only measured progress

• Techniques to estimate the effects of anisoplanatism on an observation taken with an SCAO system are under active development. With an estimate of the on-axis PSF from telemetry data, these techniques may be used to derive the PSF throughout the field.

• An attractive method for obtaining the field dependent PSF of an SCAO system is to use an auxiliary camera to observe an isolated point source in the field. Together with a model for anisoplanatism, this observed PSF may be used to estimate the PSF elsewhere in the field.



Photometry IPT Initial Findings

• Consider requiring real-time turbulence monitoring capability at Keck for use with NGAO (e.g. DIMM/MASS or SLODAR)

• Consider conducting a PSF estimation experiment using the imaging camera on OSIRIS to test differential photometric stability

• Given the lack of astronomical observing experience with MCAO, at this time it is difficult to recommend an architectural choice of MCAO vs. MOAO based on photometric precision requirements.

Astrometric Accuracy IPT Status

Brian Cameron (IPT Lead)Matthew Britton, Richard Dekany, Andrea Ghez, Jessica Lu



Astrometry IPT Summary• Science cases

– Astrometry of the Galactic Center– Faint target astrometric in isolated fields

• Key Drivers for initial Budget– Atmospheric anisoplanatism

» Leaped to forefront (?) in absence of anisoplanatism calibration» Jessica and Andrea to quantify

– Atmospheric tilt anisoplanatism» Matt to parameterize

– Imperfect knowledge of geometric distortions» Jessica to consider time variability

– Stellar Confusion» Andrea to study via parametric simulations for differing WFE (provided by Chris) - TBC

– SNR for isolated stars» Brian to parameterize and confirm precision based on SNR and PSF FWHM

– Differential atmospheric refraction (as well as achromatic refraction)» Brian to consider limits to calibration (e.g. meteorological calibrations)



Current astrometric error is as low as 0.25 mas.

• Galactic Center observed with NIRC2 on Keck

• astrometric accuracy is a function of atmospheric conditions.

• astrometric floor at ~0.25 mas

What sets the floor?

Slides from UCLA Galactic Center Group (Ghez, Lu)

Individual stars in one night

Nightly averages for 3 different nights.



Astrometric accuracy is a function of location in the field.

Use 1 night of GC data:• LGSAO, NIRC2 • 107 exposures• tint = 60 sec each• Strehls: 0.3 - 0.4• FWHM: 53 - 63 mas• WFE ~ 345 nm (Marechal)

Simultaneous MASS/DIMM (estimated at zenith):• r0 = 10 - 15 cm• theta0 = 1.5’’ - 3.0’’

Courtesy of Matthew Britton: http://eraserhead.caltech.edu/keck/galactic_center/turbulence_plots/turbulence_plots.html




Galactic Center data shows strong anisoplanatism driver for astrometric error.

• In each frame, measure the position relative to the reference star, which is close to the laser spot.

• Take the RMS from all frames.

• The RMS positional error can be decomposed into radial and tangential components relative to the laser position (or reference source).




PSF elongation seems strongest in elevation direction.


• PSF degrades due to both isoplanatic and isokinetic effects.

• Isoplanatic effects dominate… isokinetic still under investigation.

Differential tip-tilt jitter masked by larger effects?• anisoplanatism• chromatic differential atmospheric refraction along elevation?

Need an astrometry experiment with the tip-tilt star and a separate guide

star in the FOV.

High-Contrast IPT Status

Ralf Flicker (IPT Lead)Richard Dekany, Mike Liu, Bruce Macintosh, Chris Neyman



High-Contrast IPT summary• Science cases

– Planets around low-mass stars and brown dwarfs– Debris disks, protostellar envelopes and outflows

• Key Drivers for initial Budget– Residual wavefront errors at offensive spatial frequencies

• Including uncorrected dynamical telescope errors, which are not well understood

– Non-common path wavefront errors• Including LGS-induced calibration errors

– Coronagraph leakage

• Methodologies– Contrast estimation from modified GPI spreadsheet tool

» Macintosh to provide

– Numerical AO simulations coupled to various coronagraph models• None, Ideal, Standard Lyot, and Apodized Lyot

» Neyman, Flicker to provide



High-Contrast IPT initial findings• Residual tomography wavefront error is slightly colored

– Initial assumption of whiteness probably sufficient for 1st calculations» Ralf has posted a draft report on this topic to TWiki

• We can proceed for now quoting contrast at 0.5 arcsec radius as a quality metric

– Detailed shape of the floor of the dark hole will await later design phases• Need clear and detailed science cases to drive the shape of the dark hole at smaller

inner working angles» Liu to provide

• There will be significant complications to understanding slowly varying non-common-path errors due to e.g., finite and variable LGS spot size, sodium layer distance, sodium density profile, Rayleigh scatter variations, LBWFS limitations, etc.

– Not being considered for GPI

ngao systems engineering status

Documents

system architecture

scao system

system uptimewbs

system uptimeeach

system psfclaire

psf estimationdetermining

axis psf

field dependent psf