070709 Claire Max's notes
NGAO Architecture Meeting


Monday 07/09/07

Wed: Take stock of needed changes of science requirements and their implications
for the various architectures.  ~3pm formal discussion, before then informal

__________

Britton talk: Performance Budgets Summary

WFE spreadsheet assumes perfect sensing and correction of null modes (e.g.
focus etc).  Use Ralf's simulations of tomography error. Needs to be included later.

Should include 25th, 50th, and 75th percentiles for both theta0 and r0 variation,
for the EGS science case in particular.

PDR costing: keep some funds aside for research and development on various methods for
getting good PSF information.

Astrometry report: asked for 140nm WFE for GC, without much specific analysis.  I
don't think this should be a requirement unless/until they understand what the
current limitations on astrometric error really are.

Contrast: need to follow up on whether the 6 to 10 lambda/D is radius or diameter

Polarization:  I need to put a requirement in the science requirements document.  
es.g. transmission for the two linear polarizations must be calibratable to within
xxx percent over a yyy time period.

Backgrounds: needs careful analysis for each system architecture candidate.
Antonin and Law have the tools to do this (or at least a good start on them.)
Antonin and Law should be joint authors on a KAON regarding backgrounds.

Observing efficiency: Currently 37% of time is lost due to operational overhead,
25% due to weather, 16% due to system faults.  My conclusion: need to budget
funding for systems engineering for PDR phase.

_________

Neyman talk:  Trade Studies Summary

MCAO astrometric distortion: can be decreased with the "right" control system
(have to know where each DM went).  Need to keep this as part of the evaluation
of the "wide field" option architecture.  How much can the astrometric distortion
be decreased, in real life?

LGS asterism: Concluded that 5 LGS wasn't adequate for the EGS science case
(but used WFE rather than EE for figure of merit: need to review given the
additional trade study on EE).  Also, Rich used a 6 LGS configuration in his
WFE spreadsheet (rather than Ralf's 5 LGS).  

LGS fratricide due to Rayleigh: needs more simulation to see how well you can
do with a CW mode-locked laser (e.g. SOR laser)

Keck AO upgrade: to succeed would need to set up a new laboratory system on which
to do development and testing.  

Instruments: Rich makes the point that instrument by instrument, we may
want to allocate more or less error budget to the instruments, so that the AO
system will be easier/cheaper to build.  Claire makes the point that imagers
(vis and NIR) can be built with low WFE (e.g. 30 nm).  Anna makes the point 
that IFUs that use lenslets have inherently lower WFE, but that they are also
inherently much larger physically than slicer-based IFUs, and they have 
inherently smaller FOV.  Anna and Sean estimate that slicer-based IFUs to
date have all had internal WFE >~ 100 nm (they need to check this by talking
with Eikenberry and the SWIFT people).

Don: Laser uplink correction.  Allow WFS's to have pulse trackers in future
that can take advantage of a very small laser spot.  Need a launch telescope
with D=1m.  Peter says see if we can include this in the functional requirements
document as an upgrade path.

_____________

Science and System Requirements:

Peter and Claire's summary spreadsheet:

Question (Anna):  does the deployable NIR instrument have to have imagers as well
as IFUs?

David says we should add a 6th column to the summary spreadsheet, for the IFU

dIFU: 120" diameter circle (not square)

Tiny fields of view for vis instruments and for the NIR IFU:  Anna says probably
want bigger FOVs because need to accommodate dithering

Nyquist sampling: note that one exo-Jupiter requirement states that they need 
1.5 x Nyquist sampling

Cases where you use the science target for TT:  exo_jups, some asteroids, Io,
etc Brian asks what fraction of the science light is permissible to take away
to use for tip-tilt measurement.  We should specify on some chart which cases
will use the science object itself for the TT information.

Claire should think about required EE for visible light spectroscopy.  Rich says
we may want higher EEs and/or in smaller lenslets/spaxels for some of the visible
light spectroscopic science.  We should think about this.

Sky coverage vs. wavefront error: SRD v1 had better treatment of WFE vs. sky coverage
requirement.  We should try to retain this in the new versions of the SCRD and SRD.
e.g. WFE xx for sky coverage of yy, WFE ww for sky coverage of zz

Need to quantify to what level of precision you need to know the PSF for each 
science case

Need to develop an error budget for astrometry, especially for GC

Drop the goal of nonsidereal tracking for the dIFU column

Acquisition accuracy: instead of 200 mas, we should write this as 1/10th of the 
narrowest dimension of the instrument field of view

Nod requirements: need to specify what size nods will be needed

long term drifts: we wrote 5 mas/hr.  Rich has been carrying 30 mas/hr.  We need
to think about what number makes the most sense here.

NGS mode for dIFU?  Now we say it's a goal.  But it would not be needed if you could
switch easily from the dIFU to the NIR spectrograph.

We should state that there is not a requirement to have a non-AO mode for our 
usually-AO instruments.

Need to think about overall distribution of instruments on whatever telescope NGAO
is on: are there reasonable non-AO instruments to switch to?

We should specify whether we need vertical angle mode or fixed angle mode for high
contrast imaging applications

Add polarimetry requirements to the summary spreadsheet

Claire: need to drop the question mark about 30% increase in sky background for 
narrow-field instruments