1. Science Priorities and Implications of Potential Cost Savings Ideas
Claire Max
Liz McGrath

2. Topics Deliverables to cost review: During build-to-cost study:
Necessary revisions to science cases and science requirements, to meet the cost cap
Scientific impact of the above
During build-to-cost study:
Use input on science cases in the trade-off process (cost saved versus science opportunities lost)
Here we will first discuss priorities, and then how they impact trade-offs in cost-benefit

3. Issues
Keck Strategic Planning document is in flux, particularly with respect to the extragalactic section
Priorities not really clear, especially with respect to use of NIR IFU for high-z galaxies
No Science Advisory Team yet
Need to agree on systematic way of doing science cost - $ benefit trades
Now: trade decisions appear on ppt slides, with no systematic evaluation of science
We are having difficulty with this approach

4. Way Forward
Agree on a systematic procedure for guaranteeing that each trade is weighed against overall science impact
Each idea/tradeoff should be individually flagged on a master list
Decisions will not be finalized until quantitative science cost is evaluated
Science team (whatever it is) will assess impacts of each item on list
Prioritize the order of consideration: the most cost-saving will be considered first, and in the greatest depth

5. B2C decisions to track (so far)
No multiplexing for d-IFU
Narrower science field
Fewer lasers in asterism
75W of laser power (50W in central asterism) instead of 100W
Fewer subapertures for narrow relay (?)
Fixed IFU instead of deployable
No ability to use OSIRIS
Extend NIR detectors to 850nm to avoid building visible instruments
Only cool science path optics
Pickoffs instead of dichroic switchyard
No ADC in front of NGS WFS

6. Implications of narrower science field
Narrower science field, no multiplexing Decided
This is a cost decision. We can’t afford multiplexed d-IFU.
There would be a clear science gain from multiplexing in the (distant?) future
Hence don’t build NGAO in a way that precludes later addition of multiplexed IFU pickoffs, presumably placed after the first relay but before the second relay
Added wavefront error due to reduced laser power and # beacons
Fewer lasers in asterism Decided?
75W of laser power (50W in central asterism) instead of 100W Decided
Potentially fewer subapertures for narrow relay - not yet decided
To do science trades, need to evaluate resulting WFE for the various Key Science Drivers

7. OSIRIS-related issues: not yet decided
Options in design of new IFU versus OSIRIS capabilities:
Have the new IFU do both low WFE science (including at J and z bands) and high-sensitivity science (possibly with higher WFE and lower spatial resolution)
Have the new IFU do only high-sensitivity science (possibly with higher WFE and lower spatial resolution), and have OSIRIS do the low-WFE science (but throughput at J and z bands is very low)
Same as above but with a new grating and/or new detector for OSIRIS to improve sensitivity
What are implications of each option for science? Need to better define IFU design, architecture, and capabilities
If OSIRIS is present on-axis: should we build the new IFU with a deployable pickoff so that it can be used simultaneously with OSIRIS?
Need to study what science would be added

8. Detectors, cooling, pickoffs
Extend NIR detectors to 850nm to avoid building visible instruments
Science cost/benefit depends on QE and read noise of the NIR and vis detectors
Need to evaluate science effects quantitatively. Also need to get deeper into instrument designs to see what would be the added (or decreased?) costs.
Cooling of AO system
To what temperature?
Need to understand the added costs (if any) of cooling to -20C instead of -15C, for example
Need to re-evaluate resulting integration times for faint-object science
Don’t cool path to LGS WFSs ?
How big is lost laser power due to windows? What is effect on WFE? How will this affect science cases?
Pickoffs instead of dichroic switchyard
Need calculation of effect on throughputs and sensitivity
Need to consider implications for sky coverage (can’t use an on-axis point source as tip-tilt star)

9. Final issues No ADC in front of NGS WFS
What is resulting expected WFE? How will it affect NGS science?
Reduced Field of Regard diameter to 120”
What is resulting expected TT error? How will it affect science cases?

10. To Do List Quantitative evaluation of WFE impacts on science cases
Need to incorporate content of Rich’s presentation
New concept for Peter’s Slide 12