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

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

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

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

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

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

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

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)

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?

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