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Science Priorities and Implications of Potential Cost Savings Ideas

Science Priorities and Implications of Potential Cost Savings Ideas. Claire Max Liz McGrath. Topics. Deliverables to cost review: Necessary revisions to science cases and science requirements, to meet the cost cap Scientific impact of the above During build-to-cost study:

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Science Priorities and Implications of Potential Cost Savings Ideas

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

  2. Topics • Deliverables to cost review: • 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

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