Transcript MaxMcGrath.ppt

Science Priorities and Implications of
Potential Cost Savings Ideas
Claire Max
Liz McGrath
Topics
1. Deliverables to cost review:
– Necessary revisions to science cases and science requirements, to
meet the cost cap
– Scientific impact of the above
2. During build-to-cost study:
– Use input on science cases in the trade-off process (cost saved versus
science opportunities lost)
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Here we will first discuss priorities, and then how they impact tradeoffs 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
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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)
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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
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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