Plan to develop system requirements through science cases Claire Max Sept 14, 2006 NGAO Team Meeting

I hope to “marry” two approaches to science-driven design of NGAO 1)Requirements driven: Scientists develop “science requirements” Hand off to technical folks Technical folks design AO system to meet the requirements Determine if meeting the requirements is feasible (dollars, technical risk, schedule,...) Iterate science requirements and AO design 2)Technology driven: Technical advances make one or more new approaches to AO possible Scientists go off and assess what new science can be done with the new technologies Decisions based on “is the new science worth the cost and risk” Iterate on which new technical approaches to implement

Both approaches have pros and cons Requirements driven: –Pros: –Better-defined from the technical point of view –Clear goals against which designs can be evaluated –Cons: –Can lead to costly and/or risky designs, if one or two difficult requirements torque around the whole process Technology driven: –Pros: –Easier to deal with “the art of the possible” –Ask “what important science can I do with this new technology?” –Cons: –Poorer understanding of specific design-trades that might really optimize performance for key science cases

How can we have the best of both worlds? Suggested approach: –Last spring we showed generically how 12 important science areas would benefit from NGAO –For next couple of months, we want to focus on the subset of science cases that push AO design the hardest –Start by considering 4 key areas today The process in brief, for each key area: 1.Understand and document science requirements x and y, including how they interact with requirement z 2.Iterate with performance budget for various AO architectures 3.Develop and document observing scenarios 4.Understand and document requirements on science instruments. Develop prioritized instrument list. Iterate with instrument selection and error budgets. 5.Deliver Science Requirements Document

For example: spectroscopy of high-z galaxies Strongest requirements driver for encircled energy AO performance requirements and trades: –Encircled energy fraction against sky coverage –If you are willing to accept larger tip-tilt errors (lower encircled energy within a given area), you can achieve a higher sky coverage fraction –Spatial resolution (lenslet or “slitlet” size) against backgrounds due to AO system and telescope –If you use a larger lenslet or “slitlet”, you are admitting more background light. So to achieve given sensitivity, need to run the AO system colder (lower background) Science instrument requirements and trades: –Strongest driver for multi-IFU instrument (MCAO or MOAO) –MOAO: potentially higher Strehl, but fewer (more costly) IFU heads –MCAO: lower Strehl, but can cover more galaxies at once

Next Plan to develop system requirements through performance budgets