Maximizing GSMT Science Return with Scientific Figures of Merit

Maximizing value Who are the interested parties? –Scientist users –Funding agencies What constitutes value to them? –Scientific return –Cost What gives greatest value? MAXIMUM SCIENTIFIC RETURN FOR COST

Quantifying value Components of value Performance –Requirements –Goals Cost –Build –Operations Schedule –First light –Operating life RISKRISK $$$ Science

Science merit function Science merit function =  ( W i x FOM i ) Figure of Merit (FOM) –For each capability, embodied as instrument + telescope –Quantitative, with analytical and numerical components –Function of instrument and telescope properties Weight (W) –Scientific judgment call

Example 1. GSMT spectroscopic capability

Example 2: CELT IR AO system emissivity Cryogenic AO system at prime focus Ultimate performance for emissivity Negative impacts on telescope design, enclosure cost Cryogenic AO system at Nasmyth focus Quantifiably almost as good Expect lower total observatory cost Warm AO system at Nasmyth focus Dramatically reduced performance Low cost, maintains spatial resolution advantage Trades against space platform sensitivity advantage

What is the science mission? Type of mission impacts FOM, weights Design reference mission –Total science program specified Timely science mission –Maximize science achieved in initial period Scientific capability mission –Instrument capabilities for wide range of potential science

Example: UKIRT WFCAM program WFCAM: widefield 1-2  m camera on 3.8 m telescope Several large scale surveys over ~10 years (DRM) Quick shallow surveys first (STM) Selected deep fields done repeatedly (STM + DRM) Instrument permits installation of custom filters (SCM)

GSMT sample imaging capabilities Enhanced seeing widefield imager –Gaussian profile –Tens of arcmin FOV Narrow field coronagraph –Highest possible Strehl and dynamic range –FOV is arcseconds Moderate field, diffraction limited imaging –Moderate Strehl over arcminute FOV

Imaging FOM inputs: telescope D, primary mirror diameter TP tel ( ), throughput  (, , t ), delivered image quality S (, , t ), Strehl ratio  ( ), emissivity E tel, operating efficiency

Imaging FOM inputs: instrument TP instrl ( ), throughput DQE( ), detector quantum efficiency , pixel sampling, , wavelength coverage and resolution R, D, read noise and dark current Sc, scattered light susceptibility E tel, system efficiency

Imaging FOM inputs: multiplex advantages , total solid angle field of view n, number of simultaneous spectral channels

Imaging FOM inputs: other science value factors Timeliness First light Other facilities Competition Access To facility To data

Enhanced native seeing imager Science –Distribution of high redshift galaxies –Integrated properties of galaxies Programmatic –Use at wavelengths where diffraction limit can’t be achieved –Use in less favorable conditions, e.g. thin cirrus Implications for FOM –Slightly extended sources with some central concentration –Wavelength coverage is  1  m

Enhanced native seeing imager Background limited, uncrowded field case Neglect  Emissivity  Strehl ratio  Read noise, dark current  Scattered light  Programmatic terms Gather terms into a Figure of Merit for (integration time) -1

Enhanced native seeing imager Background limited, uncrowded field FOM 1/time  [ (D 2 /  2 ) TP tel ( ) E tel ] [  DQE TP tinstr ( ) E tinstr f(  /  ) f(n) f(,  ) ] Track telescope, instrument separately Some factors require simulations to determine appropriate formulations Some factors may include weighting functions  Telescope  Instrument

Formulation of image quality   arcsec , arcminutes Delivered image quality vs field angle and conditions Poor conditions Good conditions

Optimizing  /  Time  // // detection photometry 1234

Weighting function for  0 1 weight , arcminutes MCAO regime Tel, atmos rolloffs 020

Enhanced native seeing imager trades Some performance (and cost) trades: –D,  – ,  –TP tel ( ) (coatings) –n (instrument complexity) – (optics complexity, coatings choices)

Narrow field coronagraphic imager Science –Discovery and characterization of planetary systems Programmatic –Diffraction limited, very high Strehl at first light –Use in best seeing conditions Implications for FOM –Wavelength coverage is 1   5  m –Treatment of systematic effects important –Independent of telescope design, AO implementation details

Coronagraphic imager FOM additional inputs d, subaperture size of primary n, number of actuators on deformable mirror , residual wavefront rms error , speckle lifetime (site characteristic) g, gain, ratio of peak intensity to halo level R, amplitude reduction of primary core and halo by coronagraph

Coronagraphic imager FOM Comparison with enhanced seeing imager:  Neglect traditional seeing measure   Include Strehl ratio S, emissivity   Use additional terms to describe AO, coronagraph impacts

Coronagraphic imager sensitivity FOM FOM for sensitivity (SNR): sensitivity  [ D 2 TP E  DQE  -1 f(  /  ) f(n) f(,  ) ] ½ [ S / (1-S) ] [ D / d  ] 2 [ 1/R ] Includes “traditional” components, Strehl and gain advantages Not yet in right units! How to account for systematic effects?

Coronagraphic imager systematics SNR limited by speckle structure in uncorrected halo –Pointlike –100% amplitude modulation –Persist for time  Variety of solutions –Decorrelation (large n, kHz AO update rate) –Simultaneous differential imaging (NICI) –PSF engineering, e.g. speckle sweeping –Data taking and reduction methods

Coronagraphic imager final FOM Characterize time – SNR relation by parameter   = 2 for photon noise limited system, less if residual systematic errors are significant 1/time  ( previous expression ) 

Narrow field coronagraphic imager trades Mirror segment size d Speckle lifetime  (site characteristics) Emissivity  and Strehl ratio S  error budget allocations  /  with Suppression of systematic error

Wide field – narrow field comparisons Wide fieldNarrow field < 1  m1 – 5  m FOV20 arcmin2 arcsec DIQ~0.5 arcsec~0.005 arcsec Tel geometryuncriticalimportant Tel opticsfast, complexslow, simple Secondarylargesmall Emissivityirrelevantimportant AO systemActive secondaryDitto + DM w/ ~10E3 actuators~10E4 actuators

Maximizing value, redux Return to performance, cost, schedule, risk mix: Is there a similar approach to maximizing value? Performance-cost index PCI = Science merit function / total cost (capital + ops) How to do optimization?

Maximizing value, redux Evaluate a few plausible approaches –Telescope type –Instruments Trade studies for key parameters –Effect on SMF –Effect on cost Creative tension between Scientist, Engineer, and Manager