SNAP

					                                 The Supernova /
                                Acceleration Probe
                                     (SNAP)

                           Presentation to the Experimental
                           Program Advisory Committee at
                           SLAC.

                           November 14, 2003




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                   SLAC Involvement in SNAP
     • With the creation of the Kavli Institute for Particle Astrophysics
       and Cosmology (KIPAC), experiments addressing issues at the
       interface between particle physics and astrophysics will play
       an increasingly prominent role in the SLAC research program.

     • Of particular interest will be the “dark sector”, the nature of
       dark energy and dark matter, and the roles they play in the
       evolution of the Universe.

     • Technology development in connection with the SNAP mission
       has been a cornerstone of the DOE-OS program addressing the
       mystery of dark energy.

     • We believe that SLAC can and should play a prominent and
       important role in this mission if it goes forward as currently
       planned.


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                   SLAC Involvement in SNAP
     • The first discussions about SLAC involvement with the
       leadership of the SNAP collaboration (S. Perlmutter, M. Levi)
       were held in February 2003.

     • At that time, a potential hardware role in the mission associated
       with the design and development of the Observatory Control
       Unit (OCU) was identified.

     • We also highlighted our science interest in the use of SNAP
       data for strong lensing investigations.

     • A letter of application for institutional membership in the SNAP
       collaboration on behalf of Stanford and SLAC was submitted in
       August 2003. That application is currently still under
       discussion, but the preliminary responses have been very
       positive.


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                   Outline of Presentations
     • The Science of Dark Energy and the Design of the SNAP
       Mission – E. Linder

     • Strong Lensing Investigations with SNAP – R. Blandford

     • The Observatory Control Unit – M. Huffer

     • Concluding Comments – S. Kahn




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                            National priorities

      HEPAP: Scientic potential and facility need – absolutely central
      Secretary of Energy (11/10/03) – SNAP has very high priority (#3 on
      list)




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                         SLAC and SNAP
      SLAC/Stanford major strengths include:

      • Strong Gravitational Lensing – Blandford
      Dark matter / dark energy / cosmology




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                         SLAC and SNAP
      Observatory control unit expertise – Huffer
      Technical experience and development resources




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                             SLAC and SNAP

          SLAC/Stanford major strengths include:

          • Space mission experience – Kahn
          Extensive design and implementation
          Knowledge of NASA culture

          • Experience with joint NASA-DOE projects from GLAST
          Collaborative agency working relationships

          •    Dark Energy and High Energy Physics –
          Existing and ongoing SNAP theory collaboration by Kallosh & Linde




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                          Revolutions in Physics

                   Lord Kelvin (1900): Two clouds on the horizon




                                                The horizon is 95% cloudy!
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                   Mapping our history




                   The subtle slowing down
                   and speeding up of the
                   expansion, of distances
                   with time: a(t), maps out
                   cosmic history like tree
                   rings map out the Earth’s
                   climate history.




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                   Accelerating universe




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                        What is dark energy?
      •    70-75% of the energy density of the universe
      •    Accelerating the expansion, like inflation
      • Determining the fate of the universe
      But what is it? Einstein’s cosmological constant ?
        Problems: fine tuning and coincidence


                                        Dark
                                       energy



                                       Matter

  Size=1/4         Size=1/2           Today                       Size=2   Size=4
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                   Dark energy – discovery!




                                                             > 0 at
                                                            99% confidence




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                    Next generation

       Supernova/Acceleration Probe: SNAP

                                                         Dedicated dark
                                                         energy probe




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                                Mission design

    • ~2 m aperture telescope
                                                          Dedicated instrument designed
      Reach very distant SNe.
                                                          to repeatedly observe an area of
    • 1 degree mosaic camera, ½ billion
    pixels
                                                          sky.

      Efficiently study large numbers of SNe.             Essentially no moving parts.
    • 0.35 – 1.7 m spectrograph
                                                          3+ year operation for experiment
      Analyze in detail each SN.
                                                            (lifetime open ended).




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                                         Mission design

    Photometry: half-billion                                                 Guider
                                                                     CCD’s
    pixel mosaic camera, high-                      HgCdTe
    resistivity, rad-tolerant p-
    type CCDs (0.35-1.0 m)
    and, HgCdTe arrays (0.9-
    1.7 m).

    Field of View Optical      ( 36
    CCD’s) = 0.34 sq. deg.                      BITE
    Four filters on each 10.5 m pixel
    CCD detector
                                               Spectrograph
    Field of View IR
    (36 HgCdTe’s) = 0.34 sq. deg.
    One filter on each 18 m pixel
    HgCdTe detector
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                                       Mission design

                  Integral field optical and
                  IR spectroscopy:
                  0.35-1.7 m,
                  3”x6” FOV,
                  low resolution,
                  high throughput.
Input port

                                  Prism
         Slicer                   BK7          Prism
                                               CaF2


                                Vis
                                Detector

                                                       NIR
                                                       detector



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                              Mission design
           15 sq.deg. Deep Survey                         ~300 sq.deg. Wide Survey




                               HDF


                       GOODS



         • 9 filters
                                                       • 9 filters
         • mAB=27.7 every 4 days
                                                       • mAB=28.1
         • 120 epochs
         • coadd AB=30.3 (31)
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                     SN control of systematics
      Each supernova sends a rich stream of information about its physical state.
                          Lightcurve & Peak Brightness




Images


                                                                          M and 
                               Redshift & SN Properties             Dark Energy Properties



Spectra




              data                     analysis                          physics
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                   High energy physics




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                           Complementarity
      Next generation data will map the acceleration of the universe so
      precisely that it can probe:
                                                                  • The nature of dark
                                                                  energy w(z)
                                                                  • Structure of the
                                                                  vacuum
                                                                  • w´(z)  V´ / V()
                                                                  • High energy physics




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                            Fate of the universe
      First and simplest DE model: linear potential (Linde 1986)
      leads to collapsing universe.
      Such models look like  in the past, but develop a strong w´.
                   wa=2w´                                          a


                                                                                        t


                                             tdoom=  ()
                                   w0        tdoom > 29 Gyr [95% SNAP]
                                             tdoom > 35 Gyr [95%SNAP+CMB]
                                             tdoom > 40 Gyr [95% SN+CMB+WL]


                                             Kallosh, Kratochvil, Linde, Linder, & Shmakova
                                             JCAP 2003; astro-ph/0307185

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                   SNAP Cosmology and Physics




                                                                     SN II

            Wide, Deep and Colorful
            • 9000 times the area of Hubble Deep Field
            • 10 billion years of detailed history
            • 108 galaxies, 105 lenses, 9 wavelength bands
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                    Strong Lensing Program
  • Multiple imaging by galaxies, groups and clusters
  • Ancillary program - complementary to:
     – Supernova cosmography
     – Weak lensing study of large scale structure
     – Galaxy-galaxy lensing study of galaxy halos
  • Telescope nearly ideal for strong lensing because of
     – 9 filters
     – 0.1(0.05)” pixels
     – 4 day cadence
     – Deep (15 sq deg) and Wide (300 sq deg) surveys
  • Lensing rate 0.001-0.002 => ~300,000 “events”
     – Quantitative, identification pipeline (cf CLASS)
     – Emphasize standard elliptical galaxy “scattering” with 0.5<z<1
  • Complementary to LSST and Square Kilometer Array

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                                 Scientific Goals
  • Source Population
     – Study the faintest galaxies – building blocks of normal galaxies
             • redshift distribution
             • luminosities
             • star formation rates etc
     – AGN microlensing
     – Rare high magnification events
  • Lens Population
     – Galaxy substructure out to R ~ 10kpc
     – Cluster substructure
             • Cosmography
  • Propagation Effects
     – Time delays Þ small scale dark matter distribution
     – Quasar absorption lines etc

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                                  Source Population
     • Understand empirically where when and how small galaxies
       merge to form larger galaxies
        – ~2 x 105 isolated elliptical galaxy lenses on deep field
        – total cross section ~ 0.02 sq deg
        – 10000 (30000) clean lenses on deep field to IAB ~ 28 (30)
        – Use lens colors to measure lens distance
        – Use color maps to separate source from lens, remove dust
        – Use Einstein ring radius to measure source distance
                   • 100 times too faint for spectroscopy
          – Infer source properties statistically and test CDM theory




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                                 Simulation
     • Massive elliptical lens, I=21.5, at zd=0.7
     • Faint blue galaxy, B=29, at higher redshift
     • Fit 9 images with two “spectral” models to reconstruct lensed
       source
     • Infer zs from Einstein ring radius
     • Input images (true color, different intensity scales!):




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                                      Simulation

                   Simulated SNAP images:

                   • 0.12” pixels, 0.14” FWHM PSF, no dither
                   • Deep survey, 1.5 mag fainter than HDF
                   • B, V and I-bands shown for illustration:




                   B (440nm)            V (582nm)                   I (770nm)

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                                     Simulation


                   Optimal weighting of 9 filters' images allows
                   lens and source components to be separated




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                                    Simulation


      Measuring source redshift with:
      • Einstein ring radius to ±1/4 pixel
      • Lens photo-z to ±0.02
      • Lens velocity dispersion to
      ±10 km s-1
      => Find 1.2 < zs < 1.5 (1)
                            (true value = 1.3)


      Lensing provides vital additional
      information to photo-z at high
      redshift




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                                 Scientific Goals
  • Source Population
     – Study the faintest galaxies – building blocks of normal galaxies
             • redshift distribution
             • luminosities
             • star formation rates etc
     – AGN microlensing
     – Rare high magnification events
  • Lens Population
     – Galaxy substructure out to R ~ 10kpc
     – Cluster substructure
             • Cosmography
  • Propagation Effects
     – Time delays => small scale dark matter distribution
     – Quasar absorption lines etc

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                           Cluster Arc Images

         Multi-colour, high resolution surveying and imaging:

         RCS0224 (CFHT):                        Cl0024 (HST):




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                                 Scientific Goals
  • Source Population
     – Study the faintest galaxies – building blocks of normal galaxies
             • redshift distribution
             • luminosities
             • star formation rates etc
     – AGN microlensing
     – Rare high magnification events
  • Lens Population
     – Galaxy substructure out to R ~ 10kpc
     – Cluster substructure
             • Cosmography
  • Propagation Effects
     – Time delays => small scale dark matter distribution
     – Quasar absorption lines etc

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                               Time delays
     • Lens time delays measure the Hubble constant, age of universe
        – Accuracy limited by lens model
     • Currently lens determinations are competitive with traditional
       astronomical methods
     • By the time SNAP is launched this will probably be settled
     • Small scale structure along the line of sight causes deviation
       from apparent pure Hubble expansion
     • Can measure statistically and check CDM predictions




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                           B1608+656 delays


       Time delays of 1-2
       months, measured to
       precision of 1-2 days...


       H0 = 75±6 km s-1 Mpc




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                     Research underway and
                            planned
     • Simulations using Hubble images and projected SNAP
       resolution (including dithering) and sky/detector noise
       (Marshall)
        – Establish procedure for data analysis pipeline to find clean
          and dirty lenses
        – Establish procedure for refining elliptical potentials
        – Use Hubble Ultradeep Field to describe source population
        – Estimate accuracy for determining source properties
     • Work with weak lensing group to develop strategy to combine
       strong and weak lensing studies of galaxy structure
       (Koopmans)
     • Study rare, higher order catastrophes as (Baltz):
        – highly magnifying telescopes
        – probes of granularity of dark matter
        – surveying instruments

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                   What instrument deliverable does
                           SLAC propose?
     • The Observatory Control Unit (OCU)

     • Both a hardware (electronics) and software system

     • Supervises and manages (on-station) observatory operation




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                             Electrical Block Diagram

                                                                                                ACS
   Filter
   Wheel                                                                  Ka xmt
                                     OCU                                   Primary
                                     Primary                                                        S-band
  Shutter                                            Mass store
                                                                                                 Transponder
                                                                                                   Primary
                                                         Primary
                         Focal
   Focus                 Plane                        200 GBytes                            CD&H
                      Assembly

  Thermal                                            Mass store                                     S-band
                                                        Redundant
                                                                                                 Transponder
                     Spectrograph                                                                 Redundant
                                     OCU
                                    Redundant
   Power                                                                  Ka xmt
                                                                          Redundant
                                                                                            Power

        After H. Heetderks                                                           1553 Bus


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                   Functional requirements
     • Executes instrument’s observation plan
        – Transfer pointing requests to ACS
        – Controls CCD array parameterization and readout
     • Science data management
        – Manage mass store
        – Route real-time and stored data to downlink transmitters
     • Mechanism management, control, and operation
        – Telescope cover, optical shutter, stepper coils, etc…
     • Power distribution and management




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                         Functional requirements…
     • Thermal management
        – Manage heater elements
                   • Primary, Secondary mirrors, telescope structure, etc…
          – Survival heaters
          – Monitor and trend temperatures
                       – Housekeeping
                           » Monitor instrument environment
                           » Packetize and route as telemetry
     • Data (Event) readout and acquisition
     • Command processing and distribution
        – Command database definition and maintenance
        – Decoding, distribution, and execution




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                   What is the scope of the OCU
                     within the observatory?
     • OCU performs electronic supervision of entire instrument

     • Encompasses design, specification and implementation of…
        – The bulk of instrument’s digital electronics
        – A modest amount of analog electronics
        – The entire Flight Software System

     • Executes the science mission …

     • Natural consequence is significant role in defining….
        – instrument architecture
        – translation of science objectives to operational program




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                         How does it fit within SLAC’s
                              current program?
     • OCU development requires a unique blend of skills…
        – Data Acquisition
        – Detector Monitoring and Control
     • SLAC has extensive experience in these areas…
        – Successful, lead role within 2 major HEP experiments:
                   • SLD
                   • BaBar
     • SLAC has space heritage…
        – Lead role in both Electronics and Flight Software for GLAST
        – Demonstrated collaboration with NASA based labs
     • SLAC has long history of successful collaboration with LBL
        – We enjoy a physical proximity…
     • Phases well with GLAST and BaBar program
        – BaBar no longer in development
        – GLAST moving out of design/development stage

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                     Concluding Comments
     • In October 2003, NASA and DOE announced the results of a
       year-long discussion regarding the possibility for cooperation
       in a space-based mission devoted to exploring the nature of
       dark energy.

     • The plan involves the development of a Joint Dark Energy
       Mission (JDEM).

     • NASA/DOE will issue a single AO soliciting a dark energy
       science investigation requiring a space-based observatory.
       The science investigation will be PI-led and will be selected via
       open competition.

     • The present schedule shows selection of the science
       investigation one year after the onset of new funding, leading
       to launch of the mission eight years later.


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                   Organization of JDEM




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                    Concluding Comments
     • The proposed plan is for the SLAC team to participate in an
       LBNL-led proposal for a JDEM science investigation based on
       the SNAP concept.

     • SLAC and LBNL have a long history of close cooperation in
       high energy physics experiments.

     • The differences in culture between the NASA and DOE
       communities will introduce some challenges in making the
       JDEM concept work.

     • SLAC’s extensive experience working with both agencies in the
       GLAST program should prove to be a key asset to the SNAP
       collaboration.


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