Fundamental Understanding of the Universe: Dark Energy

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Fundamental Understanding of the Universe Dark
Energy
Physics Discoveries
Launch
Assembly
Configuration
Development
Supernova Acceleration Probe
2010
2001
Integration
Technology
Engineering
Physics
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Critical Questions in Cosmology
Time Magazine Person of the Century
There are critical questions in cosmology whose
answers eluded Einstein
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Fundamental questions

• What is the nature of matter and energy at its
  most fundamental level?
• What is the evolution and fate of the universe
  and how is it affected by the fundamental
  interactions of energy, matter, time and space?
• Is general relativity the ultimate theory of
  gravity for the universe?
• What is the connection between dark energy,
  gravity and the fate of the universe?

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Some History

• Einstein 1917
• How does the presence of matter effect the
  expansion? Gravity should cause a deceleration.
• field equations show contracting or expanding
  universe, but the universe is static
• Einstein postulated a cosmological constant, L
  (negative pressure) or Dark Energy to maintain a
  static universe.
• E. Hubble 1924-1929
• observation of galaxies, the universe is not
  static!
• Einstein 1929
• cosmological constant is unnecessary, L ? 0

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Type Ia Supernova
Difference
Reference
Explosion
Credit STScI
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Type Ia Supernova

• Type Ia supernovae are astronomical standard
  candles
• Variations in SNe Ia light curves can be
  corrected so their peak brightness can be used
  to measure distance (time) to the supernova.

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The Accelerating Universe Sciences Breakthrough
of the Year

• Redshift of spectral features measures the
  expansion of the universe.
• A magnitude vs. redshift plot provide a Hubble
  diagram measuring the expansion rate
• Ground-based work thus far has uncovered a major
  surprise

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Accelerating Expansion
Credit STScI
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Expanding Univserse
Credit STScI
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The Implications of an Accelerating Universe
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Implications

• Gravity should cause a deceleration. Supernova
  data shows an acceleration of the expansion!
• Remarkable agreement between Supernovae recent
  CMB.

• SNe inconsistent with a L 0 universe
• CMB measurements ? ?TOT 1
• Cluster measurements ? ?M 0.3
• L 0.7, ?M 0.3 universe favored by SNe
• Statistical uncertainties in SNe measurements
  only 2? greater than known systematic errors.

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Composition of the Cosmos
Credit STScI
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Theoretical Questions

• What is the Nature of the dark energy
• dark energy is energy associated with the
  simmering sea of particles living on borrowed
  time and borrowed energy that are the quantum
  vacuum of nature? or, maybe
• influence of hidden space dimensions as
  predicted by super-string theory?, or
• Our main achievement in understanding dark
  energy is to give it a name Michael Turner

Would be number one on my list of things to
figure out - Edward Witten Right now, not
only for cosmology but for elementary particle
theory this is the bone in the throat - Steven
Weinberg

• Why is the energy density so small?
• 120 orders of magnitude too small and yet not
  zero
• fine tuning?
• Why now?
• the energy density is about equal to the critical
  energy density
• coincidence?
• Will these be answered by new theories beyond
  Einstein?
• quintessence
• string theory
• In string theory, to get ? gt 0 but extremely
  small is impossible Ed Witten

Maybe the most fundamentally mysterious thing
in basic science - Frank Wilczek This is the
biggest embarrassment in theoretical physics -
Michael Turner
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How Can We Address These New Questions?

• It is necessary but NOT sufficient to find and
  study
• more Sne Ia
• farther Sne Ia
• because the statistical uncertainty is already
  within a factor of two of the systematic
  uncertainty.

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SNAPs Target Results

• The most demanding SNAP requirements are devoted
  to eliminating and controlling all systematic
  uncertainties.
• All data taken with single dedicated, instrument.
• Above atmospheric interference
• Imaging for discovery photometry
• Spectroscopy to classify Type Ia supernovae and
  for redshift
• Reduce systematic errors to ?M lt 0.02
• Need 1000s of SNe to improve statistical
  accuracy.
• Expected measurement uncertainties
• ?? to ? 0.05, ?M to ? 0.02

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Dark Energy Characterized by the
Pressure/Density Ratio
Pressure/Density Ratio ? w (Equation of State)
Magnitude residuals (vs a ?0.7 model)
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SNAP Baseline Sample

• Large statistics, 2000 Sne Ias, distributed in
  redshift to zlt1.7, with minimal selection bias
  and clean Ia ID.

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What makes the SN measurement special?Control of
systematic uncertainties

• At every moment in the explosion event, each
  individual supernova is sending us a rich
  stream of information about its internal physical
  state.

Lightcurve Peak Brightness
Images
?M and ?L Dark Energy Properties
Redshift SN Properties
Spectra
data
analysis
physics
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Advantages of Space
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Mission Requirements

• Minimum data set criteria
• Discovery within 2 days (rest frame) of explosion
  (peak 3.8 magnitude),
• Ten high S/N photometry points on lightcurve,
• Lightcurve out to plateau (2.5 magnitude from
  peak),
• High quality peak spectrophotometry
• How to obtain both data quantity AND data
  quality?
• Batch processing techniques with wide field --
  large multiplex advantage,
• Wide field imager designed to repeatedly observe
  an area of sky
• Mostly preprogrammed observations, fixed fields /
  spin filter wheel
• Very simple experiment, passive expt.
• SNAP design meets these scientific objectives
• Dedicated instrument, essentially no moving parts
• Mirror 2 meter aperture sensitive to light from
  distant SN
• Optical Photometry with 1x 1 billion pixel
  mosaic camera, high-resistivity, rad-tolerant
  p-type CCDs sensitive over 0.35-1mm
• IR photometry 10x10 FOV or larger, HgCdTe
  array (1-1.7 mm)
• Integral field optical and IR spectroscopy
  0.35-1.7 mm, 2x2 FOV

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Mission Overview
Simple Observatory consists of 1) 3 mirror
telescope w/ separable kinematic mount 2) Baffled
Sun Shade w/ body mounted solar panel and
instrument radiator on opposing side 3)
Instrument Suite 4) Spacecraft bus supporting
telemetry (multiple antennae), propulsion,
instrument electronics, etc No moving parts (ex.
filter wheels, shutters), rigid simple structure.

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GigaCAM

• GigaCAM, a one billion pixel array
• Depending on pixel scale approximately 1 billion
  pixels
• 140 Large format CCD detectors required
• Looks like the SLD vertex detector in Si area
  (0.1 - 0.2 m2)
• Larger than SDSS camera, smaller than BaBar
  Vertex Detector (1 m2)

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Optical Photometry Parameters
CCD
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Imaging Strategy
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GigaCAM detectorAnnular layout

• Layout is rotationally symmetric
• 142 3kx3k CCDs

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One-square meter Silicon Detector

• One-square meter silicon-strip detector arrays
  (five concentric layers, outer shown in fig)
• 200,000 channels of electronics
• LBNL designed 10 Mrad tolerant ICs (preamp, ADC,
  memory 128 channels/chip)

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IR Photometry Parameters
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Shortwave HdCdTe Development

• Hubble Space Telescope Wide Field Camera 3
• WFC-3 replaces WFPC-2
• CCDs IR HgCdTe array
• Ready for flight July 2003
• 1.7 mm cut off
• 18 mm pixel
• 1024 x 1024 format
• Hawaii-1R MUX
• NGST to use Hawaii-2RG
• Dark current consistent with thermoelectric
  cooling
• lt0.05 e-/s at 140 K (compare to SNAPs lt0.1 e-/s
  zodiacal background)
• Expected QE gt 50 0.9-1.7 mm
• Individual diodes show good QE
• Effective CdZnTe AR coating
• No hybrid device yet with simultaneous good dark
  current QE

NIC-2
WFC-3 IR
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Camera Example

• Components
• 236 CCDs
• 24 2k x 2k HgCdTe
• 2 spectrographs
• 8 star guider CCDs

IR 0.12 sq. deg. 0.125 asec/pixel Visible 0.88
sq. deg. 0.07 asec/pixel
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Filters Shutters
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IR Enhanced Camerawith Fixed Filter Set
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Camera Assembly
GigaCam
Shield
Folding Mirror
Filter Wheel
Heat radiator
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Mosaic Packaging
With precision CCD modules, precision baseplate,
and adequate clearances designed in, the focal
plane assemble is plug and play.
140 K plate attached to space radiator.
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CCD Subassembly
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Typical CCDs
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Silicon Absorption Length
Photoactive region of standard CCDs are 10-20
microns thick Photoactive region of LBNL CCDs
are 300 microns thick
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High-Resistivity CCDs

• New kind of CCD developed at LBNL
• Better overall response than more costly
  thinned devices in use
• High-purity silicon has better radiation
  tolerance for space applications
• The CCDs can be abutted on all four sides
  enabling very large mosaic arrays
• Measured Quantum Efficiency at Lick Observatory
  (R. Stover)

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LBNL 2k x 4k
Trap sites found by pocket pumping.
USAF test pattern.
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Industrialization of Technology
The LBNL CCD technology, layout, and recipe were
transferred to a commercial foundry.
Commercial 6 wafer run in process
Commercial 4 wafer run completed
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Radiation Damage

• Space particle backgrounds have two components
• Solar protons sub-100 MeV
• Galactic cosmic rays
• (we are ignoring electrons here)
• Solar protons are most damaging to CCDs.
• WFPC2 on HST developed losses up to 40 across
  its CCD due to radiation damage.
• Hot pixels also developed.
• Radiation testing is done at the LBNL 88
  Cyclotron with 12 MeV protons.
• SNAP expected lifetime dose 5 x 109 protons/cm2

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Radiation Damage
CTI is the charge transfer inefficiency Q Q0
(1-CTI)Ntransfer, Ntransfer 2000
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Spectrograph Parameters
Optical Arm
IR Arm
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Spectroscopic Integral Field Unit Techniques
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Integral Field Spectrograph Design with Image
Slicer

• Complete spectrograph
• 0.6-1.7 microns
• 0.12 arcsec/resolution element
• R15A

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Secondary Metering Structure

• Key requirements
• Minimize obscuration (lt3.5) interference
  spikes
• Dimensional stability
• 35 Hz minimum fundamental frequency
• Baseline design hexapod truss with fixed end
• Simple design with low obscuration (3.5)
• 6-spiked diffraction pattern
• Ø 23 mm by 1 mm wall tubular composite (250 GPa
  material) struts with invar end-fittings.

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Primary Mirror Substrate

• Key requirements and issues
• Dimensional stability
• High specific stiffness (1g sag, acoustic
  response)
• Stresses during launch
• Design of supports
• Baseline technology
• Multi-piece, fusion bonded, with egg-crate core
• Meniscus shaped
• Triangular core cells
• Material
• Baseline ULE Glass (Corning)

Initial design for primary mirror substrate 334
kg
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Spacecraft Assembly
Movie courtesy of Hytec
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Observatory Parameters
Primary Mirror diameter 200 cm Secondary
Mirror diameter 42 cm Tertiary
Mirror diameter64 cm
Optical Solution
Edge Ray Spot Diagram (box 1 pixel)
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Optical Train
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Telescope Assembly
Movie courtesy of Hytec
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Launch Vehicle Study
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Orbit Trade-Study

• Feasibility Trade-Study

Selected Lunar Assist Prometheus Orbit 14 day
orbit 19Re Perigee/57Re Apogee
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Orbit Optimization

• "Prometheus" Orbit Baselined Following
  Preliminary Trade Study
• Uses Lunar Assist to Achieve a 14 day (19 X 57
  Re) Orbit, with a Delta III 8930 or Delta IV-M
  Launch Vehicle
• Good Overall Optimization of Mission Trade-offs
• Low Earth Albedo Provides Multiple Advantages
• Minimum Thermal Change on Structure Reduces
  Demand on Attitude Control
• Excellent Coverage from Berkeley Groundstation
• Outside Radiation Belts
• Passive Cooling of Detectors
• Minimizes Stray Light

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Orbital Stability
Semi-major axis (km) Intrinsic stability of
semi-major axis due to lunar influence
Inclination (deg) Some reduction of inclination
over lifetime of spacecraft
Perigee radius (Re) Five year nominal stability
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Project History and Status

• Project is being developed as a multi-agency
  partnership
• Team that produced current results was supported
  by DOE, NSF, and NASA.
• Science review by SAGENAP of 260 page proposal
  March 2000 strong endorsement of science,
  recommendation for study funding.
• Entire session at Jan. meeting of the American
  Astronomical Society devoted to SNAP 9 talks, 4
  posters.
• Dark Energy a subject of the recent National
  Academies of Science Committee on the Physics of
  the Universe (looking at the intersection of
  physics and astronomy). One of eleven compelling
  questions What is the Nature of the Dark
  Energy?
• SNAP to be reviewed by the NRC/Committee on the
  Physics of the Universe during 2001 as part of
  their Phase II review of projects.
• International collaboration is growing, currently
  15 institutions.

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SNAP Collaboration
G. Aldering, C. Bebek, S. Deustua, W. Edwards, B.
Frye, D. Groom, S. Holland, D. Kasen, R. Knop, R.
Lafever, M. Levi, S. Loken, P. Nugent, S.
Perlmutter, K. Robinson (Lawrence Berkeley
National Laboratory) E. Commins, D. Curtis, G.
Goldhaber, J. R. Graham, S. Harris, P. Harvey, H.
Heetderks, A. Kim, M. Lampton, R. Lin, D. Pankow,
C. Pennypacker, A. Spadafora, G. F. Smoot (UC
Berkeley) C. Akerlof, D. Amidei, G. Bernstein, M.
Campbell, D. Levin, T. McKay, S. McKee, M.
Schubnell, G. Tarle , A. Tomasch (U. Michigan)
P. Astier, J.F. Genat, D. Hardin, J.- M. Levy,
R. Pain, K. Schamahneche (IN2P3) A. Baden, J.
Goodman, G. Sullivan (U.Maryland) R. Ellis, M.
Metzger (CalTech) D. Huterer (U.Chicago -gt Case
Western) A. Fruchter (STScI) L. Bergstrom, A.
Goobar (U. Stockholm) C. Lidman (ESO) J. Rich
(CEA/DAPNIA) A. Mourao (Inst. Superior
Tecnico,Lisbon)
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RD Review

• Recent DOE/Science RD Review (Jan 2001)
• SNAP is a science-driven project with compelling
  scientific goals.
• SNAP will have a unique ability to measure the
  variation in the equation of state of the
  universe.
• We believe that it is not an overstatement to
  say that the Type Ia supernova measurements will
  uniquely address issues at the very heart of the
  field Implications for particle physics
• Issues Raised at RD Review
• Look at greatly increasing the near-infrared
  capabilities
• Is the proposed IR spectrograph throughput
  adequate?
• Look at a descoped instrument complement Can the
  visible spectroscopy be done by ground-based
  facilities?
• Develop a calibration strategy and plan.

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Science Goals
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N.Y. Times weighs in on Dark Energy
N.Y. Times 4/10/01
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Time Magazine weighs in on Dark Energy
Time Magazine 4/16/01
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Conclusion

• Type Ia Supernova
• Are light sources visible across the Cosmos
• Show that expansion of the universe is
  accelerating through distance-redshift relation
• Reveal evidence for a mysterious dark energy in
  the universe
• SNAP
• Space observations of thousands of supernovae
  will provide the vital breakthrough in precision
  cosmology to characterize the dark energy
• SNAP will measure the matter and energy densities
  with exquisite precision
• SNAP will precisely determine the expansion rate
  of the universe as a function of time.