OTA10

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SNAP Mission
M. Lampton U.Calif. Berkeley
Public Domain Document This information is in
the Public Domain. For an electronic copy see
http//snap.lbl.gov/pub/bscw.cgi/198989
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Breakthrough of the Year
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Current Crisis

• General Relativity
• A.Einstein 1915 10,000 follow-on papers books
  movies etc.
• Amazingly accurate and well verified!
• Deflection of starlight observed 1919 mass
  curves space!
• Explained Galileos principle of equivalence
• Predicted gravitational redshift
• Explained gravity as geometry
• Explained precession of Mercurys orbit
• Predicted frame dragging!
• Predicted black holes!
• overall, an amazing success
• Quantum Mechanics
• M.Planck, W.Heisenberg, E.Schroedinger 10,000
  papers books movies etc.
• Amazingly accurate and well verified!
• Extensions to chromodynamics etc
• overall, an amazing success
• GR and QM are inconsistent. They are
  approximations to something else.

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1998 Acceleration not deceleration!

• Supernova Cosmology Project (S.Perlmutter et al)
• High-Z Supernova Team (B.Schmidt, R.Kirshner, et
  al)
• both teams began searching for high-Z supernovae
  1990
• By 1998, 42 cosmological supernovae had been
  found
• Distant supernovae recede more slowly than nearby
  Hubble-law predictions
• Dark energy confirmed by cosmic microwave
  background
• 2000 Balloon experiments
• 2003 WMAP satellite
• By 2006, 154 cosmological supernovae are known
• Goal measure expansion rate throughout cosmic
  history
• enable models of quintessence, phantom energy,
  etc etc to be tested
• Issue how to achieve random systematic errors
  1?
• Issue how to use gravitational lensing as a
  diagnostic of early structure formation within
  the universe?

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The Expansion History of the Universe
Expansion vs Time
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Current Results on Cosmological Parameters
What people used to think...
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Energy budget of Universe
Dark Matter 30
Dark Energy 65
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Whats going on?

• Maybe gravity is wrong
• lots of alternative theories! PPN, MOND, ....
• but so far, Einsteins gravity well proven
• Maybe space-time is wrong
• lots of alternative theories!
• more dimensions of space? time? braneworlds?
  multiverse?
• but so far, 31 works very well.
• Maybe there is merely some new form of energy
• For now, we call the energy source responsible
  for the acceleration of the universe expansion
  dark energy
• meaningless, except to say not from stars
• era of precision cosmology is beginning now
• SNAP is one component of this effort.

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SNAP Collaboration 2006
LBNL G. Aldering, S. Bailey, C. Bebek, W. Carithers, T. Davis, K. Dawson, C. Day, R. DiGennaro, S. Deustua, D. Groom, M. Hoff, S. Holland, D. Huterer, A. Karcher, A. Kim, W. Kolbe, W. Kramer, B. Krieger, G. Kushner, N. Kuznetsova, R. Lafever, J. Lamoureux, M. Levi, S. Loken, B. McGinnis, R. Miquel, P. Nugent, H. Oluseyi, N. Palaio, S. Perlmutter, N. Roe, H. Shukla, A. Spadafora, H. Von Der Lippe, J-P. Walder, G. Wang
U.C. Berkeley M. Bester, E. Commins, G. Goldhaber, H. Heetderks, P. Jelinsky, M. Lampton, E. Linder, D. Pankow, M. Sholl, G. Smoot, C. Vale, M. White
Caltech R. Ellis, R. Massey, A. Refregier, J. Rhodes, R. Smith, K. Taylor, A. Weintein
Fermi National Laboratory J. Annis, F. DeJongh, S. Dodelson, T. Diehl, J. Frieman, D. Holz, L. Hui, S. Kent, P. Limon, J. Marriner, H. Lin, J. Peoples, V. Scarpine, A. Stebbins, C. Stoughton, D. Tucker, W. Wester
Indiana U. IN2P3-Paris -Marseille C. Bower, N. Mostek, S.Mufson, J. Musser P. Astier, E. Barrelet, R. Pain, G. Smadja, D. Vincent A. Bonissent, A. Ealet, D. Fouchez, A. Tilquin
JPL D. Cole, M. Frerking, J. Rhodes, M. Seiffert
LAM (France) S. Basa, R. Malina, A. Mazure, E. Prieto
U. Michigan B. Bigelow, M. Brown, M. Campbell, D. Gerdes, W. Lorenzon, T. McKay, S. McKee, M. Schubnell, G. Tarle, A. Tomasch
U. Penn G. Bernstein, L. Gladney, B. Jain, D. Rusin
U. Stockholm R. Amanullah, L. Bergström, A. Goobar, E. Mörtsell
SLAC W. Althouse, R. Blandford, W. Craig, S. Kahn, M. Huffer, P. Marshall
STScI R. Bohlin, D. Figer, A. Fruchter
Yale U. C. Baltay, W. Emmet, J. Snyder, A. Szymkowiak, D. Rabinowitz, N. Morgan
Institutional affiliation
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How to measure dark energy?

• Standard candles ltltSNAP
• idea is the inverse square law flux
  luminosity/distance2
• a standard candle has a calibrated luminosity
• a measured flux gives the distance hence the
  lookback time
• the lights redshift gives the universes
  expansion
• use many candles, many redshifts get cosmic
  history of the expansion
• Weak gravitational lensing ltltSNAP
• matter has mass, hence gravity
• over cosmic history, matter aggregates through
  gravitation
• mass aggregation w.r.t. redshift is determined by
  expansion history
• mapping lensing vs. redshift can constrain
  expansion models
• Other methods
• Baryon oscillations use individual galaxy
  redshifts as tracers
• Sunyaev-Zeldovich effect probe cluster masses

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What would it take for a major advance?

• Huge amount of observing time!
• Dedicated facility
• Large survey speed sensitivity
  AreaSolidAngle
• Lots of pixels running in parallel
• revisit every field every few days
• moon, weather must not interfere with schedule of
  reobservation
• gtgtgt space observatory
• Need to go beyond the atmospheric NIR cutoff to
  get our redshift range
• gtgtgt space observatory
• Must eliminate telluric features that would
  corrupt key classification lines CaII, SiII, H,
  as we chase them out into the near infrared
• gtgtgt space observatory
• Need extremely dark sky free of varying
  emission/absorption lines
• gtgtgt space observatory
• Must have rock steady seeing 24/7 to do precision
  weak lensing
• gtgtgt space observatory

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From Science Goals to Project Design
Science

• Measure ?M and ?
• Measure w and w (z)

Systematics Requirements
Statistical Requirements

• Identified and proposed systematics
• Measurements to eliminate / bound each one to
  /0.02 mag

• Sufficient (2000) numbers of SNe Ia
• distributed in redshift
• out to z lt 1.7

Data Set Requirements

• Discoveries 3.8 mag before max
• Spectroscopy with l/dl100
• Near-IR spectroscopy to 1.7 ?m

Satellite / Instrumentation Requirements

• 2-meter mirror Derived requirements
• 1-degree imager L2 orbit
• Low resolution spectrograph 150 Mb/s downlink
  (0.4 ?m to 1.7 ?m)

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SNAP Observatory Cross Section
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Payload Features

• 90 deg Symmetric Focal Plane allows continuous
  year round science data taking
• one side always sunward, allowing fixed solar
  panels hence a rigid spacecraft (resonances gt
  10Hz)
• other side always dark, allowing fixed passive
  thermal radiator serving sensor array
• Telescope assembly is thermally and structurally
  separate from surrounding outer baffle and from
  spacecraft
• maneuvers do not compromise PSF stability
• Innovative telescope design does IR imaging with
  room temperature optics
• three mirror anastigmat has accessible exit pupil
  and complete cold stop baffling
• Built in end-to-end optical test capability
  simplifies integration and testing
• The fixed telemetry antenna eliminates major
  mission risks and costs
• no gimbals, no flex waveguide
• rigid spacecraft eases ACS task
• No onboard data analysis all images are
  downlinked to Earth 21 Rice compression assumed

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DoE NASA other
Evolution of SNAP/JDEM
Nov 1999 Original SNAP proposal submitted to DOE
Mar 2000 DOE/NSF SAGENAP committee recommends
SNAP RD Sep 2000 NASA Structure and Evolution of
the Universe (SEU) Dec 2000 National Academy of
Sciences Committee on Astro. Astrophysics Jan
2001 DOE-HEP Review RD (SNAP is uniquely
able...) Mar 2001 DOE High Energy Physics
Advisory Panel (HEPAP) Jun 2001 NASA Integrated
Mission Design Center (determines
feasibility) July 2001 National Academy of
Sciences, Committee on Physics of the
Universe Dec 2001 NASA/SEU Strategic Planning
Panel Dec 2001 NASA Instrument Synthesis
Analysis Lab Jan 2002 DOE subpanel report High
Energy Physics Long Range Planning Mar
2002 DOE/NSF SAGENAP committee update Apr
2002 National Academy of Sciences Physics of the
Universe report July 2002 DOE Office of Science
RD Review (Lehman) Dec 2002 JPL Team-X Study
(studies potential NASA cost) Jan 2003 NASA
releases SEU roadmap Beyond Einstein Feb
2003 DOE High Energy Physics Facilities
Prioritization Panel Feb 2003 SNAP RD in the
DOE budget Mar 2003 DOE High Energy Physics
panel releases Facilities 20 Year Roadmap Nov
2003 JDEM Announcement DOE NASA Nov 2003
Secretary of Energys 20-year Facilities
Plan May 2004 OSTP Strategic Plan (JDEM top
recommendation) Mar 2005 NASA GSFC IMDC study of
mission implementation top marks! Aug 2006 JDEM
Advanced Concept Study awarded to SNAP, Destiny,
Adept.
1998 Discovery of the acceleration of the
universe and dark energy using supernovae.
2000 Confirmation of dark energy using cosmic
microwave background measured from balloons.
2003 Confirmation of dark energy using cosmic
microwave background measured from space (WMAP).
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Ready for Construction Start?

• Highly optimized and detailed mission concept
• With 5 years of work and 3 years of funded RD,
  much progress has been made on retiring
  programmatic risks
• Major studies completed at ITT and Ball Aerospace
  on telescope
• Spacecraft well studied, reference design is now
  being detailed
• Highly refined instrument concept
• NIR detectors have two competitive sources
  Rockwell Raytheon
• Our rad-tolerant CCDs meet specs, ready for mass
  production
• Spectrograph demonstration unit in development
• Calibration hardware and flow-down finally
  understood
• Cold, low-power, focal plane electronics past
  proof-of-principle
• Well developed operations data flow concept
• Broad community and international involvement
• Must now address long-lead procurement items
• Ready to launch in 2012-13 (5-6 year construction
  period)

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Select Recent Highlights

• Mission
• NASA/GSFC IMDC (Mar 2005) studied attitude
  control, payload accommodation, telemetry, IT
  helped identify solutions that minimize cost,
  mission risk
• Telescope
• Study contracts with industry for feasibility
  cost are complete (Mar 2006)
• Focal plane
• SNAP v2 CCD design and fabrication meets spec
• CCD analog processing ASIC
• Delivery, operation, and measurement of NIR
  detectors
• Two NIR vendor parts meet or close to spec
• Calibration
• Established path from NIST-traceable standard to
  standard star network to SNAP science targets
  will be within 2 budget for color.
• Computing and Simulation
• Delivery of computing framework
• Light curve, spectrograph, and grism simulations
• End-to-end SNe mission simulation to cosmology
  analysis
• Technical papers/ conference papers
• gt35 scientific papers
• gt17 detector/instrument papers
• 40 controlled docs and 75 tech notes, publicly
  available at ww.snap.lbl.gov/docindex.html

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SNAP has 5 teams at work

• Science
• Continuing groundbased HST observing
• Supernova Cosmology Project (Perlmutter)
• Supernova Factory (Aldering)
• Requirements
• Simulation team
• Theory modelling
• Calibration Team
• Instruments
• Silicon CCD group
• HgCdTe NIR groups
• Spectrometer
• Electronics
• Telescope
• Design, tolerances, optical performance
• Stray light
• Fabrication, Integration Test
• Science ops, especially software pipeline
• works closely with the simulation team

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Focal plane effort
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Focal plane structure
Spectrograph
Sensors
Filters
Radiator
Shield
Cold plate
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(No Transcript)
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Instrument Control Unit and Image Cache

• Instrument control unit (SLAC)
• Overall coordination and monitoring of instrument
• Leverage SLAC experience
• Readout Slice/Image Cache (FNAL)
• 2 terabits of flash memory storage required for
  one day of exposures (total).
• FNAL doing radiation tolerance experiments

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Computing Simulation Activities

• Computing
• Simulation Framework LBNL, UCB
• Collaborative infrastructure U. Michigan, FNAL,
  LBNL, UCB
• Mission Simulation Software
• Design U. Pennsylvania, LBNL
• Mission definition U. Pennsylvania, LBNL
• Photometric Channels
• Parametric LBNL, U. Pennsylvania
• Pixel-level FNAL, U. Michigan, CPPM, LBNL
• Spectroscopic Channels
• Parametric LBNL
• SNAP Spectrometer CPPM/LAM, UCB
• Grism U. Michigan, CPPM, UCB
• Calibration Simulation FNAL, LBNL, Indiana U.

• Data Analysis Software
• SN light-curve fitting LBNL, CPPM
• Spectroscopy CPPM/IPNL, U. Michigan, LBNL
• SN Hubble Diagram Cosmology LBNL
• Mission Studies (Requirements, trades,
  optimization)
• Ground SN missions LBNL, U. Pennsylvania
• SNAP CPPM, LBNL
• Baryon Oscillation U. Michigan, CPPM, LBNL
• Galaxy Clusters FNAL
• Gravitational lensing U. Pennsylvania

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A Possible 6-year Timeline
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Telescope Requirements

• Light Gathering Power
• SNR on faint targets with limited time-on-target
• photometry magnitude reach, accuracy, SN harvest
  rate
• spectroscopy magnitude reach, accuracy, SN
  harvest rate
• weak lensing magnitude reach, survey speed
• requires geometric aperture diameter 1.8 to 2.0
  meters
• Angular resolution and PSF stability over time
• drives SNR hence survey speed
• drives WL shear accuracy, hence survey speed
• goal is nearly diffraction limited at one
  micron wavelength
• Strehl gt 80 at one micron WFE lt 70 nm RMS
• Rate of change of PSF lt 2 milli arcseconds /
  hour TBC
• Field of View
• driven by required supernova discovery rate
• driven by required WL survey speed
• 1.3 sq deg optical, 0.7 sq deg instrumented field
• Wavelength Coverage
• 0.4 to 1.7 microns to span SN and WL redshift
  range
• requires all-reflector optical train

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Three-mirror anastigmat D.Korsch,
Applied Optics v.16 2074 1977.

• Prolate ellipsoid concave primary mirror
• Hyperbolic convex secondary mirror
• Flat folding mirror with central hole
• Prolate ellipsoid concave tertiary mirror
• Delivers lt 0.07 arcsecond FWHM geometrical blur
  over annular field 1.37 sqdeg
• Flat focal surface
• EFL adapts 15 to gt30meters
• baseline currently 22m
• Side-mounted detector
• Telephoto advantage 6

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Telescope within outer baffle
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The Metering Structure
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Stray light Cassegrain Baffle

• Developing stray light budget
• Operate in full sun light
• Operate in presence of bright stars
• Modeling for
• Mirror roughness
• Mirror particulate contamination
• Ghosting (filters)
• Baffle reflectance
• Test Plan

• Cassegrain stray light baffle effectively shadows
  inactive areas of focal plane.
• Baffle is warm, but not visible to detector
  pixels
• Baffle includes a four-blade shutter

sun
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Cassegrain shutter
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Image Quality (schematic!)
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Image Quality continued
Total
Diffraction
MCT pixel
silicon pixel
detector diffusion
aberrations
attitude control jitter
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Image Quality modulation transfer function
Principle 2 pixels/cycle at f(10) f(10) is 52
cycles/mm gt 9.5um compare our 10.5 um pixels
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Geometric Aberrations, TMA72
detector pattern 46.2mm grid
detector pattern 44mm grid
central vignetted zone
r.s.s.
radial
circum
pixel population with 44mm grid
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Mechanical Tolerances

• Initial alignment to surveying levels
• Secondary mirror used for final alignment
• Interferometer (terrestrial)
• Starfield (on orbit)
• Allowable mechanical tolerances are determined as
  follows
• Generate WFE budget line items corresponding to
  misalignment
• Misalign/SM correct until corrected WFE
  approaches budget allocation
• Initial mechanical misalignment becomes tolerance
• Tolerances are well within capability of
  surveying equipment
• Leica TM5100A theodolite (3 units) 10µm linear,
  2.5µrad angular
• Leica Laser tracker 25µm linear (10ppm), µrad
  angular

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SNAP-TECH-06008 Primary Mirror Dwg
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Flat fold mirror

• Optical design of TMA requires tight packaging
  between FM and passive cold stop while avoiding
  vignetting
• ULE, Zerodur, Be, SiC are OK
• Not a development driver

Zerodur SEVIRI mirror, Zeiss, 53x83cm, 16kg
SiC S. Roberts, DAO 2001 ASTRIUM 50 x 80cm
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1-G testing vertical vs horizontal

• Full end to end test planned
• Vertical vs Horizontal axis were traded
• vendor facilities experience
• 1-G deformations 100 nm rms
• lt 15 nm rms FEM uncertainty
• 12 to 15 offloaders on PM if vertical axis
• None on PM if horizontal axis
• No need to offload SM, FM, TM

PM horizontal axis, no offloaders 78nm RMS
Mirror Figure error Allowed figure error
Primary 10 nm rms lt 15 nm rms
Secondary 7.5 nm rms lt 10 nm rms
Fold 6 nm rms lt 10 nm rms
Tertiary 7.5 nm rms lt 10 nm rms
PM vertical axis, no offloaders 1500nm RMS
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Integration Test

• The SNAP observatory was designed to be simple to
  test, calibrate, and verify
• Built-in optical test equipment
• Interface ring between payload and spacecraft
  (spacecraft bolts on)
• Direct insertion and removal of science package
  from telescope without telescope deintegration
• Semi-kinematic mount for focal plane assembly and
  spectrograph
• Comprehensive test plan developed

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Integration Test Buyoff

• Mechanical integrity
• mirrors, bipods etc under compression and
  tension
• satisfied with horizontal axis testing, various
  roll angles
• test is regarded as easy to conduct
• Image quality
• mirrors, struts, structure under zero stress,
  zero strain
• similar to what will be seen on orbit
• requires flotation for PM
• requires precision flat or collimated star
  simulator
• requires interferometer for pupil wavefront
  display
• accommodates point source reflex test
• Stray light
• requires specialized test fixtures e.g. pulsed
  laser
• Define the facilities needed during IT flats,
  towers, ....

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PSF Stability

• Weak Lensing requires lt 2 milli-arcseconds / hour
  PSF change
• Expect chief thermal effect is daily attitude
  maneuver plan
• target selection
• data downlink
• Mitigators
• L2 orbit w/o shadows
• Low CTE materials in mirrors and structure
• Telescope is thermally mechanically decoupled
  from outer barrel
• active thermal control system
• Predict daily effect 0.12 milli-arcseconds
  change, 24h time scale

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Telescope Activities

• Optics design -- detailed clearances, tolerances,
  fabrication budgets
• Stray light baffles, struts, shield, detectors
• Passive cold stop design, clearances,
  accommodation
• Flat field illuminator integral with passive cold
  stop
• Cassegrain baffle reject stray light from focal
  plane
• Shutter at Cassegrain focus speed, accuracy,
  reliability
• Test plan component level, telescope level,
  observatory level
• Integration plan facilities, staff,
  verification matrix
• Observatory design has begun based on this
  telescope concept

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Telescope summary

• Accomplishments
• Mature design prescription, materials,
  fabrication test methods, are all within
  current state-of-art
• Extensive baffling design and simulation for
  stray light control
• Built-in test equipment may provide added
  assurance while reducing cost schedule impact
  of optical reverification
• Integration and test flow plan has been baselined
• Cassegrain shutter location ends operational
  concerns
• Flat field illuminator has been adopted and
  appears workable
• Long-lead procurement has begun!
• Future
• Update stray light, FEM, and integration plan
  studies
• Integrate industry recommendations into telescope
  test plan
• Pursue partnerships with industry to refine cost,
  schedule, test plans
• Proceed with the Zerodur primary mirror option
• Proceed into observatory mission design
  modelling, system engineering, spacecraft bus
  definition, data flow processing pipeline....

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Simulated SNAP data
Each SNAP point represents 50-supernovae per bin
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Further Information
M. Lampton et al, SNAP Telescope Proc. SPIE
4854, 2002. M. Lampton et al, SNAP Telescope
Progress Proc. SPIE 5166, 2003. M. Sholl et al,
Proc. SNAP Telescope Image Quality  SPIE 5487,
2004. M.Sholl et al SNAP Point Spread Function
SPIE v. 5899, 2005.
...and many more public documents at
http//snap.lbl.gov SNAP-TECH-06008 Primary
Mirror Dwg SNAP-TECH-06009 1-G Strain SNAP-TECH-06
010 Telescope Summary