Large Synoptic Survey Telescope Review

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Large Synoptic SurveyTelescope Review

• Kirk Gilmore - SLAC
• DOE Review
• June 15, 2005

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LSST Technical Concept

• 8.4 Meter Primary Aperture
• 3.4 M Secondary
• 5.0 M Tertiary
• 3.5 degree Field Of View
• 3 Gigapixel Camera
• 4k x 4k CCD Baseline
• 65 cm Diameter
• 30 Second Cadence
• Highly Dynamic Structure
• Two 15 second Exposures
• Data Storage and Pipelines Included in Project

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Science Objectives Drive System Requirements

• Image Quality
• Is the Key
• f/1.25 beam
• High Etendue
• Large focal Plane
• Construction
• Techniques

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From Science Reqts to Sensor Reqts

• High QE to 1000nm ? thick silicon (gt 75 µm)
• PSF ltlt 0.7 (0.2) ? high internal field in the
  sensor
• ? high resistivity substrate (gt 5 kohmcm)
• ? high applied voltages (30 - 50 V)
• Fast f/1.2 focal ratio ? sensor flatness lt 5µm
• ? package with piston, tip, tilt adj. to
  1µm
• Wide FOV ? 3200 cm2 focal plane
• ? gt 200-CCD mosaic (16 cm2 each)
• ? industrialized production process required
• High throughput ? gt 90 fill factor
• ? 4-side buttable package, sub-mm gaps
• Fast readout (1 - 2 s) ? segmented sensors 6400
  TOTAL PORTS

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Optical Design
Optical Design
0.6
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Why is the LSST unique?
Primary mirror diameter
Field of view (full moon is 0.5 degrees)
0.2 degrees
10 m
3.5 degrees
Keck Telescope
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Meeting the FPA Requirements
_______________________________________________

• SLAC personnel will provide major technical and
• management effort to meet camera goals
• Focal Plane Motion Control
• Focal Plane Metrology (warm/cold)
• Thermal Analysis Control
• Focal Plane Assembly 25
  people at SLAC
• Vacuum Control
  working on LSST
• Cryostat Integration Testing (FEE
  BEE)
• Camera Controls
• Data Acquisition

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Focal plane array
3.5 FOV ? 64 cm ?
Strawman CCD layout 4K x 4K, 10 µm pixels 32
output ports
201 CCDs total
Raft 9 CCDs 1cm x 1cm reservedfor wavefront
sensors
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FPA Flatness Image Quality
Sensor Module 5mm p-v flatness over entire
sensor surface
Raft Assembly 6.5mm p-v flatness over entire
surfaces of sensors
Focal Plane Assembly 10mm p-v flatness over
entire surfaces of sensors
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Monte-Carlo simulation of long-wavelength light
absorption in silicon sensor.
PSF Simulations
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Why good image quality (PSF) is essentialfor
LSST science
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Raft Assembly
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The LSST FPA

• Assembled and tested at SLAC
• 25 Rafts with nine 4 Mpixel x 4 Mpixel CCDs each
• except corners 3 CCDs each
• Total of 201 CCDs, 3.3 Gpixel
• Active area diameter 640 mm
• Lens L3 25 mm above FPA
• Inner diameter of support for L3 680 mm.
• Space between support and active area 20 mm.

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Spot Measurement and Accuracy
Metrology at SLAC

• Measure the location of spots using standard
  centroiding methods.
• Even in low S/N environment can obtain accuracy
  of better than 1/30 of a pixel size.
• With LSST pixel size of 10 microns, accuracy
  should be of order 0.3 microns.

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AlN
UP
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Camera Assembly at SLAC
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Camera layout
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Camera Electronics
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LSST Filter Development at SLAC

• CHALLENGE
• Fabricate large curved filters with uniform
  coating
• STATUS
• Discussions with multiple vendors ongoing
• Preliminary feedback from vendors no
  show-stoppers
• Study RFQs going out to vendors in FY06
• Will include solicitation for design and
  development funding needed to qualify vendors for
  fixed price contract

• Current LSST baseline uses filter set comprised
  of g, r, i, z, and Y bands. Approximate FWHM
  transmission points are shown below.

• Final specifications beingdriven by simulations
  modeling.

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Science Simulator Overview
Simulations
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Cerro Pachon Atmosphere Experiment

• Cerro Pachon Facilities
• SOAR 4.2m Telescope
• Gemini 8m Telescope
• MASS
• DIMM
• Weather
• All-sky Camera

DIMM Integrated Measurement
MASS Structure above 500m
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Data Management
2 PB disk (6 mo) 120 PB archival 20 (?) TFLOP 30
TB/night 200 nights observing/yr 10 years 60
PB images 60 PB catalogs
Archive Computing Center
Mirror Sites
103 to 4 kM .35 GB/s
GRID, Internet 2
GRID, Internet 2
Portal User
Portal Users
103 to 4 kM .35 GB/s 30 TB/night 1/8.64104 full
days/sec
Portal Users
45 TB disk, 1 TFLOP 6.0 GB/image5
images/minute 500 minutes observing/night 3
nights 45 TB raw images
Telescope Site
150 TB disk 10 TFLOP 6.0 GB/image5
images/minute 500 minutes observing/night 5
nights 75 TB raw images 75 TB processed
images
Focal plane
Base Camp Center
10-1 kM, .625 GB/s RateRO 3.0 109
pixels/read-out (16 image 4 eng, ops,
control, etc.) bits/pixel 0.5 read-outs/second
30 Gb/s RateAVG RateRO 2 /12 read-out
time/(exposure time read-out time) 5 Gb/s
.625 GB/s
101 to 2 kM 1.25 GB/s Rate RateAVG 2 for
redundancy/ reliability
Notes B bytes, b bits Raw image data is
transferred/stored compressed (assume 75
reduction), uncompressed to 64 bit words locally
for processing