Optical Telescope Assembly WBS 2'2

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Optical Telescope AssemblyWBS 2.2

• M. Lampton
• Space Sciences Laboratory
• University of California Berkeley
• 09 July 2002

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Telescope Overview

• Schedule and WBS Overview
• Science Driven Requirements
• Baseline Characteristics
• Telescope Status
• RD Issues
• RD Goals
• RD Schedule
• RD Manpower
• RD Costs
• RD Management
• Summary

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Overall Scheduledraft May 28 2002
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Telescope WBS Overview
2.2.1 TELESCOPE MANAGEMENT 2.2.1.1
Telescope Management 2.2.1.2 Resource
Management 2.2.1.3 Schedule
Management 2.2.1.4 Configuration
Management 2.2.1.5 Reviews 2.2.1.6
Travel 2.2.1.7 Contracts 2.2.2
TELESCOPE SYSTEMS ENGINEERING 2.2.2.1
Develop telescope requirements 2.2.2.2
Telescope design and evaluate trades 2.2.2.3
Telescope analyses 2.2.2.3.1 Optical
performance 2.2.2.3.2 Stray light 2.2.2.4
Telescope IT planning 2.2.3 TELESCOPE
SUBSYSTEMS 2.2.3.1 Optical subsystems
GSE 2.2.3.1.1 Mirrors 2.2.3.1.2
Baffles 2.2.3.2 Mechanical structure
GSE 2.2.3.2.1 Precision metering
structure 2.2.3.2.2 Mechanisms focussers,
alignment... 2.2.3.2.2.1 Mirror
actuators 2.2.3.2.2.2 Shutter 2.2.3.3
Thermal control 2.2.3.4 Electrical 2.2.4
TELESCOPE INTEGRATION AND TEST 2.2.5
TELESCOPE SOFTWARE 2.2.6 TELESCOPE
SUPPORTING ACTIVITIES
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Telescope Science Driven Requirements

• Light Gathering Power
• must measure SNe 4 magnitudes fainter than 26
  magnitude peak
• want SNR of 301 at peak brightness, aggregate
  exposure fit
• presence of zodiacal light foreground radiation
• time-on-target limited by revisit rate number
  of fields
• spectroscopy demands comparable time-on-target
• requires geometric diameter 2 meters
• Angular resolution
• signal to noise ratio is driver
• diffraction limit is an obvious bound
• Airy disk at one micron wavelength is 0.12
  arcseconds FWHM
• all blur contributions must be budgeted
• Field of View
• determined by required supernova discovery rate
• volume of space is proportional to field of view
• one degree field of view will deliver the
  requisite discovery rate
• Wavelength Coverage
• 0.35 to 1.7 microns requires all-reflector
  optical train

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Telescope Status Baseline Configuration

• Prolate ellipsoid concave primary mirror
• Hyperbolic convex secondary mirror
• Flat folding mirror with central hole
• Prolate ellipsoid concave tertiary mirror
• Flat focal plane
• Delivers lt 0.06 arcsecond FWHM geometrical blur
  over annular field 1.37 sqdeg
• Adapts to focal lengths 15
• meters through 30 meters
• baseline21.66m
• Provides side-mounted
• detector location for best
• detector cooling

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Baseline OTA Characteristics

• Aperture 2 meters
• Annular Field of View 1 sq deg
• Wavelength Range 0.35 to 1.7 microns
• Strehl gt90 at 1.0 microns
• WFE lt50 nm RMS
• Focal surface flat
• EFL 21.66 meters, f/11
• Stray light ltlt Zodiacal foreground

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Telescope Status History

• Wide-field high-resolution telescopes are NOT new
• Schmidt cameras (1930 to present)
• Wynne cameras (e.g. FAUST)
• Field-widened cassegrains, Gascoigne (1977-)
  SDSS
• Paul three-mirror telescopes (1935) and
  Baker-Paul
• Cook three-mirror anastigmats TMAs (1979)
• Williams TMA variants (1979)
• Korsch family of TMAs (1980)
• Angel-Woolf-Epps three-mirror design (1982)
• McGraw three-mirror system (1982)
• Willstrop Mersenne Schmidt family (1984)
• Kodak IKONOS Earth Resources telescope TMA
• LANL/Sandia/DoE Multispectral Thermal Imager TMA

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Telescope Status Milestones Accomplished

• 1999
• comparisons of alternative wide field telescope
  configurations
• found off-axis designs attractive but
  unpackageable rejected
• explored, discarded coaxial TMTs (Willstrop etc)
  unworkable thermally
• annular-field TMA concept rediscovered, developed
  
• 2000
• TMA43 (f/10) longitudinal rear axis, separate
  NIR/VIS filter wheel
• began mechanical, structural studies w/
  subcontractor
• explored vignetting (marginal), stray light
  (marginal)
• 2001
• US DoE RD Review
• efforts to achieve shorter optical package for
  stiffness, stray light TMA55/56
• explored longer focal lengths for potentially
  higher sampling TMA59 (f/15)
• design validated at NASA/GSFC Instrument Systems
  Analysis Laboratory
• image quality stray light metering structure
  actuators
• 2002
• FIDO detector package, single focal plane,
  transverse rear axis
• TMA62 (f/11) transverse rear axis with filter
  wheel
• TMA63 (f/11) transverse rear axis, no filter
  wheel

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Payload Layout 1
Secondary Mirror Hexapod Bonnet
Door Assembly
Main Baffle Assembly
Secondary Metering structure
Solar Array, Sun side
Primary Mirror
Optical Bench
Solar Array, Dark side
Instrument Metering Structure
Instrument Radiator
Tertiary Mirror
Instrument Bay
CCD detectorsNIR detectorsSpectrographFocal
Plane guiders Cryo/Particle shield
Fold-Flat Mirror
Spacecraft
ACS CD H Comm Power Data
Solid-state recorders
Shutter
Hi Gain Antenna
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Payload Layout 2
Telescope is a three-mirror anastigmat 2.0 meter
aperture 1.37 square degree field Lightweight
primary mirror Low-expansion materials Optics
kept near 290K Transverse rear axis Side Gigacam
location passive detector cooling combines Si
HgCdTe detectors Spectrometers share Gigacam
focal plane Few moving parts in
payload two-blade shutter for Gigacam focussers/ad
justers at secondary tertiary
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Payload Layout 3
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Telescope Image Quality Issues

• Image quality drives science SNR, exposure times,
  ....
• Many factors contribute to science image quality
• diffraction size of aperture, secondary baffle,
  struts, ...
• aberrations theoretical imaging performance
  over field
• manufacturing errors in mirrors
• misalignments misfocussing of optical elements
• dirt, contamination, or nonuniformity in mirror
  coating
• guiding errors
• spacecraft jitter
• detector issues
• constancy of the PSF is important to the weak
  lensing science
• Work has begun on a comprehensive budget
• ongoing simulation team efforts
• Bernsteins Advanced Exposure Time Calculator
  PASP
• telescope studies feed into the simulations

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Telescope Status Ray TraceTMA62/TMA63
configuration
Airy-disk zero at one micron wavelength 26
microns diam0.244arcsec
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Telescope Status Pupil Obscuration Trades
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Telescope Status Stray Light Trades

• Guiding principle keep total stray light FAR
  BELOW natural Zodi
• R.O.M. assessment gives...
• Natural Zodi (G.Aldering) 1 photon/pixel/sec/mic
  ron
• StarlightZodi scattered off primary mirror
  0.002
• StarlightZodi scattered off support spider lt
  0.001
• Sunlight scattered off forward outer baffle edge
  2E-5
• Earthlight scattered off forward outer baffle
  inner surface 0.02
• Total stray 0.02 photon/pixel/sec/micron
• Long outer baffle is clearly preferred
• limit is launch fairing and S/C size
• ASAP software in place
• ASAP training 2001 further training in 2003
• Preliminary telescope ASAP models being built
• ASAP illumination environment models being built
• Our intension is to track hardware ops changes
  as they occur, allowing a system engineering
  management of stray light.

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Telescope Technology Roadmap

• Existing technologies are suitable for SNAP
  Optical Telescope Assembly
• New materials, processes, test evaluation
  methods are unnecessary
• Mirror materials
• science driver stable figure to guarantee
  constant focus and PSF
• Corning ULE glass extensive NRO flight history
  lightweight
• Schott Zerodur glass/ceramic composite lower
  cost, widely used in ground based astronomical
  telescopes huge industrial base
• Metering structure materials
• science driver stable structure for constant
  focus and PSF
• M55J carbon fiber cyanate ester resin epoxy
  adhesive bonds
• full report in Pankow presentation
• Mirror finishing technology
• conventional grind/polish/figure using abrasives
• ion-beam figuring available from two vendors
• Mirror surface metrology
• same as other space telescopes, e.g.
  cassegrains
• standard interferometer setups will do the job
  for SNAP

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Telescope Status Mirror Materials Trade

• Corning ULE ultra-low expansion glass
• extremely low CTE 20-50 parts per billion per
  dec C
• face sheets bonded to honeycomb core
• achieves 85-90 lightweight anticipate 200kg
  primary
• extensive manufacturing test history
• meets our performance requirements
• attractive for its high natural resonance
  frequencies, low sag
• eases mass margin for entire mission
• Schott Zerodur glass/ceramic material
• extremely low CTE 20-50 parts per billion per
  deg C
• solid blank, weight relieved by milling backside
• achieves 70-85 lightweight anticipate 250kg
  primary
• extensive manufacturing test history
• meets our performance requirements

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Telescope Trade Studies Summary

• Trade Studies worked during Pre-RD Phase
• Optical configuration
  gtgtTMA
• Warm optics vs cold optics
  gtgtwarm
• FIDO integrated sensor array vs separated
  gtgtintegrated
• Trade Studies continuing through RD Phase
• Exact aperture cost schedule vs aperture
• Wavefront error cost vs performance
• focal length is 21.66m the best choice?
• pupil obsuration, diffraction, stray light...
• Primary mirror thickness, stiffness, mass trade
• resonance freqs, sag under 1G testing, ...
• Protoflight vs Prototype Flight metering
  structures
• Vendor-dependent issues
• mirror material ULE? Zerodur?
• test gravity unloading scheme
• test full aperture vs partial aperture

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Telescope Overall Risk Assessment

• Mirror fab/test risks
• Far less demanding than HST we are NIR not NUV
• yet -- need comprehensive test plan.
• Mechanical structural risks
• comprehensive test plan static, dynamic, etc
• Thermal and mechanical disturbance issues
• Easy thermal environment HEO has few eclipses
• Schedule risks OTA is a long lead item!
• Error budget fixturing, optical test equipment,
  etc
• Do we need a full-aperture reference test flat?
• Contamination control materials test plan
• Stray light control management test plan

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Telescope Main RD Issues

• Critical path telescope is a long lead item.
• how big is our slack?
• Need to begin development of the OTA
  requirements document for potential bidders
• Need to refine performance specifications
• optical image quality
• stability of focus, point spread function, ...
• Need to understand communicate tolerances
• Need to prepare draft Interface Control Documents
• optical
• thermal
• mechanical
• electrical
• Need to assess risks and take steps to minimize
  them
• Need to perform trade studies (outlined above)

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Telescope RD Phase Deliverables

• Telescope Requirements Specification Document
• include manufacturing tolerance alignment
  specifications
• Subcontractors Final Reports
• Metering Structure Concept Trades
• Telescope Mirror Materials Trade Study
• OTA Thermal Model and Results Summary
• Focusing/Alignment Tolerance Analysis
• Focusing/Alignment Mechanism Trade Study
• Front Aperture Door Trade Study
• Integration Flow and Test Plan
• Preliminary Stray Light Analysis
• Shutter Mechanism Reliability Failure Modes
  Study
• Telescope acquisition plan schedule/milestones,
  cost.

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Telescope Acquisition Plan

• Potential Vendors Identified
• Ball Aerospace Systems Division (Boulder)
• Boeing-SVS (Albuquerque/Boulder)
• Brashear LP (Pittsburgh)
• Composite Optics Inc (San Diego)
• Corning Glass Works (Corning NY)
• Eastman Kodak (Rochester)
• Goodrich (Danbury)
• Lockheed-Martin Missiles Space Co (Sunnyvale)
• SAGEM/REOSC (Paris)
• These vendors have been briefed on SNAP mission
• Each has responded to our Request for Information
• Identify a route (materials, fabrication, test,
  integration, test)
• Milestones with appropriate incentives
• Visibility into contractor(s) activities

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Telescope RD Phase Management

• Management objective biddable Requirements
  Document that reflects all science requirements
  and trades
• Experienced team has been assembled
• Have begun dialogs with prospective vendors
• Have begun examining potential fab/test/integratio
  n flows
• No need for high-risk advanced materials or
  processes
• Emphasize proven manufacturing test techniques
• We plan on selection of contractor(s) with
  sufficient experience to bring successful
  delivery cost schedule
• This contractor mix defines the overall
  acquisition plan

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OTA RD Schedule
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OTA RD Schedule
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Deliverables WBS 2.2 Telescope
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Telescope CDR Preparations Plan

• Fully complete and document all trade studies
• Supplement these with industry commentary
• Use system-engineering budgets to identify
  optimum allocation of tolerances resources
• Identify materials and fabrication alternatives
  taking into account schedule risk and overall
  cost
• Detail the acquisition plan and milestones
• Prepare acceptance test plan, including
  acceptance tests
• Structural stability, thermal, stiffness, normal
  modes, creep
• Alignment and focussing plan
• Thermal vacuum and optical stability
• Stray light
• Gravity unloading plan
• Full-aperture and limited-aperture test
  opportunities
• Facilities needed, facilities available

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Telescope Summary

• Pre-RD
• converted science drivers into telescope
  requirements
• reviewed existing optical telescope concepts
• developed annular-field TMA configuration
• preliminary materials assessment
• begun to explore vendor capabilities
• started a budget for image quality
• RD Phase
• engineering trade studies and budgets
• manufacturing process risk assessments
• test plans and associated cost/risk trades
• facilities equipment
• prepare the acquisition plan
• performance specifications tolerance analysis
• create draft ICDs
• develop preliminary cost schedule ranges