Transcript Optical Telescope Assembly R&D Phase WBS 2.2

Optical Telescope Assembly
R&D Phase WBS 2.2
M. Lampton
Space Sciences Laboratory
University of California Berkeley
09 July 2002
Draft OTA10, 5 June 2002
Telescope: Overview
Schedule and WBS Overview
 Science Driven Requirements
 Baseline Characteristics
 Telescope Status
 R&D Issues
 R&D Goals
 R&D Schedule
 R&D Manpower
 R&D Costs
 R&D Management
 Summary
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Overall Schedule
draft May 28 2002
Telescope: WBS Overview
2.2.2
2.2.2.1
2.2.2.2
2.2.2.3
2.2.2.3.1
2.2.2.3.2
2.2.2.4
2.2.3
2.2.3.1
2.2.3.1.1
2.2.3.1.2
2.2.3.2
2.2.3.2.1
2.2.3.2.2
2.2.3.2.2.1
2.2.3.2.2.2
2.2.3.3
2.2.3.4
2.2.4
2.2.5
2.2.6
TELESCOPE SYSTEMS ENGINEERING
Develop telescope requirements
Telescope design and evaluate trades
Telescope analyses
Optical performance
Stray light
Telescope I&T planning
TELESCOPE SUBSYSTEMS
Optical subsystems; GSE
Mirrors
Baffles
Mechanical: structure & GSE
Precision metering structure
Mechanisms: focussers, alignment...
Mirror actuators
Shutter
Thermal control
Electrical
TELESCOPE INTEGRATION AND TEST
TELESCOPE SOFTWARE (alignment; focussing)
TELESCOPE SUPPORTING ACTIVITIES
Telescope: Science Driven Requirements
• Light Gathering Power
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must measure SNe 4 magnitudes fainter than 26 magnitude peak
require SNR of 50:1 at peak brightness
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
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signal to noise ratio is driver
diffraction limit is an obvious bound
Airy disk at one micron wavelength is 0.12 arcseconds FWHM
other blur contributions must be kept well below this limit.
• 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
Telescope Status: Baseline Configuration
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Prolate ellipsoid concave primary mirror
Hyperbolic convex secondary mirror
Flat folding mirror with central hole
Prolate ellipsoid concave tertiary mirror
Flat focal plane
Delivers < 0.06 arcsecond FWHM geometrical blur over annular field 1.37 sqdeg
Adapts to focal lengths 15 meters through 30 meters; baseline=21.66m
Provides side-mounted detector location for best detector cooling
Baseline OTA Characteristics
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Aperture: 2 meters
Annular Field of View: ~1 sq deg
Wavelength Range: 0.35 to 1.7 microns
Strehl: >90% at 1.0 microns
WFE: <50 nm RMS
Focal surface: flat
EFL: 21.66 meters, f/11
Stray light: << Zodiacal foreground
What is new here is the huge diffractio n - limited field :
 fieldof view
N resolutionElements 
 3E 9 at 0.5m
 diffraction blur
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
Telescope Status: Downselection
• 1999-2002: TMA Suitability Assessments
—off-axis designs attractive but unpackagable; rejected
—four, five, and six-mirror variants explored; rejected
—annular field TMA concept rediscovered & developed
—TMA43 (f/10): satisfactory performance but lacked
margins for adjustment
—TMA55 (f/10): improved performance, shorter pri-sec,
margins OK
—TMA59 (f/15): same but with longer focal length
—TMA62 (f/11): transverse rear axis with filter wheel
—TMA63 (f/11): transverse rear axis, no filter wheel
Payload Layout 1
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
Minimum moving parts in payload
shutter for detector readouts
Payload Layout 2
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
• Work has begun on a comprehensive budget
— ongoing simulation team efforts
— Bernstein’s “Advanced Exposure Time Calculator” PASP
— telescope studies feed into the simulations
Telescope Status: Ray Trace
TMA62/TMA63 configuration
Airy-disk zero at one micron wavelength
26 microns diam=0.244arcsec
Telescope Status: Pupil Obscuration Trades
3X 4cm
Ø2m
Ø45cm
Six 2cm thick
Tangential Vanes
Ø2m
Ø45cm
Four 4cm Thick
Radial Vanes
Ø2m
Ø45cm
Three 4cm Thick
Radial Vanes
3X 4cm
6X 2cm
6X 2cm
Ø45cm
Eight 2cm thick
Tangential Vanes
Ø2m
Telescope Status: Stray Light Trades
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Guiding principle: keep total stray light FAR BELOW natural Zodi
R.O.M. assessment gives...
— Natural Zodi (G.Aldering) = 1 photon/pixel/sec/micron
— Starlight+Zodi scattered off primary mirror = 0.002
— Starlight+Zodi scattered off support spider < 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.
Telescope Technology Roadmap
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Existing technologies are suitable for SNAP Optical Telescope Assembly
New materials, processes, test & evaluation methods are unnecessary
Mirror materials
— 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
— Astrium/Boostec SiC-100: newcomer; unproven in space optics; higher CTE;
adoped for Herschel/FIRST in infrared
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Metering structure materials
— M55J carbon fiber + cyanate ester resin; epoxy adhesive bonds
— full report in Pankow presentation
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Mirror finishing technology
— conventional grind/polish/figure using abrasives
— ion-beam figuring available from two vendors
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Mirror surface metrology
— same as other space telescopes, e.g. cassegrains
— standard interferometer setups will do the job for SNAP
— no unusual accuracy drivers have been encountered
Telescope Status: Mirror Materials Trade
• Corning ULE ultra-low expansion glass
— face sheets bonded to honeycomb core
— achieves 85-90% lightweight; anticipate 250kg 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
— solid blank, weight relieved by milling backside
— achieves 70-80% lightweight; anticipate 350kg primary
— extensive manufacturing & test history
— meets our performance requirements
• Study contract is in place
Telescope Trade Studies Summary
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Trade Studies worked during Pre-R&D Phase
— Optical configuration:
>>TMA
— Warm optics vs cold optics:
>>warm
— FIDO integrated sensor array vs separated: >>integrated
Trade Studies continuing through R&D Phase
— Mirror materials: ULE vs Zerodur vs others
— Exact aperture: cost & schedule vs aperture
— Strehl ratio: cost vs performance
— Focal length: is 21.66m the right value?
— Pupil obscuration issues
• secondary mirror baffle
• strut configuration
— Mirror thickness, rib design, stiffness, mass....
— Protoflight vs Prototype + Flight metering structures
— Detailed test & acceptance sequence
• gravity unloading scheme
• full aperture vs partial aperture
• during thermal-vacuum testing?
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
Telescope: Main R&D 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
—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)
Telescope: R&D Phase Deliverables
• Telescope Requirements Specification Document
— include manufacturing tolerance; alignment specifications
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Subcontractors’ Final Reports
Metering Structure Concept Trades
Telescope Mirror Materials Trade Study
OTA Thermal Model and Results Summary
Focussing/Alignment Tolerance Analysis
Focussing/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.
Telescope Acquisition Plan
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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
Telescope: R&D Schedule
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Zero-order Design Report
Draft Requirements Review
Long Lead Procurement Budget Request
Systems Engineering Management Plan
Performance Assurance Implementation Draft
Risk Management Plan
OTA Study RFP
OTA Study Contract in place
Preliminary Project Execution Plan
Preliminary Hazards Analysis
Systems Requirements Review
Conceptual Design Report
1 Aug 2003
1 Aug 2003
1 Oct 2003
1 Feb 2004
1 Feb 2004
1 Feb 2004
1 Feb 2004
1 Apr 2004
1 May 2004
1 May 2004
1 May 2004
1 Aug 2004
Telescope: R&D Phase Manpower
U.C.B. SSL Personnel -- Telescope
FY03
FY04
FTE
FTE
--------------------------------------------------------------------------------M.Lampton, SSL
Team Lead
0.75
0.80
D.Pankow, SSL
Mech/Therm Lead
0.40
0.40
M.Sholl, SSL
Optics Lead
0.70
0.70
R.Pratt, SSL
Mech Design
0.3
0.30
H.Heetderks, SSL
Systems
(SE)
(SE)
In addition -- we make use of varying amounts
of support from LBNL engineering personnel.
Telescope: R&D Phase Contracts
Contracts -- Telescope
FY03
FY04
FTE
FTE
--------------------------------------------------------------------------------Krim Consulting
0.25
0.5
Boeing-SVS
-00.25
Corning
-00.25
Breault Research Organization
-00.1
Telescope: R&D 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 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
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 flight qual 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
Telescope: Summary
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Pre-R&D
— 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
R&D 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