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Technology Demonstration Mirror TDM

Gary Matthews Manager, Image Collection Systems Eastman Kodak Company April 11, 2003

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Key Kodak Innovations in Space Mirror Technology
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200 Areal Density (kg/m2)
Hubble Space Telescope BU 2.5m Primary Mirror

100 50 25
AOSD Telescope Segmented 2.6m Primary Mirror

Advanced Demonstrator 0.6m LTF/Pocket-milled (scaled to 2.5 meters)

AMSD - Class Technology 1.4 meter (scaled to 2.5 meter)

1980

1990

2000

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Technology Demonstration Mirror Program
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TPF TDM Purpose
Can mid-spatial performance supporting a visible coronagraphic TPF be achieve on a large scale, space-qualifiable, ultra-lightweight, coated mirror substrate? Is the metrology of mid-spatial surface content consistent with the above achievable on a large scale? Once produced, can a large scale, ultra-lightweight mirror maintain the required TPF mid-spatial performance through transportation, handling, launch, deployment and operation in its orbital environment?

Kodak's TDM concept provides a major step forward in answering the above questions with direct traceability to the larger mirror required for TPF
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Kodak TDM Baseline Concept
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Material: Corning ULETM Segmented Core
Advanced Waterjet Light-weighted

Low Temperature Fused Low Temperature Slumped Areal Density: 47.5 Kg/m
Includes Mount I/F Is 42.5 Kg/m2 for mirror alone Requirement is 60 Kg/m2
2

First Free Mode: 304 Hz
Requirement is 200 Hz

First Mounted Mode: 87 Hz
Requirement is 85 Hz

On-orbit PV Quilting: < 1nm
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Kodak TDM Study Conclusions
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TDM mirror fabrication requirements are achievable
Risks understood and manageable

Baseline concept for Demo Phase Proposal established
Successful analytical verification provides risk mitigation

Bottoms-up Budgeting Approach was Used
Minimized known big contributors such as 1-G quilting Used standard best practice design approaches elsewhere
Reallocate/redesign in problem areas

Goal was to maximize allowable residual surface error for mirror processing
Maintain reasonable metrology uncertainty Meet operation performance requirements
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Baseline Blank Design
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Parameter M ater ial / constr uction Finished Plate OD - Back Plate - Fr ont Plate Cor e OD (Plano Blank) Cor e depth Cor e cell geometr y (hex, flat-flat) Initial plate thickness Fr ont plate final thickness Back plate final thickness Cor e str ut thickness - inter ior - edge walls - mo u n t Best fit ROC M ount pad location M id Spatial Gr avity Quilting Number of cells

Descr iption ULE / LT F / LT S mm 1879.6 1861.3 920.8 139.7 128.7 12.7 9.3 5.1 in 74.000 73.280 36.252 5.500 5.067 0.500 0.366 0.201

1.4 0.055 1.9 0.075 2.8 0.110 7401.6 291.402 675.6 26.598 3.4 nm-r ms 260

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Detailed FEA Model
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Back Facesheet Removed for Illustration
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Material Trades
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ULETM
Excellent thermal stability, CTE < 30 ppb/°C Good stiffness and strength Many Manufacturing Options
Closed-back ("built up")
­ Frit, LTF, LTF/LTS ­ Kodak has considerable heritage with FRIT, LTF and LTF/LTS processes

Machined open back

For equal performance, a closed-back blank will be generally weigh less than a machined blank For equal performance, a closed-back blank will be generally cost more than a machined blank

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AWJ/LTF/LTS Fabrication Approach
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Glass Selection Shine plate and core segment blanks Waterjet core segments Assemble and fuse plano core blank Prepare plano blank surfaces for LTS
Shine back plate at final thickness

LTS blank to near net shape
Aspheric mandrill to maintain uniform face-sheet thickness

Final Processing
Shape and figure front surface Clean up mount pad locations if necessary
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Closed-back vs. Open-back Construction
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Inherently more efficient than open-back from stiffness perspective Not possible to have open back ULE/Zerodur mirror that meets stiffness goals and space envelope Closed back is compatible with existing Kodak processes
Airbag test/process support Compatible with other support equipment
Lifting fixtures

Able to utilize Kodak's traditional mounting techniques Closed back construction inherently more expensive

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Processing Technology
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Small tool processing
slow - processing time is weighted by coverage fraction requires large edge overhang for figuring edge effects both from large overhang and incomplete coverage solutions do not "span the space" does not efficiently remove high spatial frequencies

Symmetric laps
passive solutions exist and efficiently remove mid spatial frequencies fast and efficient, but cannot be used on an off-axis part

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Surface Figure Metrology
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Measurement Regimes
Low-spatial Mid-spatial High-spatial Micro Roughness > > 40 cm 40 cm 2 cm 2 cm > > 1 mm 1 mm > > 1 µm > > 2 cm

Proposed Methods
Low- & Mid-spatial Frequencies
Full Aperture Interferometry 1 M-pixel detector (meets 5x Nyquist Goal) 2 element Offner-type Null Lens

High-spatial & Micro Roughness
Sub-aperture surface profiling Chapman Instruments Profiler

2 cm > > 1 µm

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Mirror Mounting
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Mounting large mirrors for Zero-g applications is not trivial
Strain induced into mirror during mounting can be significant Strain is generated by friction at the strut mirror interface
May lock strain into flexures and not know it Looks good on ground, unacceptable on-orbit
­ Risk can be mitigated through costly strut instrumentation

Kodak has proprietary design to virtually eliminate mount strain
No strut instrumentation required Allows for quick integration of PM onto mount struts Allows for pre and post strut engagement optical testing
Mount strain can be verified

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TDM Performance Analyses
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Mirror stiffness
Will meet 300 Hz first free-free mode goal Will meet 85 Hz first mounted mode requirement
Strut geometry was optimized to minimize bending stiffness while maintaining axial stiffness and strength

Mirror 1-g quilting performance
Kodak intent is to backout 1-g quilting effect Currently carrying 10% finite element modeling uncertainty in budget
Can be reduced further through detailed model correlation if needed

Current uncertainty from detailed model and Tf=9.27 mm (0.365")
LSF: 0.63 nm-rms MSF: 0.34 nm-rms HSF: 0.002 nm-rms

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Mechanical Contributors to Test Set and Processing Uncertainty
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Gravity back-out
Quilting modeling uncertainty Uncertainty in offloading forces and locations

Airbag repeatability
Airbag ability to provide uniform support Ability to center mirror on airbag and repeat inflation volume

Coating Strain
Kodak employ ion figuring to correct local quilting effects Budget 10% uncertainty on error

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Thermal Stability
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Nominal CTE
Primary driver for thermoelastic deformation effects Standard ULE: -30 ppb/°C < CTE < 30 ppb/°C

CTE variability
ULE CTE varies as function of location in boule Kodak specifies more restrictive CTE ranges for individual components
CTE mismatch between facesheet CTE mismatch from core segment to core segment

Specified CTE requirements based on analysis of actual geometry
Models were developed to assess this Worst case CTE variation was used for stability predictions Demo phase predictions will updated based on selected boules

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Thermal Stability Modeling Approach
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Assumed all blank components matched within 20 ppb/°C
2 Facesheets 7 Core segments

Evaluated thermoelastic response for 10 unique CTE combination cases
Isothermal Axial Gradient Radial Gradient

Used worst case response for error budget

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Thermal Stability Error Contributors
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Glass stability during ground testing
Assumed isothermal environment held to ±1°C Nominal case
Assumed all ULE CTE=30ppb/°C Effect is negligible

Inhomogeneity
Took worst case isothermal

Operational Performance
Nominal case
Assumed all ULE CTE=30ppb/°C Isothermal and radial gradient effects negligible

Inhomogeneity
Took RSS combination of worst case isothermal, radial and axial cases

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TDM Coating Trades
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Bare Gold
Meets reflectivity () requirements (specification baseline) Durability/cleanability a major concern

Protected Silver
Meets reflectivity () requirements Higher durability/cleanability than bare gold
Qualified cleaning process exists at EK

Lower life-cycle cost

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Processing Summary
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Kodak identified technology required to process high volume off-axis segments several years ago
Kodak is investing in these technologies The same technologies which enable high volume production also enable off-axis aspheres with extremely low mid spatial frequencies

TPF TDM will demonstrate that these technologies will meet the needs for coronographic missions TPF TDM builds on Kodak's significant R&D investment off-axis segment processing

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TPF Traceability Summary
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Areal Density
TDM Design has Traceability to TPF Requirement of 25 kg/m
2

Metrology
Null Test Partially Traceable - TPF would probably use a CGH/refractive null (TDM baseline is a CGH/reflective null) Chapman Profilometry Scalable to TPF

Blank Construction
Highly Traceable - TPF study suggests LTF, LTS Segments Kodak and Corning Collaborating on a ULE Welding Technique
Enables Construction of Super-large Cores from Smaller Hex Segments

Open Back "Hogged Out" Construction More Difficult

Surface Finish
New processing technology being developed under Kodak IR&D provides the same surface quality as that generated by traditional full aperture laps
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Conclusion
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Kodak TDM design achieves all requirements
Risks understood and manageable

Baseline concept for Demonstration Phase established
Successful analytical verification provides risk mitigation

Requirements flow-down understood
Error Budgets / Sensitivities, derived requirements

Kodak demonstration phase cost significantly improved via CAIV trades , cost sharing, and capital investment

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