# Presentation: 766470

## David Pankow
     Space Sciences Laboratory,
Mechanical Engr. Department
University of California Berkeley
July 2002

**     ****Space Sciences Laboratory,**
**Mechanical Engr. Department**
**University of California Berkeley**
**July 2002**

**SC-3 Telescope Structural/Thermal****WBS 2.2**

## SNAP Telescope Structural / Thermal

- Mechanical Requirements
- Telescope Optical Elements
- Telescope Packaging (TMA-63)
- Stray Light Baffle and Cover
- Telescope Structure
- Telescope Mechanisms
- Telescope Thermal
- Camera (passive) Thermal
- R & D Activities
- Summary

## SNAP DESIGN PHILOSOPHY

**Passive Cold Biased Bus & Baffle / Warm Optics**
- Active Coolers are not Mature, Cryogen's are Short Lived
- High Earth Orbit allows Passive Cooling and Stable Pointing
- Build, Test, and Fly Warm Optics (...*like Hubble*)
- Cold Optics would be a Significant Cost & Schedule Driver
- Compact Telescope with the Longest Light Baffle that will Fit !
**Generic *****and*****  Rigid Spacecraft**
- One Mission Thermal Attitude   ...near Sun Line Normal Viewing
- No Appendages and Minimal Mechanisms
- On Board Momentum Management
- Structural Noise Isolation at the Sources
- Generic RSDO spacecraft with Needed Upgrades

## Telescope Configuration from IMDC

- Propulsion Tanks

- Sub-system
- electronics

- Secondary Mirror
- and
- Active Mount

- Optical Bench

- Primary Mirror

- Thermal
- Radiator

- Solar Array
- Wrap around, body mounted
- 50% OSR & 50% Cells

- Detector/Camera
- Assembly

**from GSFC - IMDC study**

## Current Telescope Evolution

- Main Baffle Assembly

- Door Assembly

- Primary Solar Array

- Secondary Mirror Hexapod
- and “Lampshade” Light Baffle

- Secondary Metering Structure

- Primary Mirror

- Optical Bench

- Instrument Metering Structure

- Tertiary Mirror

- Fold-Flat Mirror

- Spacecraft

- Shutter

- Instrument Bay

- Instrument Radiator

- Solar Array, ‘Dark-Side’

**Current Telescope Evolution**

## MECHANICAL REQUIREMENTS

**Launch Environments (Delta IV)**
- Stiffness: > 25 Hz (axial) > 10 Hz (lateral)
- Strength: 6.5 Gs Axial; 2.0 Gs Lateral
- Minimum Required Safety Factors
- Two for ‘Ordinary’ Engineering Materials
- Four for Composite Materials
- Ten for Glass & Ceramic Materials
- Vibro-Acoustics: *mostly for Boxes *
**Mission Environments**
- Stiffness > 5 Hz to Minimize ACS Interactions
- ~ ppm Optics Path Stability, periodic Focus is acceptable
- Low Outgassing; Low Water Absorption; Low *(particulate)* Contamination
**Integration & Test Environments**
- Handling Fixture Accommodation on OTA
- Needed (Large) Inventory of Handling Fixtures

**10Gs**

**100 kg**

**MASS ACCELERATION CURVE**
- FOR SPACECRAFT STRUCTURAL DESIGN
- JPL Document: JPL D-5882
- by: Marc Trubert	dated Nov 1, 1989

## Corning ULE ultra-low expansion glass
Face sheets bonded to honeycomb core
Achieves 85-90% lightweight
Extensive manufacturing history
Meets our  performance requirements

Schott Zerodur glass/ceramic material
Solid blank, weight relieved by milling backside
Achieves 70-85% lightweight
Extensive manufacturing history
Meets our performance requirements

Astrium/Boostec sintered SiC (distant 3rd choice)
Relatively new in astronomy; limited flight history
Appreciable CTE is a concern
Ongoing work in France and Germany; also JPL

- Face sheets bonded to honeycomb core
- Achieves 85-90% lightweight
- Extensive manufacturing history
- Meets our  performance requirements
**Schott Zerodur glass/ceramic material**
- Solid blank, weight relieved by milling backside
- Achieves 70-85% lightweight
- Extensive manufacturing history
- Meets our performance requirements
**Astrium/Boostec sintered SiC ***(distant 3**rd** choice)*
- Relatively new in astronomy; limited flight history
- Appreciable CTE is a concern
- Ongoing work in France and Germany; also JPL

**TELESCOPE OPTICS****Mirror Materials & Processing**

## TELESCOPE OPTICSMirror Materials & Processing

| Material | Supplier | Modulus
( Gpa ) | Density
( gm/cm3 ) | CTE (300K)
( ppm /K ) | Conductivity
( w/m/K ) | Ht. Capacity
( J/kg/K ) |
| --- | --- | --- | --- | --- | --- | --- |
| ULE | Corning | 68 | 2.20 | < 0.03 | 1.31 | 776 |
| Zerodur | Schott | 91 | 2.53 | <0.05 | 1.46 | 821 |
| Silica | Many | 73 | 2.20 | 0.52 | 1.38 | 703 |
| SiC | Many | 466 | 3.05 | 2.37 | 240 | 660 |
| BoroFloat | Schott | 63 | 2.22 | 3.20 | 1.10 | 830 |
| Pyrex | Corning | 64 | 2.23 | 3.20 | 1.30 | 726 |

**TELESCOPE OPTICS****Mirror Materials & Processing**

## Corning ULE
3 pieces: slump face sheets & core
Water-jet the thick core section
fuse them under compression
grind  polish  & inspect
figure;  measure...
coat  and acceptance test
Schott Zerodur
generate the curved front & back
weight  relieve  the  back
grind  polish  & inspect 
figure;  measure...
coat  and acceptance test
Boostec SiC
mix  binder  and  press  petals
machine  and  sinter  petals
braze  petals  together
apply CVD  surface  layer
grind  polish  & inspect  
figure;  measure...
coat  and acceptance test

- 3 pieces: slump face sheets & core
- Water-jet the thick core section
- fuse them under compression
- grind  polish  & inspect
- figure;  measure...
- coat  and acceptance test
**Schott Zerodur**
- generate the curved front & back
- weight  relieve  the  back
- grind  polish  & inspect
- figure;  measure...
- coat  and acceptance test
**Boostec SiC**
- mix  binder  and  press  petals
- machine  and  sinter  petals
- braze  petals  together
- apply CVD  surface  layer
- grind  polish  & inspect
- figure;  measure...
- coat  and acceptance test

**Corning ULE risks**
- availability
- improper fusion
**Schott Zerodur risks**
- Open backed mirror
**Boostec risks**
- material homogenienity?
- braze strength?
- braze distortions?
- figure stability in space environment?
- how to deal with CTE?

**TELESCOPE OPTICS****Mirror Materials & Processing**

## Key requirements and issues
Dimensional stability
High specific stiffness (1g sag, acoustic response)
Stresses during launch
Design of supports
Baseline technology
Multi-piece, fusion bonded, with egg-crate core
Meniscus shaped
Triangular core cells

**Dimensional stability**
**High specific stiffness (1g sag, acoustic response)**
**Stresses during launch**
**Design of supports**
**Baseline technology**
**Multi-piece, fusion bonded, with egg-crate core**
**Meniscus shaped**
**Triangular core cells**

- Initial design for primary mirror

- Deformations of mirror top face under pseudo-static launch loads: peak deflection = 20 m

- Design with locally thicker web plates
- Standard web thickness = 5 mm (orange)
- Thickened plates = 10 mm (red)

- 1g front face ripple on perfect back-side support
- P-P Z deflection = 0.018 m

**TELESCOPE OPTICS****Mirror Materials & Processing**

## TELESCOPE OPTICS Transverse Rear Optics Selected

**TMA-56 *****(coaxial)***** vs. TMA-63 *****(lateral)***
**Key Requirements**
- Dimensional Stability
- Stiffness and Gravity Deflection
**Better Packing than Axial Tertiary**
- Overall Length is Reduced
- Longer Stray Light Baffle is Possible
- No Structural Obscurations
- Metering Struts Possible (like  secondary)
- Rear Coffin Design is Attractive
- Encloses Transverse Rear Optics
- Accommodates Extensive Baffling

## Stray Light Baffle had Optics Requirements, only Modest Precision
Supported by Spacecraft, NOT TELESCOPE

Secondary Mirror Metering Structure Concepts
FEM Modal Resonances Explored for Promising Candidates

Tertiary Mirror Support Metering Structure
Transverse “Coffin” is Presently Baselined

Kinematic Support for All Optics
Normal or ‘Inverted’ Bipods

**Supported by Spacecraft, *****NOT TELESCOPE***
**Secondary Mirror Metering Structure Concepts**
**FEM Modal Resonances Explored for Promising Candidates**
**Tertiary Mirror Support Metering Structure**
**Transverse “Coffin” is Presently Baselined**
**Kinematic Support for All Optics**
**Normal or ‘Inverted’ Bipods**

**TELESCOPE OPTICS  ****Mechanical & Packaging Options**

## STRAY LIGHT BAFFLE DESIGN

**FUNDAMENTAL BAFFLE DESIGN CONSIDERATIONS**Angled Top Cut Must Prevent Block Sunlight in All Science AttitudesEarth-Light Region must be Fully Baffled	- minimum of two diffraction bounces to Primary Mirror	- knife edge sharpness governs diffracted light intensityBaffle –to- Lamp Shade –to- Stove Pipe diffraction line dictates the “Hat Size”  	- Longer Baffle Reduces Secondary Hat Obscuration

## STRAY LIGHT BAFFLE DESIGN

| Construction Method | Mass (kg) | Comments |
| --- | --- | --- |
| Aluminum Shell with Disposable Cover | 159 | Many Vendors Available |
| Honeycomb Sandwich with Cover | 138 | Curved Panels are Costly |
| Composite Shell with Disposable Cover | 108 | Few Vendors |
| Aluminum Shell with Split ‘One Shot’ Door | 175 | Solves Space Debris Issues |
| Aluminum Shell with 77 kg HST Door | 365 | Re-Closeable |

**Baffle Preliminary FEM Design Studies are Complete & Posted***** **Study Constraints:	>35 Hz Lateral Mode             > 10 Hz On Orbit *(Open Doors)**	*	- Thermally Isolated Base Mounting	- Launch Loads Safety Factor > 4

**STRAY LIGHT BAFFLE DESIGN**

## STRAY LIGHT BAFFLE COVER

**“****ONE SHOT” BARN DOORS ****- Ribbed Split & Edge Attachments****- Domed Center & Stiffening Ribs****- COMPOSITE shell construction****- Spring Preload Against Baffle When Open for >10 Hz**

**STRAY LIGHT BAFFLE COVER**

**NOTE:** *the Baffle Cover is not a Science Requirement, but an Anticipated Need for the Integration and Contamination Planning*

## LIGHT BAFFLE COVER RELEASE

**LIGHT BAFFLE COVER RELEASE**

## TELESCOPE STRUCTURE

**SECONDARY MIRROR SUPPORT STRUCTURE IS THE CRITICAL ITEM**- Secondary Mirror is the most Sensitive Element in TMA Optics- Strong Science Desires to Minimize Obscuration- Remote Location Presents a Unique Design Challenge

**REQUIRED MATERIAL Properties**** ***(driven by ppm Optics Rqm’t)*- Cyanate Ester matrix for low CME (moisture)- High Modulus & Conductivity Fibers for sub-ppm/C stability- On Orbit Temperature Controlled (few C) Telescope Structure- Quasi-Isotropic Patterning highly desired, given the non-linear Geometry- ***These are Today’s Technology***

## TELESCOPE STRUCTURE

**TELESCOPE STRUCTURE**

**SECONDARY MIRROR STRUCTURE**

## Optical Telescope Assembly (OTA)

**- OPTICS, THERMAL, AND GEOMETRIC DEFINITIONS COMPLETE****- ****DETAILED DESIGN AND FEM ANALYSIS NOW IN PROGRESS**

**LOWER OPTICS BENCH ASSEMBLY**

## Mathematically, 13 Mechanical Adjustments are Possible
Focusing, Centering, and Collimation
6 DOF Hexapod is Attractive for Alignment of Secondary (z  is a spare)
Complete Tolerance & Alignment Budget is being Generated
Tertiary Mirror may also need to be ‘motorized’

Focusing & Alignment Procedure
How Complicated are the Commissioning, and later On-Orbit Alignments?
Least Squares Optimization and Monti-Carlo Approaches Show Promise
Alternate Methods Will be Explored in the R&D Phase

Shutter Concepts are being Examined
Flying Slit Concept is Quite Attractive
Butterfly Shutter, or Counter-Rotating Blades are Possible
Spacecraft Fit and Image Disturbance are Issues
Speed and Uniformity of Exposure Times over the Field
Light Path for the ACS Guider 
Reliability is a Big Concern

- Focusing, Centering, and Collimation
- 6 DOF Hexapod is Attractive for Alignment of Secondary (***z*  is a spare)
- Complete Tolerance & Alignment Budget is being Generated
- Tertiary Mirror may also need to be ‘motorized’
**Focusing & Alignment Procedure**
- How Complicated are the Commissioning, and later On-Orbit Alignments?
- Least Squares Optimization and Monti-Carlo Approaches Show Promise
- Alternate Methods Will be Explored in the R&D Phase
**Shutter Concepts are being Examined**
- Flying Slit Concept is Quite Attractive
- Butterfly Shutter, or Counter-Rotating Blades are Possible
- Spacecraft Fit and Image Disturbance are Issues
- Speed and Uniformity of Exposure Times over the Field
- Light Path for the ACS Guider
- Reliability is a Big Concern

**TELESCOPE MECHANISMS**

## TELESCOPE MECHANISMS

**HEXAPOD FOCUS CONTROL**
**Needed on Secondary Mirror**
** ****micron steps & mm Range Needed**
** ****Tolerances by M.Lampton p.13-15**
** ****Several Designs have Flown**
**Not a Pioneering Design**

*TERTIARY HEXAPOD ADJUSTER IS A RETAINED OPTION*

**ACTUATOR PRECISION CONSIDERATIONS**
- - Stepper with Ball Screw		m
- - Stepper with Roller Screw
- - Torque Motors w/ encoder
- - Piezo / Magneto / Thermal		nm

## TELESCOPE MECHANISMS

**“****Flying Slit” is Current Best Candidate**
**“****Bow-Tie” style is alternative**
**- momentum compensation planned**

**TELESCOPE MECHANISMS**

**Located Behind Folding Flat**
-   Now Beam Normal
-   Can Block Solar Flux

**- many variants considered**

## TELESCOPE THERMAL

**Launch Environments (Delta IV)**
- KSC Launch Pad Temperature & Humidity
- Minor Aerodynamic Heating After Fairing Jettison (mostly Baffle)
**Mission Environments**
- Controlled 290K during on-orbit operation
- Flight Thermal Control System will Maintain ~few K Stability
- Details of Mirror and Structure Heaters, Sensors are TBS
- Localized Heating is a Concern for Optical Quilting & General Deformations
- Safe Hold Temperature Excursions TBS
**Integration & Test Environments**
- 0 to 40C Anticipated for Shipping, Storage, and Processing

## TELESCOPE THERMAL

**OPTICS: Build,Test, & Fly Warm... like Hubble !**

**KEY DESIGN FEATURES**
** ****High Earth orbit (HEO) to minimize IR Earth-glow loading**
** ****GaAs cell - OSR striping of the (hot) solar array panels**
** ****Front surface heat rejection OK**
** ****Optical Solar Reflectors are back silvered Quartz tiles (*********** *****~ 8%, *********** *****~ 80%)**
** ****Low emissivity silvered mirrors**
** ****Thermal Isolation mounting and MLI blanketing**

## OTA WARM OPTICS THERMAL BUDGET

**LARGE STRAY LIGHT BAFFLE (~180K)**
** ****478 w ****	****Absorbed Sunlight if MLI covered (****************** *****~ 2%)**
** ****100 w ****	****Telescope Internal Parasitics and 5m****2**** Solar Array coupling (MLI behind)**
**< 62w>****	****Radiant Loss from Baffle Outer Cylinder (*********** ************* *****~ 2%)**
**<480w>****	****Radiant Loss from Baffle Open BB End (***large axial Temp gradient***)**
**PRIMARY MIRROR HEATER LOAD AT 280K**
**< 6w>****	****Radiant Loss to Space (********** ***** ~ 2%*****)**
**<14w>****	****Radiant Face Loss to 180K Baffle (********** ***** ~ 2%*****)**
**< 4w>****	****Radiant MLI covered Edge Loss to 180K Baffle (********** ************ ~ 1%*****)**
**< 1w>****	****Radiant Loss from Central MLI Stovepipe BB hole**
**SECONDARY MIRROR HEATER LOAD AT 280K**
**<10w>****	****Radiant and Conductive Losses to Baffle and Structure (Est.)**
**TBS****	****HEATED SECONDARY STRUCTURE (black MLI covered)**
*Cool Optics means cool figuring and testing – possible but a cost & schedule driver*
*Hubble budgeted 63w for heaters – now may be higher*

## OTA CAMERA THERMAL ROM

**PASSIVE GIGA-CAM 140K DEWAR THERMAL BUDGET**
** ****32 w ****	****Radiating Capacity from 2m****2**** unobstructed 130K Radiator to Space**
**< 4w>****	****Radiator Thermal Isolation Mounts & MLI behind**
**	****	****RADIANT COUPLING LOSSES**
**< 6w>****	****CONICAL Cosmic Ray Shield - MLI outside (********** ************ *****~ 1%)**
**< 4w>****	****Open End CONE Blackbody Loss to warm Coffin Cavity**
**	****	****CONDUCTIVE COUPLING LOSSES**
**< 1w>****	****Giga-Cam Thermal Isolation Mounts**
**< 2w>****	****Dewar Thermal Isolation Mounts and Cold Plate Gaskets**
**< 1w>****	****Electrical “Flex-Print” (~ 5800 traces)**
**< 8w>****	****Average Electrical Power Dissipated in HgCdTe & CCD’s**
** ****~ 6w ****	****CURRENT MARGIN (ROM)**
**~10°C ****	****Gradient allocated for Cold Plate, Radiator, and Flex-Links**

## OTA THERMAL

**Mariner 6&7 (Mars ‘69) **
**IR Spectrometer**
**Joule-Thompson Cryostat**
**Thermal Isolation Mount**

**HESSI Sapphire & S-LINK **
**High Conductivity Thermal Strap**
**~ 700 layers Al Foil**

**SOME “KEY ITEM” THERMAL HARDWARE EXAMPLES**

**8x higher Conductivity Graphite Fiber based Thermal Strap Assembly**

## OTA THERMAL

**HESSI S-Glass Thermal Isolation Strap Assembly**
**~140mW loss for the set at 200°********T**

**SOME RECENT THERMAL HARDWARE EXAMPLES**

**HESSI COLD PLATE ASSEMBLY**
**supports 38 kg Ge Detector Assembly under Vacuum**

**HESSI DETECTOR ASSEMBLY**
**Extensive Thermal Isolation**
**used to achieve 75K with only ~3W of active cooling**

## OTA THERMAL +

**SOLUTIONS FOR COMMON CONTAMINATION CONCERNS**
** ****Moisture or Frost is a Primary Culprit**
-  FEP Teflon MLI Blanketing is a Stock Item (0.005% hygroscopic)
-  Cyanate Ester Resins Absorb ~7ppm Water vs ~70 ppm for Epoxies
-  Concentric Gold Plated Cans Tend to be Heavy & More Conductive
** “****Structured” Cool-down Approach**
** **Focal Plane Camera will be the Last Item to Cool-Down in LEO
-  Residual Moisture can be Frozen into Structure & Blankets
** ****Preferred Vent Paths & Cover Strategies are Frequently Used**

## TELESCOPE RISK ASSESSMENT

**Mirror Fabrication and Testing**
- Far less demanding than HST: we are NIR, not NUV
- Yet, we will need comprehensive test plans
**Mechanical and Structural**
- Comprehensive Test Plans:  Static, Dynamic, Thermal
**Thermal and Mechanical Disturbances**
- “Easy” Thermal  Environment in HEO, few eclipses
**Schedule: Optic Elements are the Long Lead Item!**
**Error Budgets**: Fixturing, Optical Test Equipment, etc
- Do we need a full-aperture reference test flat?
**Contamination Control**: Material Choices & Test Plan
**Stray Light Control**: Management & Test Plan

## R&D ACTIVITIES

** ****Expand Instrument Project Office Infrastructure as needed to properly ‘Architect’ the SNAP Mission**
** ****Typical Instrument Engineering Team**
- Instrument Manager, Structural, Thermal, Cryogenic, Mechanisms, Optics, Quality Assurance, Contamination, Configuration Management, Procurement
** ****Develop the “Proof of Concept” Spacecraft & Instrument Designs**
-  Detailed Camera and Dewar Mechanical, Thermal, and Electrical Designs
-  Partner with Industry(s) to develop Telescope and OTA Structure
-  Develop Compatible Primary, or the Load Bearing Spacecraft Structure
-  Conceptual Design of Test / Ground Support Equipment needs

##  SYSTEMS ENGINEERING MANAGEMENT TOOLS & BUDGETING

 TRADITIONAL
 MASS
 POWER

 MISSION UNIQUES
 INTEGRATED THERMAL MODEL
 TEMPERATURES
 HEAT FLUX

 INTEGRATED STRUCTURAL MODEL
 LINEAR MOMENTUM
 ANGULAR MOMENTUM
 RANDOM NOISE SPECTRA

STRAY LIGHT MODEL
 PARTICULATE & VOLATILE CONTAMINANTS
 BOTH STRAY & LEAKED LIGHT

** ****TRADITIONAL**
-  MASS
-  POWER
** ****MISSION UNIQUES**
** ****INTEGRATED THERMAL MODEL**
** **TEMPERATURES
-  HEAT FLUX
** ****INTEGRATED STRUCTURAL MODEL**
** **LINEAR MOMENTUM
-  ANGULAR MOMENTUM
-  RANDOM NOISE SPECTRA
**STRAY LIGHT MODEL**
** **PARTICULATE & VOLATILE CONTAMINANTS
-  BOTH STRAY & LEAKED LIGHT
** **

**R&D ACTIVITIES**

## R&D ACTIVITY HIGHLGHTS

** ****Design Activity Flow Downs, or Design Related Activities**
** **Preliminary Coupled Loads Analysis (includes Launcher)
-  Preliminary  Observatory Level Integrated Thermal Model
-  Generate Viable Optics Test plan, plus the general I&T plans
-  Develop draft Instrument & Spacecraft Interface Documents
-  Science and Mission Requirements Review(s)
** ****Optical Element Studies Commissioned with Promising Vendors**
**Generate the Long Lead Item Optics Procurement Plan**
** ****Generate EM Spacecraft & Telescope Structure Plan and Schedule**
***Staffing, Costs, and Schedule was presented by M. Lampton***

## SUMMARY & COMMENTS

** ****Optics Fabrication Plan Retains Options for Program Flexibility**
-  SNAP has several Options for Lightweight, Low CTE Mirrors
** **
** ****Stray Light Baffle may be a Conventional Construction**
** ****Composite Telescope Structures are well Understood and this    ****	****Technology Continues to Advance**
** ****Build, Test, & Fly Warm is both Proven and Cost Effective**
** ****Passive Thermal Approach is Viable for Camera **