SC-3 Telescope Structural

1. 1 David Pankow Space Sciences Laboratory, Mechanical Engr. Department University of California Berkeley July 2002 SC-3 Telescope Structural/ThermalWBS 2.2

2. 2 SNAP Telescope Structural / Thermal

3. 3 SNAP DESIGN PHILOSOPHY

4. 4 Telescope Configuration from IMDC

5. 5 Current Telescope Evolution

6. 6 MECHANICAL REQUIREMENTS

7. 7 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

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9. 9 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 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?

10. 10 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

11. 11 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

12. 12 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

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17. 17 TELESCOPE STRUCTURE

18. 18 TELESCOPE STRUCTURE

19. 19 Optical Telescope Assembly (OTA)

20. 20 Mathematically, 13 Mechanical Adjustments are Possible Focusing, Centering, and Collimation 6 DOF Hexapod is Attractive for Alignment of Secondary (qz 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

21. 21 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

22. 22 TELESCOPE MECHANISMS

23. 23 TELESCOPE THERMAL

24. 24 TELESCOPE THERMAL OPTICS: Build,Test, & Fly Warm� like Hubble !

25. 25 OTA WARM OPTICS THERMAL BUDGET LARGE STRAY LIGHT BAFFLE (~180K) 478 w Absorbed Sunlight if MLI covered (a* ~ 2%) 100 w Telescope Internal Parasitics and 5m2 Solar Array coupling (MLI behind) < 62w> Radiant Loss from Baffle Outer Cylinder (e * ~ 2%) <480w> Radiant Loss from Baffle Open BB End (large axial Temp gradient) PRIMARY MIRROR HEATER LOAD AT 280K < 6w> Radiant Loss to Space (e ~ 2%) <14w> Radiant Face Loss to 180K Baffle (e ~ 2%) < 4w> Radiant MLI covered Edge Loss to 180K Baffle (e * ~ 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

26. 26 OTA CAMERA THERMAL ROM PASSIVE GIGA-CAM 140K DEWAR THERMAL BUDGET 32 w Radiating Capacity from 2m2 unobstructed 130K Radiator to Space < 4w> Radiator Thermal Isolation Mounts & MLI behind RADIANT COUPLING LOSSES < 6w> CONICAL Cosmic Ray Shield - MLI outside (e * ~ 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

27. 27 OTA THERMAL Mariner 6&7 (Mars �69) IR Spectrometer Joule-Thompson Cryostat Thermal Isolation Mount

28. 28 OTA THERMAL

29. 29 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

30. 30 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

31. 31 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

32. 32 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 R&D ACTIVITIES

33. 33 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

34. 34 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