FOCAL PLANE and CRYO-SHIELD BIPOD MOUNTS June 2005 After the Collaboration Meeting Update Bobby Besuner, Herman Ceas

1. FOCAL PLANEand CRYO-SHIELD BIPOD MOUNTSJune 2005 After the Collaboration Meeting UpdateBobby Besuner, Herman Cease (Fermilab), Mike Sholl (SSL)

2. Design Requirements Stress Requirements • Factor of 25 on gravity stresses during launch. Based on NASA launch requirements • Factor of 3-4 on thermal loading, independent of gravity. Exact requirement not so clear. Distortion Requirements. Based on Optics and pre-launch testing, exact requirement is not clear. • Lateral motion of the focal plane in 1G -a few microns • Axial motion of the focal plane on cool down +/- 100 microns can be refocused by 2nd mirror. • Minimal warping of focal plane due to supports when cold. • Cryo-shield shrinking is an issue for light tightness, and vignetting.

3. TMA-65 Model Geometry Shield Aluminum 25 Kg mass with support flange 2 mm wall at the top, 6mm wall elsewhere supported from flange on the shield Optics Bench (not modeled) Polyimide Carbon Fiber 2 mm thick skins, Ribbed Interior between walls Bipods (Strut, Foot) Titanium Strut is a hollow tube Foot is a solid block Focal Plane Molybdenum 65 Kg mass (100 Kg allocated including spectrograph) Thickness: 50 mm, Radius: 304 mm Edge flange: 25 mm thick, 50 mm in the radial direction Mounts attached to Focal plane on flange at the mid-plane

4. Focal Plane Bipod Geometry Warm Optics Bench Warm Optics Bench Cold Focal Plane Cold Focal Plane Case 1 Hollow Tube Focal Plane Bipods Strut OD 32 mm, 0.5 mm wall,100 mm long Boss OD 47 mm, 90 degree opening angle, all Titanium Case 2 Flexure Focal Plane Bipods Strut OD 22 mm, 0.5 mm wall, 50 mm long Boss OD 47 mm, 90 degree opening angle, all Titanium Flexures, Radial and Tangential 2 mm thickness, 9 mm long Not nested

5. Focal Plane Hollow Tube BIPODSThermal Gradients Conduction only, no radiation Thermal path is from Focal Plane thru Bipod to the Optics Bench Red = 18 ºC, Blue = -130 ºC Titanium has CTE and K temperature dependency from SNAP Materials Page

6. Focal Plane Hollow Tube BIPODSThermal Deflections Bipods fixed in X,Y,Z at the optics bench Magnitude Distortion = 0.332 mm, Axial displacement = 0.118 mm at Focal Plane Face. 0.003 mm out of plane warping due to stiff bipods.

7. Focal Plane Hollow Tube BIPODSThermal Stresses Max Stress 162 MPa in Bipod Tube Walls due to radial shrinking of Focal Plane Safety Factor ≈ 5

8. Focal Plane Hollow Tube BIPODSGravity Loading Distortion (magnitude) Max sag: ≈ 14 microns Tilt: 2 microns Max strut tube Stress: 15 MPa (SF ≈ 55x)

9. Focal Plane Bipod Geometry Warm Optics Bench Warm Optics Bench Cold Focal Plane Cold Focal Plane Case 1 Hollow Tube Focal Plane Bipods Strut OD 32 mm, 0.5 mm wall,100 mm long Boss OD 47 mm, 90 degree opening angle, all Titanium Case 2 Flexure Focal Plane Bipods Strut OD 22 mm, 0.5 mm wall, 50 mm long Boss OD 47 mm, 90 degree opening angle, all Titanium Flexures, Radial and Tangential 2 mm thickness, 9 mm long Not nested

10. Focal Plane Flexure BIPODSThermal Gradients Conduction only, no radiation Thermal path is from Focal Plane thru Bipod to the Optics Bench Red = 18 ºC, Blue = -130 ºC Titanium CTE and K, temperature dependency taken from SNAP Materials Page.

11. Focal Plane Flexure BIPODS Thermal Deflections Bipods fixed in X,Y,Z at the optics bench Magnitude Distortion = 0.332 mm, Axial displacement = 0.166 mm at Focal Plane Face.

12. Focal Plane Flexure BIPODS Thermal Stresses Max Stress 73 MPa due to CTE mis-match Max stress in flexure 37 MPa Safety Factor ≈ 22

13. Focal Plane Flexure BIPODS Gravity Loading Distortion (magnitude) Max sag: ≈ 31 microns Out of plane: 1 microns Max strut tube Stress: 26 MPa (SF ≈ 31x)

14. Shield Bipod Geometry Cold Shield Mounting Flange Warm Optics Bench Cryo-Shield Bipods Strut OD 15 mm, 0.64 mm wall, 123 mm long Boss OD 32 mm at base of hollow tube strut, 90 degree opening angle, all Titanium

15. Cryo-Shield BIPODS Thermal Gradient Conduction only, no radiation Thermal path is from Aluminum Shield thru Bipod to the Optics Bench Red = 18 ºC, Blue = -130 ºC Titanium and Aluminum have CTE and K temperature dependency per SNAP materials page

16. Cryo-Shield BIPODS Thermal Deflections Distortion (Magnitude) Max distortion, ≈ 1.54 mm (red) with respect to the optics bench Distortion (Axial only) Red = 0.48 mm Blue = -1.54 mm 2.0 mm total axial dL

17. Cryo-Shield BIPODS Thermal Stresses Max Stress 245 Mpa in the hollow wall support tube Attachment points will be optimized to reduce stresses (SF ≈ 3.3)

18. Cryo-Shield BIPODS Gravity Loading Max Stress in Bipod Tube 2.5 MPa (SF ≈ 330x) Distortion (Magnitude) Max distortion, ≈ 0.026 mm

19. Summary • Focal plane bipods • Case 1 hollow tubes • Thermal motions ~ 118 microns axial, 3 microns warp • Stress SF ~ 3 (3-4 required) • Gravity motions ~ 14 microns lateral, 2 microns tilt • Stress SF ~ 55 (25required) • Case 2 Flexures • Thermal motions ~ 166 microns axial, • Stress SF ~ 22 (3-4 required) • Gravity motions ~ 31 microns lateral, 1 microns tilt • Stress SF 31 (25 required) • Cryo Shield bipods • Case 1 Hollow Tubes • Thermal motions ~ 2mm axial delta L in shield • Stress ~ SF 3 (3-4 required) • Gravity motions 26 microns lateral • Stress SF ~330 (25 required)

20. What’s Next • Wait for TMA-68 • Heat Loads • Beat down heat loads from 3 Watts down to 1 Watt • Possibly done by hollowing out the Bipod foot • Optics Bench Geometry issues • Work out details for stiff optics bench, • Work out insertion of Cryo-Shield mounts into Optics bench • TMA 68 Pushes focal plane closer to thermal radiator • May invert the direction of the cryo-shield bipods to ease assembly. I don’t feel this is necessary. • Include Spectrograph

21. What’s Next –TMA68 ?