# Presentation: 693628

## FOCAL PLANEand CRYO-SHIELD BIPOD MOUNTSJune 2005 After the Collaboration Meeting UpdateBobby Besuner, Herman Cease (Fermilab), Mike Sholl (SSL)

## 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.

## 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

## Focal Plane Bipod Geometry

- 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

- Warm Optics Bench

- 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

- Warm Optics Bench

- Cold Focal Plane

## Focal Plane Hollow Tube BIPODSThermal 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

## Focal Plane Hollow Tube BIPODSThermal Deflections

- 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.

- Bipods fixed in X,Y,Z at the optics bench

## Focal Plane Hollow Tube BIPODSThermal Stresses

- Max Stress 162 MPa in Bipod Tube Walls
- due to radial shrinking of Focal Plane
- Safety Factor ≈ 5

## Focal Plane Hollow Tube BIPODSGravity Loading

- Max strut tube Stress:
- 	 15 MPa (SF ≈ 55x)

- Distortion (magnitude)
- Max sag: ≈ 14 microns
- Tilt: 2 microns

## Focal Plane Bipod Geometry

- 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

- Warm Optics Bench

- 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

- Warm Optics Bench

- Cold Focal Plane

## Focal Plane Flexure BIPODSThermal 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.

## Focal Plane Flexure BIPODS Thermal Deflections

- Magnitude Distortion = 0.332 mm,
-  					Axial displacement = 0.166 mm
- 					      at Focal Plane Face.

- Bipods fixed in X,Y,Z at the optics bench

## Focal Plane Flexure BIPODS Thermal Stresses

- Max Stress 73 MPa
- due to CTE mis-match
- Max stress in flexure 37 MPa
- Safety Factor ≈ 22

## Focal Plane Flexure BIPODS Gravity Loading

- Focal Plane Flexure BIPODS Gravity Loading

- Max strut tube Stress:
- 	 26 MPa (SF ≈ 31x)

- Distortion (magnitude)
- Max sag: ≈ 31 microns
- Out of plane: 1 microns

## Shield Bipod Geometry

- 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

- Cold Shield Mounting Flange

- Warm Optics Bench

## 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

## Cryo-Shield BIPODS Thermal Deflections

- Distortion (Axial only)
- Red = 0.48 mm
- Blue = -1.54 mm
- 2.0 mm total axial L

- Distortion (Magnitude)
- Max distortion, ≈ 1.54 mm (red)
-   with respect to the optics bench

## 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)

## Cryo-Shield BIPODS Gravity Loading

- Cryo-Shield BIPODS Gravity Loading

- Max Stress in Bipod Tube
- 2.5 MPa (SF ≈ 330x)

- Distortion (Magnitude)
- Max distortion, ≈ 0.026 mm

## 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)

## 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

## What’s Next –TMA68 ?