Another Modular Focal Plane: Part 1 Submodules

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Another Modular Focal PlanePart 1 Sub-modules

• Bruce C. Bigelow
• University of Michigan
• Department of Physics
• 5/17/04

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Focal Plane Sub-modules

• Motivations
• install/remove single detectors from front of
  FP
• assemble detectors in modules of 3 x 3
• simplify assembly, integration, and test
• reduce part counts, simplify part design
• simplify part fabrication
• individual module thermal control (Vis vs. IR)
• optimize materials for detector packages (CTE)
• local, discrete control of focal plane surface
  height
• minimize mechanical mass
• minimize thermal time constants
• minimize gravity deflections for ground testing
• maximize resonant frequencies

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Focal Plane Sub-modules

• Requirements
• final focal plane flatness /- 25 microns
• support different optimal temperatures for Vis
  and IR
• detector temperature stability /- 1K
• high stiffness high first resonance

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Focal Plane Sub-modules

• This talk
• sub-module designs
• sub-module FEA

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IR sub-module
Rockwell H2RG package
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IR sub-module
Rockwell H2RG package with filter and frame
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IR sub-module
Rockwell H2RG package on moly MZT sub-plate
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IR sub-module
Rockwell H2RG 3 x 3 sub array
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IR sub-module
3 x 3 sub array with flexure mounts
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IR sub-module
Sub-array with CRICs, flex circuits, connectors,
local IR electronics (cold), sub-plate heater
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IR sub-module
Finished IR module with aperture mask
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CCD sub-module
Finished CCD module with aperture mask
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Sub-module FEA

• FE Analyses
• Static analysis gravity deflections
• package mass modeled by doubling sub-plate
  density
• moly packages and sub-plate, invar flexures
• omit package cutouts, mounting holes, etc.
• focal plane axis vertical and horizontal

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Sub-module static FEA
(meters)
Sub-module, Gy, Y deflection 1.1 microns
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Sub-module static FEA
(meters)
Sub-module, Gy, Z deflection /- 0.3 microns
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Sub-module static FEA
(meters)
Sub-module, Gz, max. Z deflection 0.8 microns
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Sub-module FEA

• FE Analyses
• Dynamic analysis - vibration modes and
  frequencies
• package mass modeled by doubling sub-plate
  density
• omit package cutouts, mounting holes, etc.
• First resonance 528 Hz for Invar/Invar case
• First resonance 630 Hz for Moly/Invar case

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Sub-module dynamic FEA

• Mode/Freq.
• 630
• 630
• 654
• 1289
• 1376

Moly sub-plate and Invar flexures first mode
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Sub-module dynamic FEA

• Mode/Freq.
• 630
• 630
• 654
• 1289
• 1376

Moly MZT sub-plate and flexures third mode
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Sub-module thermal FEA

• Thermal analysis stress and distortion
• omit package cutouts, mounting holes, etc.
• omit package mass, stiffness
• -160 K temperature shift
• static, isothermal analysis
• no effort yet to optimize flexure design
• no effort yet to optimize stiffness of sub-plate

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Sub-module thermal FEA
Elements Purple Invar Red Moly
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Sub-module thermal FEA
(Pascals)
Purple invar Red moly
Max stress at Invar/Moly joint (not realistic),
86.8 MPa (12,557 Psi), (Invar yield 250 MPa)
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Sub-module thermal FEA
(meters)
Purple invar Red moly
Shrinkage of Invar vs. Moly in X direction, /-
50 microns
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Sub-module thermal FEA
(meters)
Purple invar Red moly
Sub-plate displacement in Z direction 15 microns
Shrinkage of Invar vs. Moly in X direction
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Sub-module thermal FEA
(meters)
Purple invar Red moly
Sub-plate displacement in Z direction 15 microns
Distortion of mounting surface 2 micron
Shrinkage of Invar vs. Moly in X direction
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FP sub-modules

• Conclusions
• sub-module designs for Vis and IR developed
• detector packages
• filters with mounts
• sub-plates
• sub-plate mounting flexures
• electrical connectors, junction boxes
• FEA demonstrates stiffness, high resonant freq.
• FEA demonstrates acceptable thermal performance