Another Modular Focal Plane:Another Modular Focal Plane:Part 2 – FP assemblyPart 2 – FP assembly

Bruce C. Bigelow

University of Michigan

Department of Physics

5/17/04

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Modular focal plane assemblyModular focal plane assembly

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 BaseplateFocal Plane Baseplate

Requirements: final focal plane flatness: +/- 25 microns detector temperature stability +/- 1K high stiffness – high first resonance

This talk: sample base-plate designs two materials examined base-plate FEA

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FP Baseplate design and FEAFP Baseplate design and FEA

Design of baseplate consider Al 7075 and Moly MZT materials three mounting points to optics bench via bipods bipods not included in design or FEA cut-outs for detector access

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Focal plane base-plate - frontFocal plane base-plate - front

Note webs in access holes – not in FEA models

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Focal plane base-plate - backFocal plane base-plate - back

Base-plate rib structure – simpler than FEA model

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Focal plane fully populatedFocal plane fully populated

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FP Baseplate design and FEAFP Baseplate design and FEA

FEA consider Al 7075 and Moly MZT materials Moly plate is 50 mm thick: 31 Kg Al. plate is 75 mm thick: 13 Kg sub-array loads modeled with point masses static and dynamic analyses completed

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FP Baseplate FEAFP Baseplate FEA

rib thickness:

red - 6 mm

purple - 5 mm

cyan - 6 mm

blue - 10 mm

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FP Baseplate FEAFP Baseplate FEA

1.0 kg

0.5 kg

16 Kg total sub- module mass

sub-modules as point masses

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FP Baseplate FEA – Al 7075FP Baseplate FEA – Al 7075

Gy, Y deflections – 1.8 microns max

(meters)

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FP Baseplate FEA – Al 7075FP Baseplate FEA – Al 7075

(meters)

Gy, Z deflections – 2.1 microns PV

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FP Baseplate FEA – Al 7075FP Baseplate FEA – Al 7075

(meters)

Gz, Z deflections – 4.8 microns

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FP Baseplate FEA – Al 7075FP Baseplate FEA – Al 7075

Mode/Freq.

1. 227 Hz

2. 238 Hz

3. 261 Hz

4. 325 Hz

5. 522 Hz

Dynamic analysis – first mode

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FP Baseplate FEA – MZTFP Baseplate FEA – MZT

(meters)

Gy, Y deflections – 0.8 microns PV

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FP Baseplate FEA – MZTFP Baseplate FEA – MZT

(meters)

Gy, Z deflections – 1.1 microns PV

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FP Baseplate FEA – MZTFP Baseplate FEA – MZT

(meters)

Gz, Z deflections – 4.2 microns PV

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FP Baseplate FEA – MZTFP Baseplate FEA – MZT

Mode/Freq.

1. 249 Hz

2. 258 Hz

3. 290 Hz

4. 491 Hz

5. 654 Hz

Dynamic analysis – first mode

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Baseplate FEA SummaryBaseplate FEA Summary

Mat. Mass Thick Gy-Uy Gy-Uz Gz-Uz Fn

Al 7075 13 Kg 75 mm 1.8um 2.1um 4.8um 227 Hz

MZT 31 Kg 50 mm 0.8um 1.1um 4.2um 249 Hz

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FP Modular Baseplate FP Modular Baseplate

Conclusions:

• sample designs stiff, high resonances

• flatness specs met in two orientations (and probably all)

• consider other substrate materials (Ti, CF)?

• refine interfaces

• spectrograph, BITE sources, cryostat mounts

• thermal links, detect. wiring, baffles, shields

• optimize design for loads and material (ribs, thicknesses, etc)