1. Another Modular Focal Plane: Part 2 – FP assembly
Bruce C. Bigelow
University of Michigan
Department of Physics
5/17/04

2. Modular 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

3. Focal 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

4. FP 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

5. Focal plane base-plate - front
Note webs in access holes – not in FEA models

6. Focal plane base-plate - back
Base-plate rib structure – simpler than FEA model

7. Focal plane fully populated

8. FP Baseplate design and 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

9. FP Baseplate FEA rib thickness: red - 6 mm purple - 5 mm cyan - 6 mm
blue - 10 mm

10. FP Baseplate FEA sub-modules as point masses 1.0 kg 0.5 kg
16 Kg total sub- module mass

11. FP Baseplate FEA – Al 7075 (meters)
Gy, Y deflections – 1.8 microns max

12. FP Baseplate FEA – Al 7075
(meters)
Gy, Z deflections – 2.1 microns PV

13. FP Baseplate FEA – Al 7075
(meters)
Gz, Z deflections – 4.8 microns

14. FP Baseplate FEA – Al 7075 Mode/Freq. 227 Hz 238 Hz 261 Hz 325 Hz
Dynamic analysis – first mode

15. FP Baseplate FEA – MZT
(meters)
Gy, Y deflections – 0.8 microns PV

16. FP Baseplate FEA – MZT
(meters)
Gy, Z deflections – 1.1 microns PV

17. FP Baseplate FEA – MZT
(meters)
Gz, Z deflections – 4.2 microns PV

18. FP Baseplate FEA – MZT Mode/Freq. 249 Hz 258 Hz 290 Hz 491 Hz 654 Hz
Dynamic analysis – first mode

19. Baseplate FEA Summary Mat. Mass Thick Gy-Uy Gy-Uz Gz-Uz Fn Al 7075
227 Hz
MZT
31 Kg
50 mm
0.8um
1.1um
4.2um
249 Hz

20. 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)