1. Matthew Smith Mechanical Engineer (617)-252-1736 matt@space.mit.edu
Mechanical Design, CRaTER Assembly and Electronics Assembly Preliminary Design Review
Matthew Smith
Mechanical Engineer
(617)

2. Overview Instrument and Assembly Description
Mechanical Environments and Requirements
Mechanical Design Details
Near Term Tasks
Back-up slides

3. Instrument and Assembly Description
Crater integrates two main sub-assemblies:
The Telescope Assembly and
The Electronics Assembly.
The Telescope Assembly is being designed and built by The Aerospace Corporation
The Analog Board is being designed by Aerospace. The Flight Analog Boards will be built by MIT
The Digital Board and Electronics Enclosure Assembly are being designed and built by MIT.
MIT will integrate the sub-assemblies and perform all functional, environmental and acceptance testing.

4. Instrument and Assembly Description

5. Mechanical Environments
From 431-RQMT , Environments Section 2.
Section
Description
Levels
2.1.2
Net cg limit load
12 g
2.4.2
Sinusoidal Vibration Loads
Frequency: Hz
Protoflight/Qual: g
Acceptance: g
2.5
Acoustics
Enclosed box without exposed thin surfaces
OASPL Protoflight/Qual: dB
OASPL Acceptance: dB
2.6.1
Random Vibration
See Random Vibration slide
2.7
Shock environment
40 g at 100 Hz
2665g at 1165 to 3000 Hz.
No self induced shock.
2.8
Venting
Per 431-SPEC LRO Thermal Subsystem spec.

6. Mechanical Requirements and Verification
From 431-RQMT , Verification Requirements Section 3.
Section
Description
Levels
Stowed fundamental Hz
Deployed fundamental Frequency
Freq >35
>3 Hz
3.2.1
Factors of Safety
See FOS table
3.2.2
Test factors
See Test Factors table
MEVR-10 Perform frequency verification test for Instruments with frequencies above 50 Hz..
MEVR-11 Report frequencies up to 200Hz
Low level sine sweep
We will be above 50Hz.
3.3
Finite Element Model requirements
We will be above 75Hz and will not be required to submit an FEM of CRaTER.

7. General Thermal Subsystem Requirements
from 431-Spec
Section
Description
4.1
Exterior facing MLI blankets shall have 3 mil Kapton with VDA in outer Coating.
4.2
MLI Blanket Grounding:
All blankets shall be grounded per 431-ICD-00018
4.3
MLI Blanket Documentation: The location and shape documented in as-built ICDs.
4.4
Attachment to MLI Blankets:
All exterior MLI blankets shall be mechanically constrained at least at one point.

8. DESIGN DETAILS Electronics Assembly
Natural Frequency Estimates
Based from Steinberg Vibration Analysis for Electronic Equipment-
(Simply supported on 4 sides.)
Top Cover~ 199 Hz
Bottom Cover ~ 159 Hz
Analog Board~ 138 Hz
Digital Board~ 149 Hz
From SOLID WORKS model of E-Box
frequency is 702Hz at the middle plate that holds the two Circuit Card Assemblies.

9. DESIGN DETAILS Mechanical Environments, Random Vibration
Random Vibration will drive most of the analysis
For resonances in the Random Vibration Spec, Miles’ Equation shows 3 sigma loading on the order of g
Assume Q=10
Overall 14.1 Grms grms

10. DESIGN DETAILS Stress Margins, Electronics Assembly Pieces
Load levels are superceded by random vibration spec
Factors of Safety used for corresponding material from 431-SPEC
Metals: Yield, 1.4 Ultimate
Composite: 1.5 Ultimate
Margin of Safety = (Allowable Stress or Load)/(Applied Stress or Load x FS) – 1
Description
Material Desc.
MS Yield
MS Ultimate
Comments
Top Cover
Aluminum 6061
+14.2
+19.5
Note 1
Bottom Cover
+13.4
+18.4
Digital Board
FR4
brittle
+1.5
Analog Board
Brittle
+0.2
E-box Structure
Aluminum 7075
> +2.8
>+3.1
Note 2
Note 1. From Steinberg, Vibration Analysis for Electronic Equipment
Note 2. From SOLID WORKS, COSMOS excluding top and bottom covers in the model.
All components have positive Margin of Safety

11. Mechanical Design Details
The first fundamental frequency is estimated to be 149 Hz.
Not required to produce an FEM since our predicted first frequency is >75 Hz.
All positive margins of safety.
Meet all factors of safety.
No Fracture Critical Items.

12. Internal Requirements for the Electronics Assembly
Derived Internal Mechanical Requirements for Electronics Enclosure
Have adequate contact area (.5 in^2 min) to the spacecraft to support Thermal requirements.
Provide safe structure, within Factors of Safety specified, to support Telescope Assembly.
Provide for mounting 2 Circuit Card Assemblies.
The Analog Board and Digital Board must be separated by an aluminum plate.
The Analog Board to provide direct linear path for electronics from the telescope interface to the Digital Board interface to reduce noise.
Provide means to route cable from telescope to the Analog side of the Electronics Enclosure.
Electrically isolate the electronics Enclosure from the Telescope, yet provide sufficient thermal conductance path.
Provide adequate surface area for mounting electrical components.
Interface to the Spacecraft to be on one side of the Electronics Enclosure.
The interface connectors to be on the Digital side of the Electronics Enclosure (separate from the Analog side)
Provide GN2 purge interface inlet and outlet ports.
Follow the octave rule for natural frequency of the PWAs to the Electronics Enclosure.
The Electronics Assembly meets all internal requirements except for …
Details need to be worked out for the GN2 design.
Electrical isolation of the E-box and Telescope needs more thought.

13. DESIGN DETAILS Electrical/Mechanical Interface
Interface Connectors
J1 9 Pin D-Sub Male P-B-12
J2 9 Pin D-sub Female S-B-12
J , BJ3150
J , BJ3150
Mounting Hardware - Six #10-32 SHCS
Surface roughness of 63 micro inches or better for interface surfaces.
Mounting surfaces have Electrically Conductive finish (MIL-C-5541 Cl 3)
PART OF MID DRAWING NUMBER

14. NEAR TERM TASKS Update MICD to reflect latest configuration.
Further develop analysis on natural frequencies and stresses using SOLID WORKS and COSMOS on the complete CRaTER Assembly.
Finalize interface between Telescope Assembly and Electronics Box Assembly.
Specify the electrical isolation material between the telescope and the E-Box.
Identify the GN2 purge system (mechanical interface to the spacecraft, internal flow, pressure measurements…)
Complete the drawings for part and assembly fabrication.
Define attachment points and outline for thermal blankets.

15. Backup Slides

16. Factors of Safety

17. BOARD ANALYSIS Analog Board Analysis 1 2 3 4 5 6
an x 5.95 board separated into two parts
Polyimide modulus of elasticity
E (lb/in sq
4.21E+05
Thickness
h (inches)
0.06
0.09
0.1
0.11
0.12
0.15
poisson ratio u
length
a (in)
4.215
width
b (in)
5.95
weight
W (lb)
0.6
0.65
0.69
0.71
0.73
0.79 g
in/secSq
386 pi
3.14
D=E*h^3/(12(1-u^2)) D=
7.69
25.95
35.60
47.38
61.51
120.14
density p
mass/area=W/gab
E-05
6.7145E-05
7.13E-05
7.33E-05
7.54E-05
8.16E-05
for a a simply supported board on 4 sides
f=pi/2((D/p)^.5)(1/a^2+1/b^2))^.5
Frequency=(Hz) 47 83 94
107
120
161
From Steinberg, vibration analysis for electronic equipment page 149
for a fixed beam on 4 sides 91
160
182
207
232
312
Average Frequency 69
121
138
157
176
237

18. number of cycles before failure
BOARD ANALYSIS
Analog Board Analysis Cont’d
STRESS
Gin=peak load(g's)=
125
Q=transmisibility= 10
Gout=Gin*Q=
1250
W=board weight(lb)=
0.6
0.65
0.69
0.71
0.73
0.79
q=load intensity=W*Gout/ab
13.393
14.509
15.402
15.848
16.295
17.634
My=bending moment at center=
6.641
7.195
7.637
7.859
8.080
8.744
DYNAMIC BENDING STRESS
Kt= stress concentration factor 3
h=height
0.06
0.09
0.1
0.11
0.12
0.15
Sb=6*Kt*My/h^2= lb/in^2
Stress due to bending
33206
15988
13747
11691
10100
6995
FACTORS OF SAFETY
FOS Yield
FOS Ultimate
24000 psi
0.7
1.5
1.7
2.1
2.4
3.4
NUMBER OF CYLES BEFORE FAILURE
check S-N curve for board type Ch 12 to determine if board will fail
number of cycles before failure
10^4
>10^8
MARGIN OF SAFETY
MOS=(Allowable stress/applied stress*FS)-1
-0.5
0.0
0.2
0.4
1.3
For a composit Fs=1.5 Ultimate

19. BOARD ANALYSIS Digital Board Analysis Average Frequency 149 1 2 3 4 56
a x board two sections
modulus of eleasticity Polyimide fiberglass
E, psi
4.21E+05
Thickness
h(inches)
0.06
0.09
0.1
0.11
0.12
0.15
poisson ratio u
length
a (in)
4.281
width
b (in)
7.488
weight
W (lb)
0.55
0.57
0.58
0.59
0.6
0.61 g
in/secSq
386 pi
D=E*h^3/(12(1-u^2)) D=
7.69
25.95
35.60
47.38
61.51
120.14
density p
mass/area=W/gab
E-05
4.6066E-05
4.69E-05
4.77E-05
4.85E-05
4.93E-05
for a a simply supported board on 4 sides
f=pi/2((D/p)^.5)(1/a^2+1/b^2))^.5
Frequency, HZ =
47.32
85.39
99.14
113.41
128.14
177.60
This is from an example by Steinberg, vibration analysis for electronic equipment page 149
for a fixed board on 4 sides
94.79
171.06
198.61
227.19
256.69
355.79
Average Frequency 71
128
149
170
192
267

20. BOARD ANALYSIS Digital Board Analysis Cont’d STRESS
Gin=peak load(g's)=
125
Q=transmisibility= 10
Gout=Gin*Q=
1250
W=board weight(lb)=
0.55
0.57
0.58
0.59
0.6
0.61
q=load intensity=W*Gout/ab
12.277
12.723
12.946
13.170
13.393
13.616
My=bending moment at center=
5.782
5.992
6.097
6.202
6.307
6.412
DYNAMIC BENDING STRESS
Kt= stress concentration factor 3
h=height
0.06
0.09
0.1
0.11
0.12
0.15
Sb=6*Kt*My/h^2= lb/in^2
28908
13315
10974
9226
7884
5130
FOS Yield
FOS Ultimate
24kpsi
0.8
1.8
2.2
2.6
3.0
4.7
check S-N curve for board type Ch 12 to determine if board will fail
>10^8
MARGIN OF SAFETY
MOS=(Allowable stress/applied stress*FS)-1
MOS
1.2
1.5
1.7
2.0
3.1
For a composite FS=1.5 (Ultimate)

21. E-BOX COVERS, ANALYSIS Top Cover Bottom Cover Elastic Modulus
E(lb/in sq
1.00E+07
Thickness
h(inches)
0.063
Poisson ratio u
0.33
length
a (in)
9.343
9.119
width
b (in)
6.623
8.443
weight
W (lb)
0.41
0.46 g
in/secSq
386 pi G
125 q
D=E*h^3/(12(1-u^2) D=
density p
mass/area=W/gab
E-05
E-05
f=pi/2((D/p)^.5)(1/a^2+1/b^2))^.5
frequency =
199
159
Bending moment at center
My= q(u/a^2=1/b^2)/(pi^2(1/a^2+1/b^2)^2
1.9009
2.0061
dynamic bending stress
Sb=6*My/h^2
Stress=
2874
3033
Check S-N curve at Stress N=
5.E+08
FOS
Yield/Stress
Tensile yield, psi
35000
12.18
11.54
Ultimate/Stress
Tensile Ultimate, psi
42000
14.6
13.8
Margin of Safety
(allowable stress/applied stress *FOS)-1
14.2
13.4
19.5
18.4

22. CURRENT BEST ESTIMATE, MASS PROPERTIES
Electronics Assembly
grams
lbs
Analog CCA
480
1.05
Digital CCA
540
1.19
Interconnect Cable, A/D 52
0.11
Internal E-box Cables
122
0.27
Mechanical Enclosure
1800
3.96
Top Cover
250
0.55
Bottom Cover
225
0.49
Hardware
166
0.36
Purge system
178
0.39
Electronics Assembly Sub-Total
3813
8.38
Detector Assembly
Circuit Board
138
0.30
Telescope Sub-Assy
1398
.87
Detector Mechanical Enclosure
525
1.15
Detector Assembly Sub- Total
1061
2.32
MLI and TPS Sub-Total
.55
Mounting Hardware Sub-Total 40
.09
CRaTER CBE Total
5164
11.34

23. Drawing List Drawing Number Drawing Title Rev. Layout Complete
Drawing Created
Checked
Released
CRaTER Assembly 0%
Electronics Assembly -
25%
Digital Electronics, PWA 02
50%
Analog Electronics PWA
Electronics Enclosure 01
95%
Cover, Top Electronics Enclosure
Cover, Bottom Electronics Enclosure

24. Material Properties MIL-HDBK-5J Efunda materials list via efunda.com 21 2
MIL-HDBK-5J
Efunda materials list via efunda.com