Mechanical Design - Massachusetts Institute of Technology

Report
CRaTER CDR
Mechanical Design
Mechanical Design,
CRaTER Assembly and Electronics Assembly
Critical Design Review
Matthew Smith
(617)-252-1736
[email protected]
June 27, 2006
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CRaTER CDR
Mechanical Design
Overview
Assembly Description
Mechanical Design Details
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
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CRaTER CDR
Mechanical Design
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 two sub-assemblies
and perform all functional, environmental
and acceptance testing.
L13.5”x W9” x H 6”
Weight 6.4Kgs max.
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CRaTER CDR
Mechanical Design
Assembly Description
32-10204
32-10201
32-10206
32-10203
32-10202
32-10205
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CRaTER CDR
Mechanical Design
Overview
Assembly Description
Mechanical Design Details
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
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CRaTER CDR
Mechanical Design
Natural Frequencies
• We put the CRaTER mock up unit on a shake table Friday June 23, 2006. We
had accelerometers on the analog and digital boards(2 single axis accels), the
two covers, the telescope(2 triax accels) and on the e-box(one triax and one
single axis).
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CRaTER CDR
Mechanical Design
Natural Frequencies
•
Natural Frequency Estimates
– From SOLID WORKS cosmos package, 2005
• CRaTER as an assembly
–
–
–
–
–
–
First frequency at 435Hz (top cover)
Dominant Frequency at 1158 Hz and 1516 Hz (main assembly)
Analog Board- 648 Hz
Digital Board- 497 Hz
Top Cover- 435 Hz
Bottom Cover – TBD (hidden in model for now)
– From SOLID WORKS cosmos package, 2005, stand alone parts.
•
•
•
•
•
Analog Board- 195 Hz
Digital Board- 198 Hz
Top Cover- 288 Hz
Bottom Cover - 337 Hz
E-Box - 992 Hz
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Natural Frequencies
•
CRaTER CDR
Mechanical Design
Natural Frequency from Low level sine sweep, June 23, 2006
• CRaTER as an assembly Z Axis (Normal to mounting surface)
–
–
–
–
–
–
First frequency at ~ 280Hz (Bottom cover)
Dominant Frequency at ~1200 and 1500 Hz (main assembly)
Analog Board ~700 Hz
Digital Board ~410 Hz
Top Cover ~410 Hz
Bottom Cover ~280 Hz
• CRaTER as an assembly X Axis
– First frequency at ~ 980 Hz Second at ~1500 Hz
• Crater as an assembly, Y Axis
–
•
First frequency at ~ 1200 Hz
These match very closely to the Solidworks Model as an assembly.
–
–
–
–
–
–
First frequency at 435Hz (top cover)
First Frequency of the system at 1158 Hz (main assembly)
Analog Board- 648 Hz
Digital Board- 497 Hz
Top Cover- 435 Hz
Bottom Cover – TBD (hidden in model for now)
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CRaTER CDR
Mechanical Design
Natural Frequencies Discussion
• Discussion of the differences in the frequency analysis:
–
–
The method used for the CRaTER assembly frequency analysis is based on the contact surfaces
(such as the boards to e-box, covers to e-box and telescope to e-box) as having a bonded interface,
which is slightly unrealistic but yields a boundary condition for frequency analysis.
The method used for the individual analysis puts a boundary condition on either the edges of the part
or their mounting holes.
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CRaTER CDR
Mechanical Design
Material Properties
Density
Material
Aluminum 6061-T6
Aluminum 7075-T73
A286 AMS 5731
Polyimide 30% glass
3
(lb/in )
0.098
0.101
0.287
0.068
Young's
Tensile
Modulus
Yield (ksi)
(ksi)
9,900
35
10,400
55
29,100
85
2,800
27
Tensile
Ultimate
(ksi)
42
65
130
50
Poisson's
Ratio
0.33
0.33
0.31
-
Where Used
Access Cover
Covers, Structure
Fasteners
Circuit Board
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CRaTER CDR
Mechanical Design
Stress Margins Results
•
Load levels are dominated by random vibration spec.
•
For resonances in the Random Vibration Spec, Miles’ Equation shows 3 sigma loading on the order of 94-228 g
•
Q varies from 20-33.
•
Factors of Safety, FS, used for corresponding material (MEV 5.1)
*
-
Metals: 1.25 Yield, 1.4 Ultimate
-
Composite: 1.5 Ultimate
Margin of Safety (MOS)= (Allowable Stress or Load)/(Applied Stress or Load x FS)-1
Description
CRaTER
Assembly
Analog
Board
Digital
Board
Top Cover
Bottom
Cover
Part No.
First
Frequency
(Hz)
Q
Associated
g load (g)
3 sigma
load (g)
32-10000
1516
20
51.3
153.9
21400
2.6
30-10201
195
20
31.3
93.9
15212
32-10202
198
20
31.5
94.6
32-10204
288
33
48.9
32-10205
337
33
52.9
Max Stress
Min FOS Y Min FOS U
(psi)
MOS
MOS
Yield
ULT
3.0
1.7
1.8
1.8
3.3
0.2
1.2
11203
2.4
4.5
0.6
2.0
146.6
4246
13.0
15.3
9.4
9.9
158.6
28742
1.9
2.3
0.5
0.6
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CRaTER Assembly Stresses
CRaTER CDR
Mechanical Design
• Dominant Frequency is 1516 Hz
• Using Miles Equation, Q=20
• 3 sigma g loading= 154 g
• Max Stress is 21,400 psi
• MOS Y= 1.7
• MOS U= 1.8
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Analog Board Resonance
CRaTER CDR
Mechanical Design
• First Mode 195 Hz
• Dim: 5.95” x 8.43” x .10”
• mass~.75 lbs
• graph shows displacement
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Analog Board Stresses
CRaTER CDR
Mechanical Design
• Using Miles Equation
• Assume Q=20,
• 3 sigma g loading= 93.9g
• Max Stress is 15,212 psi
• MOS Ult= 1.2
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CRaTER CDR
Mechanical Design
Digital Board Resonance
• First frequency is 198 Hz.
• Dim: 8.66” x 7.55” x .093”
• Mass ~.80 lbs
• Graph is showing
displacement
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CRaTER CDR
Mechanical Design
Digital Board Stresses
• Using Miles Equation
• Assume Q=20,
• 3 sigma g loading= 94.6 g
• Max Stress is 11,203 psi
• MOS Ult= 2.0
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• First Mode 288 Hz
Top Cover Resonance
CRaTER CDR
Mechanical Design
• Dim: 9.35” x 6.94” x .16”
• mass = .43 lbs
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CRaTER CDR
Mechanical Design
Top Cover Stresses
• Using Miles Equation,
Assume Q=33,
• 3 sigma g loading=106 g
• Material is aluminum
• Max Stress is 4246 psi
• MOS Y= 9.4
• MOS U= 9.9
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Bottom Cover Frequency
CRaTER CDR
Mechanical Design
• First frequency is 337 Hz.
• Dim: 8.4” x 9.1” x .21”
• Mass =.53 lbs
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Bottom Cover Stresses
CRaTER CDR
Mechanical Design
• Using Miles Equation,
• Assume Q=33,
• 3 sigma g loading= 158.6 g
• Max Stress is 28.7 kpsi
• MOS Y= 0.5
• MOS U= 0.6
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CRaTER CDR
Mechanical Design
DESIGN DETAILS
Stress Margins, Hardware
•
•
•
Load levels are driven by random vibration spec
Factors of Safety used for corresponding material from 431-SPEC-000012.
– Metals:
1.25 Yield, 1.4 Ultimate
Margin of Safety = (Allowable Stress or Load)/(Applied Stress or Load x FS) – 1
Description
Location/ # of bolts
Material Desc.
MS Yield
MS Ultimate
Comments
#4-40 SHCS
Analog Board/30
CRES, A 286
> +14.2
> +19.5
4 Bolts used
in the analysis
# 4-40 SHCS
Digital Board/35
CRES, A 286
> +13.4
> +18.4
8 Bolts used
in the analysis
#4-40 SHCS
Top Cover/37
CRES, A 286
> +447
> +597
4 Bolts used
in the analysis
#2-56 SHCS
Bottom Cover/32
CRES, A 286
> +24.6
> +32.8
4 Bolts used
in the analysis
#10-32 SHCS
Mounting Feet/6
CRES, A 286
+2.8
+3.1
6 Bolts used
in the analysis
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CRaTER CDR
Mechanical Design
Overview
Assembly Description
Mechanical Design Details
-peer review summary
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
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Significant Peer Review Comments
•
Observation:
–
–
The CRaTER design team should use its finite element model to determine what the expected bolt loads
are and provide this information to the host spacecraft to verify that the individual bolt loads are
acceptable.
CRaTER Group Response:
•
•
In process of determining loads and will add to the MID.
Observation:
–
–
•
CRaTER CDR
Mechanical Design
The electronics structure is very stiff in the vertical direction at the six mounting feet. The flatness of the
mounting surface is specified to be flat to within 0.005”. When the housing is mounted to a very stiff
surface (such as a shake fixture) the feet will be displaced causing stresses within the housing to develop.
If the force required to get contact at each foot exceeds the tension in the mounting screw there will be a gap
between the bottom of the foot and the mounting surface.
CRaTER Group Response:
• In process of determining loads and factors of safety.
Observation:
–
–
The printed circuit boards are presently listed as being stress limited due to highly localized stresses at the
mounting holes. Either the fidelity of the modeling has to be increased to show that the stress
concentrations are not as severe as presently shown or the mounting configuration has to be modified to
make for more robust PCB mounting.
CRaTER Group Response:
•
In process of determining loads and factors of safety.
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Significant Peer Review Comments
•
Observation:
–
–
The shock test levels specified in the Mechanical Systems Specification (431-SPEC-000012) apply at the
payload adaptor fitting (Table 3-12) and the Deployable Interface (Table 3-11), not at the CRaTER
mounting location. The levels as given are very high and may pose a significant challenge to the CRaTER
instrument, particularly the detectors. Presently there are no plans to subject the instrument to shock
testing prior to the testing that will be performed after integration with the host spacecraft.
Crater Group Response
•
•
CRaTER CDR
Mechanical Design
We are working with the space craft group to specify a more viable shock spec.
Observation:
–
–
The detectors are sensitive to visible light as well as the cosmic ray radiation that they are intended to
measure. A specification on how much visible light attenuation should be specified. The test program
should include a test to verify the integrity of the light sealing.
Crater Group Response
•
In process of determining acceptable levels.
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Other Peer Review Comments
•
Observation:
–
–
The CRaTER instrument has provisions to periodically purge the interior of the instrument during storage
and integration activities. Presently there are no filters on the inlet or outlet ends of the purge path .
CRaTER Group Response
•
•
•
A 316 SS, 2 micron filter will be added on the exit side of the purge system.
A GSE filter will be placed in the fore line of the purge fitting and removed at installation to the space craft.
Observation:
–
–
The CRaTER instrument’s purge gas will be supplied by a supply line on the spacecraft that will also be
supplying other instruments. Proper proportioning of the supply gas to the various instruments requires
control of the back pressure and supply pressure to create the desired flow rates. This issue is not covered
by the interface control document.
CRaTER Group Response:
•
•
CRaTER CDR
Mechanical Design
We have determined a flow rate and will add it to the MID.
Observation:
–
–
The host spacecraft will supply electrical power for and control of a survival heater for the CRaTER
payload. At this point in time there is no decision on where the heater will be located (on the S/C panel or
within the CRaTER assembly) nor the power dissipation required.
CRaTER Group Response:
•
CRaTER has allocated space and wiring for the heater on the internal part of the Electronics Housing.
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CURRENT BEST ESTIMATE, MASS PROPERTIES
grams
lbs
Analog CCA
340
0.75
Electronics Assembly
Digital CCA
453
1.00
DC/DC converters and EMI filter
100
0.22
Interconnect Cable, A/D
91
0.20
Internal E-box wire, heater, Thermostats,
connectors
227
.50
Mechanical Enclosure
1948
4.30
Top Cover
195
0.43
Connector access cover
32
0.07
Bottom Cover
240
0.53
Internal Hardware
163
0.36
Purge system
113
0.25
Electronics Assembly Sub-Total
3900
8.61
Telescope Assembly Sub- Total
1273
2.81
MLI and TPS Sub-Total
249
.55
Mounting Hardware Sub-Total
41
.09
5463
12.06
CRaTER CBE Total
CRaTER CDR
Mechanical Design
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CRaTER CDR
Mechanical Design
Overview
Assembly Description
Mechanical Design Details
Mechanical Environments and Requirements
(Changes from PDR)
Near Term Tasks
Back-up slides
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Mechanical Environments - Imposed
•
CRaTER CDR
Mechanical Design
From 431-RQMT-000012, Rev A, Environments Section 3.1.
Section
Description
Levels
3.1.1.2
Net cg limit load
28.9 g*1
3.1.4.2
Sinusoidal Vibration Loads
Protoflight;
Frequency (Hz)
5 - 17.7
17.7 – 50
Level
1.27cm D.A.
8 g’s
3.1.5
Acoustics
Delta IV Medium: Protoflight OASPL 140.0 dB
Atlas V 401: Protoflight OASPL: 137.0 dB
3.1.6.1
Random Vibration
See Random Vibration slide
3.1.7
Shock environment
See Shock Environment slide
3.1.8
Venting
Minimum of .25 in^2 of vent area per cubic foot
volume
•1 Interpolated from Table 3-1 for CRaTER at 6.4Kgs.
• Red colors indicated changes from PDR
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CRaTER CDR
Mechanical Design
Updated Shock Environment
Frequency
Level (Q=10)
100 Hz
20 g
800 Hz
930 g
10,000 Hz
930 g
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CRaTER CDR
Mechanical Design
Mechanical Environments, Imposed
Shock Environment
Table 3-12 LRO/PAF Shock Response Spectrum
Delta IV (1194 PAF)
Frequency (Hz)
Atlas (Type B1194 PAF)
Level (Q=10)
100
100-1,000
1,000-10,000
150 g
+9.2 dB/Octave
5,000 g
Frequency (Hz)
Level (Q=10)
100
100-1,400
1,00-10,000
100 g
+7.6 dB/Octave
2,800 g
Table 3-13 Deployable Separation Mechanism Shock Response Spectrum
Separation Nut (SN9423-2)
Frequency (Hz)
Level (Q=10)
100
100-3,000
3,000-10,000
50 g
+7.8 dB/Octave
4,000 g
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CRaTER CDR
Mechanical Design
Overview
Assembly Description
Mechanical Environments and Requirements
Mechanical Design Details
Near Term Tasks
Back-up slides
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CRaTER CDR
Mechanical Design
NEAR TERM TASKS FROM PDR
– Update MICD to reflect latest configuration.
• Released the MICD.
– Further develop analysis on natural frequencies and stresses using SOLID WORKS and
COSMOS on the complete CRaTER Assembly.
• Continuing to work on all natural frequency and stress analysis.
– 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…)
• Completed the design of purge system.
– Complete the drawings for part and assembly fabrication.
• Completed the fabrication drawings for the engineering unit. Assembly drawings are in process.
– Define attachment points and outline for thermal blankets.
• To be completed after Engineering unit is finished.
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CRaTER CDR
Mechanical Design
NEAR TERM TASKS-Post CDR
–
–
–
–
Low level sine sweep analysis of the Engineering Unit mock up.
Close out peer review comments.
Finish assembly of the Engineering Unit.
Complete the drawings for fabricated Flight parts and Flight assembly drawings.
• Release of the Flight Electronics Box Housing drawing and purchase order by July 17, 2006.
– Vibration testing of Engineering Unit. Generate procedures for Vibe tests.
– Define attachment points and outline for thermal blankets.
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CRaTER CDR
Mechanical Design
Backup Slides
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CRaTER CDR
Mechanical Design
Mechanical Environments, Imposed
Random Vibration
Random Vibration Levels
Random Vibration Spec
Protoflight/
Qual
Acceptance
20
0.026
50
0.16
800
0.16
2000
0.026
Overall 14.1 Grms
Frequency (Hz)
1
10
100
1000
0.013
0.08
0.08
0.013
10.0 Grms
10000
Protoflight/ Qual
1
0.1
Acceptance
Power Spectral Density (g^2/Hz)
Freq
(Hz)
0.01
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Mechanical Requirements - Imposed
CRaTER CDR
Mechanical Design
Test Factors Table 3-16
Test
Structural Loads
Level
Duration
Centrifuge
Sine Burst
Protoflight
Comments
1.25 x Limit Load
30 seconds
5 Cycles Full Level
Acoustic
Level
Duration
Will be tested at LRO Level
Limit Level +3 dB
1 minute
Random Vibration
Level
Duration
Limit Level +3 dB
1 minute per axis
Sine Vibration
Level
Sweep Rate
1.25 x Limit Level
4 Octave/Minute per Axis
Shock
Actual Device
Simulated
2 Actuations
1.4 x Limit Level
1 Actuation/Axis
Will be tested at LRO Level
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Mechanical Requirements and Verification
•
CRaTER CDR
Mechanical Design
From 431-RQMT-000012, Rev A, Verification Requirements Section 3.3.
Section
Description
Levels/Comments
3.3.1
Factors of Safety
See FOS table
3.3.2
Test factors
See Test Factors table
3.3.3.2
Perform frequency verification test for Instruments
with frequencies above 50 Hz..
Verify and report frequencies up to 200Hz
Low level sine sweep
3.4
Finite Element Model requirements: Instruments
with predicted first frequencies below 75 Hz shall
provide Finite Element Models.
CRaTERs first fundamental frequency is
well above 75Hz.
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CRaTER CDR
Mechanical Design
Mechanical Requirements and Verification
•
From 431-RQMT-000012, Rev A, Frequency Requirements Section 3.2.
Section
Description
Levels
3.2.2.1
Fundamental frequency, Hz
> 35 Hz
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CRaTER CDR
Mechanical Design
Mechanical Requirements- Imposed
Factors of Safety
Table 3-1 from 431-SPEC-000012
Design Factor of Safety
Type of Hardware
Yield
Ultimate
Tested Flight Structure - Metallic
1.25
1.4
Tested Flgiht Structure - Beryllium
1.4
1.6
Tested Flight Structure - Composite
N/A
1.5
Pressure Loaded Structure
1.25
1.5
Pressure Lines and Fittings
1.25
4.0
Untestest Flight Structure - Metallic Only
2.0
2.6
These are applied to the Protoflight level testing
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CRaTER CDR
Mechanical Design
General Thermal Subsystem Requirements
from 431-Spec-000091
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.
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CRaTER CDR
Mechanical Design
Mechanical Requirements and Verification Summary
•
We also meet all of our internal requirements:
–
–
–
–
–
–
–
–
Have adequate contact area (.5 in^2 min) to the spacecraft to support Thermal requirements. (min is .51 in^2)
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.
Provide means to route cable from telescope to the Analog side of the Electronics Enclosure with minimizing noise.
Electrically isolate the Electronics Enclosure from the Telescope, yet provide sufficient thermal conductance path.
Electrical 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.
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CRaTER CDR
Mechanical Design
Engineering Unit Drawing List
Drawing Number
Drawing Title
Rev.
Layout Complete
Drawing Created
Checked
Released
32-20000
CRaTER Assembly
90%
32-20200
Electronics Assembly
90%
32-20201
Digital Electronics, PWA
√
75%
32-20201.0101
Digital Electronics, PWB
√
√
√
√
32-20201.01
Digital Electronics, Outline Dwg.
B
√
√
√
√
32-20202.01
Analog Electronics, Outline Dwg.
A
√
√
√
√
32-20203
Electronics Enclosure
√
√
√
A
√
32-20204
Cover, Top
√
√
01
√
32-20205
Cover, Bottom
√
√
√
01
√
√
√
√
01
√
32-20206
Cover, Access
32-20208
Cable, Interconnect D/A
√
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Electronics Box Housing Resonance
CRaTER CDR
Mechanical Design
• First Mode 992 Hz
• Dim: 9.40” x 9.06” x 6.15”
• mass= 4.04 lbs
• graph shows displacement
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