1. Matthew Smith (617)-252-1736 matt@space.mit.edu June 27, 2006
Mechanical Design, CRaTER Assembly and Electronics Assembly Critical Design Review
Matthew Smith
(617)
June 27, 2006
9/21/2018

2. Overview Assembly Description Mechanical Design Details
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
9/21/2018

3. 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.
9/21/2018

4. Assembly Description 32-10204 32-10201 32-10206 32-10203 32-10202
9/21/2018

5. Overview Assembly Description Mechanical Design Details
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
9/21/2018

6. Natural Frequencies
We put the CRaTER mock up unit on a shake table Friday June 23, 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).
9/21/2018

7. 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 Hz
E-Box Hz
9/21/2018

8. Natural Frequencies
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)
9/21/2018

9. 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.
9/21/2018

10. Material Properties
9/21/2018

11. 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 g
Q varies from
Factors of Safety, FS, used for corresponding material (MEV 5.1)
Metals: Yield, 1.4 Ultimate
Composite: 1.5 Ultimate
* Margin of Safety (MOS)= (Allowable Stress or Load)/(Applied Stress or Load x FS)-1
9/21/2018

12. CRaTER Assembly Stresses
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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13. Analog Board Resonance
First Mode 195 Hz
Dim: 5.95” x 8.43” x .10”
mass~.75 lbs
graph shows displacement
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14. Analog Board Stresses 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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15. 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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16. 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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17. Top Cover Resonance First Mode 288 Hz Dim: 9.35” x 6.94” x .16”
mass = .43 lbs
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18. 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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19. Bottom Cover Frequency
First frequency is 337 Hz.
Dim: 8.4” x 9.1” x .21”
Mass =.53 lbs
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20. Bottom Cover Stresses Using Miles Equation, Assume Q=33,
3 sigma g loading= g
Max Stress is 28.7 kpsi
MOS Y= 0.5
MOS U= 0.6
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21. DESIGN DETAILS Stress Margins, Hardware
Load levels are driven by random vibration spec
Factors of Safety used for corresponding material from 431-SPEC
Metals: 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
> +13.4
> +18.4
8 Bolts used in the analysis
Top Cover/37
> +447
> +597
#2-56 SHCS
Bottom Cover/32
> +24.6
> +32.8
#10-32 SHCS
Mounting Feet/6
+2.8
+3.1
6 Bolts used in the analysis
9/21/2018

22. Overview Assembly Description Mechanical Design Details
-peer review summary
Mechanical Environments and Requirements
Near Term Tasks
Back-up slides
9/21/2018

23. 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.
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.
In process of determining loads and factors of safety.
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.
9/21/2018

24. Significant Peer Review Comments
Observation:
The shock test levels specified in the Mechanical Systems Specification (431-SPEC ) 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
We are working with the space craft group to specify a more viable shock spec.
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.
In process of determining acceptable levels.
9/21/2018

25. 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.
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:
We have determined a flow rate and will add it to the MID.
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 has allocated space and wiring for the heater on the internal part of the Electronics Housing.
9/21/2018

26. CURRENT BEST ESTIMATE, MASS PROPERTIES
Electronics Assembly
grams
lbs
Analog CCA
340
0.75
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
CRaTER CBE Total
5463
12.06
9/21/2018

27. Overview Assembly Description Mechanical Design Details
Mechanical Environments and Requirements
(Changes from PDR)
Near Term Tasks
Back-up slides
9/21/2018

28. Mechanical Environments - Imposed
From 431-RQMT , Rev A, Environments Section 3.1.
Section
Description
Levels
Net cg limit load
28.9 g*1
Sinusoidal Vibration Loads
Protoflight;
Frequency (Hz) Level
cm D.A.
17.7 – g’s
3.1.5
Acoustics
Delta IV Medium: Protoflight OASPL dB
Atlas V 401: Protoflight OASPL: dB
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
9/21/2018

29. Updated Shock Environment
Frequency
Level (Q=10)
100 Hz
20 g
800 Hz
930 g
10,000 Hz
9/21/2018

30. Mechanical Environments, Imposed Shock Environment
Table LRO/PAF Shock Response Spectrum
Delta IV (1194 PAF)
Atlas (Type B1194 PAF)
Frequency (Hz)
Level (Q=10)
100
100-1,000
1,000-10,000
150 g
+9.2 dB/Octave
5,000 g
100-1,400
1,00-10,000
100 g
+7.6 dB/Octave
2,800 g
Table 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
9/21/2018

31. Overview Assembly Description Mechanical Environments and Requirements
Mechanical Design Details
Near Term Tasks
Back-up slides
9/21/2018

32. 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.
9/21/2018

33. 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.
9/21/2018

34. Backup Slides
9/21/2018

35. Mechanical Environments, Imposed Random Vibration
Random Vibration Levels
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36. Mechanical Requirements - Imposed
Test Factors Table 3-16
Test
Protoflight
Comments
Structural Loads
Level
Duration
Centrifuge
Sine Burst
1.25 x Limit Load
30 seconds
5 Cycles Full Level
Acoustic
Limit Level +3 dB
1 minute
Will be tested at LRO Level
Random Vibration
1 minute per axis
Sine Vibration
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
9/21/2018

37. Mechanical Requirements and Verification
From 431-RQMT , 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
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.
9/21/2018

38. Mechanical Requirements and Verification
From 431-RQMT , Rev A, Frequency Requirements Section 3.2.
Section
Description
Levels
Fundamental frequency, Hz
> 35 Hz
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39. Mechanical Requirements- Imposed
Factors of Safety
These are applied to the Protoflight level testing
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40. 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.
9/21/2018

41. 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.
9/21/2018

42. Engineering Unit Drawing List
Drawing Number
Drawing Title
Rev.
Layout Complete
Drawing Created
Checked
Released
CRaTER Assembly
90%
Electronics Assembly
Digital Electronics, PWA √
75% 
Digital Electronics, PWB
Digital Electronics, Outline Dwg. B  √
Analog Electronics, Outline Dwg. A
Electronics Enclosure
Cover, Top 01
  √
Cover, Bottom
Cover, Access
Cable, Interconnect D/A
9/21/2018

43. Electronics Box Housing Resonance
First Mode 992 Hz
Dim: 9.40” x 9.06” x 6.15”
mass= 4.04 lbs
graph shows displacement
9/21/2018