Mechanical Design, CRaTER Assembly and Electronics ... · PDF fileCRaTER CDR Mechanical Design ... CRaTER Assembly and Electronics Assembly Critical Design Review Matthew Smith (617)

6/20/2006 1

Cosmic RAy Telescope for the Effects of Radiation

CRaTER CDRMechanical Design

Mechanical Design, CRaTER Assembly and Electronics Assembly

Critical Design Review

Matthew Smith(617)-252-1736

[email protected]

June 27, 2006

6/20/2006 2



Overview

Assembly Description

Mechanical Design Details

Mechanical Environments and Requirements

Near Term Tasks

Back-up slides

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• 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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32-10206

32-10201

32-10204

32-10202

32-10205

32-10203

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Overview




Near Term Tasks

Back-up slides

6/20/2006 6



Material Properties

Material

Density

(lb/in3)

Young's Modulus

(ksi)Tensile

Yield (ksi)

Tensile Ultimate

(ksi)Poisson's

Ratio Where UsedAluminum 6061-T6 0.098 9,900 35 42 0.33 Access CoverAluminum 7075-T73 0.101 10,400 55 65 0.33 Covers, StructureA286 AMS 5731 0.287 29,100 85 130 0.31 FastenersPolyimide 30% glass 0.068 2,800 27 50 - Circuit Board

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Natural Frequencies

• We will be putting the CRaTER mock up unit on a shake table Friday June 23, 2006. We will have accelerometers on the analog and digital boards, the two covers, one on the telescope and one on the e-box. The results will then be compared to our models. Any changes to the model will result in a change to the stress analysis.

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Natural Frequencies

• Natural Frequency Estimates

– From SOLID WORKS cosmos package, 2005 • CRaTER as an assembly

– First frequency at 435Hz (top cover)– Dominant Frequency at 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

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• 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.

Natural Frequencies Discussion

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CRaTER CDRMechanical DesignStress Margins Results

Description Part No.First

Frequency (Hz)

QAssociated g load (g)

3 sigma load (g)

Max Stress (psi)

Min FOS Y Min FOS U MOS Yield

MOS ULT

CRaTER Assembly

32-10000 1516 20 51.3 153.9 21400 2.6 3.0 1.7 1.8

Analog Board

30-10201 195 20 31.3 93.9 15212 1.8 3.3 0.2 1.2

Digital Board

32-10202 198 20 31.5 94.6 11203 2.4 4.5 0.6 2.0

Top Cover 32-10204 288 33 48.9 146.6 4246 13.0 15.3 9.4 9.9Bottom Cover

32-10205 337 33 52.9 158.6 28742 1.9 2.3 0.5 0.6

• 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

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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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CRaTER CDRMechanical DesignAnalog Board Resonance

• First Mode 195 Hz

• Dim: 5.95” x 8.43” x .10”

• mass~.75 lbs

• graph shows displacement

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CRaTER CDRMechanical DesignAnalog Board Stresses

• Using Miles Equation

• Assume Q=20,

• 3 sigma g loading= 93.9g


• MOS Ult= 1.2

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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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Digital Board Stresses• Using Miles Equation

• Assume Q=20,

• 3 sigma g loading= 94.6 g


• MOS Ult= 2.0

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Top Cover Resonance• First Mode 288 Hz

• Dim: 9.35” x 6.94” x .16”

• mass = .43 lbs

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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

• First frequency is 337 Hz.

• Dim: 8.4” x 9.1” x .21”

• Mass =.53 lbs

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Bottom Cover Stresses

• 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

6/20/2006 20


CRaTER CDRMechanical DesignDESIGN 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

Mounting Feet/6

Bottom Cover/32

Top Cover/37

Digital Board/35

Analog Board/30

Location/ # of bolts

#10-32 SHCS

#2-56 SHCS

#4-40 SHCS

# 4-40 SHCS

#4-40 SHCS

Description

+3.1

> +32.8

> +597

> +18.4

> +19.5

MS Ultimate

8 Bolts used in the analysis

> +13.4CRES, A 286


> +24.6CRES, A 286


+2.8CRES, A 286

> +447

> +14.2

MS Yield CommentsMaterial Desc.


CRES, A 286


CRES, A 286

6/20/2006 21



Overview


Mechanical Design Details-peer review summary


Near Term Tasks

Back-up slides

6/20/2006 22


CRaTER CDRMechanical DesignSignificant 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:– 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.

6/20/2006 23


CRaTER CDRMechanical DesignSignificant 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• 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.

6/20/2006 24



• 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:• 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.

Other Peer Review Comments

6/20/2006 25



0.0732Connector access cover

0.22100DC/DC converters and EMI filter

.55249MLI and TPS Sub-Total

12.065463CRaTER CBE Total

.0941Mounting Hardware Sub-Total

2.811273Telescope Assembly Sub- Total

8.613900Electronics Assembly Sub-Total

0.25113Purge system

0.36163Internal Hardware

0.53240Bottom Cover

0.43195Top Cover

4.301948Mechanical Enclosure

.50227Internal E-box wire, heater, Thermostats,

connectors

0.2091Interconnect Cable, A/D

1.00453Digital CCA

0.75340Analog CCA

lbsgramsElectronics Assembly

CURRENT BEST ESTIMATE, MASS PROPERTIES

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Overview



Mechanical Environments and Requirements(Changes from PDR)

Near Term Tasks

Back-up slides

6/20/2006 27


CRaTER CDRMechanical DesignMechanical Environments - Imposed

• From 431-RQMT-000012, Rev A, Environments Section 3.1.

Minimum of .25 in^2 of vent area per cubic foot volume

Venting3.1.8

See Shock Environment slideShock environment3.1.7

See Random Vibration slide Random Vibration3.1.6.1

Delta IV Medium: Protoflight OASPL 140.0 dBAtlas V 401: Protoflight OASPL: 137.0 dB

Acoustics3.1.5

Protoflight;Frequency (Hz) Level5 - 17.7 1.27cm D.A.17.7 – 50 8 g’s

Sinusoidal Vibration Loads3.1.4.2

28.9 g*1Net cg limit load3.1.1.2

LevelsDescriptionSection

•1 Interpolated from Table 3-1 for CRaTER at 6.4Kgs.

• Red colors indicated changes from PDR

6/20/2006 28



Updated Shock Environment

Level (Q=10)Frequency

930 g10,000 Hz

930 g800 Hz

20 g100 Hz

6/20/2006 29



100 g+7.6 dB/Octave

2,800 g

100100-1,400

1,00-10,000

150 g+9.2 dB/Octave

5,000 g

100100-1,000

1,000-10,000

Level (Q=10)Frequency (Hz)Level (Q=10)Frequency (Hz)

Atlas (Type B1194 PAF)Delta IV (1194 PAF)

Mechanical Environments, ImposedShock Environment

Table 3-12 LRO/PAF Shock Response Spectrum

50 g+7.8 dB/Octave

4,000 g

100100-3,000

3,000-10,000

Level (Q=10)Frequency (Hz)

Separation Nut (SN9423-2)

Table 3-13 Deployable Separation Mechanism Shock Response Spectrum

6/20/2006 30



Overview




Near Term Tasks

Back-up slides

6/20/2006 31



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.

6/20/2006 32



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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Backup Slides

6/20/2006 34



Mechanical Environments, ImposedRandom Vibration

Random Vibration LevelsRandom Vibration Spec

0.01

0.1

1

1 10 100 1000 10000

Frequency (Hz)

Po

wer

Sp

ectr

al D

ensi

ty (

g^2

/Hz)

Protoflight/ Qual

Acceptance

Freq (Hz)

Protoflight/ Qual Acceptance

20 0.026 0.01350 0.16 0.08

800 0.16 0.082000 0.026 0.013

Overall 14.1 Grms 10.0 Grms

6/20/2006 35


CRaTER CDRMechanical DesignMechanical Requirements - Imposed

Test Factors Table 3-16

2 Actuations1.4 x Limit Level1 Actuation/Axis

1.25 x Limit Level4 Octave/Minute per Axis

Limit Level +3 dB1 minute per axis

Limit Level +3 dB1 minute

1.25 x Limit Load

30 seconds5 Cycles Full Level

Protoflight

Will be tested at LRO LevelShock

Actual DeviceSimulated

Sine VibrationLevelSweep Rate

Random VibrationLevelDuration

Will be tested at LRO LevelAcoustic LevelDuration

Structural LoadsLevelDuration

CentrifugeSine Burst

CommentsTest

6/20/2006 36



Mechanical Requirements and Verification

• From 431-RQMT-000012, Rev A, Verification Requirements Section 3.3.

CRaTERs first fundamental frequency is well above 75Hz.

Finite Element Model requirements: Instruments with predicted first frequencies below 75 Hz shall provide Finite Element Models.

3.4

Low level sine sweepPerform frequency verification test for Instruments with frequencies above 50 Hz..Verify and report frequencies up to 200Hz

3.3.3.2

See Test Factors tableTest factors3.3.2

See FOS tableFactors of Safety3.3.1

Levels/CommentsDescriptionSection

6/20/2006 37



Mechanical Requirements and Verification

• From 431-RQMT-000012, Rev A, Frequency Requirements Section 3.2.

> 35 HzFundamental frequency, Hz3.2.2.1

LevelsDescriptionSection

6/20/2006 38



Table 3-1 from 431-SPEC-000012Type of Hardware Yield UltimateTested Flight Structure - Metallic 1.25 1.4Tested Flgiht Structure - Beryllium 1.4 1.6Tested Flight Structure - Composite N/A 1.5Pressure Loaded Structure 1.25 1.5Pressure Lines and Fittings 1.25 4.0Untestest Flight Structure - Metallic Only 2.0 2.6

Design Factor of Safety

Mechanical Requirements- ImposedFactors of Safety

These are applied to the Protoflight level testing

6/20/2006 39



General Thermal Subsystem Requirements from 431-Spec-000091

Attachment to MLI Blankets:All exterior MLI blankets shall be mechanically constrained at least at one point.

4.4

MLI Blanket Documentation:The location and shape documented in as-built ICDs.

4.3

MLI Blanket Grounding:All blankets shall be grounded per 431-ICD-00018

4.2

Exterior facing MLI blankets shall have 3 mil Kapton with VDA in outer Coating.

4.1

DescriptionSection

6/20/2006 40



• 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.

Mechanical Requirements and Verification Summary

6/20/2006 41



Engineering Unit Drawing List

Cable, Interconnect D/A32-20208

vvvvBDigital Electronics, Outline Dwg.32-20201.01

vvvvDigital Electronics, PWB32-20201.0101

vvvvAAnalog Electronics, Outline Dwg.32-20202.01

vvvv01Cover, Access32-20206

90%CRaTER Assembly32-20000

vvvv01

Cover, Bottom32-20205

vvvv01Cover, Top 32-20204

vvvvAElectronics Enclosure32-20203

75%vDigital Electronics, PWA32-20201

90%Electronics Assembly32-20200

ReleasedChecked Drawing Created Layout CompleteRev.Drawing TitleDrawing Number

6/20/2006 42


CRaTER CDRMechanical DesignElectronics Box Housing Resonance

• First Mode 992 Hz

• Dim: 9.40” x 9.06” x 6.15”

• mass= 4.04 lbs

• graph shows displacement

Mechanical Design, CRaTER Assembly and Electronics ... · PDF fileCRaTER CDR Mechanical Design ... CRaTER Assembly and Electronics Assembly Critical Design Review Matthew Smith (617)

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