Mechanical Design, CRaTER Assembly and Electronics Assembly Preliminary Design Review

Transcription

1 , CRaTER Assembly and Electronics Assembly Preliminary Design Review Matthew Smith Mechanical Engineer (617)

2 Overview Instrument and Assembly Description Mechanical Environments and Requirements 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 41-RQMT , Environments Section 2. Section Description Net cg limit load Sinusoidal Vibration Loads Acoustics Enclosed box without exposed thin surfaces Random Vibration Shock environment Venting Levels 12 g Frequency: Protoflight/Qual: OASPL Protoflight/Qual: db OASPL Acceptance: 18.1 db See Random Vibration slide 40 g at 100 Hz 2665g at 1165 to 000 Hz. No self induced shock Hz 8g Acceptance: 6.4g Per 41-SPEC LRO Thermal Subsystem spec.

6 Mechanical Requirements and Verification From 41-RQMT , Verification Requirements Section. Section Description Stowed fundamental Hz Deployed fundamental Frequency Levels Freq >5 > Hz.2.1 Factors of Safety See FOS table.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 Finite Element Model requirements Low level sine sweep We will be above 50Hz. We will be above 75Hz and will not be required to submit an FEM of CRaTER.

7 General Thermal Subsystem Requirements from 41-Spec Section Description Exterior facing MLI blankets shall have mil Kapton with VDA in outer Coating. MLI Blanket Grounding: All blankets shall be grounded per 41-ICD MLI Blanket Documentation: The location and shape documented in as-built ICDs. 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~ 18 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 sigma loading on the order of g Assume Q=10 Random Vibration Spec Frequency (Hz) Protoflight/ Qual 1 Acceptance Freq (Hz) Protoflight/ Qual Acceptance Overall 14.1 Grms 10.0 grms Power Spectral Density (g^2/hz)

10 DESIGN DETAILS Stress Margins, Electronics Assembly Pieces Load levels are superceded by random vibration spec Factors of Safety used for corresponding material from 41-SPEC Metals: 1.25 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 Note 1 Bottom Cover Aluminum Note 1 Digital Board FR4 brittle +1.5 Note 1 Analog Board FR4 Brittle +0.2 Note 1 E-box Structure Aluminum 7075 > +2.8 >+.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 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 155, BJ150 J4 155, BJ150 PART OF MID DRAWING NUMBER Mounting Hardware - Six #10-2 SHCS Surface roughness of 6 micro inches or better for interface surfaces. Mounting surfaces have Electrically Conductive finish (MIL-C-5541 Cl )

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 Table -1 from 41-SPEC Design Factor of Safety Type of Hardware Yield Ultimate Tested Flight Structure - Metallic Tested Flgiht Structure - Beryllium Tested Flight Structure - Composite N/A 1.5 Pressure Loaded Structure Pressure Lines and Fittings Untestest Flight Structure - Metallic Only

17 Analog Board Analysis BOARD ANALYSIS an x 5.95 board separated into two parts Polyimide modulus of elasticity E (lb/in sq 4.21E E E E E E+05 Thickness h (inches) poisson ratio u length a (in) width b (in) weight W (lb) g in/secsq pi D=E*h^/(12(1-u^2)) D= density p mass/area=w/gab E E E-05 7.E E E-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) From Steinberg, vibration analysis for electronic equipment page 149 for a fixed beam on 4 sides Frequency=(Hz) Average Frequency

18 BOARD ANALYSIS Analog Board Analysis Cont d STRESS Gin=peak load(g's)= Q=transmisibility= Gout=Gin*Q= W=board weight(lb)= q=load intensity=w*gout/ab My=bending moment at center= DYNAMIC BENDING STRESS Kt= stress concentration factor h=height Sb=6*Kt*My/h^2= lb/in^2 Stress due to bending FACTORS OF SAFETY FOS Yield FOS Ultimate psi 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 >10^8 >10^8 >10^8 >10^8 MARGIN OF SAFETY MOS=(Allowable stress/applied stress*fs) For a composit Fs=1.5 Ultimate

19 BOARD ANALYSIS Digital Board Analysis a x board two sections modulus of eleasticity Polyimide fiberglass E, psi 4.21E E E E E E+05 Thickness h(inches) poisson ratio u length a (in) width b (in) weight W (lb) g in/secsq pi D=E*h^/(12(1-u^2)) D= density p mass/area=w/gab E E E E E E-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 = This is from an example by Steinberg, vibration analysis for electronic equipment page 149 for a fixed board on 4 sides Frequency, HZ = Average Frequency

20 BOARD ANALYSIS Digital Board Analysis Cont d STRESS Gin=peak load(g's)= Q=transmisibility= Gout=Gin*Q= W=board weight(lb)= q=load intensity=w*gout/ab My=bending moment at center= DYNAMIC BENDING STRESS Kt= stress concentration factor h=height Sb=6*Kt*My/h^2= lb/in^ FOS Yield FOS Ultimate 24kpsi check S-N curve for board type Ch 12 to determine if board will fail >10^8 >10^8 >10^8 >10^8 >10^8 >10^8 MARGIN OF SAFETY MOS=(Allowable stress/applied stress*fs)-1 MOS For a composite FS=1.5 (Ultimate)

21 E-BOX COVERS, ANALYSIS Top Cover Bottom Cover Elastic Modulus E(lb/in sq 1.00E E+07 Thickness h(inches) Poisson ratio u length a (in) width b (in) weight W (lb) g in/secsq pi G q D=E*h^/(12(1-u^2) D= density p mass/area=w/gab E E-05 f=pi/2((d/p)^.5)(1/a^2+1/b^2))^.5 frequency = Bending moment at center My= q(u/a^2=1/b^2)/(pi^2(1/a^2+1/b^2)^ dynamic bending stress Sb=6*My/h^2 Stress= Check S-N curve at Stress N= 5.E+08 5.E+08 FOS Yield/Stress Tensile yield, psi Ultimate/Stress Tensile Ultimate, psi Margin of Safety (allowable stress/applied stress *FOS)-1 Tensile yield, psi Tensile Ultimate, psi

22 CURRENT BEST ESTIMATE, MASS PROPERTIES Electronics Assembly grams lbs Analog CCA Digital CCA Interconnect Cable, A/D Internal E-box Cables Mechanical Enclosure Top Cover Bottom Cover Hardware Purge system Electronics Assembly Sub-Total Detector Assembly Circuit Board Telescope Sub-Assy Detector Mechanical Enclosure Detector Assembly Sub- Total MLI and TPS Sub-Total Mounting Hardware Sub-Total CRaTER CBE Total

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 02 50% Electronics Enclosure 01 95% Cover, Top Electronics Enclosure 01 95% Cover, Bottom Electronics Enclosure - 95%

24 Material Properties Material Density (lb/in ) Young's Modulus (ksi) Tensile Yield (ksi) Tensile Ultimate (ksi) Poisson's Ratio Where Used Aluminum 6061-T , Covers Aluminum , Structure A286 AMS , Fasteners Polyimide 0% glass Circuit Board 1. MIL-HDBK-5J 2. Efunda materials list via efunda.com