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Design, Analysis, Fabrication, and Testing of a Nanosatellite Structure

Design, Analysis, Fabrication, and Testing of a Nanosatellite Structure. Craig L. Stevens cls@vt.edu Aerospace and Ocean Engineering Virginia Tech Blacksburg, Virginia. Thesis Defense May 28, 2002. Overview. 2. Introduction Design Fabrication Structural Verification Conclusions. 3.

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Design, Analysis, Fabrication, and Testing of a Nanosatellite Structure

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  1. Design, Analysis, Fabrication, and Testing of a Nanosatellite Structure Craig L. Stevens cls@vt.edu Aerospace and Ocean Engineering Virginia Tech Blacksburg, Virginia Thesis Defense May 28, 2002

  2. Overview 2 • Introduction • Design • Fabrication • Structural Verification • Conclusions 3 4

  3. Introduction Satellites • Thousands of satellite designs • Structural design depends upon: • Mission • Orbit • Launch vehicle • Technology

  4. Introduction • NASA Satellite History NASA Spacecraft Mass History 5 10 4 10 3 10 Mass, kg 2 10 1 10 0 10 1950 1960 1970 1980 1990 2000 2010 Launch Year

  5. Introduction • Commerical Satellite History Commercial Spacecraft Mass History 3000 2500 2000 Mass, kg 1500 1000 500 0 1965 1970 1975 1980 1985 1990 1995 2000 Launch Year

  6. Introduction Previous Missions Explorer 1: Launched January 31, 1958 Size: 6 ft long Mass: 31 lbs First US satellite Discovered Van Allen Belts Compton Gamma-Ray Observatory: Launched April 5, 1991 Size: 12.5 ft diameter 25 ft long Mass: 34371 lbs Gathered data on galactic radiation

  7. Introduction Previous Missions Solar, Anomalous and Magnetic Particle Explorer (SAMPEX): Launched July 3, 1992 Size: 2.8 ft diameter 4.9 ft long Mass: 348 lbs Began NASA “faster, better, cheaper” program Measured galactic charged particles ORBCOMM: Constellation of 35 spacecraft Launched between 1995 and 2000 Size: 40” diameter 6” height Mass: 99 lbs Provide global two-way messaging

  8. Introduction • Virginia Tech Ionospheric Scintillation Measurement Mission (VTISMM) aka HokieSat • Ionospheric Observation Nanosatellite Formation (ION-F) • Utah State University • University of Washington • Virginia Tech • AFRL Multi-Satellite Deployment System (MSDS) • NASA Shuttle Hitchhiker Experiment Launch System (SHELS) • Sponsors: AFRL, AFOSR, DARPA, NASA GSFC, SDL Ionospheric Observation Nanosatellite Formation (ION-F) AFRL Multi-Satellite Deployment System (MSDS) NASA Shuttle Hitchhiker Experiment Launch System (SHELS)

  9. Introduction ION-F USUSat Dawgstar HokieSat Multiple Satellite Deployment System Configuration: Scenario:

  10. Design Design Process:

  11. Design Initial Criteria • Configuration • Stack of 3 spacecraft • HokieSat at base of stack • Lightband separation system • Hexagonal • Stiffness • SHELS Users Guide: payload natural frequency > 35 Hz • Mass • SHELS Users Guide: payload mass < 400 lbs • Cost • Minimize cost • Student program

  12. Design Objective Function: • Previous fabrication materials and methods investigated • List of criteria created • Criteria score, Sj, based on literature review and correspondence • Criteria weighting factors, Wj, selected for program

  13. Design Objective Function: • Three weighting factor conditions: • Structural engineer • Chief engineer • Student • Results: Metallic panels optimum choice for design

  14. Design Preliminary Design • Hexagonal prism • 18” major diameter • 11.5” height • Separation Systems • Lightband • Starsys • Isogrid construction • Manufacture using computer numerical controlled (CNC) milling machines • 200% increase in structural efficiency • Al 6061-T651 • High efficiency • Inexpensive • Good workability

  15. Design Final Design • 18.25” major diameter hexagonal prism • 11.725” tall • 39 lbs total mass • 13.5 lbs structural mass • Isogrid structure • Aluminum 6061 T-651 • Isogrid end panels • 0.25” isogrid • Composite side panels • 0.23” isogrid • 0.02” skins

  16. Fabrication Hardware • Isogrid panels manufactured using CNC milling machine • End panels machined from 0.25” aluminum plate • Side panels machined from 1” aluminum plate • Separation system flatness requirements verified • 0.0005” per inch tolerance • Final verification during assembly • Skin panels machined from 0.02” aluminum • Brackets machined from 0.063” and 0.25” aluminum • Treated with chromate conversion coating per MIL-C-5541C • #10-32 fasteners

  17. Fabrication Epoxy Process • Composite structure comprised of 0.23” isogrid and 0.02” skin • Used 3M 2216 Gray • Spaceflight heritage • Simple lay-up • Procedure: • Surfaces prepared • Scoured using steel wool • Methyl ethyl ketone • Isopropyl alcohol • Seven 0.005” monofilament lines placed across isogrid surface • Epoxy applied • Isogrid • Skin • Spatula used to evenly distribute • Cured for 120 minutes at 80° C

  18. Structural Verification Structural Verification Procedure • Establish structural requirements • Perform preliminary analysis • Isogrid • Modal analysis and testing of panels • Modal analysis and testing of assembly • Composite • Modal analysis and testing of side panels • Three-point-bend testing of side panels • Environmental testing of assembly • ION-F stack configuration • Strength and stiffness testing • Modal analysis of stack • Stress analyses

  19. Structural Verification Requirements • Withstand all inertial loading with limit load factors: (simultaneous, all permutations) • Margin of Safety (MS)  0, where • Factor of Safety (FS) • Fundamental frequency > 35 Hz

  20. Structural Verification Preliminary Analysis • Isogrid geometry b: width of web d: depth of web h: height of triangle a: length of web • Equivalent monocoque panel • Equivalent Young’s modulus, • Equivalent panel thickness = d • Stress analysis using open isogrid theory where Nx, Ny, Nxy are membrane stress resultants

  21. Structural Verification Preliminary Analysis • Finite element analysis to calculate stress resultants • Analysis demonstrates that 0.200” thick isogrid panels sufficient • HOWEVER, forced to increase panel thickness to 0.250” • Stiffness requirements • Model deficiencies • Integration Shell Elements thickness = d

  22. Structural Verification Finite Element Analysis of Isogrid Structure Shell Elements • Linear beam elements: • 0.25” ×0.08” • 0.23” × 0.08” • Linear quadrilateral and triangular shell elements: • 0.25” thick • 0.23” thick • Separation system attachment points modeled • Thruster holes neglected • Flanges and overhangs • Side panel model • Neglected in assembly Beam Elements Attachment Points

  23. Structural Verification Finite Element Analysis of Isogrid Side Panel Mode 1 fn = 131 Hz Mode 2 fn = 171 Hz

  24. Structural Verification Finite Element Analysis of Isogrid End Panel Mode 1 fn = 105 Hz Mode 2 fn = 182 Hz

  25. Structural Verification Modal (tap) Testing of Panels • Panels tethered using bungee cords and tape • Hammer provides impulsive input at several points • Accelerometer measures accelerations at fixed point • Frequency response function magnitudes and phases examined • Verification of predictions of finite element analysis

  26. Structural Verification Modal Testing of Isogrid Side Panels Mode 1 fn = 131 Hz (vs 131 Hz predicted) Mode 2 fn = 169 Hz (vs 171 Hz predicted)

  27. Structural Verification Modal Testing of Isogrid End Panels Mode 1 fn = 111 Hz (vs 105 Hz predicted) Mode 2 fn = 193 Hz (vs 182 Hz predicted)

  28. Structural Verification Finite Element Analysis of Isogrid Structural Assembly Mode 1 fn = 249 Hz

  29. Structural Verification Finite Element Analysis of Isogrid Structural Assembly Mode 2 fn = 263 Hz

  30. Structural Verification Modal Testing of Isogrid Structural Assembly Mode 2 fn = 272 Hz (vs 263 Hzpredicted) Mode 1 fn = 245 Hz (vs 249 Hz predicted)

  31. Structural Verification Finite Element Analysis of Composite Side Panel • Offset neutral axis nodes of isogrid panels • Linear shell elements created • 0.02” quadrilateral • 0.02” triangular • Rigid elements connect neutral axis nodes Beam Element Neutral Axis Rigid Element Shell Element Neutral Axis

  32. Structural Verification Finite Element Analysis of Composite Side Panel Mode 1 fn = 159 Hz Mode 2 fn = 219 Hz

  33. Structural Verification Modal Testing of Composite Side Panels Chladni Patterns: Mode 2 fn = 220 Hz (vs 219 Hz predicted) Mode 1 fn = 159 Hz (vs 159 Hz predicted) Mode 1: fn = 159 Hz Mode 2: fn = 220 Hz Results demonstrate 22% gain in efficiency using skins

  34. Structural Verification Composite Panel Strength Test Results 600 Side 1 Side 2 Side 3 500 Side 4 Side 5 Side 6 400 Load, lbs 300 200 100 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Displacement, in Three-Point-Bend Testing of Composite Side Panels • Stiffness curves lie within 5% of mean • Verify bond strength • Verify assumption to neglect thruster holes • Supported on all edges • Load applied at center web • First loaded prototype panel to localized failure • Loaded flight panels to 70% failure load

  35. Structural Verification ION-F Random Vibration Spectrum 0 10 -1 10 ASD, G2/Hz -2 10 -3 10 1 2 3 4 10 10 10 10 Frequency, Hz Composite Structure Environmental Testing • Sine sweep test • Determines restrained fundamental frequency • 20-2000 Hz, 0.5 g • Sine burst test • Quasi-static strength test at less than one-third fundamental frequency • 23.8 g’s • Random vibration test • Verifies structural integrity • 9 g RMS, 1 minute duration • Power spectrum:

  36. Structural Verification Z X Y Prototype Environmental Testing Accelerometer Placement • Side panel 1 • Side panel 2 • Zenith panel • GPS (3 axis) • CEE (3 axis) • PPU (3 axis) • Battery box (3 axis)

  37. Structural Verification Zenith Panel FRF: Hzz(f) 1 10 Log H(f) 0 10 -1 10 2 3 10 10 Log Frequency, Hz Testing Results: • Structure survived all tests • Fundamental frequency: • 78 Hz • Zenith panel • Torque coil damaged • Modified integration scheme • Raise fundamental frequency • Prevent damage

  38. Structural Verification Z X Y Flight Environmental Testing Accelerometer Placement • Side panel 1 • Side panel 2 • Zenith panel • Honeycomb • GPS • GPS Preamp • CEE • PPT (3 axis) • Fuel bar support (3 axis) • Battery box

  39. Structural Verification Zenith Panel FRF: Hzz(f) 1 10 0 10 Log H(f) -1 10 -2 10 2 3 10 10 Log Frequency, Hz CEE FRF: Hzz(f) 1 10 Log H(f) 0 10 -1 10 2 3 10 10 Log Frequency, Hz Testing Results: • Structure survived all tests • Fundamental frequency: • 105 Hz • Nadir panel • Raised fundamental frequency 35% • Epoxied honeycomb • Relocation of GPS components

  40. Structural Verification Mass Properties Testing • Measured • Center of mass • Moments of inertia • Oriented in seven configurations to calculate principal moments of inertia • No data recorded for products of inertia Ixz and Iyz • Assumed z-axis is principal axis x y z

  41. Structural Verification Finite Element Analysis of Complete ION-F Stack • USUSat: • 0.25” thick linear shell • Non-structural point masses • Dawgstar • 0.12” thick linear quadrilateral shell elements • Linear beam elements • Nonstructural mass • Lightband • 0.15” thick linear quadrilateral shell elements • HokieSat • Nonstructural mass USUSat Lightband Dawgstar Lightband HokieSat

  42. Structural Verification Strength and Stiffness Test Truss loading fixture • Three cantilever tests • Truss • Isogrid • Composite • Evaluate gain in efficiency using composite structure • Determine boundary conditions Isogrid and composite structures

  43. Structural Verification Strength and Stiffness Test Load vs Displacement Plot • Experiment demonstrated a 32% gain in stiffness in the cantilever mode due to addition of skins • Skins added less than 8% to the total mass • Overall 22% gain in structural efficiency for cantilever mode Truss Isogrid & Truss 300 Composite & Truss 250 200 Load, p (lb) 150 100 50 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Displacement, u (in)

  44. Structural Verification Boundary Condition Correlation • Model of truss fixture • 0.15” linear shell elements • Hexagonal protrusion • Attached at nodes simulating • Lightband attachment points Load vs Displacement of Truss Fixture 300 Test Analysis 250 200 • Correlation of truss data • Lightband attachment points fixed on end panel • Load applied at end • Young’s modulus modified • Stiffness curves correlate within 1% Load, p (lb) 150 100 50 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Displacement, u (in)

  45. Structural Verification Truss and Composite Structure Data 300 Test Analysis 250 200 Load, p (lb) 150 100 50 0 0 0.02 0.04 0.06 0.08 0.1 0.12 Displacement, u (in) Boundary Condition Correlation • Correlation of truss and composite data • Nadir Starsys attachment point node translations fixed (fixed base) • Flanges modeled using solid elements • End panels attach to flanges using rigid elements • Stiffness curves of model and test data correlate within 5%

  46. Structural Verification Modal Analysis of Complete ION-F Stack Mode 1 fn = 47 Hz Mode 2 fn = 48 Hz • Majority of strain energy concentrated in Lightband • Possible stiffness problems revealed

  47. Structural Verification Stress Analysis of Complete ION-F Stack • Apply uniform acceleration • Fixed base boundary conditions • Required design criteria: • Minimum MS = 0.094 > 0 • Sine burst stress analysis results • No yielding or buckling

  48. Conclusions • Aluminum isogrid increases structural performance at reduced mass • Modal testing verifies accuracy of isogrid and composite side panel finite element models within ~1% error • Modal testing demonstrates 22% increase in structural efficiency of side panel by adding thin aluminum skins • Three-point bend testing validates assumption to neglect thruster hole cutouts in model and verifies bond strength • Sine sweep testing demonstrates a fundamental frequency of 105 Hz for the restrained composite assembly • Strength and stiffness testing demonstrates 22% gain in structural stiffness of assembly by adding thin aluminum skins • Analyses and experiments verify structure survives Shuttle payload environment

  49. Acknowledgements • Professor C. Hall • Professor W. Hallauer • Professor E. Johnson • Air Force Research Laboratory • Air Force Office of Scientific Research • Defense Advanced Research Projects Agency • NASA Goddard Space Flight Center • NASA Wallops Flight Facility Test Center • University of Washington • Utah State University • Virginia Tech • Professor A. Wicks • Professor B. Love • Members of structures team • Members of ION-F

  50. Design External Configuration Solar Cells Crosslink Antenna GPS Antenna LightBand Pulsed Plasma Thrusters Data Port Camera Uplink Antenna Downlink Antenna Science Patches

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