structural verification of the rigidizable inflatable get
TRANSCRIPT
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2020thth ANNUAL CONFERENCE ON SMALL SATELLITESANNUAL CONFERENCE ON SMALL SATELLITESSession IV: The Past & Coming YearsSession IV: The Past & Coming Years
Structural Verification of the Rigidizable Inflatable Get-Away-
Special Experiment (RIGEX)1Lt Sarah Helms
2Lt Anna Gunn-GolkinDr. Richard Cobb
AIR FORCE INSTITUTE OF TECHNOLOGY
15 August 2006
I n t e g r i t y - S e r v i c e - E x c e l l e n c e
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Overview
Payload Motivation
RIGEX Overview
Structural Model Development
Bolt Analysis
Summary
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Payload MotivationMany new space technology concepts require large space structures
Large aperture sensorcraft, deployable booms, solar sails, etc.
Space-based experiments bounded by launch vehicle constraints:
Physical dimension, weight and cost
Inflatable, rigidizable structures have potential benefits compared to mechanical options
Lighter weight, smaller packaging volume, and lower costProvide packing flexibility and structural stiffnessRigidization eliminates the need for prolonged pressurization
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RIGEX OverviewThermoplastic composite Sub-Tg tubes
Kevlar fibers, proprietary polyurethane-based resinRigidization via second-order transition change -125oC glass-transition temperature (Tg)Supplied by L’Garde, Inc.
Sub-Tg Tube Deployment: Heat – to induce flexibilityInflate – using NitrogenCool – rigidization step, still pressurized VentExcite – using PZT patches to obtain modal characterizationData Acquisition – environmental and photo sensors record inflation process, temperature, excitation
20” Tall
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RIGEX OverviewA step in the path toward inflatable, rigidizable space structures
as a mature technology for operational applications
20” Tall
RIGEX Science:RIGEX Science:SubSub--Tg Inflatable, Tg Inflatable, Rigidizable TubesRigidizable Tubes
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RIGEX OverviewNine AFIT masters theses on RIGEX project since 2001
Originally Get-Away-Special (GAS) Canister experiment
Modified for Canister for all Payload Ejections (CAPE) platform
Cut-Away View of RIGEX within CAPE
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RIGEX Overview
Shroud
Lifting Handle/Stabilizing Feet (x4)
Lifting Handle
Oven
ComputerOven Power RelaysPower Distribution Plate
Ribs
Bumpers
Sub Tg-Tube
LED
CameraExperiment Top Plate
CAPE Mounting Plate
Bottom Plate
Oven Latch
Pin Puller
Connector Hole Cover
Total Mass: 237 lbs (0.32, 0.12, 11.50) inAssumptions
Uniform density of componentsWiring and fasteners not included in SolidWorks model but are estimated in analysis
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Structural Model DevelopmentStructural Model / Finite Element Model (FEM)
Analytical calculations paired with physical hardware testing toensure structural compatibility with Shuttle
Used NX Nastran for FEMAP software
FEM method validation via use of separate finite element models (preliminary FEMs) representing the GAS RIGEX Engineering Model (EM) structure
Analyses:Eigenvalue analysis to satisfy minimum natural frequency parameter (50 Hz)Static limit loads analysis at bolt locations
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Structural Model DevelopmentFEM ASSUMPTIONSFEM ASSUMPTIONS
6061-T651 plate aluminum modeled as isotropic, homogeneous
Small wire routing, vent, and bolt holes not included in model
Subsystems modeled as point masses, adds no stiffness to structure
Subsystem components <0.25 lbs considered negligible and not included in model
Bolt connections modeled by shared nodes at bolt locations
1.5” CAPE Mounting Plate assumed perfectly stiff and not included in model, Top Plate bolt pattern fixed to mimic boundary condition
CAPE Mounting Plate(not included in FEM)
Experiment Top Plate
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Structural Model DevelopmentFEM VALIDATION ANALYSISFEM VALIDATION ANALYSIS
Similar Structure:Engineering Model
Available in Lab
Ping Test and LaserVibrometer Scan of
EM Structure
Preliminary FEMsBuilt With Varied
Modeling Methods
Comparison BetweenLab Data and FEM
Modal Analysis Results
Most Accurate FEMMethod Identified –
Applied to RIGEX FEM
Mode 1: 250.6012 Hz
Solid Element Coarse MeshSolid Element Coarse Mesh
RIGEX Engineering RIGEX Engineering Model Structure (GAS Design) Model Structure (GAS Design)
Preliminary FEMFour models assessed:
2-D Linear Plate3-D Quadratic Solid coarse mesh3-D Quad Solid intermediate mesh 3-D Quad Solid fine mesh
Laboratory TestsPing TestLaser Vibrometer Scan
Comparisons showed best correlation with Plate FEM (0.5% difference in first mode, 8% difference in second mode)
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Structural Model Development
FEM Construction
Key Numbers
4 Ribs3 Rectangular
Pressure System Plates
3 Tube Cylinder Elements Top PlateOven Mounting
PlateBolt locationsPoint MassesShroudNodes merged
at bolt locations
6252 Nodes
6845 Elements
28 Fixed Constraints
37344 Degrees of Freedom
151.19 lbs
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Structural Model Development
RIGEX FEM:Bolt locations represented by merged nodes
Coarse Mesh: Plate area with no bolts or subsystem components
Fine Mesh: Bolts connect plates at this location
Fine Mesh: Location of subsystem components
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Structural Model DevelopmentFEM Natural Frequency Results (Hz)
Mode #1 Mode #2 Mode #3RIGEX FEM 185 198 304
Mode #2 Mode #3Mode #1
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Bolt AnalysisBOLT ANALYSIS OVERVIEWBOLT ANALYSIS OVERVIEW
NASA Requires 2 Locking Devices:Patchlock, Locking Helical Insert or Locknut andPreload (determined through analysis)
At limit load, with preload, bolts will:Have adequate strengthDemonstrate a joint separation safety factor of 1.2
Updates since SmallSat paper submission:Bolt SelectionThermal gradient
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Bolt AnalysisFlight Event Load Factor (g) Angular Acceleration (Rad/s2)
Lift-Off ± 7 ± 7 ± 6 ± 195 ± 60 ± 75
Low Freq. Vibration± 5.4 ± 8 ± 5.4
1 ± 8.8 ± 7 ± 6 ± 195 ± 60 ± 75
2 ± 7 ± 10.6 ± 6 ± 195 ± 60 ± 75
3 ± 7 ± 7 ± 8.1 ± 195 ± 60 ± 75
Landing ± 6 ± 7 ± 8 ± 108 ± 34 ± 80
Source: CAPE-SVP-0001
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Bolt AnalysisBOLT ANALYSIS ASSUMPTIONSBOLT ANALYSIS ASSUMPTIONS
All fasteners comply with applicable NAS or MSInternal tap will comply with UNJ thread standards per AS8879Structural 6061-T6 Aluminum complies with MIL-HDBK-5BFastener A286 CRES complies with MIL-HDBK-5BSubsystem components modeled as secured by 1 bolt onlyBending loads are negligiblePrevailing torque for the helical inserts as published from Heli-CoilPrevailing torque for bolts with patchlock as published in MIL-F-18240E.Bolt yield is considered failure RIGEX will be built at room temperature (70ºF). Possible orbital temperature range: -75º to 165ºF.
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Bolt AnalysisConstraint Bolts: NAS1189E6P18B
3/8-24, 1.25” Socket Cap bolt threaded into a locking Heli-Coil
Criteria PASS/FAIL MarginMin Cross-Section of
Bolt PAt/(SF*P)-1>0 PASS 4.953
PAt/Pb-1>0 PASS 0.031Shear Pull-Out of
Threads Pas/(SF*P)-1>0 PASS 4.778
Pas/Pb-1>0 PASS 0.001
Shear Load VA/(SF*V)-1 PASS 1.644
Combined Loads (1/(Ra^2+Rs^3))-1>0 PASS 0.005
Separation CriteriaPLDmin/((1-
n*ø)*Psep)-1>0 PASS 0.004
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Summary
• Payload Motivation•Flight test heritage for Rigidizable Inflatable Tubes
•RIGEX System Overview
•Structural Model (FEM) Development•RIGEX Engineering Model Testing•Eigenvalue Analysis
•Bolt Analysis•Adequate strength•Separation factor of safety
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Questions?
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Bolt Analysis
Component Hardware Bolts:
CameraComputer ContainerComputer Mounting PlatePower Distribution PlateOvenOven Mounting Bracket/LatchPressure Transducer Mounting BlockIndividually Mounted Transformers and Power Relays
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Bolt AnalysisBOLT PATTERNSBOLT PATTERNS
Primary Structure Bolts Patterns:“Constraint Bolts” – Top Plate CAPE Mounting Plate
• “Z-axis axial bolts” – Oven Plate/Top Plate Ribs
• “Y-axis axial bolts” – Ribs Ribs/Pressure System Mounting Plates
• “X-axis axial bolts” – Ribs Ribs/PressureSystem Mounting Plates
• “Shroud Coord 1-7 bolts” – 7 different boltorientations connecting shroud to oven plate and top plate
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Bolt Analysis
ProcessSubjected FEM to 64 maximum loading scenarios in FEMAP/NASTRAN
Retrieved results for applied loads and constraint forces at each node location
MATLAB algorithm rotated and sorted load results
Maximum expected loading scenario used in computing margins per NSTS 08307 ‘Criteria for Preloaded Bolts’ for each bolt pattern and specific NAS bolt
Worst case loading scenario FEM used
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Bolt AnalysisBOLT ANALYSIS AXIAL STRENGTHBOLT ANALYSIS AXIAL STRENGTH
1 0tPASF P
− ≥×
1 0t
b
PAP
− >
BOLT ANALYSIS SHEAR PULL OUT OF THREADSBOLT ANALYSIS SHEAR PULL OUT OF THREADS
1 0sPASF P
− ≥×
1 0s
b
PAP
− >
BOLT ANALYSIS SHEAR STRENGTHBOLT ANALYSIS SHEAR STRENGTH
1 0VASF V
− ≥×
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Bolt AnalysisBOLT ANALYSIS COMBINED LOADSBOLT ANALYSIS COMBINED LOADS
2 3
1 1 0a sR R
− >+
min 1 0(1 ) sep
PLDn Pφ
− ≥−
BOLT ANALYSIS SEPARATION CRITIERABOLT ANALYSIS SEPARATION CRITIERA