Structural Verification of the Rigidizable Inflatable Get ...

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

AIAA/USU Conference on Small Satellites – 15 August 2006 2

Overview

Payload Motivation

RIGEX Overview

Structural Model Development

Bolt Analysis

Summary


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


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


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


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


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


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


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


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)



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



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


Structural Model DevelopmentFEM Natural Frequency Results (Hz)

Mode #1 Mode #2 Mode #3RIGEX FEM 185 198 304

Mode #2 Mode #3Mode #1


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


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


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.


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


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


Questions?


Bolt Analysis

Component Hardware Bolts:

CameraComputer ContainerComputer Mounting PlatePower Distribution PlateOvenOven Mounting Bracket/LatchPressure Transducer Mounting BlockIndividually Mounted Transformers and Power Relays


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


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


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

− ≥×


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

Structural Verification of the Rigidizable Inflatable Get ...

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