design, analysis, fabrication, and testing of a nanosatellite structure

Design, Analysis, Fabrication, and Testing of a Nanosatellite

Structure

Craig L. [email protected]

Aerospace and Ocean EngineeringVirginia Tech

Blacksburg, Virginia

Craig L. [email protected]

Aerospace and Ocean EngineeringVirginia Tech

Blacksburg, Virginia

Thesis DefenseMay 28, 2002

Thesis DefenseMay 28, 2002

OverviewOverview

1.Introduction2.Design3.Fabrication4.Structural Verification5.Conclusions

2

4

3

IntroductionIntroductionSatellites

Thousands of satellite designs Structural design depends upon:

1. Mission2. Orbit3. Launch vehicle4. Technology

IntroductionIntroductionNASA Satellite History

1950 1960 1970 1980 1990 2000 201010

0

101

102

103

104

105 NASA Spacecraft Mass History

Launch Year

Mas

s, k

g

IntroductionIntroductionCommerical Satellite History

1965 1970 1975 1980 1985 1990 1995 20000

500

1000

1500

2000

2500

3000Commercial Spacecraft Mass History

Launch Year

Mas

s, k

g

IntroductionIntroductionPrevious 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 lbsGathered data on galactic radiation

IntroductionIntroductionPrevious 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

NASA Shuttle Hitchhiker Experiment

Launch System (SHELS)

AFRL Multi-Satellite

Deployment System (MSDS)

Ionospheric Observation Nanosatellite

Formation (ION-F)

IntroductionIntroduction 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

T4T1 = TSafe, All Systems ExceptRecontact Hazards

= 20 minutes

= 0:00 T3 = T SEP

= T0 + 96 hours, 4 secs

= TSEP, Nanosat

Stack separation signalreleases both stacks

Intersatellite separationMSDS is 20 minutes outfrom Orbiter,timers

time-out

T0

Safety inhibits removedfor all MSDS systems

without recontacthazards.

Safety inhibits removedfor Nanosat systems


MSDS released fromOrbiter/SHELS

MSDS timers initiatedRecontact hazard inhibits

removed aboardNanosats

Recontact hazard inhibitsremoved aboard MSDS

T2 = TSafe,Recontact Hazards

= T0 + 96 hours

INHIBITS STATUS MSDS AND NANOSAT

RecontactHazards

All othersystems

In-place

In-place

In-place

Removed

Removed

Removed Removed

Removed

Removed

Removed


ION-F

USUSat

Dawgstar

HokieSatMultiple Satellite

Deployment System


= 20 minutes

= 0:00 T3 = T SEP


= TSEP, Nanosat



time-out

T0










= T0 + 96 hours


RecontactHazards

All othersystems

In-place

In-place

In-place

Removed

Removed

Removed Removed

Removed

Removed

Removed

= T0 + 102 hours, 4 secsT4T1 = TSafe, All Systems ExceptRecontact Hazards

= 20 minutes

= 0:00 T3 = T SEP


= TSEP, Nanosat



time-out

T0










= T0 + 96 hours


RecontactHazards

All othersystems

In-place

In-place

In-place

Removed

Removed

Removed Removed

Removed

Removed

Removed



= 20 minutes

= 0:00 T3 = T SEP


= TSEP, Nanosat



time-out

T0










= T0 + 96 hours


RecontactHazards

All othersystems

In-place

In-place

In-place

Removed

Removed

Removed Removed

Removed

Removed

Removed


Configuration:

Scenario:

IntroductionIntroduction

DesignDesignDesign Process:

SELECTI NI TI ALCRI TERI A

ESTABLI SHPRELI MI NARY

DESI GN

WI LL ALLSUBSYSTEMS FI T?

STRUCTURAL &MASS PROPERTI ES

ACCEPTABLE?

COST ACCEPTABLE?BUI LT WI THI N

SCHEDULECONSTRAI NTS?

EASY TOMANUFACTURE AND

ASSEMBLE?

OPERATI ONSASPECTS ACCEPTABLE?

STOP

OPTI MI ZE USI NGPRELI MI NARY

ANALYSI S

MODI FYDESI GN

YES

NO

YES

YES

YES

YES

YES

NO

NO NO

NO

NO

START

DesignDesign

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

Initial Criteria

DesignDesignObjective 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

DesignDesignObjective Function: Three weighting factor conditions: 1. Structural engineer2. Chief engineer3. Student

Results: Metallic panels optimum choice for 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

DesignDesign

Isogrid structure Aluminum 6061 T-

651 Isogrid end panels

0.25” isogrid Composite side

panels– 0.23” isogrid– 0.02” skins

18.25” major diameter hexagonal prism 11.725” tall

39 lbs total mass 13.5 lbs structural mass

DesignDesignFinal Design

FabricationFabricationHardware

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

FabricationFabrication

Composite structure comprised of 0.23” isogrid and 0.02” skin

Used 3M 2216 Gray– Spaceflight heritage– Simple lay-up

Procedure:1. Surfaces prepared

– Scoured using steel wool– Methyl ethyl ketone– Isopropyl alcohol

2. Seven 0.005” monofilament lines placed across isogrid surface

3. Epoxy applied– Isogrid– Skin

4. Spatula used to evenly distribute

5. Cured for 120 minutes at 80° C

Epoxy Process

Structural VerificationStructural Verification

1. Establish structural requirements2. Perform preliminary analysis3. Isogrid

Modal analysis and testing of panels Modal analysis and testing of

assembly4. Composite

Modal analysis and testing of side panels

Three-point-bend testing of side panels

Environmental testing of assembly5. ION-F stack configuration

Strength and stiffness testing Modal analysis of stack Stress analyses

Structural Verification Procedure

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

01)()(

ssActualStreFS

tressAllowableSMS


AnalysisFS Limit 1.25FS Ultimate 1.4

Requirements

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

Structural VerificationStructural VerificationPreliminary 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

Structural VerificationStructural VerificationPreliminary Analysis

Shell Elementsthickness = d

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

Finite Element Analysis of Isogrid Structure


AttachmentPoints

Beam Elements

ShellElements

Mode 1fn = 131 Hz

Mode 2fn = 171 Hz

Finite Element Analysis of Isogrid Side PanelStructural VerificationStructural Verification

Mode 1fn = 105 Hz

Mode 2fn = 182 Hz

Finite Element Analysis of Isogrid End PanelStructural VerificationStructural 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


0

5

10

0

5

10

-5

0

5

x

First Mode (fn = 131 Hz)

y

z

0

5

10

0

5

10

-5

0

5

x

Second Mode (fn = 169 Hz)

y

z

Mode 1fn = 131 Hz

(vs 131 Hz predicted)

Mode 2fn = 169 Hz


Modal Testing of Isogrid Side PanelsStructural VerificationStructural Verification

Mode 1fn = 111 Hz


Mode 2fn = 193 Hz


Modal Testing of Isogrid End Panels Structural VerificationStructural Verification

Mode 1fn = 249 Hz

Finite Element Analysis of Isogrid Structural Assembly


Mode 2fn = 263 Hz

Structural VerificationStructural VerificationFinite Element Analysis of Isogrid Structural

Assembly

Modal Testing of Isogrid Structural Assembly

Mode 1fn = 245 Hz


Mode 2fn = 272 Hz

(vs 263 Hzpredicted)


1. Offset neutral axis nodes of isogrid panels

2. Linear shell elements created 0.02” quadrilateral 0.02” triangular

3. Rigid elements connect neutral axis nodes

Finite Element Analysis of Composite Side Panel


Neutral AxisNeutral Axis

Neutral AxisNeutral Axis

Rigid ElementRigid Element

Beam ElementBeam Element

Shell ElementShell Element

Mode 1fn = 159 Hz

Mode 2fn = 219 Hz

Finite Element Analysis of Composite Side Panel


0

5

10

0

5

10

-5

0

5

x

First Mode (fn = 131 Hz)

y

z

0

5

10

0

5

10

-5

0

5

x

Second Mode (fn = 169 Hz)

y

z

Mode 1fn = 159 Hz


Mode 2fn = 220 Hz


Modal Testing of Composite Side PanelsChladni Patterns:


Mode 1:fn = 159 Hz

Mode 2:fn = 220 Hz

Results demonstrate 22% gain in efficiency using skins

Three-Point-Bend Testing of Composite Side PanelsStructural VerificationStructural Verification

0 0.05 0.1 0.15 0.2 0.25 0.3 0.350

100

200

300

400

500

600Composite Panel Strength Test Results

Displacement, in

Load

, lbs

Side 1Side 2Side 3Side 4Side 5Side 6

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

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:

101

102

103

10410

-3

10-2

10-1

100

ION-F Random Vibration Spectrum

Frequency, Hz

AS

D, G

2 /H

z

Structural VerificationStructural VerificationComposite Structure Environmental Testing

1. Side panel 12. Side panel 23. Zenith panel4. GPS (3 axis)5. CEE (3 axis)6. PPU (3 axis)7. Battery box (3 axis)

Accelerometer Placement

Y

X

ZStructural VerificationStructural Verification

Prototype Environmental Testing

Testing Results:Structural VerificationStructural Verification

Structure survived all tests Fundamental frequency:

– 78 Hz– Zenith panel

Torque coil damaged Modified integration scheme

– Raise fundamental frequency– Prevent damage 10

210

3

10-1

100

101

Log Frequency, Hz

Log

H(f

)

Zenith Panel FRF: Hzz(f)

1. Side panel 12. Side panel 23. Zenith panel4. Honeycomb5. GPS6. GPS Preamp7. CEE8. PPT (3 axis)9. Fuel bar support (3 axis)10. Battery box

Accelerometer Placement

Y

X

ZStructural VerificationStructural Verification

Flight Environmental Testing

Structural VerificationStructural VerificationTesting Results:

Structure survived all tests Fundamental frequency:

– 105 Hz– Nadir panel

Raised fundamental frequency 35%

– Epoxied honeycomb– Relocation of GPS components

102 10310-2

10-1

100

101

Log Frequency, Hz

Lo

g H

(f)

Zenith Panel FRF: Hzz(f)

102 103

10-1

100

101

Log Frequency, Hz

Lo

g H

(f)

CEE FRF: Hzz(f)

Mass Properties TestingStructural VerificationStructural Verification

x y z

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

Finite Element Analysis of Complete ION-F Stack


USUSatUSUSat

DawgstarDawgstar

LightbandLightband

LightbandLightband

HokieSatHokieSat

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

Isogrid and composite structures

Strength and Stiffness Test


Truss l loading fixture Three cantilever tests

– Truss– Isogrid– Composite

Evaluate gain in efficiency using composite structure

Determine boundary conditions

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

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

50

100

150

200

250

300

Load vs Displacement Plot

Displacement, u (in)

Load

, p (

lb)

TrussIsogrid & TrussComposite & Truss

Structural VerificationStructural VerificationStrength and Stiffness Test

Boundary Condition Correlation

0 0.01 0.02 0.03 0.04 0.05 0.06 0.070

50

100

150

200

250

300Load vs Displacement of Truss Fixture

Displacement, u (in)

Loa

d, p

(lb

)

TestAnalysis

1. Model of truss fixture 0.15” linear shell elements Hexagonal protrusion Attached at nodes

simulatingLightband attachment points

2. Correlation of truss data Lightband attachment points Lightband attachment points

fixed on end panelfixed on end panel Load applied at endLoad applied at end Young’s modulus modified Stiffness curves correlate

within 1%


3. 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

Boundary Condition Correlation


0 0.02 0.04 0.06 0.08 0.1 0.120

50

100

150

200

250

300Truss and Composite Structure Data

Displacement, u (in)Lo

ad,

p (

lb)

TestAnalysis

Stiffness curves of model and test data correlate within 5%

Modal Analysis of Complete ION-F Stack


Mode 1fn = 47 Hz

Mode 2fn = 48 Hz

Majority of strain energy concentrated in Lightband Possible stiffness problems revealed

Apply uniform acceleration Fixed base boundary conditions Required design criteria:

Minimum MS = 0.094 > 0 Sine burst stress analysis results

– No yielding or buckling

Stress Analysis of Complete ION-F Stack


ConclusionsConclusions 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

AcknowledgementsAcknowledgements 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

Data Port

Crosslink Antenna

Uplink Antenna

Downlink Antenna

SciencePatches

LightBand

GPS Antenna

Pulsed PlasmaThrusters

Solar Cells

Camera

External ConfigurationDesignDesign

Torque Coils (3)

Rate Gyros (3)

Downlink Transmitter

Cameras

Camera

Electronics Enclosure

Battery Enclosure

MagnetometerCamer

a

PowerProcessing Unit

Crosslink Components

Internal ConfigurationDesignDesign

Pulsed PlasmaThrusters (2)

HokieSat

DesignDesign

Panel 6

Panel 5

Panel 4

Panel 1

Panel 2

Panel 3

Proto FRF10

210

3

10-1

100

101

Log Frequency, Hz

Log

H(f

)

CEE FRF: Hzz

(f)

DesignDesign

1.Previous Designs:• Materials• Bus Designs

design, analysis, fabrication, and testing of a nanosatellite structure

Documents

ft long mass

payload mass

height mass

ft diameter

nanosatellite structurecraig

nasa gsfc

hzmassshels users guide

structural efficiencyal