System Identification of a Nanosatellite Structure Craig L. Stevens, Jana L. Schwartz, and Christopher D. Hall Aerospace and Ocean Engineering Virginia Tech Blacksburg, Virginia Session 7, Earth and Lunar Missions AAS/AIAA Astrodynamics Conference Quebec City, Canada July 30 – August 2 2001
System Identification of a Nanosatellite Structure
Feb 09, 2016
System Identification of a Nanosatellite Structure. Craig L. Stevens, Jana L. Schwartz, and Christopher D. Hall Aerospace and Ocean Engineering Virginia Tech Blacksburg, Virginia. Session 7, Earth and Lunar Missions AAS/AIAA Astrodynamics Conference Quebec City, Canada - PowerPoint PPT Presentation
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System Identification of a Nanosatellite Structure
Craig L. Stevens, Jana L. Schwartz,and Christopher D. Hall
Aerospace and Ocean EngineeringVirginia Tech
Blacksburg, Virginia
Craig L. Stevens, Jana L. Schwartz,and Christopher D. Hall
Aerospace and Ocean EngineeringVirginia Tech
Blacksburg, Virginia
Session 7, Earth and Lunar MissionsAAS/AIAA Astrodynamics Conference
Quebec City, CanadaJuly 30 – August 2 2001
Session 7, Earth and Lunar MissionsAAS/AIAA Astrodynamics Conference
Quebec City, CanadaJuly 30 – August 2 2001
OverviewOverview
1.Introduction2.Design3.Analysis4.Fabrication5.Testing6.Conclusions
2
4
3
5
NASA Shuttle Hitchhiker Experiment
Launch System (SHELS)
AFRL Multi-Satellite
Deployment System (MSDS)
University Nanosatellites
IntroductionIntroduction• Virginia Tech Ionospheric
Scintillation Measurement Mission (VTISMM) aka HokieSat
• Ionospheric Observation Nanosatellite Formation (ION-F)– Utah State University– University of Washington
– Virginia Tech• University Nanosatellite Program
– 2 stacks of 3 satellites
• 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
without recontacthazards.
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
= T0 + 102 hours, 4 secs
3CSION-F
USUSat
Dawgstar
HokieSat
Multiple Satellite
Deployment System
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
without recontacthazards.
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
= T0 + 102 hours, 4 secsT4T1 = 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
without recontacthazards.
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
= T0 + 102 hours, 4 secs
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
without recontacthazards.
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
= T0 + 102 hours, 4 secs
MissionMissionConfiguration:
Scenario:
• Isogrid Structure• Aluminum 6061 T-
651• Composite Side
Panels– 0.23” isogrid– 0.02” skins
HokieSat• 18.25” major diameter hexagonal
prism• 12” tall • 39 lbs (~18 kg)
DesignDesign
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)
max (psi)
ult (psi) MS(ult)
v 7240 38000 1.019
Requirement: Withstand ±11.0 g accelerations (all directions) Margin of Safety 0, where
Factor of Safety (FS)
Finite Element Analysis Results
01)()(
ssActualStreFS
tressAllowableSMS
Static AnalysisStatic Analysis
AnalysisFS Limit 2FS Ultimate 2.6
Mode 1fn = 131 Hz
Dynamic AnalysisDynamic Analysis
Mode 2fn = 171 Hz
Finite Element Analysis of Isogrid Side Panel (Without Skin)
Dynamic AnalysisDynamic Analysis
Mode 1fn = 249 Hz
Finite Element Analysis of Complete Isogrid Structure (Without Skin)
Dynamic AnalysisDynamic Analysis
Mode 2fn = 263 Hz
Finite Element Analysis of Complete Isogrid Structure (Without Skin)
Requirement: First mode natural frequency: >100 Hz
Results: First mode natural frequency: 74.6 Hz
Solution: Stiffen joints around attachment points to raise first mode natural frequency ~100Hz
Dynamic AnalysisDynamic AnalysisFinite Element Analysis of Complete ION-F
Stack
FabricationFabrication
Composite structure comprised of 0.23” isogrid and 0.02” skin
Static test Stiffness test to simulate expected loading conditions during launch
Sine sweep test Vibration test to determine free and fixed-base natural frequency
Sine burst test Vibration test to verify structural strength at extreme loads
Random vibration test Vibration test to verify structural integrity
Test RequirementsTest Requirements
Random Vibe Requirements:
Strength & stiffness test of structure without skin panels
Strength & stiffness test of loading fixture
Static TestingStatic Testing
Strength & stiffness test of structure with skin panels
Static TestingStatic Testing
• 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
Dynamic TestingDynamic TestingModal (tap) Testing of Side Panels
• Hammer provides impulsive input
• Accelerometer measures accelerations used to characterize natural frequencies
• Tap testing with and without skins
• 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
(vs 171 Hz predicted)
Dynamic TestingDynamic TestingModal Testing of Side Panels (Without Skin)
0
5
10
0
5
10
-5
0
5
x
First Mode (fn = 213 Hz)
y
z
0
5
10
0
5
10
-5
0
5
x
Second Mode (fn = 453 Hz)
y
z
Dynamic TestingDynamic Testing
Mode 1fn = 213 Hz
(vs 131 Hz without skin)
Mode 2fn = 453 Hz
(vs 169 Hz without skin)
Modal Testing of Side Panels (With Skin)
Modal Testing of Structure (Without Skins)
Dynamic TestingDynamic Testing
Mode 1fn = 245 Hz
(vs 249 Hz predicted)
Mode 2fn = 272 Hz
(vs 263 Hzpredicted)
1. X-axis control2. Y-axis control3. Z-axis control4. Side panel 15. Side panel 26. Zenith panel7. GPS (3 axis)8. CPU (3 axis)9. PPU (3 axis)10. Battery box (3 axis)
Accelerometer Placement
X
Y
Z
Dynamic TestingDynamic Testing
•Structure survived all tests
•Determined component locations to raise natural frequencies
ConclusionsConclusions•Aluminum isogrid increases structural performance at reduced mass
•Modal testing verifies accuracy of isogrid side panel finite element model within ~1% error
•Modal testing demonstrates 26% increase in structural stiffness of side panel by adding thin aluminum skins
•Analyses and experiments verify structure satisfies all Shuttle payload requirements
AcknowledgementsAcknowledgements•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 ION-F
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