AeroSpace and Ocean Engineering

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AeroSpace and Ocean Engineering
HokieSat Virginia Techs Nanosatellite Program

• Chris HallAssociate Professor
• AeroSpace and Ocean Engineering
• Virginia Polytechnic Institute and State
  University

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Virginia Polytechnic Institute and State
University

• Founded as a Land Grant College in 1872
• Offers 200 degree programs to 25,000 students
• 100 buildings on a 2600 acre campus in Blacksburg
• 1500 full-time faculty
• 500M annual budget
• 8 different colleges

Burruss Hall is the main administration building
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College of Engineering

• Twelve departments offer 15 degree programs at
  B.S., M.S., and Ph.D. level
• Graduate program ranked 16th in the nation by
  professional engineers and recruiters
• 30 different Research Centers, e.g.
• Commercial Space Communications
• Intelligent Materials, Systems, and Structures
• Multidisciplinary Analysis and Design Center for
  Advanced Vehicles (MAD)
• More than 300 full-time faculty
• Annual research expenditure of more than 60M
• 570 M.S. 99 Ph.D. degrees awarded in 1998

Norris Hall is the main Engineering building
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AeroSpace Engineering at Virginia Tech

• Aerospace and Ocean Engineering Department
  Overview
• Space Systems Research
• Space Systems Design
• HokieSat!

Randolph Hall houses AOE, as well as
Engineering Fundamentals, Mechanical
Engineering, and Chemical Engineering
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Aerospace and Ocean Engineering

• 19 Faculty in
• aerodynamics and hydrodynamics
• structural mechanics
• dynamics and control
• design
• Yearly graduation rate of approximately
• 49-60 Bachelor of Science
• 20-25 Master of Science
• 8-12 Doctor of Philosophy
• 3.5 million annual research funding
• Extensive research facilities
• Innovative wind tunnels
• Water tunnels
• Full-scale flight simulator
• Spacecraft simulator

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National Ranking

• 1. Massachusetts Institute of Technology
• 2. California Institute of Technology
• 3. Stanford University (CA)
• 4. University of MichiganAnn Arbor
• 5. Georgia Institute of Technology
• 6. Purdue UniversityWest Lafayette (IN)
• 7. University of IllinoisUrbana-Champaign
• 7. University of TexasAustin
• 9. Princeton University (NJ)
• 10. Virginia Tech
• Aerospace Engineering Departments in U.S. News
  and World Report

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Recent Faculty Honors

• Gene Cliff
• 1999 Deans Award for Research Excellence
• Bernie Grossman
• 2000-2001 President Aerospace Department Chairs
  Association
• Chris Hall
• 2001 Deans Award for Teaching Excellence
• Rakesh Kapania
• 2000 Deans Award for Research Excellence
• Fred Lutze
• 1999 AIAA Faculty Advisor Award (National Award)
• Jim Marchman
• 1999 Deans Award for Advising
• Joe Schetz
• 1999 AIAA Contribution to Society Award (National
  Award)
• Roger Simpson
• AIAA Vice President - Publications

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Graduation Statistics
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Space Systems Research

• Formation Flying
• attitude and orbit dynamics and control
• Spacecraft Dynamics and Control
• with gimbaled momentum wheels (GMWs)
• Integrated Energy Storage and Attitude Control
• using high-speed flywheels as batteries and
  GMWs
• Optimal Continuous Thrust Orbit Transfer
• approximations for indirect methods
• Supported by Air Force, NASA, and NSF
• Graduated 31 M.S. students and 4 Ph.D. students
• Currently advising 7 M.S. students and 1 Ph.D.
  student
• 25 refereed journal articles and 36 conference
  papers

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Senior Design at VT

• All seniors complete one year of capstone
  design
• two semesters with 3 credit hours each semester
• Choose between Aircraft and Spacecraft(Ocean
  Engineering students choose Ship Design)
• Students work in groups of 6 to 12 students
• typically include freshmen in second semester
• Access to Senior Design Lab
• PCs, Workstations, Printers, Plotters, Software
• Typically compete in national and international
  design competitions
• In 1998, two 1st Place, one 2nd Place, one 3rd
  Place

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Senior Design 99

• Aug 1998 - May 1999
• 5 different projects, 7 different teams
• Aircraft Projects
• 2 projects, 4 teams
• 17 AE seniors, 3 AE freshmen, 6 other seniors
• international collaboration - 13 British
  students
• industry sponsorship - Boeing British
  Aerospace
• Spacecraft Projects
• 3 projects, 3 teams
• 26 AE seniors, 2 AE freshmen, 2 AE juniors
• inter-university collaboration - 2 Georgia Tech
  students
• NASA sponsorship - Goddard Space Flight Center

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Space Design Projects 99

• Single-Stage-to-Orbit Reusable Launch Vehicle
  Using Rocket-Based Combined Cycle Technology
• 8 AE seniors 2 Georgia Tech students
• took 1st Prize in AIAA Design Competition
• Virginia Tech Ionospheric Scintillation
  Measurement Mission
• 9 AE seniors, 2 AE freshmen, 2 AE juniors, 20 EE
  juniors/seniors
• also called HokieSat - 1st VT-built
  spacecraft
• 15 kg nanosatellite will launch on shuttle in
  2003
• funded by Air Force and NASA
• Leonardo a small group of Earth-sensing
  satellites flying in formation
• 8 AE seniors, 1 AE freshman
• supporting research sponsored by NASA Goddard

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HokieSat
University Nanosatellites

• 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

AFRL Multi-Satellite Deployment System (MSDS)
NASA Shuttle Hitchhiker Experiment Launch
System (SHELS)
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The ION-F Mission

• The Ionospheric Observation Nanosatellite
  Formation mission addresses the following science
  topics
• Evolution of ionospheric plasma structure,
  irregularities and scintillations
• Spectral characteristics of ionospheric plasma
  waves
• Global latitudinal distribution of ionospheric
  plasma structures and irregularities
• Accomplished using
• Plasma Impedance Probe (PIP)
• Global Positioning System (GPS)
• Uniqueness of measurements lies in the ability to
  vary satellite separation
• Complement data collected with ground-based radar
  and concurrent observations from other satellites

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ION-F Mission
Configuration
Multiple Satellite Deployment System
Scenario
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Structural Design
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1

• Design
• Analysis
• Fabrication
• Testing

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4
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Structural Design

• 18.25 major diameter hexagonal prism
• 12 tall
• 39 lbs (18 kg)

• Isogrid Structure
• Aluminum 6061 T-651
• Composite Side Panels
• 0.23 isogrid
• 0.02 skins

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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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Internal Configuration
Crosslink Components
Cameras
Power Processing Unit
Torque Coils (3)
Magnetometer
Camera
Pulsed Plasma Thrusters (2)
Camera
Battery Enclosure
Downlink Transmitter
Electronics Enclosure
Rate Gyros (3)
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Static Analysis

• Requirement Withstand 11.0 g accelerations
  (all directions)
• Margin of Safety ? 0, where
• Factor of Safety (FS)
• Finite Element Analysis Results

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Dynamic Analysis
Finite Element Analysis of Isogrid Side Panel
(Without Skin)
Mode 1 fn 131 Hz
Mode 2 fn 171 Hz
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Dynamic Analysis
Finite Element Analysis of Complete Isogrid
Structure (Without Skin)
Mode 1 fn 249 Hz
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Dynamic Analysis
Finite Element Analysis of Complete Isogrid
Structure (Without Skin)
Mode 2 fn 263 Hz
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Dynamic Analysis
Finite Element Analysis of Complete ION-F Stack

• Requirement First mode natural frequency
  gt100 Hz
• Results First mode natural frequency 74.6
  Hz
• Solution Stiffen joints around attachment
  points to raise first mode natural frequency
  100Hz

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Fabrication
Composite structure comprised of 0.23 isogrid
and 0.02 skin
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Test Requirements

• 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

• Random Vibe Requirements

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Static Testing
Strength stiffness test of structure without
skin panels
Strength stiffness test of loading fixture
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Static Testing
Strength stiffness test of structure with skin
panels

• 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

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Dynamic Testing
Modal (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

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Dynamic Testing
Modal Testing of Side Panels (Without Skin)
Mode 1 fn 131 Hz (vs 131 Hz predicted)
Mode 2 fn 169 Hz (vs 171 Hz predicted)
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Dynamic Testing
Modal Testing of Side Panels (With Skin)
Mode 1 fn 213 Hz (vs 131 Hz without skin)
Mode 2 fn 453 Hz (vs 169 Hz without skin)
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Dynamic Testing
Modal Testing of Structure (Without Skins)


Mode 2 fn 272 Hz (vs 263 Hzpredicted)
Mode 1 fn 245 Hz (vs 249 Hz predicted)
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Dynamic Testing
Accelerometer Placement

1. X-axis control
2. Y-axis control
3. Z-axis control
4. Side panel 1
5. Side panel 2
6. Zenith panel
7. GPS (3 axis)
8. CPU (3 axis)
9. PPU (3 axis)
10. Battery box (3 axis)

• Structure survived
• all tests
• Determined component locations to raise natural
  frequencies

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Summary

• 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

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Acknowledgements

• Air Force Research Lab
• 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
• Members of ION-F