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The Pennsylvania State University The Graduate School College of Engineering LOW-EARTH-ORBIT TARGET DESIGN FOR OPTICAL CALIBRATION OF THE FALCON TELESCOPE NETWORK A Thesis in Aerospace Engineering by Heather C. Nelson © 2014 Heather C. Nelson Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science December 2014 The thesis of Heather C. Nelson was reviewed and approved* by the following: Sven G. Bilén Associate Professor of Engineering Design, Electrical Engineering, and Aerospace Engineering Thesis Co-Advisor Timothy J. Kane Professor of Electrical Engineering and Meteorology Thesis Co-Advisor George A. Lesieutre Department Head, Department of Aerospace Engineering *Signatures are on file in the Graduate School. ii ABSTRACT In an era in which the orbital space around Earth becomes increasingly crowded with debris, Space Situational Awareness is becoming more and more critical. As a result, innovative and inexpensive methods of tracking and identifying this debris are becoming increasingly popular. The Falcon Telescope Network, a set of 13 small (20-in) telescopes stationed at sites around the world, is one such solution to the issue of debris tracking and identification. The goal of this network is to determine how much information can be obtained about an object in space from the optical signature of an unresolved image. In order to help determine how much information can be learned about a given unknown target, it is useful to have access to a target whose exact properties are known. A target that is passively controlled by a gravity-gradient boom and that has four panels with unique optical signatures (aluminized Kapton film, aluminum, gold, and pyrolitic graphite with two opposing solar panels) is the proposed initial target design for this program. In order to improve the reflection geometry, the sides of the target will fold down after deployment from the P-POD. This target will provide some degree of stabilization, as well as unique optical signatures, while minimizing costs. Future target designs can incorporate more complex stabilization techniques and communication systems that will allow for commanded attitude and exchange of attitude information. iii TABLE OF CONTENTS LIST OF ABBREVIATIONS ............................................................................................ vi LIST OF SYMBOLS ........................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES ............................................................................................................. ix ACKNOWLEDGMENTS .................................................................................................. x Chapter 1: Introduction ....................................................................................................... 1 Problem Statement .......................................................................................................... 1 Telescope Specifications ................................................................................................. 2 Telescope Locations ........................................................................................................ 4 Thesis Contributions ....................................................................................................... 4 Thesis Overview .............................................................................................................. 5 Chapter 2: Background ....................................................................................................... 6 Previous Calibration Campaigns ..................................................................................... 6 CubeSat History .............................................................................................................. 8 Orbital Mechanics ......................................................................................................... 12 External Torques and Disturbances............................................................................... 15 Chapter 3: Imaging Theory ............................................................................................... 24 Diffraction-Limited Performance .................................................................................. 24 Atmospheric Effects ...................................................................................................... 24 Imaging Goal of the Falcon Telescope Network .......................................................... 26 Target Detection ............................................................................................................ 27 Chapter 4: Design Proposals ............................................................................................. 31 “Dumb” Targets ............................................................................................................ 32 Passively Changing Targets .......................................................................................... 33 Passively Controlled Targets ......................................................................................... 36 Actively Controlled Targets .......................................................................................... 37 Chapter 5: Design Proposal Comparison and Selection ................................................... 38 Design Comparison ....................................................................................................... 38 Design Selection: Gravity-Gradient Boom ................................................................... 42 Material Properties ........................................................................................................ 43 iv Design Considerations................................................................................................... 46 Expected Signal ............................................................................................................. 49 Chapter 6: Conclusions ..................................................................................................... 51 Final Design Recommendation ..................................................................................... 51 Recommendations for Future Work .............................................................................. 51 References ......................................................................................................................... 53 v LIST OF ABBREVIATIONS ADCS Attitude Determination and Control System AFOSR Air Force Office of Scientific Research AFIT Air Force Institute of Technology AFRL Air Force Research Lab ALICE AFIT LEO iMESA CNT Experiment AMOS Air Force Maui Optical Station AO Atomic Oxygen AU Astronomical Units CCD Charged-Coupled Device CNT Carbon Nanotube COTS Commercial Off-The-Shelf DARPA Defense Advanced Research Projects Agency FTN Falcon Telescope Network GEO Geosynchronous Earth Orbit HF High Frequency iMESA Integrated Miniaturized Electrostatic Analyzer ISIS Innovative Solutions In Space ISS International Space Station LCS Lincoln Calibration Sphere LEO Low Earth Orbit MEO Middle Earth Orbit MISSE Materials International Space Station Experiments NASA National Aeronautics and Space Administration NRL Naval Research Laboratory NRO National Reconnaissance Organization NSF National Science Foundation PEACE Polymer Erosion and Contamination Experiment PERCS Precision Expandable Radar Calibration Target PMAC Passive Magnetic Attitude Control P-POD Poly Picosatellite Orbital Deployer RCOS Ritchey–Chretien Optical Systems RMS Root Mean Square SRP Solar Radiation Pressure STP Space Test Program SURCAL Surveillance Calibration USAFA United States Air Force Academy vi LIST OF SYMBOLS 훿 Collapsed side panel angle 휁 Zenith angle 휃 Angular resolution 휃 Angle of incidence 휃푟 Angle of reflection 휃푠 Satellite attitude angle 휆 Wavelength 휆퐵 Magnetic latitude factor 휇 Earth’s standard gravitational parameter 휈 Frequency of light 휌 Mean atmospheric density 휙 Solar constant 휔 Tracking speed 푐 Speed of light in a vacuum 푐푚 Center of mass 푐푝푠 Canter of solar pressure ℎ Height above optic 푚 Satellite mass 푟 Altitude of satellite 푟0 Fried parameter 푠 Separation distance (arc length) 푡orb Orbital lifetime 푞 Reflectance factor 퐴 Cross-sectional area 퐴푙 Lens area 퐴푠 Sunlit surface area 퐵 Residual dipole moment 퐶퐷 Drag coefficient 퐶푛 Refractive index structure constant 퐷 Aperture diameter 퐸photon Energy of a single photon 퐹퐺 Reflected solar flux that reaches Earth’s surface 퐹푅 Reflected solar flux at the satellite surface 퐼푦 Moment of inertia about y-axis 퐼푧 Moment of inertia about z-axis 푃 Photons detected per pixel per microsecond Q. E. Quantum efficiency 푅 Distance from center of Earth to satellite 푇 Orbital period 푇푎 Atmospheric drag torque 푇 Gravity-gradient torque 푇푚 Magnetic torque 푇푠 Solar radiation pressure torque 푉 Orbital speed vii LIST OF FIGURES Figure 1: RCOS 20–in f/8.1 Telescope Figure 2: Apogee Alta F47 CCD Sensitivity Figure 3: Locations of Fixed Sites for the FTN and Approximate Ground Station Coverage for Geosynchronous Orbit Figure 4: Example of P-POD and P-POD Packing and Placement Scheme for the Atlas-5 Rideshare System Figure 5: Effects of Major Environmental Disturbances on Spacecraft Attitude System Design Figure 6: Density vs. Altitude for Various F10.7 Values Figure