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963837070-MIT.Pdf Characterization of Redundant UHF Communication Systems for CubeSats by Stephen J. Shea Jr. B.S. Astronautical Engineering United States Air Force Academy, 2014 SUBMITTED TO THE DEPARTMENT OF AERONATICS AND ASTRONAUTICS IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN AERONAUTICS AND ASTRONAUTICS AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUNE 2016 C 2016 Massachusetts Institute of Technology. All rights reserved. Signature of Author: Signature redacted Department of AfironauticWoUnd XeronaTtics May 19, 2016 Certified by: _____Signature redacted KerCahoy Assistant Professor of Aeronautics and Astronautics Thesis Supervisor Accepted by: Signature redacted / Paulo C. Lozano Associate Professor of Aerofautics and Astronautics Chair, Graduate Program Committee MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUN 2 8 2016 LIBRARIES ARCHIVES The opinions expressed in this thesis are the author's own and do not reflect the view of the United States Air Force, the Department of Defense, or the United States government. 2 Characterization of Redundant UHF Communication Systems for CubeSats by Stephen Joseph Shea, Jr Submitted to the Department of Aeronautics and Astronautics on , in partial fulfillment of the requirements for the degree of Master of Science in Aeronautics and Astronautics Abstract In this thesis we describe the process of determining the likelihood of two different Ultra High Frequency (UHF) radios damaging each other on orbit, determining how to mitigate the damage, and testing to prove the radios are protected by the mitigation. The example case is the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat. We conducted a trade study over three available radio architectures: primary radio and a beacon, high speed primary and low speed backup radios, and two fully capable radios. MiRaTA's communication architecture is a high speed primary radio and a low speed backup radio. This configuration was chosen to balance between capability and size, mass and power requirements. We present the process of redesigning the communication from its first revision with a primary radio and a beacon to a high speed primary radio and a low speed backup radio. We discuss the important factors that drive the architecture decisions and then the radio system component selections for CubeSat radios. The main factors for MiRaTA were form factor and power efficiency. The primary radio is the L-3 Cadet-U Radio and the backup radio is a MIT custom Micron Radio based on the Planet Labs Low Speed Transceiver's design. The Cadet Radio is 468 MHz and 3 MHz bandwidth for downlink and 450 MHz and 20 kHz for uplink. The Micron Radio is 401 MHz downlink, 450 MHz uplink and both signals have a bandwidth of 20 kHz. The primary and backup radios are both UHF-band, which means there is a risk of the radios damaging each other on orbit that we must factor into design and testing. After presenting the process of determining the damage thresholds of the radios and the signal strength they need to be protected from. We find that the backup radio may be at higher risk of being damaged than the primary radio, and discuss mitigation strategies. Our goal is to modify the communication system design to make sure neither radio is damaged. After reviewing the available methods of mitigations, we decided to add a limiter to the backup radio and add a high pass filter to protect the primary radio. We test the mitigation strategies on both radios. We find that with the limiter installed on the backup radio, it can be connected to a signal generator with power incremented up to 25 dBm (which is 8 dB above the damage threshold without including a limiter) without a degradation in 3 performance. We install a filter on the primary radio's input, and demonstrate that it attenuates the backup radio's signal without degrading the primary radio's performance. We then test both radios together in a test representative of operational scenarios and find that they appear to be sufficiently protected. We discuss the success of this approach and how flight testing should be conducted as well as how it might be implemented on other CubeSats. Thesis Supervisor: Kerri Cahoy Title: Assistant Professor of Aeronautics of Astronautics 4 Acknowledgments A great number of people of have helped me along the way to my Master's. First and foremost is my advisor Professor Kerri Cahoy. She was willing to take a chance on me and pushed me to learn a new focus of spacecraft engineering. And I have learned so much about communications. I would like to acknowledge Mike Shields at Lincoln Laboratory, from whom I learned so much about RF engineering. A significant portion of the knowledge I applied in this thesis I learned directly from him and another significant portion of the testing was done with him. I would also like to acknowledge Mike DiLiberto at Lincoln Laboratory with whom I learned how operate and test the Cadet as well as properly plan tests and operate Ubuntu. Andy Siegel of Lincoln Laboratory was another significant teacher during a circuit level testing campaign of the Cadet. I would like to acknowledge Col John Kuconis, USAF (ret.) and Bill Blackwell for selecting me for the LL Military Fellows Program and finding funding for me to attend MIT and work with the many great engineers at Lincoln Laboratory. I would also like to acknowledge everyone on the Microwave Radiometer Technology Acceleration (MiRaTA) team. It has been a pleasure working with you all. It has been fantastic getting to know many in the MIT community, particularly those at the AeroAstro Muddy Fridays and those in the Tech Catholic Community. I'd like to acknowledge those that helped get to MIT, such as my many mentors at United States Air Force Academy like Lt Col David Barnhart, USAF. Lastly I would not be where I am today without the incredible love and support of my parents Stephen and Maria Shea. 5 Table of Contents A b stra ct ........................................................................................................................................ 3 Acknowledgm ents........................................................................................................................ 5 List of Figures.............................................................................................................................. 9 1 Introduction.......................................................................................................................... 12 1.1 Introduction ............................................................................................................... 12 1.2 Exam ples of CubeSat Failures .............................................................................. 12 1.2.1 AAU-1................................................................................................................ 12 1.2.2 CAPE-1.............................................................................................................. 13 1.2.3 M icroM A S-1 ................................................................................................... 14 1.3 M iRaTA Overview ................................................................................................. 17 1.4 Redundant Com m unication System s...................................................................... 18 1.4.1 Prim ary Radio and Secondary Beacon Architecture ..................................... 18 1.4.2 Primary High Speed Radio and Low Speed Back Up Radio Architecture........ 19 1.4.3 Two Full Capability Radios Architecture ..................................................... 20 1.5 M iRaTA 's Radio Architecture D ecision............................................................... 20 1.5.1 Overview ............................................................................................................ 20 1.5.2 Rationale Against Beacon and Primary Radio Architecture........................... 22 1.5.3 Rationale Against Two Fully Capable Radios Architecture........................... 23 1.5.4 UHF Band Conflict ........................................................................................ 23 1.5.5 Methods for Mitigating Interference with Multiple UHF Radios.......... 24 1.5.6 MiRaTA's Two Radio Interference Mitigation Approach ............................. 27 2 Approach.............................................................................................................................. 28 2.1 M icron Radio Decision .......................................................................................... 28 2.1.1 Key Factors in Backup Radio Decision.......................................................... 28 6 2.1.2 Radios Considered .......................................................................................... 31 2.2 Im plem enting the M icron Radio ............................................................................ 34 2.2.1 Options............................................................................................................... 34 2.2.2 Decision ............................................................................................................. 35 2.3 Dam age Analysis Approach................................................................................... 35 2.3.1 Basic Radio Design ........................................................................................ 35 2.3.2 A ssessing Dam age Potential.......................................................................... 36 2.3.3
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