Simulation of Precise Automatic Radio Frequency Ground Station Tracking For S- Band Satellites Akila Wajirakumara Space Engineering, master's level (120 credits) 2021 Luleå University of Technology Department of Computer Science, Electrical and Space Engineering Simulation of Precise Automatic Radio Frequency Ground Station Tracking For S-Band Satellites MASTER THESIS By Akila Wajirakumara Luleå University of Technology MSc in Space Science and Technology 2021 1 | P a g e CERTIFICATION STATEMENT I hereby certify that this paper constitutes my own product, that where the language of others is set forth, quotation marks so indicate, and that appropriate credit is given where I have used the language, ideas, expressions or writings of another. Signature: .…………………………… Akila Wajirakumara 2 | P a g e ABSTRACT Satellites are often known for possessing invariable motion causing its apparent position to drift in the sky from the perspective of a ground station. If these irregular drifts are not compensated, the performance of the communication link would be greatly affected. Hence, the satellite motion has to be tracked by the ground station antenna. Arctic Space Technologies is a company based in northern Sweden that focuses on highly reliable and secure satellite data handling solutions; main with S-Band satellites in the Low Earth Orbit (LEO). This thesis consolidates a comprehensive research to implement a robust approach for ground stations to establish a secure connection for optimum satellite communication performance. The implementation will be conducted in the form of a software simulation using MATLAB and SIMULINK. The system proposed in this thesis relies on Two Line Elements (TLE) to obtain the parameters for the calculation of the orbital motion of the satellites and providing the azimuth and elevation angles for the antenna to point towards. However, although TLE data are fairly accurate; LEO satellites have a very small time period passing over a ground station for signals to be received and thus it is vital to ensure maximum signal strength is received for optimum performance in satellite communication. In order to do so, a Kalman filter is incorporated to reduce the antenna’s pointing error by adjusting the estimated trajectory in real time and manoeuvre the ground station accordingly. This thesis uncovers through a theoretical review and simulation that accumulates and ensures the investigation of the primary data from the TLE; the main elements affecting the current situation and rectifying them to a certain extent using control systems. It furnishes with guidelines on how Radio Frequency (RF) signals from S-Band LEO satellites can be effectively communicated through a parabolic reflector as a ground station. 3 | P a g e ACKNOWLEDGEMENT I would like to thank my master thesis supervisor Benjamin Fischer for all his support and guidance along with his team at Arctic Space Technologies. Also, to all my colleagues and professors at Luleå University of Technology who provided a fantastic learning experience with a solid foundation to execute my thesis smoothly. I would like to thank my friends, family and my better half Sharon Tanusha for all their support, motivation, and persistence all through this strenuous process. All of you made my goal of accomplishing my MSc degree a reality. Lastly, I would like to thank my master thesis examiner Shailesh Singh Chouhan D.Sc.(Tech.) for taking the time to grade my efforts. 4 | P a g e TABLE OF CONTENTS LIST OF ABBREVIATIONS .................................................................................................... 9 CHAPTER 1: INTRODUCTION ............................................................................................ 10 1.1 Motivation ...................................................................................................................... 10 1.2 Thesis Aim and Problem Statement ............................................................................... 11 1.3 Thesis Objective ............................................................................................................. 11 1.4 Thesis Structure .............................................................................................................. 11 CHAPTER 2: LITERATURE REVIEW ................................................................................. 12 2.1 Background of Satellite Communication ....................................................................... 12 2.1.1 Low Earth Orbit ....................................................................................................... 12 2.1.2 S-Band Satellite ....................................................................................................... 14 2.1.3 Parabolic Reflector .................................................................................................. 15 2.1.4 Link Budget ............................................................................................................. 20 2.2 Orbital Mechanics .......................................................................................................... 21 2.2.1 Two Line Element (TLE) ........................................................................................ 21 2.2.2 Orbital Elements ...................................................................................................... 24 2.2.3 Perifocal coordinate system ..................................................................................... 27 2.2.4 ECI coordinate system ............................................................................................. 28 2.2.5 ECEF coordinate system ......................................................................................... 29 2.2.6 Calculating the azimuth and elevation angles and distance from ground station .... 30 2.3 CONTROL MODEL FOR GROUND STATION TRACKING ................................... 32 2.3.1 Kalman Filter ........................................................................................................... 32 CHAPTER 3: METHODOLOGY ........................................................................................... 37 3.1 Extract Orbital Elements from TLE Data ...................................................................... 37 3.2 Satellite’s Orbital motion Simulation ............................................................................. 38 3.3 Determine the Satellite motion from the Ground Station .............................................. 40 3.4 Formulate a Mathematical Model for the System .......................................................... 43 3.5 Signal Transmission and Reception Simulation ............................................................ 49 3.6 Controller Simulation ..................................................................................................... 51 CHAPTER 4: RESULTS ......................................................................................................... 55 4.1 Comparing the Azimuth and Elevation angles ............................................................... 55 4.2 Comparing the pointing errors ....................................................................................... 56 4.3 Discussion ...................................................................................................................... 59 5 | P a g e CHAPTER 5: CONCLUSION ................................................................................................ 60 5.1 Summary ........................................................................................................................ 60 5.2 Limitations ..................................................................................................................... 61 5.3 Future Work ................................................................................................................... 61 REFERENCES ........................................................................................................................ 62 APPENDIX .............................................................................................................................. 65 Additional Figures ................................................................................................................ 65 MATLAB Scripts ................................................................................................................. 69 6 | P a g e TABLE OF FIGURES Figure 1: Satellite Orbits (ESOA, 2016) .................................................................................. 13 Figure 2: Parabolic Antenna (Tutorialspoint, 2020) ................................................................ 15 Figure 3: Mathematical diagram of a parabolic reflector ........................................................ 16 Figure 4: Pointing Error (Barth et al, 2018) ............................................................................. 18 Figure 5: Diagrammatic representation of an Elevation over Azimuth mounting (Crawford & Brush, 1995) ............................................................................................................................. 19 Figure 6: Comparison of real and reference trajectories (Braga, 2018) .................................. 22 Figure 7: TLE Data example (Rijal, 2017) .............................................................................. 22 Figure 8: TLE format description (Rahal, 2008) ..................................................................... 23