LEE- Savunma Teknolojileri-Yüksek Lisans

Bu koleksiyon için kalıcı URI

http://hdl.handle.net/11527/19451

Gözat

Yazar "Aslan, Alim Rüstem" ile LEE- Savunma Teknolojileri-Yüksek Lisans'a göz atma
  • Öge
    Development of a comprehensive simulation software for spacecraft missions
    (Graduate School, 2023-01-27) Gül, Emirhan Eser ; Aslan, Alim Rüstem ; 514191007 ; Defense Technologies
    The growth of satellite mission, especially CubeSats, in terms of complexity and capabilities has required the development of dedicated orbit simulation software for mission planning and analysis. This thesis presents the development and uses of a simulation software that will be used to aid in the design of spacecraft missions. The process of developing the software architecture is described in stages from software requirement analysis to test and verification of the final implementation. During a space mission, a spacecraft may be placed in a variety of orbits for different purposes. Preliminary mission design needs to consider all mission phases to meet the needs of more complex missions. To effectively design an orbit, it is important to clearly define the purpose of the orbit and regularly review and reassess this purpose as mission requirements evolve or become more defined. It is also important to consider alternative orbit designs, as there may be multiple options that are viable. For example, a single large satellite in a geosynchronous orbit or a group of smaller satellites in low-Earth orbit may both be effective for communication purposes. Multiple different designs are often compared to find the orbit that best accommodate the mission requirements. There are various criteria that have to be considered according to the mission, such as determining the communication links between satellites and ground stations, and finding the time intervals when there is a pass or eclipse, which allow determining the requirements of communication and power systems. For an Earth-observing satellite, the orbit that has the most revisit time for desired locations and properties of the optical system such as the field of view should be determined. The aim of this work is to make use of the software tools to create a simulation software that provides a framework for efficient analysis and planning of satellite missions that include earth observation, communication, and scientific objectives in order to helps the mission design process by giving the ability to make fast and reliable decisions regarding the satellite system requirements. The developed software implements multiple orbit propagators, with the most prominent being the High-precision Orbit Propagator (HPOP) which takes into account all of the forces that can be modelled so far. However, physics-based models alone are insufficient for accurately predicting orbits and avoiding collisions, as demonstrated by previous collisions caused by such predictions. Our knowledge of the physical world is not sufficient enough to create perfect models as it is near impossible to predict some perturbations precisely, such as solar activity which is only an approximation based on statistical data, as well as the atmosphere models and the area of the satellite that drag force affects, which also change depending on the attitude model. In order to improve the accuracy of these models, a machine-learning approach that utilizes the past flight data is proposed. Models of orbit prediction errors can be learned directly from a large amount of historical data, allowing for predictions without explicitly modeling forces or perturbations. Hence, a neural-networks model was trained and its impact was demonstrated. The software is developed using various programming languages. The user interface is programmed in JavaScript, using HTML and CSS. Orbital analyses and other computation heavy tasks were performed in C++ as it has the benefits of modular design, less resource use and fast execution speed, as well as good portability. Python was used for model training and artificial intelligence methods due to the enormous number of scientific libraries it includes. Electron framework was used to provide cross-platform compatibility. For real-time data visualization in both 2D and 3D, the Cesium framework was implemented using Bing as data provider for satellite imagery and terrain modelling. The simulation results show that the software succeeds in attaining high execution speed and precision. The results indicate that the proposed solution can be useful in reducing time and effort put into the mission design process as well as increase the rate of success for both Earth and interplanetary missions. The developed software can be used for real-world mission design and operations, as a tool for education and engineering studies, and public engagement. The structure of the thesis is as follows. First the mathematical background and celestial relationships that are widely used in mission planning are explained along with the algorithms used to implement them into the software. These include coordinate system transformations, various orbital elements, and time systems. Then orbital propagation is explained starting from two-body motion, which is the basis for all equations of motion, followed by adding perturbations and other forces acting on the satellite to facilitate the high-precision numerical propagator. Analytical propagators that are widely used are explained as well. Then, the design and implementation of a neural-networks model that is trained to improve the accuracy of the numerical propagators is described. The next chapter focuses on the simulation environment and the capabilities of the software. It is possible to easily create mission-specific orbits such as SSO, GEO, and Molniya, predict the visibility of satellites from different locations on the ground, determine the eclipse intervals, compute communication link budget, analyze on-orbit power generation, and perform basic maneuvers within the simulation environment. The software principles, architecture, development process, and user interface design is thoroughly explained as well. Finally, verifications using real data and satellite observations are performed and results are presented, which show that the developed software is ready for real mission use, and possible future developments are discussed.
  • Öge
    Miniature electrical propulsion system design for cube satellites
    (Graduate School, 2022-08-11) Çatal, Egemen ; Aslan, Alim Rüstem ; 514191041 ; Defense Technologies
    Cube satellites, also known as cubesats, are compact spacecraft that are made up from 10x10x10cm sized cubes. Each one of these cubes are named units or U for short. Based on mission requirements the size of the cubesat can range from 1U to 27Us. Ever since their establishment in 1999 they have been used for academic and educational purposes. Advancements in the miniature electronic now enables these cubesats to perform at a higher grade and be used for commercial and scientific missions. Their compact nature make them affordable and easy to access. This compactness also means that the power and mass budget is very limited compared to the bigger satellite classes. Thanks to these restraints very few cubesats with propulsion systems have been launched into space to date. A propulsion system has the potential to provide greater missions envelope, extended lifespan, precise control for close formation flying and space debris reduction. Propulsion systems are grouped under two main categories as chemical and electric propulsion systems. Compared to the electrical propulsion systems chemical systems provide greater thrust at the cost of reduced efficiency. Since greater efficiency is vital due to compact nature of the cubesat, electric propulsion systems constitute a tempting solution as a propulsion systems. Among them, RF ion thrusters are viable candidates due to their scalability and simple design. Ion thrusters provide greatest propellant consumption efficiency among electric propulsion systems which makes them very preferable. This study presents the design of an RF ion thruster fit to be used in a cubesat. Theoretical knowledge and calculations are presented and the system is calculated to provide 550 µN of maximum thrust and up to 3000 s of specific imoulse. Design and experimental details are provided and based on these designs the actual model of the thruster is manufactured. Manufactured model was then tested at the Space Technologies Laboratory of Bogazici University (BUSTLab). During the tests it was observed that the ions are successfully accelerated and thrust is generated. Measurements of actual thrust levels and ion beam characteristics are left as future work.