Attitude Determination and Control System for Low Earth Orbit CubeSat Considering Operation Scenario

장주영 서울대학교 대학원 2016 국내석사

SNUGLITE (Seoul National University GNSS Laboratory satellITE), a cubesat scheduling for launch in 2017, must maintain nadir pointing attitude control in order to obtain mission data successfully and send them to ground station using S-band antenna. This thesis will examine the ADCS (Attitude Determination and Control System) algorithm and how the proposed algorithm satisfies the ADCS requirements for this particular operation scenario. The ADCS is composed of 3-axis MEMs gyroscope sensor, 2-axis coarse photodiode type sun sensors, 3-axis MEMs magnetometer, dual frequency GPS receivers, and 3-axis magnetic torquers. In the simulation environment, studies were done on the eclipse and various disturbance torques, including gravity gradient torque, solar radiation torque, and aerodynamic torque. The LQG (Linear Quadratic Gaussian) controller has been chosen for ADCS algorithm for SNUGLITE. Furthermore, this thesis will provide SILS (Simulation In the Loop System)—which takes low earth orbit environments into account—to verify the proposed ADCS algorithm. Due to the fact that the precise launch schedule of the cubesat has not yet been decided, the orbit elements have been chosen for the worst case scenario: it will provide a maximum eclipse time in altitude of 600[km] from the circular sun’s synchronous orbit. In order to monitor the low earth orbit environment which has a direct effect on the attitude dynamics, we developed a low earth orbit simulator that is comprised of attitude dynamics and orbit dynamics which can influence each other. We used two computers, one for the ADCS algorithm and one for the orbit environment, and transmitted data using serial communication. Thus, the team of scholars after us could use this SILS we developed to further the research on PILS (Processor In the Loop System). The operation scenario consists of two parts. The first step starts from deployment of cubesat from P-POD (Poly Picosatellite Orbital Deployer), and detumbling using B-dot control. Second, the use of LQG controller for nadir pointing control. However, the second part of the operation scenario is also divided into two segments. In the first phase, only GPS is used as a payload but magnetic boom is not deployed, while in the second phase, magnetic boom is used for the earthquake mission. After evaluating the simulation results, we have come to a conclusion that all the ADCS requirements were met. For instance, the attitude estimation errors were less than 5 [deg] in eclipse and less than 2 [deg] per day. In addition, the attitude control errors were less than 10 [deg] in eclipse and less than 5[deg] per day. Finally, the ADCS algorithm enabled the cubesat to turn over even in an up-side-down position. In summary, this thesis developed and verified the ADCS algorithm which was based on the Matlab by using the LQG controller; moreover, it offers the space environment simulator which could be used for the PILS (Processor In the Loop System) study in the future. We expect these results will contribute to making SNUGLTIE’s mission a success.

Lifetime Enhancement of Real-Time Satellite Embedded Systems via Multi-Core Task Mapping and DVFS

김범식 아주대학교 2021 국내석사

Recently, thanks to the miniaturization and high performance of commercial-off-the-shelf (COTS) computer systems, small satellites get popular. However, due to the very expensive launching cost, it is critical to reduce the physical size and weight of the satellite systems as in cube satellites (CubeSats), making it infeasible to install high capacity batteries or solar panels. Thus, the low-power design is one of the most critical issues in the design of such systems. In addition, as satellites make periodic revolutions around the Earth in a vacuum, their operating temperature varies greatly. For instance, in a low earth orbit (LEO) CubeSats, called SwissCube, the temperatures vary from 30 to −30 degrees Celsius, resulting in a big thermal cycle (TC) in the electronic parts that is known to be one of the most critical reliability threats. Moreover, such LEO CubeSats are not fully protected by active thermal control and thermal insulation due to the cost, volume, and weight problems. In this paper, I propose to utilize temperature sensors to maximize the lifetime reliability of the LEO satellite systems via multi-core mapping and dynamic voltage and frequency scaling (DVFS) under power constraint. As conventional reliability enhancement techniques primarily focus on reducing the temperature, it may still cause enlarged TCs, making them even less reliable. On the contrary, I try to maintain the TC optimal in terms of reliability with respect to the given power constraint. Experimental evaluation shows that the proposed technique improves the expected lifetime of the satellite embedded systems by up to 8.03 times in the simulation of Nvidia’s Jetson TK1. 최근 상용 기성품(Commercial Off-The-Shelf, COTS) 컴퓨터 시스템의 소형화 및 고성능 덕분에 소형인공위성에서 인기를 얻고 있다. 그러나 로켓 발사 비용이 매우 비싸기 때문에 큐브 위성(Cube Satellites, CubeSats)과 같이 물리적인 크기와 무게를 줄이는 것이 굉장히 중요하고, 고용량 배터리나 태양광 패널을 장착하기에 어려움이 있다. 따라서 저전력 설계는 이러한 시스템 설계에서 가장 중요한 문제 중 하나이다. 또한 인공위성은 진공 상태에서 지구 주위를 주기적으로 회전하며 동작 온도가 크게 달라진다. 예를 들어 SwissCube라는 저궤도(Low Earth Orbit, LEO) 큐브 위성의 온도가 섭씨 약 30℃에서 -30℃로 변하며 전자 부품에 큰 열주기(Thermal Cycle, TC)를 발생하고, 이는 가장 중요한 신뢰성 위협 중 하나로 알려져 있다. 또한 이러한 저궤도 큐브위성은 비용, 부피, 및 무게 제약으로 인해 능동적인 열 제어 및 단열로 충분히 보호하기에 어려움이 있다. 본 논문에서는 전력 제약에서 저궤도 인공위성 시스템의 수명 신뢰성을 최대화하기 위한 멀티 코어 매핑과 동적 전압 및 주파수 스케일링(Dynamic Voltage and Frequency Scaling, DVFS) 기법을 제안한다. 기존의 신뢰성 향상 기법들은 주로 온도를 낮추는 것을 중점으로하는데, 이는 저궤도 인공위성 환경에서 열주기를 확대하여 오히려 신뢰성을 악화시킬 수 있다. 이에 반하여 본 논문에서는 주어진 전력 제약에 대해 신뢰성 측면에서 열주기를 최적으로 유지하고자 노력한다. 실험 결과 제안된 기법은 Nvidia의 Jetson TK1 시뮬레이션에서 인공위성 임베디드 시스템의 기대수명을 최대 8.03배까지 향상시키는 것으로 나타났다.

태양동기궤도 위성군의 운영궤도 최적화에 관한 연구

김화영 전북대학교 일반대학원 2014 국내석사

In this thesis, a purely numerical simulation and optimization approach are proposed in designing a sun-synchronous orbit. The classical method of designing a sun-synchronous orbit is modified to effectively include the requirements such as sun-synchronicity and ground track repeatability during a certain period etc. The preliminary design results obtained from the conventional analytical approach used J2 effect only are further refined by using the high-fidelity simulation and analysis capabilities provided by Commercially-Off-The-Shelf software such as Satellite Tool Kit(STK) and MATLAB. Not only its simplicity but the further advantages are that the operational requirements such as contact with a ground station or access to a target can be incorporated. For this purpose, operation parameters are defined as Contact, Contact Gap, Access, Access Gap, Contact Overlap, Contact Overlap Gap, Access Overlap Time and Access Overlap Gap Time. These parameters are used to form a Figure of Merit that reflects the operational requirements. Then this Figure of Merit is optimized to increase the efficiency of operating multiple spacecraft in constellation, and used to determine the operational orbit of each spacecraft that constitutes the constellation.

Transceiver Designs for Enhanced Vehicular and Non-terrestrial Communications: Developments and Deployments

Lin, Chia-Hung North Carolina State University ProQuest Dissertat 2023 해외박사(DDOD)

In the era of next-generation communications, or 6G, the ability to provide seamless connectivity to users anywhere and anytime is crucial. While 5G systems have already provided stable and fast communication capabilities for conventional mobile communications scenarios, the challenge now lies in extending these guarantees to fast-moving objects in vehicular communications and non-terrestrial communications. These scenarios differ from mobile communications as the fast-changing wireless channels caused by fast-moving objects significantly reduce the response time of transceivers. Therefore, suitable algorithms are needed that can offer high performance, low complexity, and fast reconfigurable attributes to perform transceiver operations based on the underlying fast-changing wireless channels.Over the past decade, the development of deep learning (DL) algorithms has transformed our daily lives and enabled new applications. These technologies have also driven the evolution of next-generation communication systems from a communication engineering perspective. DL algorithms can be used as powerful tools to solve problems and create DL-aided communication system designs with low complexity, high performance, and fast reconfigurable attributes. Additionally, as users perform training or inference on DL algorithms, next-generation communication systems are expected to better support those learning processes by utilizing in-network communication and computing resources. After a comprehensive literature survey, we noticed that DL-based communication system designs are particularly well-suited for aiding transceiver designs in vehicular and non-terrestrial communications, especially when conventional optimization-based algorithms encounter imprecise system models or computationally demanding issues. As such, this thesis focuses on developing learning-based transceiver designs to better serve vehicular and non-terrestrial communications, along with framework designs to facilitate the real deployment of these proposed designs. The first part of this thesis presents dedicated designs for vehicular communications, with a focus on vehicle-to-vehicle (V2V) communications in Chapters 2, 3, and 4. The thesis then proposes a platform for system designers to deploy the proposed designs with 6G infrastructure in Chapter 5, aiming to provide next-generation communication systems that better aid the training and inference processes of users. To handle the communication and computation costs in the learning process, the proposed framework can dynamically orchestrate resources among heterogeneous physical units, including in-network mobile devices, edge and cloud computing centers, to efficiently fulfill deep learning objectives. The framework can also dynamically allocate resources and intelligently assign communications and computation tasks to these units. The second part of this thesis extends these designs to satellite communications, taking into account the special channel features in this context. Using the extra information provided by the geometry relationship of satellite communication scenarios, this thesis discusses the satellite transceiver designs incorporating the geometry relationship to achieve better different communication quality of service indicators in Chapters 6 and 7. Through the proposed designs, this thesis aims to provide next-generation communication systems that offer greater efficiency to users, enabled by the power of advanced DL-based algorithms. Additionally, the thesis aims to present next-generation communication system designs that facilitate training and inference processes when users deploy learning algorithms in distributed environments.

Novel Algorithms for Motion Detection and Imaging in Complex Scenes

Leibovich, Matan ProQuest Dissertations & Theses Stanford Universit 2020 해외박사(DDOD)

This thesis focuses on data structures and algorithms used in motion detection and imaging in complex settings. The work consists of four projects, addressing different aspects of imaging with a synthetic aperture radar (SAR) system or in an inverse synthetic aperture radar (iSAR) setting. In the first project, I analyzed an algorithm for the detection of moving targets in SAR using robust principal component analysis (RPCA). In the second project, I introduced an extension of the SAR data structure to tensors and a modified tensor RPCA algorithm, to improve detection of slowly moving targets. In the third project, I introduced a cross correlation data structure for iSAR imaging of low earth orbit (LEO) fast moving satellites, as well as novel imaging algorithms adapted to the cross correlation data structure. In the fourth project, I extended the problem to rotating satellites, analyzed the effect rotation has on performance, and showed how the rotation parameters can be extracted from the data. In a broad sense, all of these projects explore the effect data representation can have in imaging algorithms. The RPCA problems show that specific features in the raw data can be be exploited to detect motion. Moreover, the specific model of the data and different ways in which they are represented can significantly improve the performance of linear algebra and optimization based tools when applied to this problem. In the correlation based imaging problems, the choice of an appropriate data representation can provide insight into both improved imaging algorithms and their analysis. While these projects are distinct, they all demonstrate the importance of the choice of data structures and representations in imaging problems. The specific data structure may not only improve the applicability of previously used algorithms, but can also provide insight into extensions and modifications, as well as a rigorous mathematical analysis of the imaging algorithms.

전력변환 시스템의 디지털 제어기법에 관한 연구

배현수 서울대학교 대학원 2009 국내박사

인공위성 RPPT 시스템을 위한 단순화된 직병렬 구조

양정환 서울대학교 대학원 2008 국내석사