• Title/Summary/Keyword: LEO satellite

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A Survey on LEO-PNT Systems

  • Hong-Woo Seok;Sangjae Cho;Seung-Hyun Kong;Jung-Min Joo;Jongwon Lim
    • Journal of Positioning, Navigation, and Timing
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    • v.12 no.3
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    • pp.323-332
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    • 2023
  • Today, services using Positioning, Navigation, and Timing (PNT) technology are provided in various fields, such as smartphone Location-Based Service (LBS) and autonomous driving. Generally, outdoor positioning techniques depend on the Global Navigation Satellite System (GNSS), and the need for positioning techniques that guarantee positioning accuracy, availability, and continuity is emerging with advances in service. In particular, continuity is not guaranteed in urban canyons where it is challenging to secure visible satellites with standalone GNSS, and even if more than four satellites are visible, the positioning accuracy and stability are reduced due to multipath channels. Research using Low Earth Orbit (LEO) satellites is already underway to overcome these limitations. In this study, we conducted a trend analysis of LEO-PNT research, an LEO satellite-based navigation and augmentation system. Through comparison with GNSS, the differentiation of LEO-PNT was confirmed, and the system design and receiver processing were analyzed according to LEO-PNT classification. Lastly, the current status of LEO-PNT development by country and institution was confirmed.

Flight Software Reprogramming for Next Generation LEO Satellites (차세대 저궤도 위성의 비행소프트웨어 리프로그래밍)

  • Yoo, Bum-Soo;Jeong, Jae-Yeop;Choi, Jong-Wook
    • Journal of Satellite, Information and Communications
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    • v.12 no.3
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    • pp.93-97
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    • 2017
  • In satellites, even a small error in flight software could cause a failure of missions. Therefore, there are strict development and verification processes for a high reliability of flight software. However, satellites on orbits could meet unexpected situations including hardware malfunction. In this case, it is necessary for flight software to be updated to cope with the unexpected situations and to continue their missions. This paper reviews reprogramming capability of next generation LEO satellites.

Analysis about Threshold Measurement Test Result of LEO Satellite Receiver (저궤도 위성 Receiver의 Threshold측정 시험 결과에 대한 분석)

  • Jo, Seung-Won;Gwon, Jae-Uk;Choe, Jong-Yeon;Choe, Seok-Won
    • Aerospace Engineering and Technology
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    • v.5 no.2
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    • pp.77-84
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    • 2006
  • We should measure receiver tracking threshold and command threshold of the satellite in Integrate System Test (IST) in order to check the normal received power range of LEO(Low Earth Orbit) satellite S-band receiver. In this paper, the algorithm of threshold measurement is examined and the result measured in Integrated System Test is displayed. And than, the factor could have an effect on the result of threshold measurement except the capability of receiver itself was analyzed and compensated as many as distorted value according to that analysis.

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LEO Satellite Time Synchronization Architecture

  • Kwon, Ki-Ho;Kim, Day-Young;Lee, Jong-In;Kim, Hak-Jung;Lee, Sang-Jeong
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • v.1
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    • pp.367-370
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    • 2006
  • A GPS-based time synchronization technique employing a refined HW circuitry and SW algorithm is considered as fine time-management system for Low Earth Orbit (LEO) remote sensing satellites. By synchronizing the On-Board Time (OBT) within satellites to the GPS 1PPS, a very expensive, highly accurate on-board clock is not required to determine the precise on-board time management. Also, the satellite command generation in ground stations and postprocessing of earth observation data which a particular image is acquired. This paper analyses on-orbit verification of the existing satellite time sync architecture and presents a new time sync architecture, operation and relation between the OBT and the GPS time.

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Thermal Analysis for Design of Propulsion System Employed in LEO Earth Observation Satellite

  • Han C.Y.;Kim J.S.;Lee K.H.;Rhee S.W.
    • 한국전산유체공학회:학술대회논문집
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    • 2003.10a
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    • pp.248-250
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    • 2003
  • Thermal analysis is performed to protect the propulsion system of low-earth-orbit earth observation satellite from unwanted thermal disaster like propellant freezing. To implement thermal design adequately, heater powers for the propulsion system estimated through the thermal analysis are decided. Based on those values anticipated herein, the average power for propulsion system becomes 22.02 watts when the only one redundant catalyst bed heater is turned on. When for the preparation of thruster firing, 25.93 watts of the average power is required. All heaters selected for propulsion components operate to prevent propellant freezing meeting the thermal requirements for the propulsion system with the worst-case average voltage, i.e. 25 volts.

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Dynamic Caching Routing Strategy for LEO Satellite Nodes Based on Gradient Boosting Regression Tree

  • Yang Yang;Shengbo Hu;Guiju Lu
    • Journal of Information Processing Systems
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    • v.20 no.1
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    • pp.131-147
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    • 2024
  • A routing strategy based on traffic prediction and dynamic cache allocation for satellite nodes is proposed to address the issues of high propagation delay and overall delay of inter-satellite and satellite-to-ground links in low Earth orbit (LEO) satellite systems. The spatial and temporal correlations of satellite network traffic were analyzed, and the relevant traffic through the target satellite was extracted as raw input for traffic prediction. An improved gradient boosting regression tree algorithm was used for traffic prediction. Based on the traffic prediction results, a dynamic cache allocation routing strategy is proposed. The satellite nodes periodically monitor the traffic load on inter-satellite links (ISLs) and dynamically allocate cache resources for each ISL with neighboring nodes. Simulation results demonstrate that the proposed routing strategy effectively reduces packet loss rate and average end-to-end delay and improves the distribution of services across the entire network.

Generalization modeling and verify for low-orbit satellite regulation converter (저궤도 위성의 정 전압 변압기 일반화 모델링 및 적용)

  • Yun, Seok-Teak
    • Journal of Satellite, Information and Communications
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    • v.6 no.2
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    • pp.136-140
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    • 2011
  • Satellites industry has been developing with the commercial and military needs. Because power system of satellites is very important to survival operation and hard to test, increasing reliability is very critical. Especially LEO small satellites are very sensitive to power system, effective stabilization control is important. Because of various need of load condition, converter design are complicated. Therefore this paper introduced general modeling of LEO small satellite converter system and analyzed stabilization control design. The performance prediction of LEO small satellites power system is typically critical. Because of verity controller and rectification value, it is hard to computation and test implementation. So, this approach has merit that will reduce cost and make more reliable system. Furthermore, it can be constraint of converter specification and controller design. This paper will examine generation a modeling of LEO small satellites power converting system, and a possible guide line to design reliable controller which optimizing power converters of LEO small satellite.

Study on The Attitude Stabilization Techniques of Leo Satellites

  • Hwan, Lho-Young;Yong, Jung-Kang
    • 제어로봇시스템학회:학술대회논문집
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    • 2001.10a
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    • pp.56.5-56
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    • 2001
  • In the three axis control of satellite by using reaction wheel and gyro, a reaction wheel produces the control torque by the wheel speed or momentum, and a gyro carries out measuring of the attitude angle and the attitude angular velocity In this study, dynamic modelling of the Low Earth Orbit (LEO) is consisted of the one from the rotational motion of the satellite with the basic rigid body and a flexible body model, and the gyro in addition to the reaction wheel model. The results obtained by the robust controller are compared with those of the PI (Proportional and Integration) controller which is commonly used for the stabilizing satellite.

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Detection Probability Evaluation of LEO Satellites based Automatic Identification System for a Maritime-Terrestrial Integrated Network (해상육상통합환경에서 저궤도 위성기반 AIS 시스템의 검출확률 성능평가)

  • Lee, Woo-Young;Choi, Jo-Chun;Lee, Jin-Seok;Lee, Seong-Ro;Lee, Yeon-Woo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.5B
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    • pp.530-538
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    • 2011
  • In this paper, the feasibility of LEO(low earth orbit) satellite-based automatic identification system (SAT-AIS) for the coastal area of the South Korea is evaluated in the context of ship AIS transmission detection probability. We evaluate and compare AIS signal detection probability of ORBCOMM satellites and LEO-one satellites considering link budget, SOTDMA protocol and satellite's swath width. The simulation determines the total number of vessels served by those satellites according to satellite's swath width and thus, By simulation results, the ORBCOMM SAT-AIS system outperforms LEO-one SAT-AIS system. The suggested ORBCOMM based SAT-AIS system can be a solution to resolve the existing limited transmission distance problem of the conventional ship-to-shore AIS system.