• Title/Summary/Keyword: LEO (Low Earth Orbit)

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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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OPERATIONAL ORBIT DETERMINATION USING GPS NAVIGATION DATA

  • Hwang Yoola;Lee Byoung-Sun;Kim Jaehoon
    • Bulletin of the Korean Space Science Society
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    • 2004.10b
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    • pp.376-379
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    • 2004
  • Operational orbit determination (OOD) depends on the capability of generating accurate prediction of spacecraft ephemeris in a short period. The predicted ephemeris is used in the operations such as instrument pointing and orbit maneuvers. In this study the orbit prediction problem consists of the estimating diverse arc length orbit using GPS navigation data, the predicted orbit for the next 48 hours, and the fitted 30-hour arc length orbits of double differenced GPS measurements for the predicted 48-hour period. For 24-hour orbit arc length, the predicted orbit difference from truth orbit was 205 meters due to the along-track error. The main error sources for the orbit prediction of the Low Earth Orbiter (LEO) satellite are solar pressure and atmosphere density.

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Analysis on Frequency Sharing between LEO Satellite Network and FS System in Space-to-Earth Direction (저궤도 위성망과 FS 시스템의 주파수 공유 방안 연구)

  • Gam, Hye-Mi;Oh, Dae-Sub;Ahn, Do-Seob
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.20 no.12
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    • pp.1279-1286
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    • 2009
  • This paper addresses the analysis of the interference produced between the LEO(Low Earth Orbit) satellite constellation and FS(Fixed Service) system operating in the same frequency and area. At first, we calculates the interference of FS system from the LEO satellite constellation depending on the number of LEO satellite antenna beams. Simulation results show that the amount of interference that was calculated from each region. This result can be used to define the carrier level for protecting FS system from total interference by LEO satellite constellation. In the second scenario, we calculates the interference of LEO satellite system earth station by the FS link depending on radius of protection area. The presented results can be used to design FS systems minimizing interference to earth station.

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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TT&C Antenna Design for LEO Satellite (저궤도 위성용 TT&C 안테나의 설계)

  • Lee, Kwang-Jae;Woo, Duk-Jae;Lee, Taek-Kyung;Lee, Jae-Wook;Lee, Woo-Kyung
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.21 no.6
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    • pp.642-650
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    • 2010
  • In this paper, we study a TT&C link to obtain a required specifications of TT&C(Telemetry Tracking and Command system) antenna for an LEO(Low Earth Orbit) satellite. The premised mission orbit is the sun-synchronized and circular orbit and it performs earth-space observations. We design minimum TT&C link-budget to obtain required antenna beamwidth and gain. The proposed turnstile antenna provides wide beamwidth and circular polarization. We suggested the attaching position that shows the most effective results by confirming the variation of antenna performance when the proposed antenna is adapted to satellite's various positions. Also we proved the proposed antenna's ability while it is performing the mission through the orbit simulation based on the electrical performance of the proposed turnstile antenna.

Fuel-Optimal Altitude Maintenance of Low-Earth-Orbit Spacecrafts by Combined Direct/Indirect Optimization

  • Kim, Kyung-Ha;Park, Chandeok;Park, Sang-Young
    • Journal of Astronomy and Space Sciences
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    • v.32 no.4
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    • pp.379-386
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    • 2015
  • This work presents fuel-optimal altitude maintenance of Low-Earth-Orbit (LEO) spacecrafts experiencing non-negligible air drag and J2 perturbation. A pseudospectral (direct) method is first applied to roughly estimate an optimal fuel consumption strategy, which is employed as an initial guess to precisely determine itself. Based on the physical specifications of KOrea Multi-Purpose SATellite-2 (KOMPSAT-2), a Korean artificial satellite, numerical simulations show that a satellite ascends with full thrust at the early stage of the maneuver period and then descends with null thrust. While the thrust profile is presumably bang-off, it is difficult to precisely determine the switching time by using a pseudospectral method only. This is expected, since the optimal switching epoch does not coincide with one of the collocation points prescribed by the pseudospectral method, in general. As an attempt to precisely determine the switching time and the associated optimal thrust history, a shooting (indirect) method is then employed with the initial guess being obtained through the pseudospectral method. This hybrid process allows the determination of the optimal fuel consumption for LEO spacecrafts and their thrust profiles efficiently and precisely.

Preliminary Thermal Analysis for LEO Satellite Optical Payload's Thermal Vacuum Test (저궤도위성 광학탑재체의 지상 열진공 시험을 위한 예비 열해석)

  • Lee, Jongl-Yul;Huh, Hwan-Il;Kim, Sang-Ho;Chang, Su-Young;Lee, Deog-Gyu;Lee, Seung-Hoon;Choi, Hae-Jin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.5
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    • pp.466-473
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    • 2011
  • The purpose of satellite thermal control design is to maintain all the elements of a spacecraft system within their temperature limits for all mission phases. The thermal analysis model for Low Earth Orbit satellite payload level simulation is established by considering thermal vacuum test environment condition, thermal vacuum chamber configuration, and satellite's payload inner thermal environment. The established thermal analysis model is used to determine thermal vacuum test conditions and test case requirements.

Analyses of Nano Epoxy-Silica Degradation in LEO Space Environment (저궤도 우주환경에서 에폭시-실리카 나노 복합소재의 열화거동 분석)

  • Jang, Seo-Hyun;Han, Yusu;Hwang, Do Soon;Jung, Joo Won;Kim, Yeong Kook
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.48 no.12
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    • pp.945-952
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    • 2020
  • In this study, the effects of Low Earth Orbit(LEO) environments on the degradation behavior of epoxy nano silica composite materials were investigated. The nanocomposite materials containing silica particles in different weight ratios of 10% and 18% were prepared and degraded in a LEO simulator to compare with the neat epoxy cases. Thermogravimetric analysis (TGA) was performed on the degraded nanocomposites and the activation energies were calculated by Friedman method, Flynn-Wall-Ozawa (FWO) method, Kissinger method, and DAEM (Distributed Activation Energy Method) based on the iso-conversional method. As the results, for the neat epoxy sample cases, it was found that the average activation energy was increased as the degradation was progressed. When the nano particles were mixed, however, the energy increased to the 15 environmental test cycles, and decreased afterwards, meaning that the particle mixture contributed adversely to the thermal degradation. Discussions on the results of the different calculation methods were also given.

THE DESIGN AND ANALYSIS PROGRAM FOR THE DEVELOPMENT OF LEO SATELLITE ELECTRICAL POWER SUBSYSTEM (저궤도 인공위성 전력계 개발을 위한 설계 분석 프로그램)

  • Lee, Sang-Kon;Ra, Sung-Woong
    • Journal of Astronomy and Space Sciences
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    • v.24 no.2
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    • pp.179-194
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    • 2007
  • The design and analysis of satellite power subsystem is an important driver for the mass, size, and capability of the satellite. Every other satellite subsystem is affected by the power subsystem, and in particular, important issues such as launch vehicle selection, thermal design, and structural design are largely influenced by the capabilities and limitations of the power system. This paper introduces a new electrical power subsystem design program for the rapid development of LEO satellite and shows an example of design results using other LEO satellite design data. The results shows that the proposed design program can be used the optimum sizing and the analytical prediction of the on-orbit performance of satellite electrical power subsystem.

Carrier Tracking and Tracing System using Low Earth Orbit

  • Byeon Eui-Seok;Ahn Sung-Bum;Kang Sang-Hun
    • Proceedings of the Korean Operations and Management Science Society Conference
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    • 2003.05a
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    • pp.704-707
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    • 2003
  • The Purpose of carrier tracking and tracing is to achieve more information over shipments via carrying in mobile business .At multimodes, especially consignor wants to be aware of the exact situation and position of goods. As an innovate business model, we present CGPS(Carrier Global Positioning System) scheme usiug LEO(Low Earth Orbital) satellite. The LEO collects the data periodically and sends to the web server, and eventually customer's PC or PDA. This provides shipping company or freight forwarder with more robust information such as door status, container inside condition, etc.

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