• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.227-233
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• 2018

This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.

• Journal of Astronomy and Space Sciences
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• v.41 no.1
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• pp.17-23
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• 2024

The safety of electronic components used in aerospace systems against cosmic rays is one of the most important requirements in their design and construction (especially satellites). In this work, by calculating the dose caused by proton beams in geostationary Earth orbit (GEO) orbit using the MCNPX Monte Carlo code and the MULLASSIS code, the effect of different structures in the protection of cosmic rays has been evaluated. A multi-layer radiation shield composed of aluminum, water and polyethylene was designed and its performance was compared with shielding made of aluminum alone. The results show that the absorbed dose by the simulated protective layers has increased by 35.3% and 44.1% for two-layer (aluminum, polyethylene) and three-layer (aluminum, water, polyethylene) protection respectively, and it is effective in the protection of electronic components. In addition to that, by replacing the multi-layer shield instead of the conventional aluminum shield, the mass reduction percentage will be 38.88 and 39.69, respectively, for the two-layer and three-layer shield compared to the aluminum shield.

• Journal of Astronomy and Space Sciences
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• v.28 no.3
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• pp.193-201
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• 2011

A strategy for geostationary orbit (or geostationary earth orbit [GEO]) surveillance based on optical angular observations is presented in this study. For the dynamic model, precise analytical orbit model developed by Lee et al. (1997) is used to improve computation performance and the unscented Kalman filer (UKF) is applied as a real-time filtering method. The UKF is known to perform well under highly nonlinear conditions such as surveillance in this study. The strategy that combines the analytical orbit propagation model and the UKF is tested for various conditions like different level of initial error and different level of measurement noise. The dependencies on observation interval and number of ground station are also tested. The test results shows that the GEO orbit determination based on the UKF and the analytical orbit model can be applied to GEO orbit tracking and surveillance effectively.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.4
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• pp.474-483
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• 2012

In this paper, a collision avoidance maneuver was sought for low Earth orbit (LEO) and geostationary Earth orbit (GEO) satellites maintained in a keeping area. A genetic algorithm was used to obtain both the maneuver start time and the delta-V to reduce the probability of collision with uncontrolled space objects or debris. Numerical simulations demonstrated the feasibility of the proposed algorithm for both LEO satellites and GEO satellites.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.426-430
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• 2005

The COMS(Communication, Ocean and Meteorological Satellite) is the first developed three-axis stabilization multi-function satellite on geostationary earth orbit(GEO) in korea, presently scheduled to be launched in 2008. The COMS propulsion system provides the thrust and torque required for the insertion into GEO, attitude and orbit control/adjustment of spacecraft. In this paper, system design of propulsion system, basic functions and design requirement of components are described.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.207-210
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• 2007

A part of the big differences between LEO(Low Earth Orbit) and GEO(Geostationary Earth Orbit) satellite is that transfer orbit is used or not or what tolerance of the position on the mission orbit is permitted. That is to say, the transfer orbit is not used and the constraint of orbit position is not adapted on LEO satellite. Whereas for GEO satellite case, the transfer orbit shall be used due to the very high altitude and the satellite shall be stayed in the station keeping box which is permitted on the mission orbit. These phases are functions for AOCS mission. The aim of this paper is to introduce the AOCS hardware configuration for COMS (Communication, Ocean and Meteorological Satellite). The AOCS hardware of COMS consist of 3 Linear Analogue Sun Sensors (LIASS), 3 Bi-Axis Sun Sensors (BASS), 2 Infra-Red Earth Sensors (IRES), 3 Fiber Optical Gyroscopes (FOG), 5 momentum wheels and 14 thrusters. In this paper, each component is explained how to be used, how to locate and what relation between the AOCS algorithm and these components.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.41-44
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• 2007

Korea Aerospace Research Institute (KARI) has jointly developed a bipropellant propulsion system for Communication, Ocean and Meteorological Satellite (COMS) with EADS Astrium in UK. The technology relevant to a bipropellant propulsion system is quite new one in Korea, which is transferred for the first time, with development of COMS propulsion system. It hasn't ever attempted before, and hasn't got any general idea itself as well, in Korea. The COMS Chemical Propulsion System (CPS) is designed to perform both the orbital injection function, to take the spacecraft from transfer orbit to Geostationary Earth Orbit (GEO), and all on-station propulsive functions throughout the lifetime of the satellite. All station keeping manoeuvres are performed using the CPS. The design, manufacture and testing of COMS CPS are addressed in this paper. Feasibility of COMS CPS applicable to the other advanced mission is investigated as well.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.411-417
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• 2015

Several optical monitoring strategies by a ground-based telescope to protect a Geostationary Earth Orbit (GEO) satellite from collisions with close approaching objects were investigated. Geostationary Transfer Orbit (GTO) objects, Inclined GeoSynchronous Orbit (IGSO) objects, and drifted GEO objects forced by natural perturbations are hazardous to operational GEO satellites regarding issues related to close approaches. The status of these objects was analyzed on the basis of their orbital characteristics in Two-Line Element (TLE) data from the Joint Space Operation Center (JSpOC). We confirmed the conjunction probability with all catalogued objects for the domestic operational GEO satellite, Communication, Ocean and Meteorological Satellite (COMS) using the Conjunction Analysis Tools by Analytical Graphics, Inc (AGI). The longitudinal drift rates of GeoSynchronous Orbit (GSO) objects were calculated, with an analytic method and they were confirmed using the Systems Tool Kit by AGI. The required monitoring area was determined from the expected drift duration and inclination of the simulated target. The optical monitoring strategy for the target area was analyzed through the orbit determination accuracy. For this purpose, the close approach of Russian satellite Raduga 1-7 to Korean COMS in 2011 was selected.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.19-25
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• 2012

GEO-KOMPSAT2 shall provide higher quality of image than the COMS and uses star tracker instead of earth sensor, which requires precise onboard orbit information. This requires precise on-ground orbit determination. For COMS, orbit determination is performed using the ranging data obtained from tracking system located in DAEJON. For accurate orbit determination of GEO-KOMPSAT2, KARI is building a secondary tracking station in CHUUK Islands. In this paper, the achievable accuracy of table based onboard orbit parameter generator which interpolates orbit data obtained from on-ground orbit determination using tracking data collected from two ground stations. Two types of approaches have been applied; covariance analysis and numerical analysis. By combining two analysis results, total orbit error has been estimated.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.1
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• pp.1-6
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• 2020

The Chinese BeiDou Satellite Navigation System consists of three kinds of constellations: the geostationary Earth orbit (GEO), the inclined geosynchronous satellite orbit (IGSO), and the medium Earth orbit (MEO). The BeiDou has expanded its service coverage from regional to global. Recently, the BeiDou has been widely used in ionospheric total electron content (TEC) research. In this study, we analyzed the BeiDou signals for ionospheric TEC monitoring over Jeju Island in South Korea. The BeiDou GEO TEC showed a clear pattern of diurnal variations. In addition, we compared the TEC values from the BeiDou GEO, the BeiDou IGSO, GPS, and International GNSS Service (IGS) Global Ionosphere Maps (GIM). There was a difference of about 5 TEC units between the BeiDou GEO and the IGS GIM. This may be due to the altitude difference between the different navigation satellites.