• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.334-341
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• 2008

Ballast track needs maintenance works because it is supported by the compressible trackbed and subgrade layers. Maintenance works are essential to secure riding comfort and extend the life cycle of it. The necessities of maintenance works are determined from track irregularities measured by EM120. Track irregularities is the results of the track deformation. Therefore, it is natural to evaluate the cause of it. This paper focuses on the points the track irregularities come from the trackbed and the subgrade. Nondestructive techniques, such as Ground Penetrating Radar (GPR) and Portable Falling Weight Deflectometer (PFWD) are applied to evaluate the trackbed conditions, ballast layer thickness and vertical track stiffness, in the test section 500m long of Gyungbu line. The trackbed investigation results are compared with the track irregularities measured by EM120 and maintenance works. Conclusively, it was found that some maintenance works were unnecessary on the test section.

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.37-44
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• 2011

COMS(Chollian) satellite which was launched on June 26, 2010 has three payloads for Ka-band communications, geostationary ocean color imaging and meteorological imaging. In order to make efficient use of the geostationary satellite, a concept of mission operations has been considered from the beginning of the satellite ground control system development. COMS satellite mission operations are classified by daily, weekly, monthly, and seasonal operations. Daily satellite operations include mission planning, command planning and transmission, telemetry processing and analysis, ranging and orbit determination, ephemeris and event prediction, and wheel off-loading set point parameter calculation. As a weekly operation, North-South station keeping maneuver and East-West station keeping maneuver should be performed on Tuesday and Thursday, respectively. Spacecraft oscillator updating parameter should be calculated and uploaded once a month. Eclipse operations should be performed during a vernal equinox and autumnal equinox season. In this paper, operational validations of the major functions in COMS SGCS are presented for the first three month of in-orbit test operations. All of the major functions have been successfully verified and the COMS SGCS will be used for the mission operations of the COMS satellite for 7 years of mission life time and even more.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.77-77
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• 2004

인공위성은 정상궤도에 들어선 후부터 수명을 다하는 시기까지 각종 복사, 열(온도차), 고진공, 미세중력, 미세운석과 우주파편 등에 의해 영향을 받게 된다. 특히, 위성체에 미치는 열환경은 위성이 궤도를 그리며 운동하는 동안 태양과 지구로부터의 복사량의 크기 및 분포에 따라 결정되는데, 약 5,50$0^{\circ}C$의 흑체온도를 갖고 있는 태양과 -27$0^{\circ}C$의 심우주는 위성체에서 태양이 비추는 부분과 반대편과의 온도를 극한으로 만들게 된다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1126-1131
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• 2008

This paper applies the Orbital Geometry-based Bias Estimation Algorithm to the magnetometer measurement data of KOMPSAT-1 and 2 and analyzes the induced magnetic field bias caused by the solar panels and electronics boxes in spacecraft bus. This paper reveals that the estimation and correction of the induced magnetic field bias copes with the aging process of magnetometer and makes it possible to carry on the satellite mission by extending its lifetime.

• Journal of Astronomy and Space Sciences
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• v.14 no.1
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• pp.142-149
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• 1997

This paper applied one of the well-known optimal control theory, namely, linear quadratic regulator(LQR), to the station-keeping maneuvers(SKM) for a geostationary satellite. The boundary conditions to transfer the system with a good accuracy at a terminal time were based upon the predicted orbital data which are created due to the Earth's non-uniform mass distribution's effect during 14 days and due to luni-solar effect during 28 days. Through the linearization of the nonlinear system equation with respect to reference orbit and the numerical integration of Riccati equation, the optimal trajectories and the corresponding control law have been obtained by using LQR. From the comparison of ${\Delta}V$ obtained by LQR with the ${\Delta}V$ obtained anatically by geometric method, Station Keeping Maneuvers(SKM) via LQR may provide comparable results to a real system. Furthermore it will demonstrate the possibility in fuel optimization and life extension of geostationary satellite.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.155.2-155.2
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• 2005

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.2
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• pp.141-151
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• 2003

Railway bridges are subject to dynamic loads generated by the interaction between moving vehicles and the bridge structures. These dynamic loads result in response fluctuations in bridge members. To investigate the real dynamic behavior of the bridge, therefore, a number of analytical and experimental Investigations should be carried out. In this paper, a train/track/bridge interaction analysis program for evaluating the dynamic characteristics of bridges due to KTX operation in terms of structural safety, operational safety and passenger comfort is developed. To build a practical model of train/track/bridge, Hertzian spring for wheel/rail contact modeling and Winkler element for ballast are applied. This program also used torsional degree of freedom and constraint equation based on geometrical relationship in order to take into consideration three-dimensional eccentricity effect due to the operation on double track through quasi-three dimensional analysis. To verify the developed Program, comparison has been made between the measured results and those of simulation of the typical PSC box bridge(2@40m=80m) of the KHSR bridges.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.8
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• pp.559-572
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• 2022

Recently, with the success of the world's first On-Orbit service (OOS) mission MEV (Mission Extension Vehicle)-1 in 2020, interest in OOS is increasing at home and abroad. In particular, the mission of OOS and active debris removal (ADR) service, which was difficult to find in the old space era in the past, is expected to enter the new space industry in the near future. Therefore, this paper examines the development cases of domestic and foreign OOS technologies, and describes the characteristics of major technologies required, domestic status and development potential, and the possibility of future OOS mission development. The technology trends and future prospects of OOS described in this paper are expected to be useful reference materials for further researching related fields in domestic situations where related research is insufficient.

• Journal of the Korean Society for Railway
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• v.13 no.6
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• pp.577-582
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• 2010

The importance of maintenance of rail surface defects is increasing according to the KTX operation. That is because during high speed operation of rolling stocks, rail surface defects shorten fatigue life of rail, accelerate track degradation and deteriorate ride comfort. Rail grinding has been applied for effective rail maintenance in Kyeong-Bu HS line. This paper evaluates the effectiveness of rail grinding in term of rail fatigue life. To this end, the stresses of the rail are measured under KTX running and the equivalent stress range is calculated by RMC after the frequency analysis done with rainflow counting method. Also, The Modified Miner's rule is applied to predict the fatigue life of ground rail. The result of the analysis shows that the fatigue life of ground rail is increased by 15%.

• Journal of Astronomy and Space Sciences
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• v.15 no.2
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• pp.449-458
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• 1998

The Korea Muliti-Purpose Satellite(KOMPSAT) uses a sun-synchronous orbit with an altitude 685km as mission orbit and undergoes earth eclipses and infrequently lunar eclipses. Lunar eclipses occur when the moon is located between the sun and the satellite and blocks partially or fully the sunlight. The eclipse causes the satellite to increase battery discharge times and affects satellite lifetime and mission operation. The KOMPSAT lunar eclipses can cause additional effects to energy balance and battery disc of the KOMPSAT lunar eclipse for 3 year mission lifetime. Also mission planning scenario is presented for lunar eclipses at the KOMPSAT Grouns Station(KGS).