• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.164.2-164.2
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• 2012

인공위성레이저추적(SLR, Satellite Laser Ranging) 시스템은 인공위성까지 레이저를 발사하여 되돌아오는 시간간격을 측정함으로서 위성까지의 거리를 측정하는 시스템으로 현존하는 인공위성 궤도결정 시스템으로는 가장 정밀하다. 한국천문연구원은 우주추적 및 감시의 필요성이 증가함에 따라 2008년부터 40cm급 이동형 인공위성레이저추적 시스템을 개발을 시작하였고, 현재 개발을 완료하여 시험운영 중에 있다. 시스템 개발 과정 중에 발생할 수 있는 문제점들을 최소화하기 위해, 설계 단계에서 부품을 포함한 광기계 구조물에 대한 구조해석과, 실험실 프로토타입 구성 등을 실시하였다. 제작된 각 서브시스템별 조립 및 평가는 한국천문연구원이 보유한 광학계 조립 및 평가 시설을 이용하였다. 개발된 이동형 레이저 추적 시스템의 광학부는 추적마운트에 장착되었고, 현장 시험관측을 통해 수신광학계 및 광신호유도계의 정렬 및 제어항목 교정 등을 실시하였으며, 성공적으로 시험 영상 관측을 완료하였다. 이 발표에서는 이동형 레이저 추적 시스템 광학계의 개발 과정과 그 결과에 대해 보고한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.49-49
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• 2010

본 논문은 진공챔버 내부에서 위성 표면의 온도를 제어하기 위한 할로겐램프를 이용한 적외선 발열장치의 개발에 관한 것으로, 인공위성이 우주궤도에서 받게 되는 복사에너지를 지상의 진공챔버 내에서 모사하기 위한 비접촉 적외선 발열장치에 관한 것이다. 진공챔버 내에서의 비접촉식 발열 방법 중, 진공환경에서의 오염을 발생시키지 않고, 발열 시간 및 냉각 시간이 가장 짧으며, 높은 열효율로 태양복사에너지를 가장 근사하게 모사할 수 있는 할로겐 램프를 이용한 발열 방법을 적용하였으며, 램프에서 방사되는 열에너지가 위성표면에 균일하게 분포될 수 있도록 위성 표면으로부터의 거리와 램프의 개수, 램프의 배열에 따른 에너지 분포 계산식을 도출하여 적용하였다. 공급 전압에 따른 램프의 저항특성을 파악하여, 원격으로 제어되는 150 VDC, 5 A의 직류전원공급기를 이용해 램프의 발열량을 조절하였으며, 발열량에 따른 위성 표면온도에 대한 해석을 수행하였다. 램프를 이용한 비접촉식 적외선 발열장치 개발을 통해 진공환경에서의 시험대상에 대한 효율적인 열에너지 부과방법 수립이 가능하였다.

• Journal of Astronomy and Space Sciences
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• v.26 no.3
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• pp.403-416
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• 2009

COMS (Communication, Ocean and Meteorological Satellite) is a geostationary satellite and developed by KARl for communication, ocean and meteorological observations. It will be tested under vacuum and very low temperature conditions in order to verify thermal design of COMS. The test will be performed by using KARI large thermal vacuum chamber, which was developed by KARI, and the COMS will be the first flight satellite tested in this chamber. The purposes of thermal balance test are to correlate analytical model used for design evaluation and predicting temperatures, and to verify and adjust thermal control concept. KARI has plan to use heating plates to simulate space hot condition especially for radiator panels of satellite such as north and south panels. They will be controlled from 90 K to 273 K by circulating GN2 and LN2 alternatively according to the test phases, while the main shroud of the vacuum chamber will be under constant temperature, 90 K, during all thermal balance test. This paper presents thermal modelling including test chamber, heating plates and the satellite without solar array wing and Ka-band reflectors and discusses temperature prediction during thermal balance test.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.363-370
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• 2021

In this paper, we presented an optimized crack and flexural strength analysis of a glass-fiber reinforced polymer (GFRP) rebar, used as reinforcements for in-site railway concrete slabs. The insulation performance of a GFRP rebar has the advantage of avoiding the loss of signal current in an audio frequency (AF) track circuit. A full-scale experiment, and three-dimensional finite element simulation results were compared to validate our approaches. Parametric numerical results revealed that the diameters and arrangements of the GFRP rebar had a significant effect on the flexural strength and crack control performances of the concrete track slabs. The results of this study could serve as a benchmark for future guidelines in designing more efficient, and economical concrete slabs using the GFRP rebar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.75-83
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• 2023

As part of a study to analyze the excessive camber occurring in prestressed concrete railway bridges, this paper presents a calculation method and analysis results for the creep coefficient which defines the increase in camber of a concrete structure over time. Using the creep coefficient formula of the design code, the coefficient is obtained by applying the climatic conditions (relative humidity and temperature) of 12 regions in Korea. The effects of differences in climatic conditions by region and starting time of load on the creep coefficient are analyzed. In order to properly calculate the creep, most of which occurs in the early stages of loading, a detailed analysis is performed by applying a time step analysis method to consider varying climate conditions through loaded period. The creep coefficient obtained by applying the average climate conditions of the region is similar to the average of the creep coefficients obtained by time step analysis. Through time step analysis, it is shown that the offset and overlap effects of relative humidity and temperature on the creep coefficient and the climate effect at the time of initial loading can be appropriately represented.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.717-726
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• 2016

Emergency tracks are necessary in case a broken down train evacuates, a train needs to make way for a faster train behind it, or a train suddenly stops and following trains must avoid colliding with it. Magnetic Levitated (maglev) Trains can change track to enter an emergency track using a segmented switch or a traverse switch. On a traverse switch, a train can change its track when the part of the track that the train is on moves to the other track. Currently manufactured Maglev trains have two bodies and the total length is 25 meters. If a traverse switch is used, it will only require 30 meters of track to move the train to the other track, so, when it comes to efficiency of costs and space, the traverse switch surpasses the articulated switch. Therefore, in this paper, an optimized design to secure structural safety and weight lightening is suggested. To achieve these results, the heights of the piled concrete and girders which are both placed on the top of the traverse switch, are set as design variables. The Finite Element Method (FEM), in application of kriging and in the design of the experiments (DOE), is used. Maximum stress, deformation, and structural weight are compared with the results, and through this process structural safety and weight lightening is proven.

• Composites Research
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• v.36 no.3
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• pp.230-240
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• 2023

The deployable reflector antenna consists of 24 unit main reflectors, and is mounted on a launch vehicle in a folded state. This satellite reaches the operating orbit and the antenna of satellite is deployed, and performs a mission. The deployable reflector antenna has the advantage of reduce the storage volume of payload of launch vehicle, allowing large space structures to be mounted in the limited storage space of the launch vehicle. In this paper, structural analysis was performed on the main reflector constituting the deployable reflector antenna, and through this, the initial conceptual design was performed. Lightweight composite main reflector was designed by applying a carbon fiber composite and honeycomb core. The laminate pattern and shape were selected as design variables and a design that satisfies the operation conditions was derived. Then, the performance of the lightweight composite reflector antenna was analyzed by performing detailed structural analysis on modal analysis, quasi-static, thermal gradient, and dynamic behavior.

• Water for future
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• v.24 no.3
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• pp.36-41
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• 1991

1960년대 초부터 미 국립항공우주국(NASA)에서 기상위성을 지구궤도에 올리면서 시작되고 우주개발 선도국들에 의해 수 없이 발사되어 지구상공을 선회하고 있는 각종 실험위성, 자원탐사위성들로부터 이전까지만해도 지엽적이고 단편적인으로 알려지던 지구환경현황들이 이제는 지구전체에 대한 시시각각의 정보로 확대되고 있다. 기상위성들에 장착된 Sensor들로는 구름과 기상현상의 분포는 물론이고 각 대양의 해수면 온도 분포들이 파악되고 있으며 식물지수에 의한 지상의 식물분포의 계절적 변화양상에서 열대림의 사막화 추세들까지도 분석된다. 특히 위성탐사에 의한 남극 오존홀 (Ozone Hole)의 확인은 최근악화 되고 있느 swlrnchs 환경문제에 대한 커다란 주의를 환기시켜 주었다. 대양의 Phytoplankton 분포가 계절에 따라 위성자료에 의해 분석되므로서 해양의 생산능력(Productivity)의 변화도 알게되고 있다. 해양수면의 높이를 측정했던 초단파(microwave)영역의 SAR 자료는 구름을 투과하여 지구표면을 전천후 Monitoring할 수 있는 다음 세대의 Sensor로 각광을 받고 있으며 앞으로 유럽과 일본, 카나다, 소련 등에서 이들 새로운 Sensor들이 탑재 될 자원탐사 위성(ERS)과 RADASAT 등의 위성이 계속해서 개발되고 있어 이들에 의한 지구환경상태 진단은 크게 각광받게 될 것이다. 그외에도 해면풍 운량, 총강우량 분포, 대기 투명도, 대기의 열수지등의 계절적 변화에 대한 인공위성자료 해석을 통하여 지구의 온난화nas제가 본격적으로 ud가되고 있다. 또한 자원탐사위성인 Landsat 과 SPOT 등의 위성에 의해서는 각대륙의 토지 이용도 변화, 토사의 이도, 지질도 작성, 입체도 제착등과 농산물수확량의 예측있어서 괄목할 만한 발전이 계속되고 있다. 더욱이 NASA와 일본, 유럽등에서 지구관측을 위해서 준비하고 있는 각종 지구관측위성(EOS)들이 실용화 될 2000년 대에는 일반 지구환경감시는 물론 수계환경 감시 체계구축에 획기적인 진전이 있을 것으로 기대된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.455-462
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• 2016

Output Characteristics of the spaceborn image sensor such as infrared(IR) sensor are varied according to time elapses and sensor repetition on/off operation. As a result, the quality of IR sensor image is decreased. Therefore, spaceborne image sensor require a periodic calibration using a black body system by correcting a non-uniformity of the sensor. In this paper, we proposed a MEMS-based black body system that can implement the high temperature uniformity at various standard temperatures ranging from low to high temperature and easily estimate the representative surface temperature. In addition, it has advantages lightweight, low-power and high accuracy. The feasibility of the proposed MEMS-based black body system was verified through the thermal analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.300-309
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• 2017

A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.