• Information and Communications Magazine
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• v.17 no.6
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• pp.100-114
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• 2000

본 논문은 정지궤도위성을 이용한 표준시각/주파수 전송시스템의 동기 오차 요인을 분석하고, 한국과 같이 영토가 작은 국가의 경우, 정지궤도 위성을 이용하는 방식의 이점을 단파 또는 광 전용망을 이용하는 지상망 방식, 그리고 저궤도 위성을 이용하는 GPS방식과 비교 분석한다. 또한, 본 논문은 현재 서비스를 제공 중이거나 연구가 진행중인 단방향 위성 시각 전송 서비스를 고찰하고 특히, 무궁화 위성을 이용한 고정밀도의 표준시각/주파수 전 송서비스를 제공하기 위해 요구되는 동기오차 보정기술에 관하여 연구한다. 국가적 통신망 동기를 위한 표준 시각/주파수의 동기 정확도를 만족시킬 수 있는 효과적인 동기 오차 보정 방식으로 차동(differential mode)보정방식을 제안하고 그 성능을 분석하였으며 시각 정확도 와 주파수 정확도의 관계를 분석하였다. 모의실험 결과, 정상적인 시스템 운영하에서 시각 정확도와 주파수 정확도는 각각 100ns(95%)와 10-11(7일이상) 보다 우수한 것으로 분석되었 으며 본 논문에서 제시한 성능 개선 방안을 적용함으로써 보다 높은 정확도의 시각/주파수 동기가 가능함을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.11
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• pp.984-997
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• 2015

Chang'e-3 consisting of a lunar lander and exploration rover was launched on December 1, 2013 aboard a Long March 3B rocket flying from Xichang space launch center. Chang'e-3 was inserted into the lunar orbit after about a 5-day transit to the Moon and landed on the targeted landing site after orbiting around the Moon for 8 days. The successful landing of the Chang'e-3 gives a lot of help to analyze the future needs of the subsystem technologies and to figure out the trajectory from launch to lunar landing as well as operation sequences in the development of Korean lunar exploration is scheduled. Therefore, the configuration and analysis of overall mission of Chang'e-3 is performed based on the public information from the press and website. As a result, overall mission trajectory is reconstructed by solving boundary condition and then estimating control variable. Visibility status and eclipse status also analyzes so communication and power charge condition is as good as to operate lunar lander. Mass budget of the lander is derived using ${\Delta}V$ according to specific impulse.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.535-541
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• 2020

A conventional elastic material replacement and performance evaluation are very complicated and time-consuming, and it is difficult to know when to replace the elastic material in advance. By comparing with the product limit and the functional limit, the necessity of elastic material replacement and the improvement of track support stiffness according to replacement can be immediately demonstrated based on experimental data. Using an evaluation system of track support stiffness, the performance evaluation data for elastic materials obtained through field tests using software for track support stiffness is integrated and managed on the administrator's computer. Therefore, the replacement plan is established and maintenance history is managed by identifying the replacement time and location of elastic materials. It is possible to evaluate the performance and condition of the elastic material at the various points during the working time of the track inspection and the track performance (track support stiffness) and durability of the elastic material (aging level, spring stiffness variation rate, etc.) at the operation condition. The elastic material could be replaced timely, and the deterioration of the elastic material can be continuously monitored.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.10
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• pp.791-799
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• 2020

Launched in October 2019, Northrop Grumman's MEV-1 was the world's first unmanned mission demonstrating the practical feasibility of on-orbit servicing. Although the concept of on-orbit servicing was proposed several decades ago, it has been developed to various mission concepts providing services such as orbit change, station keeping, propellant and equipment supply, upgrade, repair, on-orbit assembly and production, and space debris removal. The historical success of MEV-1 is expected to expand the market of on-orbit servicing for government agencies and commercial sectors worldwide. The on-orbit servicing essentially requires the utilization of a highly propellant efficient electric propulsion system due to the nature of the mission. In this study, the space mission analysis for a simple on-orbit mission involving Hall thruster is conducted, which is life extension mission for geostationary orbit satellites. In order to analyze the mission, design space exploration for various Hall thruster design variable combinations is performed. The values of design variables and operational parameters of Hall thruster suitable for the mission are proposed through design space analysis and optimization, and mission performance is derived. In addition, the direction of further improvement for the current on-orbit mission analysis process and space mission analysis involving Hall thruster is reviewed.

• Polymer(Korea)
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• v.29 no.2
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• pp.107-121
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• 2005

Electrophosphorescent light emitting diodes (LEDs) using phosphorescent dyes as triplet emitter, which incorporate a heavy metal atom to mix singlet and triplet states by the strong spin-orbit coupling, can achieve the theoretically $100\%$ internal quantum efficiency. In this paper, we report on the performance and the energy transfer mechanism of polymer based highly efficient electrophosphorescent LEDs. The effect of phase separation and aggregation to the energy transfer between polymer hosts and phosphorescent guests and performance of polymer electrophosphorescent LEDs were investigated. Finally, the effect of introducing substitute group and ligand modification of phosphorescent dyes on optical and electrical properties are reported.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.11
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• pp.1021-1032
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• 2011

This paper presents the results of a parametric study for the design of optimal Earth-Moon transfer trajectory using mixed impulsive and continuous thrust. Various types of the optimal Earth-Moon transfer trajectories were designed by adjusting the relative weight between the impulsive and the continuous thrust, and flight time. Two very different transfer trajectories can be obtained by different combination of design parameters. Furthermore, it was found that all thus designed trajectories permit the ballistic capture by the Moon gravity. Finally, the required thrust profiles are presented and analyzed in detail.

• The Science & Technology
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• v.31 no.2 s.345
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• pp.33-35
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• 1998

6천만년 전부터 지구의 기온이 냉각한 것은 대기 속의 이산화탄소가 줄어들었기 때문이라는 데는 대부분의 과학자들의 의견이 일치한다. 무슨 이유로 이산화탄소의 수준이 떨어졌느냐에는 해석이 다양하다. 2백50만년 전부터 유럽과 북미 지역에서 시작된 국지적인 빙하의 원인은 지구의 궤도가 천천히 바뀌면서 햇빛의 패턴에 변화가 생겼기 때문이라는 「밀란코비치 모델」이 널리 받아들여지고 있다. 그러나 빙하시대의 기상데이터를 정확히 알 수 없기 때문에 빙하시대를 일으킨 원인에 대한 해답을 얻을 수 엇다는 비관론도 있다.

• Life and Agrochemicals
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• s.253
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• pp.33-35
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• 2009

공직 36년동안 오로지 국민의 행복을 위해 부의와 타협하지 않고 소신 있는 일처리로 정평이 났던 이정운(67) 전 농촌진흥청 연구관리국장. 고교시절부터 좌우명인 '일근천하무난사 백인당중유태화(一根天下無難事, 百忍堂中有泰和)'를 실천할 수 있었던 초석은 아마도 늘 '정직'을 강조하셨던 어머니의 가르침과 독실한 가톨릭 신자로서 가진 신앙의 힘이 아니었을까 싶다. 한결같이 부지런하면 천하에 어려운 일이 없고 백번 참으면 집안에 큰 평화가 있다는 의미의 좌우명이다. 가훈 또한 '하느님 은총아래 겸손하게 감사하며 사랑으로 살자'이며 애창곡 역시도 '사랑으로'일만큼 그 삶은 온통 감사와 사랑, 정직의 궤를 벗어난 예가 없다. 사랑을 실천하며 멘토의 역할을 마다 않는 이 국장을 용인시에 위치한 고풍스러운 한정식집에서 만나보았다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.283-288
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• 2019

In this paper, there is summarized the validation of ground test results through the telemetry acquired during on-orbit initial activation on solar-array drive assembly(SDA) of GK2A launched at Dec-5, 2018. Especially, the decision logic of SDA initial position and the compensation logic are validated and confirmed. The SDA initial position is needed when GK2A enter to geostationary orbit from transfer orbit and the compensation logic is for the accumulated position error due to the open-loop control. Up to now, it is normal operating. Also the periodic offset between the geostationary orbit and Sun position is found that it is not checked on design phase, and then the proper threshold value is applied.