• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.177-184
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• 2006

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers' orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites' mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite's orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.

• 한국소음진동공학회논문집
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• 제21권10호
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• pp.951-959
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• 2011

In this study, an OTM(on-the-move) antenna which is mounted on ground vehicles and is used for mobile communication between vehicle and satellite while moving was addressed. Since LOS(line-of-sight) of antenna should direct satellite consistently while vehicle moving to guarantee high satellite communication quality, active antenna LOS stabilization is a core technology for OTM antenna. Stabilization of a satellite tracking antenna which consists of 2-DOF gimbals, an elevation gimbal over an azimuth gimbal, was considered in this study. In consideration of driving mechanism which consists of gear train and flexible driving shafts, a two-mass-system dynamic model coupled with vehicle motion was presented. An internal PI-control loop + outer PI-control loop structure has been suggested in order to damp the torsional vibration and stabilize control system. The classical pole-placement method was applied to design control gains. In addition, a vehicle motion compensation control beside of the feedback control loop has been suggested to improve LOS stabilization performances. The feasibility of the proposed control design was verified along with some experimental results.

• 전기학회논문지
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• 제59권11호
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• pp.2073-2082
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• 2010

The 4-th generation of mobile communication aims to realize global, fast and mobile communication service. The satellite communication charges a key role in this field. In this study, an OTM(On-The-Move) antenna which is mounted on ground vehicles and is used for mobile communication between vehicle and satellite was addressed. Since vehicles move during communication, active antenna line-of-sight stabilization is a core technology to guarantee high satellite communication quality. Stabilization of a satellite tracking antenna which consists of 2-DOF gimbals, an elevation gimbal over an azimuth gimbal, was considered in this study. Various disturbance torques such as static and dynamic mass imbalance torques, variation of moment of inertia according to elevation angle, friction torque related to vehicle motion, equivalent disturbance torque due to antenna roll motion, etc. were analyzed. As a robust stabilization control, rate feedback with sliding mode control and position feedback with proportional+integral control was suggested. To compensate antenna roll motion, a supplementary roll rate feed forward control was included beside of the feedback control loop. The feasibility of the analysis and the proposed control design were verified along with some simulation results.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.209-220
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• 1998

The stability problem of steady motion of a rigid body with multi-elastic appendages and multi-liquid-filled cavities, in the presence of no external forces or torque, is considered in this paper. The flexible appendages are modeled as the clamped -free-free-free rectangular plates, or/and as the discrete mass- spring sub-system. The motion of liquid in every single ellipsoidal cavity is modeled as the uniform vortex motion with a finite number of degrees of freedom. Assuming that stationary holonomic constraints imposed on the body allow its rotation about a spatially fixed axis, the equation of motion for such a systematic configuration can be very complex. It consists of a set of ordinary differential equations for the motion of the rigid body, the uniform rotation of the contained liquids, the motion of discrete elastic parts, and a set of partial differential equations for the elastic appendages supplemented by appropriate initial and boundary conditions. In addition, for such a hybrid system, under suitable assumptions, their equations of motion have four types of first integrals, i.e., energy and area, Helmholtz' constancy of liquid - vortexes, and the constant of the Poisson equation of motion. Chetaev's effective method for constructing Liapunov functions in the form of a set of first integrals of the equations of the perturbed motion is employed to investigate the sufficient stability conditions of steady motions of the complete system in the sense of Liapunov, i.e., with respect to the variables determining the motion of the solid body and to some quantities which define integrally the motion of flexible appendages. These sufficient conditions take into account the vortexes of the contained liquids, the vibration of the flexible components, and coupling among the liquid-elasticity solid.

• 한국항행학회논문지
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• 제21권5호
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• pp.428-434
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• 2017

최근 이동형 글로벌 광대역 통신 및 위성기반의 양방향 인터넷 서비스에 대한 수요가 증가함에 따라 ESIM(Earth Station in Motion)이라는 새로운 형태의 위성 터미널이 개발되고 있다. 이 시스템은 ITU-R Resolution 158(WRC-15)에서 FSS(Fixed Satellite Service) 업링크에 27.5-29.5 GHz 대역사용을 고려하고 있어 동일 대역에 이미 분배된 FS와의 간섭분석에 대한 연구가 요구되고 있다. 이에 본 논문에서는 FS(Fixed Service) 무선국 방향으로 보어사이트를 향하는 ESIM의 방위각을 일양분포의 랜덤특성을 고려하여 FS 수신안테나의 -10 dB 빔폭 내의 평균 수신전력 및 간섭기준 초과확률에 대해 이론해석과 시뮬레이션 분석을 수행하였다. 그 결과 이론해석의 타당성을 보여주며, 동일 대역의 FS를 보호하기 위해서는 ESIM 이동 터미널의 보어사이트에 대한 이동경로 기울기 각도, 운영시간, 이동속도 등을 종합적으로 고려해서 간섭기준이 마련되어야 한다.

• International Journal of Aeronautical and Space Sciences
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• 제4권2호
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• pp.1-8
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• 2003

Satellite formation flying is the placing micro-satellites with the same mission into nearby orbits to form a cluster. Clohessy-Wiltshire equations are used to describe the relative motion and control strategies between satellites within a cluster, which are known as Hill's equations. Even though Hill's equations are powerful in determining initial conditions for the satellite formation flying, they can not accurately express the relative motion under J2 perturbation. Some methods have been developed for the determination of initial conditions to avoid limits of Hill's equation. This paper gives a new method of determining initial conditions using mean elements. For this research mean elements were transformed to osculating elements using Brouwer's theory and the orbit was propaeated with the consideration of J2-J8 to get a relative position. The results show that satellites within a cluster are maintained in the desired boundary for long period and the method is effective on a fuel saving for satellite formation flying.

• 한국위성정보통신학회논문지
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• 제3권2호
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• pp.26-31
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• 2008

As a multi-mission GEO satellite, Communication, Ocean, and Meteorological Satellite (COMS) is scheduled to be launched in the year 2009. COMS has three different payloads: Ka-band communication payload, Geostationary Ocean Color Imager (GOCI) and Meteorological Imager (MI). Among the three payloads, MI and GOCI have several conflict relationships; one of them is that if MI mirror moves vertically larger than 4 Line Of Sight (LOS) angle while GOCI is imaging, image quality of GOCI becomes degraded. In this paper, MI scheduling algorithm to prevent GOCI's image quality degradation will be presented.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.301-304
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• 2008

Since longer wavelength microwave radiation can penetrate clouds, satellite passive microwave sensors can observe sea ice of the entire polar region on a daily basis. Thus, it is becoming popular to derive sea ice motion vectors from a pair of satellite passive microwave sensor images observed at one or few day interval. Usually, the accuracies of derived vectors are validated by comparing with the position data of drifting buoys. However, the number of buoys for validation is always quite limited compared to a large number of vectors derived from satellite images. In this study, the sea ice motion vectors automatically derived from pairs of AMSR-E 89GHz images (IFOV = 3.5 ${\times}$ 5.9km) by an image-to-image cross correlation were validated by comparing with sea ice motion vectors manually derived from pairs of cloudless MODIS images (IFOV=250 ${\times}$ 250m). Since AMSR-E and MODIS are both on the same Aqua satellite of NASA, the observation time of both sensors are the same. The relative errors of AMSR-E vectors against MODIS vectors were calculated. The accuracy validation has been conducted for 5 scenes. If we accept relative error of less than 30% as correct vectors, 75% to 92% of AMSR-E vectors derived from one scene were correct. On the other hand, the percentage of correct sea ice vectors derived from a pair of SSM/I 85GHz images (IFOV = 15 ${\times}$ 13km) observed nearly simultaneously with one of the AMSR-E images was 46%. The difference of the accuracy between AMSR-E and SSM/I is reflecting the difference of IFOV. The accuracies of H and V polarization were different from scene to scene, which may reflect the difference of sea ice distributions and their snow cover of each scene.

• 대한원격탐사학회지
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• 제34권6_2호
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• pp.1215-1227
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• 2018

해빙의 이동은 지역적 분포뿐만 아니라 해빙의 생성 및 두께에도 영향을 미치기 때문에 해빙의 변화를 평가하는 데에 중요한 정보가 된다. 이 연구에서는 북극해 해빙의 이동 특성 탐지를 위해 Korea Multi-Purpose Satellite-2(KOMPSAT-2)와 Korea Multi-Purpose Satellite-3(KOMPSAT-3)의 두 위성 센서로부터 다중 시기 고해상도 광학 위성 영상을 획득하고, SIFT(Scale-Invariant Feature Transform), SURF(Speeded Up Robust Features) 및 ORB(Oriented FAST and Rotated BRIEF)의 특징점 추적 기법을 적용하였다. 두 위성 센서에서 획득된 영상의 활용을 위해 전처리 단계에서 공간해상도와 방사해상도를 일치시킨 후 특징점 추적 기법을 적용한 결과 SIFT의 경우 영상 전반에 걸쳐 특징점의 고른 공간 분포가 나타났고, SURF의 경우 해빙과 해양의 경계 부분에 특징점이 주요하게 분포하는 경향이 관찰되었으며 이러한 경향은 ORB에서 가장 현저하게 나타났다. 특징점 추적 기법별 연산 시간 측정 결과 SIFT, SURF 및 ORB의 순서로 연산 시간이 감소하였다. ORB의 경우 SIFT 기법 대비 추적된 특징점 수가 평균 59.8%로 줄어들었지만 연산 시간은 평균 8.7%에 해당하는 시간이 소요되어 해빙 이동 특성의 고속 탐지에 적합한 기법으로 판단된다.

• 한국정보통신학회논문지
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• 제14권1호
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• pp.31-37
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• 2010

본 논문에서는 저궤도 운동 특성을 갖는 다목적실용 위성2호의 위성 거리 측정을 해석하고 최적의 운용 방안을 제안하였다. 위성의 궤도 특성은 방사속도 성분, 가속도 성분 그리고 가속도 속도 성분으로 해석하고, 위성 궤도 운동에 따른 위성 거리 측정 신호는 도플러 주파수, 도플러 주파수 변화율 그리고 도플러 주파수 변화율 속도 성분으로 해석하였다. 위성 거리 측정에 영향을 미치는 성분에 대한 거리의 정확성 그리고 거리 측정의 모호성 가능성을 정량적으로 해석하여 거리 측정의 최적 운용 파라미터를 분석하였다. 본 논문에서 해석된 결과는 위성 거리 측정을 위한 소형 지구국 시스템 제원 및 설계 파라미터로 활용할 수 있다.