• 항공우주시스템공학회지
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• 제4권4호
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• pp.37-43
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• 2010

Need for agile satellites increases for performing various mission due to increase of satellite image applications and users. This paper performs attitude maneuver analysis by using Satellite Tool Kit(STK) made by AGI. In order to automate the STK analysis process, a MATLAB program is developed to generate STK input data and to process STK output data. Five attitude maneuver modes are analyzed and attitude angle variation and required torques are calculated.

• 한국통신학회논문지
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• 제36권5B호
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• pp.530-538
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• 2011

본 논문에서는 저궤도 위성기반 AIS에 대한 검출확률의 성능을 평가하여 우리나라 환경에서의 저궤도 위성 AIS 시스템의 적용 가능성에 대하여 평가 및 분석하였다. 본 논문에서는 현재 사용되고 있는 AIS 시스템이 저궤도 위성을 사용하여 AIS서비스를 제공할 경우 필요한 고려사항과 위성과 선박간의 링크 값을 바탕으로 하여 위성 AIS시스템의 적용가능성을 제시하였다. 제안한 방식은 저궤도 위성인 오브컴 (ORBCOMM)과 LEO one을 고려하여 위성의 swath 폭의 변화에 따른 검출확률을 비교 평가하였다. 시뮬레이션과 검출확률 수식에 의한 분석결과, 오브컴 시스템에 의한 검출확률이 LEO one시스템보다 우수하다는 결론을 얻었다. 또한, 위성 AIS시스템은 기존의 AIS에서 문제가 되었던 연안으로 한정되었던 공간문제를 해결할 수 있는 대안으로 활용될 수 있음을 제시하였다.

• 천문학회보
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• 제35권1호
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• pp.30.2-30.2
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• 2010

Numerous operational anomalies and satellite failures have been reported since the beginnings of the "space age". Space weather effects on modern spacecraft systems have been emphasized more and more as increasing their complexity and capability. Energetic particles potentially can destroy and degrade electronic components in satellites. We analyzed the geostationary (GEO) satellite anomalies during 1997-2009 to search possible influences of space weather on the satellite anomalies like power problem, control processor problem, attitude control problem, etc. For this we use particle data from GOES and LANL satellites to investigate space weather effects on the GEO satellites' anomalies depending on Kp index, local time, seasonal variation, and high-energy electron contribution. As results, we obtained following results: (1) there is a good correlation between geomagnetic index(Kp) and anomaly occurrences of the GEO satellite; (2) especially during the solar minimum, occurrence of the satellite anomalies are related to electron flux increase due to high speed solar wind; (3) satellite anomalies occurred more preferentially in the midnight and dawn sector than noon and dusk sector; (4) and the anomalies occurred twice more in Spring and Fall than Summer and Winter; (5) the electron with the lowest energy channel (50-75keV) has the highest correlation (cc=0.758) with the anomalies. High association between the anomalies and the low energy electrons could be understand by the facts that electron fluxes in the spring and fall are stronger than those in the summer and winter, and low-energy electron flux is more concentrated in the dawn sector where the GEO satellite anomalies occurred more frequently than high-energy electron flux. While we could not identify what cause such local time dependences, our results shows that low-energy electrons (~100keV) could be main source of the satellite anomaly, which should be carefully taken into account of operating satellites.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.56.1-56.1
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• 2011

The solar and meteorological resources map is calculated using by one-layer solar radiation model (GWNU model), satellites data and numerical model output on the Korean peninsula. The Meteorological input data to perform the GWNU model are retrieved aerosol optical thickness from MODIS (TERA/AQUA), total ozone amount from OMI (AURA), cloud fraction from geostationary satellites (MTSAT-1R) and temperature, pressure and total precipitable water from output of RDAPS (Regional Data Assimilation and Prediction System) and KLAPS (Korea Local Analysis and Prediction System) model operated by KMA (Korea Meteorological Administration). The model is carried out every hour using by the meteorological data (total ozone amount, aerosol optical thickness, temperature, pressure and cloud amount) and the basic data (surface albedo and DEM). And the result is analyzed the distribution in time and space and validated with 22 meteorological solar observations. The solar resources map is used to the solar energy-related industries and assessment of the potential resources for solar plant. The National Institute of Meteorological Research in KMA released $4km{\times}4km$ solar map in 2008 and updated solar map with $1km{\times}1km$ resolution and topological effect in 2010. The meteorological resources map homepage (http://www.greenmap.go.kr) is provided the various information and result for the meteorological-solar resources map.

• Smart Structures and Systems
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• 제12권3_4호
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• pp.251-269
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• 2013

Measurement of deflections of certain bridges is usually hampered by corruption of the GPS signal by multipath associated with passing vehicles, resulting to unrealistically large apparent displacements. Field data from the Gorgopotamos train bridge in Greece and systematic experiments revealed that such bias is due to superimposition of two major effects, (i) changes in the geometry of satellites because of partial masking of certain satellites by the passing vehicles (this effect can be faced with solutions excluding satellites that get temporarily blocked by passing vehicles) and (ii) dynamic multipath caused from reflection of satellite signals on the passing trains, a high frequency multipath effect, different from the static multipath. Dynamic multipath seems to have rather irregular amplitude, depending on the geometry of measured satellites, but a typical pattern, mainly consisting of a baseline offset, wide base peaks correlating with the sequence of main reflective surfaces of the vehicles passing next to the antenna. In cases of limited corruption of GPS signal by dynamic multipath, corresponding to scale distortion of the short-period component of the GPS waveforms, we propose an algorithm which permits to reconstruct the waveform of bridge deflections using a weak fusion of GPS and RTS data, based on the complementary characteristics of the two instruments. By application of the proposed algorithm we managed to extract semi-static and dynamic displacements and oscillation frequencies of a historical railway bridge under train loading by using noisy GPS and RTS recordings. The combination of GPS and RTS is possible because these two sensors can be fully collocated and have complementary characteristics, with RTS and GPS focusing on the long- and short-period characteristics of the displacement, respectively.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.15-19
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• 2006

GPS has been increasingly exploited to provide positioning and navigation solutions for a variety of applications. In vessel berthing application, however, there are stringent requirements in terms of positioning accuracy, availability and integrity that cannot be satisfied by GPS alone. This is because the performance of satellite-based positioning and navigation systems are heavily dependent on both the number and the geometric distribution of satellite tracked by receivers. Due to the limited number of GPS satellites, a sufficient number of ‘visible’ satellites cannot be sometimes guaranteed. This paper discusses some issues associated with the implementation of ground-based pseudolite augmentation for vessel berthing. Pseudolite means small transmitter that transmits GPS-like signals in local area. Actually, pseudolite can play three different roles in GPS augmentation scheme, depending on the operational conditions. Firstly, in the case of kinematic GPS operation where there are no signal blockages, and more than five satellites are available, additional pseudolites strengthen the GPS satellite-pseudolite geometry, and more accurate and reliable positioning solution can be achieved. Secondly, in the case when there are adverse GPS operational environments in which the number of tracked satellites is less than four, pseudolites can complement the GPS signals. In the third case, GPS signals are completely unavailable, such as when operated indoor. In such cases the pseudolites can replace the satellite constellation. However, the first role will be considered in this paper, since more than four satellite signals can usually be tracked in most marine applications. This paper presents that the pseudolite-augmented precise positioning system can provides continuous centimeter-level positioning accuracy through comparison analysis of RDOP simulation result of the GPS satellite constellation and the pseudolite-augmented GPS satellite constellation.

• 대한원격탐사학회지
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• 제26권6호
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• pp.653-664
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• 2010

The land surface reflectance is a key parameter influencing the climate near the surface. Therefore, it must be determined with sufficient accuracy for climate change research. In particular, the characteristics of the bidirectional reflectance distribution function (BRDF) when using earth observation system (EOS) are important for normalizing the reflected solar radiation from the earth's surface. Also, wide swath satellites like SPOT/VGT (VEGETATION) permit sufficient angular sampling, but high resolution satellites are impossible to obtain sufficient angular sampling over a pixel during short period because of their narrow swath scanning. This gives a difficulty to BRDF model based reflectance normalization of high resolution satellites. The principal objective of the study is to add BRDF modeling of high resolution satellites and to supply insufficient angular sampling through identifying BRDF components from SPOT/VGT. This study is performed as the preliminary data for apply to high-resolution satellite. The study provides surface parameters by eliminating BRD effect when calculated biophysical index of plant by BRDF model. We use semi-empirical BRDF model to identify the BRD components. This study uses SPOT/VGT satellite data acquired in the S1 (daily) data. Modeled reflectance values show a good agreement with measured reflectance values from SPOT satellite. This study analyzes BRD effect components by using the NDVI(Normalized Difference Vegetation Index) and the angle components such as solar zenith angle, satellite zenith angle and relative azimuth angle. Geometric scattering kernel mainly depends on the azimuth angle variation and volumetric scattering kernel is less dependent on the azimuth angle variation. Also, forest from land cover shows the wider distribution of value than cropland, overall tendency is similar. Forest shows relatively larger value of geometric term ($K_1{\cdot}f_1$) than cropland, When performed comparison between cropland and forest. Angle and NDVI value are closely related.

• 한국항공우주학회지
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• 제47권10호
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• pp.728-737
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• 2019

본 연구에서는 초소형 위성을 이용한 위성 편대 및 군집 운용 시 실시간으로 위성 간의 상대 위치 정보를 제공할 수 있는 통합 항법용 모듈형 온보드 컴퓨터(On-board Computer, OBC)를 개발하였다. 모듈은 구조적으로는 큐브위성의 기준 규격에 맞게 설계하되 사용자가 원하는 무선 통신모듈 및 항법용 Global Positioning System(GPS) 장비를 적용할 수 있도록 확장성을 고려하였다. 개발된 OBC는 제품 개발 및 제작 이후 야외 테스트를 통해 저전력 Micro Controller Unit(MCU)로 군집 운용을 수행하는 초소형 위성들의 통합 항법 및 실시간 데이터 동기화 요구 처리속도를 만족함을 확인하였다. 또한, 열진공, 방사능 시험을 거쳐 우주급 환경에서 정상 작동함을 확인하였으며, 진동시험의 경우 underfill 공정을 추가하면 정상적으로 요구조건을 만족할 수 있음을 확인하였다. 이를 통해 향후 수요가 늘어날 군집 운용을 위한 위성군 개발의 핵심 부품인 OBC의 대량생산 체계를 구축하였다.

• 한국정보통신학회논문지
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• 제23권3호
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• pp.318-325
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• 2019

다광역성과 고효율을 장점으로 하는 위성 통신 기술의 진화함에 따라, 위성 간의 간격과 주파수 자원의 제약으로 인해 보다 효율적인 위성방송 서비스에 대한 요구가 증가하고 있다. 최근에 하나의 리플렉터를 사용하여 동일한 수의 이전 수신 채널을 유지하면서 여러 위성으로 부터 여러 대역의 신호를 동시에 수신할 수 있는 안테나에 대한 연구가 진행되고 있다. 본 논문에서는 위성들로부터 전송되는 Ku band (12 ~ 18GHz) 와 Ka band (18 ~ 30GHz) 위성 신호가 반사체를 통해 반사되어 유입될 때, 단일체로 구성된 3개의 피드 혼을 통합한 하나의 피드 혼으로 구성된 안테나를 제안한다. 안테나 설계 및 특성 시뮬레이션은 상용 프로그램인 TICRA사의 CHAMP와 CST사(社)의 Microwave Studio를 사용하였다. 제작한 안테나는 Ku band 대역과 Ka band 대역에서 각각 -10 dB 이하, 40 dBi 이상의 반사손실 특성과 안테나 이득을 나타내었다.

• 항공우주시스템공학회지
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• 제18권2호
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• pp.21-28
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• 2024

최근 뉴스페이스 시대라고 불릴 만큼 우주 산업 분야는 점점 커져가고 있으며, 초소형 위성의 중요성도 또한 커지는 추세이다. 초소형 위성은 주로 COTS 부품을 사용하며 우주급 부품에 비해 낮은 신뢰도를 가지고 있지만 개발 기간, 비용, 성능 측면에서 장점을 가지고 있어 사용성이 확대되고 있다. COTS(Commercial Off-The-Shelf)는 상용으로 판매되는 제품을 가리키며, 이는 특정 조직이나 프로젝트에서 직접 제작하는 대신 시장에서 구입하여 사용되는 것을 의미한다. 위성은 발사되는 순간부터 수리가 불가능 하기 때문에 신뢰도 예측의 중요성은 크게 작용한다. 근래에는 신뢰도 예측 시 부품에 대한 인자 뿐만 아니라 시스템 level에서의 신뢰도를 예측하는 것이 더 중요하게 적용되고 있다. 따라서 본 연구에서는 신뢰도 예측 규격인 MIL-HDBK-217F와 업데이트된 RiAC-HDBK-217Plus와 FIDES를 비교해 본다. 그리고 FIDES 예측 기준에서 다양한 산업 분야에 적용될 수 있도록 구성한 제조업체의 품질 보증 요소를 세분화하여 우주 산업에 적합한 점수가 반영될 수 있도록 하였다.