• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.345-352
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• 2010

Korea multi-purpose satellite-5 (KOMPSAT-5) is a low earth orbit (LEO) satellite scheduled to be launched in 2010. To satisfy the precision orbit determination (POD) requirement for a high resolution synthetic aperture radar image of KOMPSAT-5, KOMPSAT-5 has atmosphere occultation POD (AOPOD) system which consists of a space-borne dual frequency global positioning system (GPS) receiver and a laser retro reflector array. A space-borne dual frequency GPS receiver on a LEO satellite provides position data for the POD and radio occultation data for scientific applications. This paper describes an overview of AOPOD system and operation concepts of the radio occultation mission in KOMPSAT-5. We showed AOPOD system satisfies the requirements of KOMPSAT-5 in performance and stability.

• Journal of Astronomy and Space Sciences
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• 제35권4호
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• pp.295-308
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• 2018

In this study, orbit determination (OD) simulation for the Korea Pathfinder Lunar Orbiter (KPLO) was accomplished for investigation of the observational arc-length effect using a sequential estimation algorithm. A lunar polar orbit located at 100 km altitude and $90^{\circ}$ inclination was mainly considered for the KPLO mission operation phase. For measurement simulation and OD for KPLO, the Analytical Graphics Inc. Systems Tool Kit 11 and Orbit Determination Tool Kit 6 software were utilized. Three deep-space ground stations, including two deep space network (DSN) antennas and the Korea Deep Space Antenna, were configured for the OD simulation. To investigate the arc-length effect on OD, 60-hr, 48-hr, 24-hr, and 12-hr tracking data were prepared. Position uncertainty by error covariance and orbit overlap precision were used for OD performance evaluation. Additionally, orbit prediction (OP) accuracy was also assessed by the position difference between the estimated and true orbits. Finally, we concluded that the 48-hr-based OD strategy is suitable for effective flight dynamics operation of KPLO. This work suggests a useful guideline for the OD strategy of KPLO mission planning and operation during the nominal lunar orbits phase.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.335-342
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• 2023

Lunar Navigation Satellite System refers to a constellation of satellite providing PNT services on the moon. LNSS consists of main satellite and navigation satellites. Navigation satellites orbiting around the moon and a main satellite moves the area between the moon and the L2 point. The navigation satellite performs the same role as the Earth's GNSS satellite, and the main satellite communicates with the Earth for time synchronization. Due to the effect of the non-uniform shape of the moon, it is necessary to focus on the influence of the lunar gravitational field when designing the orbit simulation for navigation satellite. Since the main satellite is farther away from the moon than the navigation satellite, both the earth's gravity and the moon's gravity must be considered simultaneously when designing the orbit simulation for main satellite. Therefore, the main satellite orbit simulation must be designed through the three-body problem between the Earth, the moon, and the main satellite. In this paper, the orbit simulation tool for main satellite and navigation satellite required for LNSS was designed. The orbit simulation considers the environment characteristics of the moon. As a result of comparing long-term data (180 days) with the commercial program GMAT, it was confirmed that there was an error of about 1 m.

• Journal of Astronomy and Space Sciences
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• 제27권3호
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• pp.253-262
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• 2010

The electrical power system (EPS) of Korean satellites in low-earth-orbit is designed to achieve energy balance based on a one-orbit mission scenario. This means that the battery has to be fully charged at the end of a one-orbit mission. To provide the maximum solar array (SA) power generation, the peak power tracking (PPT) method has been developed for a spacecraft power system. The PPT is operated by a software algorithm, which tracks the peak power of the SA and ensures the battery is fully charged in one orbit. The EPS should be designed to avoid the stress of electronics in order to handle the main bus power from the SA power. This paper summarizes the results of energy balance to achieve optimal power sizing and the actual trend analysis of EPS performance in orbit. It describes the results of required power for the satellite operation in the worst power conditions at the end-of-life, the methods and input data used in the energy balance, and the case study of energy balance analyses for the normal operation in orbit. Both 10:35 AM and 10:50 AM crossing times are considered, so the power performance in each case is analyzed with the satellite roll maneuver according to the payload operation concept. In addition, the data transmission to the Korea Ground Station during eclipse is investigated at the local-time-ascending-node of 11:00 AM to assess the greatest battery depth-of-discharge in normal operation.

• Journal of the Optical Society of Korea
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• 제5권1호
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• pp.9-15
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• 2001

The ocean Scanning Multi-spectral Imager (OSMI) is a payload on the KOrea Multi-Purpose SATellite (KOMPSAT) to perform worldwide ocean color monitoring f the study of biological oceanography. OSMI performs solar and dark calibrations for on-orbit instrument calibration. The purpose of the solar calibration is to monitor the degradation of imaging performance for each pixel of 6 spectral bands and to correct the degradation effect on OSMI image during the ground station date processing. The design, the operation concept, and the radiometric characteristics of the solar calibration are investigated. A linear model of image response and a solar calibration radiance model are proposed to study the instrument characteristics using the solar calibration data. The performance of spectral responsivity and spatial response uniformity. The first solar calibration data and the analysis results are important references for further study on the on-orbit stability of OSMI response during its lifetime.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.1-9
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• 2011

국내 최초의 정지궤도 관측 위성인 천리안(통신해양기상위성)이 2010년 6월 27일에 성공적으로 발사되었다. 천리안에의 기상탑재체와 해양탑재체의 원시 영상은 지상에서 처리 과정을 거쳐 사용자에게 전달되다. 한국항공우주연구원의 주도로 국내 개발된 송수신자료전처리시스템은 원시 영상에 복사 및 기하 보정을 수행하고, 전처리된 영상과 부가 자료들을 위성을 통해 사용자들에게 분배하는 기능을 수행한다. 궤도상 시험을 성공적으로 완료한 송수신자료전처리시스템은 기상위성센터, 해양위성센터, 그리고 위성운영센터에 설치되어 현재 정상 운영 중에 있다. 궤도상 시험 기간 동안 송수신자료전처리시스템의 기능과 성능에 대한 검증은 1) 영상 송수신, 2) 기상 및 해양 영상의 전처리, 그리고 3) 사용자 분배 기능으로 나뉘어 수행되었다. 이 논문은 천리안 위성 발사 후 수행된 송수신자료전처리시스템의 궤도상 시험 운영 검증 결과를 기술한다.

• 한국항행학회논문지
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• 제13권2호
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• pp.178-186
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• 2009

SBAS(Satellite Based Augmentation System) 시스템에서는 GNSS 사용자들의 위치 정확도 향상을 위해 위성궤도 및 시계보정정보를 제공하고 있는데, 본 논문에서는 이러한 보정정보의 정확도에 대해 분석하였다. IGS(International GNSS Service)에서 제공하는 GPS 위성의 정밀궤도력을 참값으로 가정하고, 그에 대한 오차를 이용하여 정확도를 분석/수행하였다. 이때 IGS 정밀궤도력과의 정확한 비교를 위해 GPS 위성에 대한 안테나 위상중심 편차와 P1-C1 편이를 고려하였다. SBAS 위성궤도 및 시계보정 정보로는 미국의 WAAS와 일본의 MSAS 보정정보를 이용하였다. 정확도 분석을 통해 SBAS에서 제공하는 위성궤도 보정정보와 위성시계 보정정보가 상당한 상관관계를 가지고 있음을 확인하였다. 또한 보정정보의 정확도는 SBAS 시스템의 지상 네트워크 크기와 위성의 궤적에 영향을 받는 것을 확인하였다.

• Journal of Astronomy and Space Sciences
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• 제8권1호
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• pp.99-113
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• 1991

수치적인 방법을 이용하여 인공위성의 궤도를 예보할 수 있는 소프트웨어 시스템 (IODS: ISSA Orbit Determination System)을 개발하였다. IODS의 궤도예보 정확도틀 평가하기 위히여 기상위성 NOAA-ll호와 정지위생 INTELSAT-V의 궤도를 예보하였고, 그 결과를 중앙기상대와 금산 위생통신지구국의 위성추적 자료와 비교하였다. 그리고 인공위성애 미치는 여러가지 섭동력을 정량적으로 분석하였다 한편, 동경 100도에 상공에 위치한 정지위성(KORSAT-l)의 궤도을 가정하여 궤도가 시간에 따라 변하는 양상을 IODS툴 이용하여 분석하였으며, KORSAT-l이 지구의 그림자에 들어가는 식현상을 예측하고 분석하였다.

• 한국항공우주학회지
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• 제44권9호
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• pp.781-788
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• 2016

본 논문에서는 실시간 On-board 궤도 결정 성능을 향상시키기 위해 고정밀 우주 섭동 모델을 구현하였고, 구현된 우주 섭동모델을 GNSS 수신기의 궤도 결정 로직에 적용하여 그 결과를 분석하였다. 궤도 결정 로직은 확장 칼만 필터(Extended Kalman Filter)로 구현되었고, 의사거리로 계산한 궤도(Standard Position Service)를 관측정보로 이용하였다. 궤도 결정 로직 성능 검증은 GPS 인공위성의 신호를 모사하는 GNSS 시뮬레이터를 이용하여 수행하였다. 고정밀 섭동모델의 궤도 결정 성능을 $J_2$ 항만 고려한 섭동모델의 궤도 결정 성능과 비교하여 분석한 결과, GPS 항행해의 위치 정밀도는 43.61 m($3{\sigma}$)에서 23.86 m($3{\sigma}$)로 46 % 개선되었으며 속도 정밀도는 0.159 m/s($3{\sigma}$)에서 0.044 m/s($3{\sigma}$)로 72 % 개선되어 정밀도가 향상된 것을 확인할 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제28권4호
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• pp.333-344
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• 2011

An optical tracking system has advantages for observing geostationary earth orbit (GEO) satellites relatively over other types of observation system. Regular surveying for unidentified space objects with the optical tracking system can be an early warning tool for the safety of five Korean active GEO satellites. Two strategies of positioning on the observed image of Communication, Ocean and Meteorological Satellite 1 are tested and compared. Photometric method has a half root mean square error against streak method. Also eccentricity method for initial orbit determination (IOD) is tested with simulation data and real observation data. Under 10 minutes observation time interval, eccentricity method shows relatively better IOD results than the other time interval. For follow-up observation of unidentified space objects, at least two consecutive observations are needed in 5 minutes to determine orbit for geosynchronous orbit space objects.