• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2003년도 한국우주과학회보 제12권2호
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• pp.46-46
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• 2003

Since its launching on 21 December 1999, the KOrea Multi-Purpose SATellite-Ⅰ (KOMPSAT-Ⅰ) has been successfully operated by the Mission Control Element (MCE), which was developed by the Electronics and Telecommunications Research Institute (ETRI). Most of the major functions of the MCE have been successfully demonstrated and verified during the three years of the mission life of the satellite. The Mission Analysis and Planning Subsystem (MAPS), which is one of the four subsystems in the MCE, played a key role in the Launch and Early Orbit Phase (LEOP) operations as well as the on-orbit mission operations. This paper presents the operational performances of the various functions in MAPS. We show the performance and analysis of orbit determinations using ground-based tracking data and GPS navigation solutions. We present four instances of the orbit maneuvers that guided the spacecraft from injection orbit into the nominal on-orbit. We include the ground-based attitude determination using telemetry data and the attitude maneuvers for imaging mission. The event prediction, mission scheduling, and command planning functions in MAPS subsequently generate the spacecraft mission operations and command plan. The fuel accounting and the realtime ground track display also support the spacecraft mission operations. We also present the orbital evolutions during the three years of the mission life of the KOMPSAT-Ⅰ.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2000년도 제14회 학술강연논문집
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• pp.6-6
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• 2000

On-orbit thermal behavior of KOMPSAT (Korea Multi-purpose Satellite) propulsion system employing hydrazine (N$_2$H$_4$) liquid monopropellant is addressed. Thermal control performance to prevent propellant freezing in spacecraft-operational orbit was verified by flight telemetry data obtained during LEOP (Launch and Early Operation Phase). Results are depicted in terms of temperature history during several orbits selected and are compared with acceptable temperature ranges of system components. Cyclic behavior of temperature is reduced into duty cycles of the avionics heaters and subsequently converted into the electrical power required to keep away from propellant freezing. Temperature of each component which was achieved under on-ground thermal-balanced condition of spacecraft, is presented for comparison with the flight data, additionally.

• Journal of the Korean Data and Information Science Society
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• 제23권3호
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• pp.595-604
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• 2012

In this article, we consider chaotic behavior happened in nonsmooth dynamical systems. To quantify such a behavior, a computation of Lyapunov exponents for chaotic orbits of a given nonsmooth dynamical system is focused. The Lyapunov exponent is a very important concept in chaotic theory, because this quantity measures the sensitive dependence on initial conditions in dynamical systems. Therefore, Lyapunov exponents can decide whether an orbit is chaos or not. To measure the sensitive dependence on initial conditions for nonsmooth dynamical systems, the calculation of Lyapunov exponent plays a key role, but in a theoretical point of view or based on the definition of Lyapunov exponents, Lyapunov exponents of nonsmooth orbit could not be calculated easily, because the Jacobian derivative at some point in the orbit may not exists. We use an algorithmic calculation method for computing Lyapunov exponents using time series for a two dimensional piecewise smooth dynamic system.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.169-180
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• 2019

In this study, a batch least square estimator that utilizes optical observation data is developed and utilized to determine geostationary orbits (GEO). Through numerical simulations, the effects of error sources, such as clock errors, measurement noise, and the a priori state error, are analyzed. The actual optical tracking data of a GEO satellite, the Communication, Ocean and Meteorological Satellite (COMS), provided by the optical wide-field patrol network (OWL-Net) is used with the developed batch filter for orbit determination. The accuracy of the determined orbit is evaluated by comparison with two-line elements (TLE) and confirmed as proper for the continuous monitoring of GEO objects. Also, the measurement residuals are converged to several arcseconds, corresponding to the OWL-Net performance. Based on these analyses, it is verified that the independent operation of electro-optic space surveillance systems is possible, and the ephemerides of space objects can be obtained.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.775-782
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• 2014

The importance of including spin-orbit interactions for the correct description of structures and vibrational frequencies of haloiodomethanes is demonstrated by density functional theory calculations with spin-orbit relativistic effective core potentials (SO-DFT). The vibrational frequencies and the molecular geometries obtained by SO-DFT calculations do not match with the experimental results as well as for other cations without significant relativistic effects. In this sense, the present data can be considered as a guideline in the development of the relativistic quantum chemical methods. The influence of spin-orbit effects on the bending frequency of the cation could well be recognized by comparing the experimental and calculated results for $CH_2BrI$ and $CH_2ClI$ cations. Spin-orbit effects on the geometries and vibrational frequencies of $CH_2XI$ (X=F, Cl, Br, and I) neutral are negligible except that C-I bond lengths of haloiodomethane neutral is slightly increased by the inclusion of spin-orbit effects. The $^2A^{\prime}$ and $^2A^{{\prime}{\prime}}$ states were found in the cations of haloiodomethanes and mix due to the spin-orbit interactions and generate two $^2E_{1/2}$ fine-structure states. The geometries of $CH_2XI^+$ (X=F and Cl) from SO-DFT calculations are roughly in the middle of two cation geometries from DFT calculations since two cation states of $CH_2XI$ (X=F and Cl) from DFT calculations are energetically close enough to mix two cation states. The geometries of $CH_2XI^+$ (X=Br and I) from SO-DFT calculations are close to that of the most stable cation from DFT calculations since two cation states of $CH_2XI$(X=Br and I) from DFT calculations are energetically well separated near the fine-structure state minimum.

• 천문학논총
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• 제8권1호
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• pp.137-151
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• 1993

We have calculated the astronomical almanac 1994 and simulated the trajectory of a satellite orbit considering all perturbative forces with various initial conditions. In this work, Gauss Jackson multistep integration method has been used to calculate our basic equation of motion with high numerical accuracy. It has beer. found that our results agree well with the Astronomical Almanac Data distributed by JPL of NASA and the orbit simulations have been carried out with fast speed, stability and excellent round-off error accumulation, comparing with other numerical methods. In order to be carried out our works on almanac and orbit calculations easily by anyone who uses a personal computer, we have made a computer program on graphical user interface to provide various menus for detail works selected by a mouse.

• 항공우주기술
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• 제12권2호
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• pp.91-98
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• 2013

LEO (Low Earth Orbit), GEO (Geosynchronous Earth Orbit) 위성을 비롯한 우주 탐사선의 컴퓨팅 환경은 지상의 내장형 시스템(Embedded System)과 동일한 범주로 간주될 수 있으며 개인용, 산업/서버용 컴퓨터와 비교했을 때 비교적 원시적이고 발전 속도도 더뎠다. 특히 개인 컴퓨터 및 서버/워크스테이션에서 필수적으로 사용되고 있는 파일 시스템도 우주 탐사선에는 최근까지 거의 사용되지 않았다. 본 논문에서는 최근에 우주 탐사선에 파일 시스템을 적용하기 위한 유럽 PUS (Packet Utilization Standard)와 CCSDS (Consultative Committee for Space Data Systems) 커뮤니티의 관련 규격 제정 등 국제적 연구 개발 동향 및 우주 탐사선에 적용가능한 응용 기술 분야에 대한 연구 결과를 기술한다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1649-1654
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• 1991

In 1995 the VSOP satellite, which is called MUSES-B in Japan, will be launched under the VLBI Space Observatory Programme(VSOP) promoted by ISAS(Institute of Space and Astronautical Science) of Japan. We are now developing the GPS Receiver(GPSR) and On-board Orbit Determination System. This paper describes the GPS(Global Positioning System), VSOP, GPSR(GPS Receiver system) configuration and the results of the GPS system analysis. The GPSR consists of three GPS antennas and 5 channel receiver package. In the receiver package, there are two 16 bits microprocessing units. The power consumption is 25 Watts in average and the weight is 8.5 kg. Three GPS antennas on board enable GPSR to receive GPS signals from any NAVSTARs(GPS satellites) which are visible. NAVSATR's visibility is described as follows. The VSOP satellite flies from 1, 000 km to 20, 000 km in height on the elliptical orbit around the earth. On the other hand, the orbit of NAVSTARs are nearly circular and about 20, 000 km in height. GPSR can't receive the GPS signals near the apogee, because NAVSTARs transmit the GPS signals through the NAVSTAR's narrow beam antennas directed toward the earth. However near the perigee, GPSR can receive from 12 to 15 GPS signals. More than 4 GPS signals can be received for 40 minutes, which are related to GDOP(Geometric Dillusion Of Precision of selected NAVSTARs). Because there are a lot of visible NAVSTARs, GDOP is small near the perigee. This is a favorqble condition for GPSR. Orbit determination system onboard VSOP satellite consists of a Kalman filter and a precise orbit propagator. Near the perigee, the Kalman filter can eliminate the orbit propagation error using the observed data by GPSR. Except a perigee, precise onboard orbit propagator propagates the orbit, taking into account accelerations such as gravities of the earth, the sun, the moon, and other acceleration caused by the solar pressure. But there remain some amount of calculation and integration errors. When VSOP satellite returns to the perigee, the Kalman filter eliminates the error of the orbit determined by the propagator. After the error is eliminated, VSOP satellite flies out towards an apogee again. The analysis of the orbit determination is performed by the covariance analysis method. Number of the states of the onboard filter is 8. As for a true model, we assume that it is based on the actual error dynamics that include the Selective Availability of GPS called 'SA', having 17 states. Analytical results for position and velocity are tabulated and illustrated, in the sequel. These show that the position and the velocity error are about 40 m and 0.008 m/sec at the perigee, and are about 110 m and 0.012 m/sec at the apogee, respectively.

• 한국항공우주학회지
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• 제31권10호
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• pp.51-59
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• 2003

본 논문에서는 위성 탑재용 궤도전파기의 자동 갱신 방안에 대하여 제안하였다. 위성 탑재용 궤도전파기는 비상시 위성 항법 장치의 대체 수단으로써 여러 이유로 지상국에 의한 갱신이 불가능할 경우에 대비하여 위성체 스스로 가장 최신의 탑재 궤도전파기 모델을 유지해야 한다. 이를 위해 GPS 수신기의 고장 시점까지 가용한 GPS 항행해나 탑재 궤도 결정 시스템으로부터의 자료를 이용하여 최소자승회귀법(Least Square Curve Fit)이나 칼만 필터를 통해 위성에 탑재된 궤도전파기를 위한 기준궤도 또는 잔차 재생함수의 계수를 반복적으로 갱신한다. 탑재 궤도전파기 갱신을 통해 만약 있을 수도 있는 지상국에서의 계산 오류를 스스로 보정할 수 있고, GPS와 탑재 궤도결정 시스템의 작동 불능 시점 직전까지의 자료에 근거하여 궤도를 예측하기 때문에 항상 최신의 궤도전파기 모델을 유지할 수 있다. 또한 아리랑 1호의 궤도 예측 자료를 이용하여 실제 운용시 최적화된 알고리즘을 통해 실시간 갱신을 이용한 궤도 전파 성능에 대하여 살펴보았다.

• 한국항공우주학회지
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• 제49권5호
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• pp.417-424
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• 2021

정지궤도위성의 원격데이터 통신 포맷은 제한된 통신 속도 대비 대량으로 생성되는 위성 데이터를 효율적으로 수신하고, 36,000km 고도에서 운영되는 정지궤도위성의 원격명령어 수신 결과를 정확하게 확인하기 위해 설계된다. 한국항공우주연구원에서 개발하여 2018년과 2020년에 각각 발사 및 운영 중인 천리안2A호와 2B호는 한국 최초의 정지궤도위성인 천리안1호의 임무를 연속하여 수행하도록 설계되었다. 따라서 정지궤도위성과 지상국의 안정적이고 효율적인 원격 통신을 위해 필요한 원격 통신 설계 요소들을 승계하였다. 한편, 원격 데이터의 처리 및 운영을 담당하는 천리안 2A호와 2B호의 탑재소프트웨어는 다목적위성시리즈를 통해 그 성능이 더욱 개선되어 왔으며 최신의 원격 데이터 처리 및 운영 알고리즘이 구축되어 있다. 본 논문에서는 정지궤도위성의 향상된 원격 데이터 송수신을 위한 원격명령어 및 원격측정데이터의 포맷 및 운영 개념 설계를 제안하고, 실제 천리안 2A호와 2B호의 탑재소프트웨어에 적용된 내용들을 상세하게 기술한다.