• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.45-50
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• 2005

To determine precise position GPS carrier phase measurements are used. In addition, the multi-antenna system consisting of 2 or more GPS antennas can make attitude determination effectively. When GPS carrier phase measurements are used the integer ambiguity must be fixed. The success rate is used to validate the integer ambiguity. For LEO satellite attitude determination the double difference carrier phase measurements are used, the success rate is calculated using the covariance matrix and the measurement matrix. The constraint that LEO satellite position vector and attitude vector is orthogonal is suggested for improving the success rate. The LEO satellite orbit model is KITSAT3. The results of the simulation are shown and analyzed.

• 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.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.187-195
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• 2008

Generation of accurate ground coordinates from high resolution satellite image are becoming increasingly of interest. The primary focus of this paper is to compute satellite direct sensor model (DSM) and rational function model (RFM) for accurate generation of ground coordinates from high resolution satellite images. Being based on this we presented an algorithm to be able to efficiently ground coordinates about large area with introducing RFM(rational function model) method applied to rigorous sensor modeling standing on basis of satellite orbit dynamics and collinearity equation, and sensor modeling of high-resolution satellite data like IKONOS, QuickBird, KOMPSAT-2 and others. The general high resolution satellite measures the position, velocity and attitude data of satellite using star, gyro, and GPS sensors.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.243-252
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• 2018

In a satellite gravimetry mission similar to GRACE, the precision of inter-satellite ranging is one of the key factors affecting the quality of gravity field recovery. In this paper, the impact of ranging precision on the accuracy of recovered geopotential coefficients is analyzed. Simulated precise orbit determination (POD) data and inter-satellite range data of formation-flying satellites containing white noise were generated, and geopotential coefficients were recovered from these simulated data sets using the crude acceleration approach. The accuracy of the recovered coefficients was quantitatively compared between data sets encompassing different ranging precisions. From this analysis, a rough prediction of the accuracy of geopotential coefficients could be obtained from the hypothetical mission. For a given POD precision, a ranging measurement precision that matches the POD precision was determined. Since the purpose of adopting inter-satellite ranging in a gravimetry mission is to overcome the imprecision of determining orbits, ranging measurements should be more precise than POD. For that reason, it can be concluded that this critical ranging precision matching the POD precision can serve as the minimum precision requirement for an on-board ranging device. Although the result obtained herein is about a very particular case, this methodology can also be applied in cases where different parameters are used.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.269-277
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• 2013

In this study, we present results of precise orbital geodetic parameter estimation using satellite laser ranging (SLR) observations for the International Laser Ranging Service (ILRS) associate analysis center (AAC). Using normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 in SLR consolidated laser ranging data format, the NASA/GSFC GEODYN II and SOLVE software programs were utilized for precise orbit determination (POD) and finding solutions of a terrestrial reference frame (TRF) and Earth orientation parameters (EOPs). For POD, a weekly-based orbit determination strategy was employed to process SLR observations taken from 20 weeks in 2013. For solutions of TRF and EOPs, loosely constrained scheme was used to integrate POD results of four geodetic SLR satellites. The coordinates of 11 ILRS core sites were determined and daily polar motion and polar motion rates were estimated. The root mean square (RMS) value of post-fit residuals was used for orbit quality assessment, and both the stability of TRF and the precision of EOPs by external comparison were analyzed for verification of our solutions. Results of post-fit residuals show that the RMS of the orbits of LAGEOS-1 and LAGEOS-2 are 1.20 and 1.12 cm, and those of ETALON-1 and ETALON-2 are 1.02 and 1.11 cm, respectively. The stability analysis of TRF shows that the mean value of 3D stability of the coordinates of 11 ILRS core sites is 7.0 mm. An external comparison, with respect to International Earth rotation and Reference systems Service (IERS) 08 C04 results, shows that standard deviations of polar motion $X_P$ and $Y_P$ are 0.754 milliarcseconds (mas) and 0.576 mas, respectively. Our results of precise orbital and geodetic parameter estimation are reasonable and help advance research at ILRS AAC.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.885-887
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• 2003

The purpose of this investigation is to generate true orthophotos from high resolution satellite images. The major works of this research include 4 parts: (1) determination of orientation parameters, (2) generating traditional orthophotos using terrain model, (3) relief correction for buildings, and (4) process for hidden areas. To determine the position of satellites, we correct the onboard orientation parameters to fine tune the orbit. In the generation of traditional orthophotos, we employ orientation parameters and digital terrain model(DTM) to rectify tilt displacements and relief displacements for terrain. We, then, compute relief displacements for buildings with digital building model (DBM). To avoid double mapping, we detect hidden areas. Due to the satellite’s small field of view, an efficient method for the detection of hidden areas and building rectification will be proposed in this paper. Test areas cover the city of Kaohsiung in southern Taiwan. Test images are from the QuickBird satellite.

• Journal of Aerospace System Engineering
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• v.12 no.1
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• pp.10-16
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• 2018

In 2018 and 2019, GEO-KOMPSAT-2A and GEO-KOMPSAT-2B will be launched in order to succeed the COMS mission. The two satellites will be collocated in $128.25{\pm}0.05$ degrees East. For precise ranging and orbit determination, the GEO-KOMPSAT-2B will be equipped with LRA (Laser Retroreflector Assembly) and SLR (Satellite Laser Ranging) systems will be utilized. This systems are located in Geochang. In this case, the laser beam emitted from the SLR station can cause problems in terms of safety of optical payloads and image quality. As a solution of this possibility, the laser ranging will be done during the night time when the shutters of the optical payloads remain closed. Still, the optical payload of the GEO-KOMPSAT-2A is not safe from the laser beam because its optical payload shall continue its mission for 24 hours a day. In order to handle this problem, the laser ranging shall be limited to time slots when the angular distance between two satellites observed from the Geochang SLR station is large enough. In this paper, through orbit simulations, the characteristics of variation of the angular distance between the two satellites is analyzed to figure out the time slots when laser ranging is allowed.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.464-466
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• 2004

Ranging and 2-way Doppler measurements are very essential source for orbit determination in LEOP (Launch and Early Operation). This paper shows ranging system features of 13M TT &C antenna and test results recently acquired with KOMPSAT-l. Ranging and 2-way Doppler measurements were compared with KOMPSAT-I GPS telemetry data. Through comparison, it was found that constant and accurate ranging measurements are available with 13M antenna system. Ranging and Doppler measurement function is expected to be used for KOMPSAT-1 and KOMPSAT-2.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.110-114
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• 1995

This paper presents the on-board attitude determination algorithm for LEO (Low Earth Orbit) three-axis stabilized spacecraft. Two advanced star trackers and a three-axis Inertial Reference Unit (IRU) are assumed to be attitude sensors. The gyro in the IRU provides a direct measurement of the attitude rates. However, the attitude estimation error increases with time due to the gyro drift and noise. An update filter with measurements of star trackers and/or sun sensor is designed to update these gyro drift bias and to compensate the attitude error. Kalman Filter is adapted for the on-board update filter algorithm. Simulation results will be presented to investigate the attitude pointing performance.

• Journal of Astronomy and Space Sciences
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• v.5 no.1
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• pp.45-51
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• 1988

Most of all methods of determining the preliminary orbit of an artificial Earth satellite are reviewed. The preliminary orbits of the methorological satellite NOAA-10 are determined using the studied methods and are compared with mean orbital elements determined at NASA. Through the comparision the preliminary orbital elements determined with Gauss type methods are more approximate to those of NASA than those calculated with Laplacian type ones. Our results indicate that Taff(1984)'s criticism on the Gauss method must be abandoned and Marsden (1985)'s analysis on the method is correct.