• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.349-355
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• 2015

As a governmentally approved domestic entity for Space Situational Awareness, Korea Astronomy and Space Science Institute (KASI) is developing and operating an optical telescopes system, Optical Wide-field PatroL (OWL) Network. During the test phase of this system, it is necessary to determine the range of brightness of the observable satellites. We have defined standard magnitude for Low Earth Orbit (LEO) satellites to calibrate their luminosity in terms of standard parameters such as distance, phase angle, and angular rate. In this work, we report the optical brightness range of five LEO Satellites using OWL-Net.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.57-62
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• 2010

SAR payload of LEO satellite will consume about 150A current. This high current makes the voltage drop between battery, satellite main bus and payload interface, which cannot guarantee the input voltage level of the satellite electrical unit and payload. So, it is necessary to predict the main bus and payload input voltage level when the payload works. In this paper, the worst case analysis of the harness and contact resistance was executed and predicted the voltage drop when the payload works.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.56.4-57
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• 2015

We present the optical design and a sensitivity analysis for a wide field of view (FOV) instrument operating at UV and IR wavelengths. The ongoing investigation is performed in collaboration with Omnisys Instruments (Sweden) and focuses on a telluric-limb-viewing instrument that will fly in a low Earth orbit to study mesospheric wave structures over a wide range of horizontal scales in the altitude range 80 - 100 km. The instrument has six wavelength channels which consist of 4 channels of IR and 2 of UV. We are proposing an optical design based on three mirror aplanatic off-axis reflective system. The entrance pupil diameter and effective focal length are 45 mm and 270 mm, respectively. The FOV is $5.5^{\circ}{\times}1^{\circ}$ and the secondary mirror is set for stop. The optical specification is required to have an encircled energy of at least 80 % within a diameter of 21 um. We performed sensitivity analysis for the longest wavelength of 772 nm in consideration of the diffraction limit of system. The results show that tolerance limits for positions and angles of the mirrors are not very sensitive compared with typical error budgets of manufacturing and assembling process. The secondary mirror has the most sensitive tolerance for surface figure of 250 nm in root-mean-square.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.31-36
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• 1999

The development of a low earth orbit microsatellite is recognized as a good means of enhancing the technological capability, to gain experience and to train engineers to acquire knowledge and experience in space systems. Most developed countries in space technology do not allow the transfer of critical space technologies such as technology involved in attitude determination and control systems. And the export of critical components and equipment such as high precision attitude sensors is tightly controlled. Therefore it is inevitable to independently acquire self-design and manufacturing capability to implement a satellite mission. The KITSAT-3 program was aimed at verifying the capability to design, develop and operate an indigenous microsatellite system, which includes such critical technologies and associated components and equipment, as well as train engineers. KITSAT-3 was launched on May 26, 1999 using the Indian launcher PSLV-C2. The operations team has successfully performed a full functional checkout during the launch and early operations phase and the satellite is presently in a normal operations mode. This paper introduces the KITSAT-3 program and the results of the initial operations.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.3
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• pp.235-241
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• 2012

The efficiency tests of automatic positioning transmitter (APT) using satellite on life jacket were carried out to minimize casualties of fishermen and to make system optimization for effective SAR (Search and Rescue) operation. As the result of the tests, average position was equaled on the comparison between SPOT using low earth orbit satellite and DGPS (Differential Global Positining System), but standard deviation of DGPS for latitude and longitude were 66.4% and 46.3% smaller than those of SPOT. The position precision of SPOT was almost two times lower than LGT using geostationary satellite to compare 95% circular error probability. However, the success rate of receiver for SPOT was revealed as 86.5~94.1% on the experiments in the South Sea and the West Sea and it was 4.5 times higher than LGT. Therefore, SPOT is expected to contribute greatly to the rapid rescue of victim.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.8
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• pp.702-709
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• 2016

By means of the our satellite development for the past 20 years, it ensure us to obtain domestic independent development capabilities. In the case of practical-class Low-Earth Orbit(LEO) remote sensing satellites, we become a world-class developer. Furthermore, we acquire the technology to develop domestic-leading geostationary satellites, depending on the mission. Currently, we proceed with the next-generation mid-size satellite development program featuring standard bus for the expansion of the world market and has embarked on the development of lunar orbiter from this year.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.34.3-34.3
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• 2008

Relative navigation system is presented using measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide real-time relative navigation results as well as absolute navigation results for two formation flying satellites separated about 1km in low earth orbit. To improve the performance, more accurate dynamic model and modified relative measurement model are developed. This modified method prevents non-linearity of the measurement model from degrading precision by applying linearization about the states from absolute navigation algorithm not about a priori states. Furthermore, absolute states are obtained using ion-free GRAPHIC pseudo-ranges and precise relative states are provided using double differential carrier-phase data based on Extended Kalman Filter. The software-based simulation is performed and achieved meter-level precision for absolute navigation and millimeter-level precision for relative navigation. The absolute and relative accuracies at steady state are about 0.77m and 4mm respectively (3D, r.m.s.). In addition, Integer ambiguity algorithm (LAMBDA method) improves simulation performances.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.36.1-36.1
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• 2008

An Unscented Kalman Filter(UKF) for estimation of attitude and rate of a spacecraft using only magnetometer vector measurement is presented. The dynamics used in the filter is nonlinear rotational equation which is augmented by the quaternion kinematics to construct a process model. The filter is designed for low Earth orbit satellite, so the disturbance torques include gravity-gradient torque, magnetic disturbance torque, and aerodynamic drag. The magnetometer measurements are simulated based on time-varying position of the spacecraft. The filter has been tested not only in the standby mode but also in the detumbling mode. To stabilize the attitude, linear PD controller is applied and the actuator is assumed to be thruster. A Monte-Carlo simulation has been done to guarantee the stability of the filter performance to the various initial conditions. The UKF performance is compared to that of EKF and it reveals that UKF outperforms EKF.

• Proceedings of the KSRS Conference
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• v.1
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• pp.232-235
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• 2006

Using 30 days of hourly visible channel data and DIScrete Ordinate Radiative Transfer (DISORT) model (6S), Aerosol optical depth (AOD) at $0.55{\mu}m$ was retrieved over the East Asia. In contrast with the AOD retrieval using low-earth-orbit satellites such as MODIS (Moderate-Res olution Spectroradiometer) or MISR (Multiangle Imaging SpectroRadiometer), this algorithm with geostationary satellite can improve the monitoring of AOD without the limitation of temporal resolution. Due to the limited number of channels in the conventional meteorological imager onboard the geostationary satellite, an AOD retrieval algorithm utilizing a single visible channel has been introduced. This single channel algorithm has larger retrieval error of AOD than other multiple-channel algorithm due to errors in surface reflectance and atmospheric property. In this study, the effects of manifold atmospheric and surface properties on the retrieval of AOD from the geostationary satellite, are investigated and compared with the AODs from AERONET and MODIS. To improve the accuracy of retrieved AOD, efforts were put together to minimize uncertainties through extensive sensitivity tests. This algorithm can be utilized to retrieve aerosol information from previous geostationary satellite for long-term climate studies.

• Current Industrial and Technological Trends in Aerospace
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• v.6 no.2
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• pp.51-59
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• 2008

While the infrared imaging satellites with the several type were developed and operated in the foreign countries, we do not have the domestic infrared imaging satellite up to now. In the paper, the general characteristics of infrared and the applications of infrared image were introduced. Also the oversea development status of the infrared imaging satellite was surveyed and introduced to this paper. According to foreign status, the infrared image is utilized in various application including the forest fire monitoring, the volcano activity research, sea surface temperature measurement, land surface temperature calculation, the climate change research, and the environment monitoring. According to these trend the development of the domestic infrared imaging satellite in low earth orbit was required.