• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.249-262
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• 2005

Optimization problems are formulated to calculate optimal impulses for deflecting Earth-Crossing Objects using a Nonlinear Programming. This formulation allows us to analyze the velocity changes in normal direction to the celestial body's orbital plane, which is neglected in many previous studies. The constrained optimization in the three-dimensional space is based on a patched conic method including the Earth's gravitational effects, and yields impulsive ${\Delta}V$ to deflect the target's orbit. The optimal solution is dependent on relative positions and velocities between the Earth and the Earth-crossing objects, and can be represented by optimal magnitude and angle of ${\Delta}V $ as a functions of a impulse time. The perpendicular component of ${\Delta}V $ to the orbit plane can sometimes play un-negligible role as the impulse time approaches the impact time. The optimal ${\Delta}V $ is increased when the original orbit of Earth-crossing object is more similar to the Earth's orbit, and is also exponentially increased as the impulse time reaches to the impact time. The analyses performed in present paper can be used to the deflection missions in the future.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.88-94
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• 2008

In this study, triaxial velocity is analyzed for COMS(Communication, Ocean and Meteorological Satellite) configuration, which is generated when thrusters are used to dump wheel momentum. Since COMS is designed to periodically change the thruster set in order to uniformly decrease the performance of thrusters, triaxial velocity would be different during the change of thruster set. So, the triaxial velocity generated due to the change of thruster set is optimized.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.62-73
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• 2024

This study analyzed the effectiveness of orbital change through attitude change in nano-satellites operating in low Earth orbit (LEO) without thrusters, focusing on collision avoidance maneuvers. The results revealed that changes in the satellite's cross-sectional area significantly impact its in-track direction, influenced by the aspect ratio of cross-sectional area change and mission altitude. Notably, satellites at lower altitudes demonstrated significant reduction in collision risks with a small amount of attitude change. Through this study, it is judged that the changing the cross-sectional area through attitude maneuver is a sufficiently suitable method in the operation of nano-satellites without thrusters, and is expected to contribute to improving the safety of satellite operations in the New Space era.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.40-46
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• 2013

Based on Korean railway design standards, the thicknesses of the reinforced roadbeds of conventional and high speed railways are different, and so too, for the size distribution of the ballast particles. Accordingly, considerable cost would be required to increase operating speeds of conventional lines, in particular related to changing from a ballasted track system to a ballastless one. In this study, applicability of a roadbed which supports conventional ballasted track, for use as a ballastless track for a high speed rail line was examined. A reinforced roadbed for a conventional railway is 20cm thick, and the type of material used for a conventional reinforced roadbed is M-40 (crushed gravel for road embankments). A dynamics test was conducted to evaluate the occurrence of the permanent settlement of the track substructure. These results suggest that, without changes to the track substructure, an operational speed of 400km/h is feasible with a ballastless track. This result; however, is from laboratory experiments. Further studies, such as numerical analyses or field validation, are required.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.163.2-163.2
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• 2012

다목적실용위성 3호는 2012년 5월 발사되어, 위성 기능점검을 위한 시험을 성공적으로 완료하였다. 위성이 발사체로부터 분리된 이후 임무궤도(고도 685km, 승교점 지방시 13시 30분을 갖는 태양동기궤도)를 획득하기 위해서는 궤도조정이 필요하다. 본 논문에서는 다목적실용위성 3호의 초기운영 기간 동안 수행한 총 10번의 궤도조정 계획 및 결과에 대해 기술하였다. 궤도조정 1 단계에서는 궤도조정 절차 및 기능을 점검하기 위해 6번의 시험 궤도조정을 순차적으로 수행하였고 이후 2 단계에서는 임무궤도 진입을 위해 4번의 궤도조정을 실시하였다. 궤도조정을 위해서는 원하는 추력분사 방향을 맞추기 위해 롤 방향 또는 피치 방향의 자세제어가 필요한데, 추력기를 사용하여 자세를 기동하는 모드(Del-V Mode)와 휠을 사용하여 자세를 기동하는 모드(Fine Del-V Mode)로 구분된다. 시험 궤도조정에서는 우선적으로 두 가지 모드에 대한 모드전환 시험을 실시하여 위성체 및 지상국 운영절차에 대한 이상 유무를 점검하였고, 이후 추력기 분사량을 10초로 설정하여 예측 대비 실제 궤도변경 결과값을 확인하였다. 시험 궤도조정의 결과를 토대로 본 궤도조정에서는 임무궤도를 획득하기 위한 경사각 조정 및 고도 조정을 수행하였다. 경사각 조정 시에는 승교점 지방시의 변화량을 줄이고, 이후 자연 교란력에 의한 궤도변화를 고려하여 목표궤도를 계획하였다. 또한, 고도 조정 단계에서는 연료 사용량 및 이심률 변화를 최소화 할 수 있도록 전형적인 호만 궤도천이 방식을 적용하였다. 궤도조정 결과 당초 목표한 값을 정확하게 달성하였고, 궤도조정 이후 궤도변화도 장기간 동안 임무궤도 범위를 유지함을 확인할 수 있었다.

• Current Industrial and Technological Trends in Aerospace
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• v.4 no.1
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• pp.74-82
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• 2006

정지궤도 상에서 기상 관측 임무를 수행하고 있는 주요 기상위성의 관측 데이터의 전송 및 분배 시스템의 구성 현황 및 주요 전송 파라미터를 분석하고 현재 개발되고 있는 통신해양기상위성의 관측 데이터 전송 시스템 구성 및 채널별 주요 전송 파라미터를 제시한다. 제한된 기상 주파수 전송 대역에 대해 갈수록 고성능화 되어가는 기상 센서에 따른 대용량 기상관측 데이터 전송 및 분배를 위한 전송 방법 및 주파수 대역의 변경, 지상망 및 상업용 위성 통신망의 활용방안을 살펴본다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.319-326
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• 2013

This paper describes the orbital dynamics operation results for the launch and early operations phase (LEOP) of KOMPSAT-3, which was successfully launched on May 18, 2012. At the initial phase, operational orbit determination was carried out using ground tracking data and GPS navigation solution. And, both in-plane and out-of plane maneuvers were executed in order to change the orbit from the injection orbit to the mission orbit. In addition, the accuracy of precise orbit determination was indirectly evaluated by overlapping method using GPS raw data of KOMPSAT-3 and international GNSS service data from worldwide-distributed ground stations. Currently, KOMPSAT-3 is operated in pre-defined mission orbit, and its various kinds of orbit data are generated and distributed to support the normal mission operations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.114-121
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• 2004

Thermal design changes and analysis on the engineering model of Command Telemetry Unit(CTU) for a geostationary communications satellite arc performed for the purpose of developing an engineering qualification model. A thermal model is developed by using power consumption measurement values of each functional board and thermal cycling test results. In modeling heat dissipated EEE parts, heat dissipation is imposed evenly on the EEE part footprint area which is projected to the printed circuit board. All the EEE parts of CTU meet the requirement of their allowable temperature range when placed on the engineering qualification level of thermal vacuum environments in accordance with the proposed thermal design changes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.39-47
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• 2005

In this paper, a method of station keeping strategy using relative orbital motion and numerical optimization technique is presented for geostationary spacecraft. Relative position vector with respect to an ideal geostationary orbit is generated using high precision orbit propagation, and compressed in terms of polynomial and trigonometric function. Then this relative orbit model is combined with optimization scheme to propose a very efficient and flexible method of station keeping planning. Proper selection of objective and constraint functions for optimization can yield a variety of station keeping methods improved over the classical ones. Results from the nonlinear simulation have been shown to support such concept.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.807-813
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• 2015

The CWR(Continuous Welded Rail) on a bridge shows complex structural behavior compared to those on the roadbed. The influence factors on the track-bridge interaction are the variation of temperature and vehicle load. The analysis methods for track-bridge interaction, material property, modeling method, loads and combination method are indicated in the domestic railway design principle, KR C-08080. The vehicle load in KR C-08080 was changed in 2014. In this study, to evaluate the effect of the changed vehicle load on the track-bridge interaction, the track-bridge interaction analyses were performed for 22 bridges by using finite element method.