• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.138.1-138.1
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• 2012

자기 구름은 자기 구조를 가지고 방출된 CME로 지구 자기장에 영향을 주는 중요한 원인 중 하나이다. 지구 자기장의 교란으로 발생하는 지자기 활동은 K 지수로 표현되는데 우주기상을 연구하는데 기본 자료로 활용된다. 따라서 자기 구름은 우주기상을 연구하는데 필요한 자료라 할 수 있다. 기존에 Lynch et al.(2005), Huttunen et al.(2005), Lepping et al.(2006), Feng et al.(2007) 등이 만든 자기 구름 리스트가 있지만 자기 구름에 적합하지 않는 이벤트가 적지 않게 포함되어 있어 이벤트를 지자기 활동 연구에 활용하기에 어려움이 있었다. 이 연구에서는 우리만의 자기 구름 기준을 정하고, 이 기준과 실린더 모델을 이용해 새로운 자기 구름 리스트를 완성하였다. 우리가 정한 자기 구름 기준은 (1)자기장의 벡터 성분이 천천히 회전하고 (2)자기장의 세기가 평균보다 세며 (3)자기 구름 지속시간이 7시간보다 짧은 이벤트도 모두 포함하는 것이다. ACE위성과 WIND 위성이 2000년에 관측한 행성간 자기장 자료에 우리의 자기 구름 기준을 적용하여 자기 구름 이벤트 후보를 선정하였고, 마루바시 박사가 만든 실린더 모델을 자기 구름 이벤트 후보에 적용하여 자기 구름 이벤트를 최종 선정하였다. 이렇게 선정된 2000년도 자기 구름 이벤트는 총 63개이고 이를 리스트로 작성하였다. 우리가 만든 자기 구름 이벤트 리스트는 CME와 K 지수 등 지자기 활동 연구에 활용되고 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.18-24
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• 2003

A three node triangular element with drilling rotations incorporating improved higher-order zig-zag theory(HZZT) is developed to analyze the vibration of pretwisted composite plates with embedded damping layer. Shear force matching conditions are enforced along the interfaces between the embedded damping patch and the border patch by matching the shear forces of the embedded damping patch to the shear forces of the adjacent border patch. The natural frequencies and modal loss factors are calculated for cantilevered pretwisted composite blade with damping core with the present triangular element, and compared to experiments and MSC/NASTRAN using a layered combination of plate and solid elements.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.26-31
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• 2005

An efficient estimation of the aerodynamic characteristics for missile configurations is essential in the preliminary stage of a missile design. In this study, a Missile DATCOM family code based on the semi-empirical method was utilized for this purpose. In order to check the accuracy and reliability of the code several test cases have been considered: subsonic flow with high angles of attack and supersonic flow with moderate angles of attack. It turned out that the code in general provides prediction in qualitative agreement with the experimental data and results by other works. Finally, the code was applied to a more complicated missile configuration with canard and freely spinning tail fin.

• Journal of Aerospace System Engineering
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• v.11 no.4
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• pp.22-29
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• 2017

A study is performed for the effective detection method of a fault which is occurred during operation in a small turbojet engine with non-linear characteristics used by unmanned air vehicle. For this study the non-linear dynamic model of the engine is derived from transient thermodynamic cycle analysis. Also for inducing real operation conditions the controller is developed associated with unscented Kalman filter to estimate noises. Sequential probability ratio test is introduced as a real time method to detect a fault which is manipulated for simulation as a malfunction of rotational speed sensor contaminated by large amount of noise. The method applied to the fault detection during operation verifies its effectiveness and high feasibility by showing good and definite decision performances of the fault.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.1
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• pp.38-43
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• 2022

As the use of unmanned aerial vehicles increases, in order to expand the operability of the unmanned aerial vehicle, it is essential to develop an unmanned aerial vehicle traffic management system, and to establish the system, it is necessary to analyze the integrated navigation performance of the unmanned aerial vehicle to be operated. Integrated navigation performance is affected by various factors such as the type of unmanned aerial vehicle, flight environment, and guidance law algorithm. In addition, since a large amount of flight data is required to obtain high-reliability analysis results, efficient and consistent flight scenarios are required. In this paper, a flight scenario that satisfies the requirements for integrated navigation performance analysis of rotary and fixed-wing unmanned aerial vehicles was designed and verified through flight experiments.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.4
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• pp.269-275
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• 2022

In ideal configuration, elapsed-time method can measure the exact reaction wheel speed. But in real configuration, the speed measurement error exists due to tacho pulse non-uniformity. In this research, we study the method which overcome the non-uniformity effects. First, we introduce the method which spin the wheel at the specific speed and measure the non-uniformity. Then, we propose the real-time measurement error correction method which uses the obtained non-uniformity information. This method calculate the speed candidates from the elapsed-time method's counts and non-uniformity information, and choose the closest speed to the real speed. Through simulation, we show that proposed method measure the exact speed regardless of non-uniformity, and fast wheel speed control is possible.

• Journal of Astronomy and Space Sciences
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• v.12 no.1
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• pp.112-122
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• 1995

We assume that the KOREASAT fails the entry of the geostationary orbit due to the error at the apogee kick motor firing. A simulation is done for the satellite that has a geosynochronous orbit with a non-zero degree inclination angle due to the failure at the apogee kick motor firing caused by the unbalance of the fuel storage and the spin of the thrust vector, etc. We analyzed the evolution of the orbit using the perturbation theory and calculated the changes of the eccentricity and the inclination. WHen a communication satellite has the figure eight trajectory, the beam point also traces the satellite. In this paper, We develope an algorithm to attack the above problem by stabilizing the beam point using the adjustment of the roll angle of the satellite. The spin action on the polarization plane that occurs when a satellite passes the ascending node and descending node affects the efficiency of the communication a lot, so we did another simulation for the better yaw angle adjustment for the KOREASAT to reduce the spin actino on the polarization plane.

• Journal of Astronomy and Space Sciences
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• v.25 no.4
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• pp.415-424
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• 2008

Kwak et al. (2008) found that the mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow than by divergent flow. As an extension of the our previous work (Kwak et al. 2008), we performed a term analysis of vorticity equation that describes the driving forces for the rotational component of the horizontal wind in order to determine key processes that causes strong rotational flow in the high-latitude lower thermospheric winds. For this study the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) is used. The primary forces that determine variations of the vorticity are the ion drag term and the horizontal advection term. Significant contributions, however, can be made by the stretching term. The effects of IMF on the vorticity forces are seen down to around 105-110km.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.12
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• pp.1103-1111
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• 2016

Korea Astronomy and Space Science Institute (KASI) has been operating SLR (Satellite Laser Ranging) system with 2kHz repetition rate for satellite precise orbit and spin determination as well as space geodesy. But the SLR system was improved to be capable of laser ranging with high repetition rate, up to 10kHz by developing new operation software and novel range gate generator, called HSLR-10. The HSLR-10 will contribute to the accurate spin rate determination of geodetic satellites and geodetic research due to its largest repetition rate in the world. In this study, the development methodology and configuration of operation software are addressed, and its validation results are also presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.10
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• pp.858-869
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• 2014

Most of the aerospace propulsion is based on the Brayton cycle, in which the combustion is held through the constant pressure process, but further improvement of performance by increasing compression ratio is challenged by mechanical limits. Detonation propulsions, regarded promising for high-speed propulsion for a lase decade, is more rigorously studied in these days as a game-changer for the improvement of thermodynamic efficiency of propulsion and power generation systems. Since, the additional compression by the strong shock of the detonation wave is considered increasing thermodynamics efficiency that is hardly achievable by the conventional compression systems. Present paper will give an introduction the latest technical trends on the Pulse Detonation Engines(PDEs) and the activities on the Pressure Gain Combustion (PGC) based on Constant Volume Combustion (CVC).