• ETRI Journal
• /
• 제22권4호
• /
• pp.32-39
• /
• 2000

In low earth orbit (LEO) satellite communication systems, more severe phase distortion due to Doppler shift is frequently detected in the received signal than in cases of geostationary earth orbit (GEO) satellite systems or terrestrial mobile systems. Therefore, an estimation of Doppler shift would be one of the most important factors to enhance performance of LEO satellite communication system. In this paper, a new adaptive Doppler compensation scheme using location information of a user terminal and satellite, as well as a weighting factor for the reduction of prediction error is proposed. The prediction performance of the proposed scheme is simulated in terms of the prediction accuracy and the cumulative density function of the prediction error, with considering the offset variation range of the initial input parameters in LEO satellite system. The simulation results showed that the proposed adaptive compensation algorithm has the better performance accuracy than Ali's method. From the simulation results, it is concluded the adaptive compensation algorithm is the most applicable method that can be applied to LEO satellite systems of a range of altitude between 1,000 km and 2,000 km for the general error tolerance level, M = 250 Hz.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2006년도 제27회 추계학술대회논문집
• /
• pp.43-46
• /
• 2006

축열식 가열기는 주로 초음속 지상추진 시험설비의 고고도 조건 모사를 위하여 구축되는 장비로 이외에도 로켓 엔진 노즐의 추력 보정시험, 가스터빈 엔진 연소기 모사시험에 범용으로 사용할 수 있다. 한국항공우주연구원에서 보유하고 있는 축열식 가열시스템은 마하 $2{\sim}5$, 고도 $0{\sim}25km$의 범위에서 구동하는 초음속 지상추진시험설비의 전온도 모사를 목적으로 설계되었으며, 최고 모사 온도 1,300 K, 최고 가압압력 3.5 MPa의 성능을 낸다. 본 논문에는 본 원에서 구축한 축열식 가열기의 목표로 한 일본 JAXA RJTF에 구축되어있는 축열식 가열기에 대하여 정리하도록 한다.

• 한국항공우주학회지
• /
• 제43권3호
• /
• pp.265-271
• /
• 2015

본 연구에서는 소형 위성카메라의 영상성능 저하를 궤도상에서 능동적으로 보정하기 위해 광학보정장치를 적용한 위성카메라의 광학설계를 수행하였다. 2개의 광학 보정장치는 각각 부반사경 및 초점면부에 부착되며 총 5자유도의 운동이 가능하다. 본 논문에서 설계한 광학부는 슈미트-카세그레인(Schmidt-Cassegrain)타입으로 주반사경의 직경은 200mm이고, GSD 3.8m, MTF 성능은 약 50% 정도이다. 설계된 광학계는 수차곡선과 Spot diagram과 MTF를 통해 성능평가를 수행하였다. 수차곡선을 통해 광학성능에 가장 큰 영향을 미치는 수차가 구면수차인 것을 확인 할 수 있고, MTF 해석을 통해서 나이퀴스트 주파수에서 MTF 30%이상의 요구 성능을 충분히 만족하는 것을 확인하였다.

• 한국군사과학기술학회지
• /
• 제22권2호
• /
• pp.233-240
• /
• 2019

High-altitude ElectroMagnetic Pulse(HEMP) is a high-power electromagnetic pulse caused by nuclear explosions at altitudes above 30 km. This pulse can cause serious damage to the electrical/electronic device. Therefore, there are a lot of studies on the effects of HEMP in the literature. When conducting studies on the effects of HEMP, it is essential to measure the simulated HEMP. Depending on the need for measurement, this paper focuses on the HEMP measurement method. This paper proposes a measurement method using frequency domain compensation to extract the correct waveform and solves the offset problem more efficiently than the conventional methods. The proposed method is verified by experiment using HEMP simulator and measurement system in ADD.

• 한국위성정보통신학회논문지
• /
• 제11권1호
• /
• pp.58-62
• /
• 2016

인공위성 추진시스템은 위성이 발사체와 분리되어 최종 임무궤도에 진입하기까지 궤도조정에 필요한 추력을 제공하고, 임무궤도에 진입한 이후에는 궤도경사각 제어 및 항력에 의한 궤도 저하를 보상하기 위한 추력을 제공한다. 위성 발사 후 초기운용 기간 동안 획득된 궤도운용결과를 바탕으로 위성의 운용모드에 따른 저궤도관측위성 추진시스템의 궤도성능 검증을 수행하였다. 또한 추진시스템을 구성하는 부품 및 배관에서의 온도변화 추이를 살펴 추진계가 정상적인 범위 내에서 운용되고 있음을 확인하였다.

• 한국군사과학기술학회지
• /
• 제14권3호
• /
• pp.405-413
• /
• 2011

Defense Systems Test Center in ADD supports increasingly various missile test requirements such as higher altitude event, multi target operation and low-altitude, high velocity target tracking. In this paper, we have proposed the development of instrumentation radar tracking status simulator based on virtual reality. This simulator can predict the tracking status and risk of failure using several modeling algorithms. It consists of target model, radar model, environment model and several algorithms includes the multipath interference effects. Simulation results show that the predict tracking status and signal are similar to the test results of the live flight test. This simulator predicts and analyze all of the status and critical parameters such as the optimal site location, servo response, optimal flight trajectory, LOS(Line of Sight). This simulator provides the mission plan with a powerful M&S tool to rehearse and analyze instrumentation tracking radar measurement plan for live flight test at DSTC(Defense Systems Test Center).

• 한국의류학회지
• /
• 제27권7호
• /
• pp.746-757
• /
• 2003

The purpose of this study was to investigate the internet perceived risk segments in regard to clothing benefits sought, internet shopping attitude, and internet purchase intention. The subjects used for the study were 210 male and 338 female college students. The internet perceived risk consisted of size/defect risk, social psychological risk, privacy risk, delivery risk, and price risk. The clothing benefits sought had impression improvement, fashion, individuality, figure flaws compensation, and comfort factors. The results showed that consumers were segmented by four groups based on internet perceived risk factors : 1) privacy risk group, 2) size risk group. 3) low risk group, and 4) price/social psychological risk group. The four segmented groups differed in regard to clothing benefits sought, internet shopping attitude, and internet purchase intention. For example, in regard to clothing benefits sought, the price/social Psychological risk group sought fashion more than other groups. The low risk group considered figure flaws compensation benefit less important than other groups. Concerning internet shopping attitude, the low risk group had more favorable altitude toward trust, safety, diversity, exchange/return attributes of internet shopping than other groups. The privacy risk group had more favorable attitude toward convenience and price attributes of internet shopping. Regarding internet purchase intention, the low risk group had higher intention to purchase formal, casual, and sportswear. The size risk group had higher intention to purchase fashion accessories. Further group differences and implications of the results were discussed.

• 한국정보통신학회논문지
• /
• 제9권8호
• /
• pp.1722-1729
• /
• 2005

본 연구에서는 OpenGL 프로그램으로 4족 보행로봇인 TITAN-VIII의 가상로봇을 설계한 후, 실제로봇의 관절각도, 본체 자세각을 가상로봇에 입력하고 벡터 회전과 평행이동을 이용하여 보행 중 본체를 수평으로 유지하는 제어를 10[ms]마다 행하였다. 디딤율 $\beta$를 0,5로 일정하게 하고, 주기가 1.5, 2.0, 3.0[sec]일 때 한주기당 이동거리를 0.2, 0.3[m]로 변경하여 좌우요동보행을 시키면서 가상로봇의 ZMP, 실제로봇의 ZMP 무게중심의 이동경로를 구하고 발바닥 좌표 변화와의 관계를 비교 분석하였다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
• /
• pp.386-388
• /
• 2007

In many applications of UAVs flying in low altitude, the steady supply of accurate height measurements is very important for the UAVs to complete their mission successfully. In order to do this, a barometer or GPS height measurements are widely used. However, because these two sensors have their limitations in the application environment, a method for fusing these two measurements to produce reference heights are required. In this paper, a reference height generation filter is designed for UAV(Unmanned Air Vehicle) applications. The barometer errors originated by the change of the atmospheric environment are modeled using random walk models, and then the errors are identified and compensated through the ZSB(zero-scan-back) filter algorithm using the GPS height measurements. The performance of the proposed filter is demonstrated by realistic simulations.

• 항공우주시스템공학회지
• /
• 제14권4호
• /
• pp.1-9
• /
• 2020

The characteristics of an aerospike pintle nozzle system with excellent altitude compensation were analyzed using cold air testing. It was confirmed that reducing the stroke of the aerospike nozzle is effective in increasing the thrust. However, the results of additional numerical analysis indicated that the discharge coefficient factor was significantly lower at the maximum stroke. The Vena contracta due to the cowl reduction angle decreased the effective nozzle throat area at the maximum stroke and hindered expansion. Complementing the cowl design may thus increase the efficiency of a solid-propellant rocket engine that uses the aerospike pintle nozzle system.