• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
• /
• pp.126-129
• /
• 2005

Change detections is carried out under the assumption that pixel boundaries of geometrically corrected time series satellite images cover the same location. However that assumption can be wrong when shifts in the pointing direction of a satellite sensor occurs. Currently, although the influence of misregistration on landcover change detection has been investigated, there has been little research on the influence of pointing direction shifts of a satellite sensor. In this study, a simple method for reducing the effects of pointing direction shifts of a satellite sensor is proposed: the classification of two ASTER images was carried out using the linear spectral mixture analysis, the two classification results were resampled into a geometrically fixed grid, and then the change detection of the two ASTER images was carried out by comparing the resampled classification results of the two images. The proposed method showed high performance in discriminating between changed areas and unchanged areas by removing the pointing direction shifts of a satellite sensor.

• 제어로봇시스템학회논문지
• /
• 제8권1호
• /
• pp.60-66
• /
• 2002

In this paper, a new target pointing guidance algorithm is proposed by combining the optimal target pointing solution and a simple time-to-Go estimator. Also investigated are some properties of the guidance algorithm which include a relation to conventional PNG, convergence region and convergence trajectories of error states according to the time-to-go estimator gain. Some guidelines for designing the pointing guidance law are commented based on the convergence properties. A design example in the case of large initial heading errors is presented and its performance is investigated by simulation.

• 한국항행학회논문지
• /
• 제20권6호
• /
• pp.503-510
• /
• 2016

최근 이동형 글로벌 광대역 통신 및 위성기반의 양방향 인터넷 서비스에 대한 수요가 증가함에 따라 ESIM (earth station in motion)이라는 새로운 형태의 위성 터미널이 개발되고 있다. 이 서비스는 ITU-R Resolution 158(WRC-15)에서 FSS 업링크에 27.5-29.5 GHz 대역사용을 고려하고 있어 동일대역에서 1순위 업무로 분배된 FS와의 간섭분석에 대한 연구가 요구되고 있다. 이에 본 논문에서는 ESIM이 기존의 FS(fixed service)에 미치는 간섭영향을 안테나의 포인팅 에러와 방위각을 고려하여 4 가지 시나리오에 대해 분석하였다. 그 결과 에러 초과확률 5% 및 10% 기준에서 앙각이 $20^{\circ}{\sim}40^{\circ}$에 따라 두 시스템간의 분리거리는 32~52 km 정도 요구되고 있다. 이에 분리거리를 최소화하면서 동일대역의 FS를 보호하기 위해서는 안테나 포인팅 에러뿐만 아니라 이동 터미널의 방위각을 제어할 수 있어야 한다.

• 한국항공우주학회지
• /
• 제49권11호
• /
• pp.953-960
• /
• 2021

거창 우주물체 레이저 추적 시스템은 인공위성 레이저 추적, 적응광학, 우주쓰레기 레이저 추적 등 과학 연구 및 국가적 미션을 수행하기 위해 100cm 크기의 광학 망원경을 가지고 있으며, 빠르고 정밀한 구동을 위하여 경위대식 방식의 추적마운트를 개발하여 테스트 관측 중에 있다. 최근 레이저 추적 시스템의 자동 관측 및 응용 연구 분야에서 추적 대상을 정밀하게 추적할 수 있는 능력은 시스템 성능을 판단할 수 있는 중요한 지표 중 하나이다. 그러기 위해서는 정밀 추적을 저해하는 요인을 파악하고 보정하기 위한 지향 보정 모델이 요구된다. 따라서 본 논문에서는 추적마운트 제작, 조립 및 설치 과정에서 발생 할 수 있는 정적 지향 오차 발생 원인들을 분석하였으며, 거창 우주물체 레이저 시스템의 추적마운트에 적용된 지향 보정 모델 및 최소자승법을 통해 추적마운트 파라미터를 추정하고, 지향 정밀도 분석 결과를 제시하였다.

• 한국군사과학기술학회지
• /
• 제4권2호
• /
• pp.157-178
• /
• 2001

In this paper, the nonlinear control of high precision pointing stabilization system using feedback-linearization design methodology based on system parameter identification is discussed. Modern nonlinear servomechanism theory is adapted to cope with the hard nonlinearities inherent in the turret system. The mathematical models of electrical turret driving system to develop a high performance control algorithm are derived, and the parameter estimation algorithm identifying the unknown system parameters such as vicious and coulomb frictions, stiffness and inertia is developed. Through computer simulation and experiments, it is shown that pointing and tracking accuracy and stabilization against the wideband stochastic disturbance induced by vehicle running on the bump course are improved. Therefore, it is considered the proposed nonlinear control technique is effective in counteracting the nonlinearities and disturbances.

• 한국안전학회지
• /
• 제24권3호
• /
• pp.71-78
• /
• 2009

During a learning process, a human being is assumed to experience knowledge-based behaviors, rule-based behaviors, and skill-based behaviors sequentially if Rasmussen was right. If any psycho-physiological symptom to those different levels can be obtained, it can be useful as a measure whether a human being is fully trained and has gotten a skill in his work. Therefore, this study aimed to draw relationships between human performance measures and psycho-physiological measures while committing a computer-simulated pointing task by utilizing the power spectrum technique of EEG data, especially with the ratio of relative beta-to-alpha band power. The result showed that, during correct responses, the ratio came to stabilize as all the performance data went stable. However, response time was not a simple linear function of task difficulty level only, but a joint function of task characteristics as well as behavior levels. Comparing relative band power ratios from errors and correct responses, activated states of one's brain could be explained, and characteristics of the task could understood. To tell that of pointing task, correlations around C3, C4, P3, P4 and 01, 02 area were significant and high in correct response cases whereas most correlation coefficients went down in error cases standing for imbalance of psycho-motor functions. Though task difficulty was the only one factor that could influence on relative band power ratio with statistical significance, it should be comprehended to mean a different way of expression indicating task characteristics since at least error-some situation could be explained with the help of relative band power ratio that absolute band power failed.

• 한국항공우주학회지
• /
• 제44권1호
• /
• pp.80-87
• /
• 2016

본 논문에서는 계절 및 주야의 온도변화를 고려한 관측위성의 열지향오차해석을 실시한다. 관측위성은 임무수행기간 동안 다채널의 관측센서를 이용해서 지구표면의 영상을 촬영한다. 그러나 주야 및 계절별로 최대 200도의 온도환경 차이가 발생하며 이로 인해 관측센서 및 별추적기의 시선벡터가 변화되고 정해진 목표지점의 영상촬영이 어렵다. 이런 문제를 사전예측하고 대응하기 위해서 열지향오차해석을 실시한다. 우선 궤도열환경해석으로부터 도출된 성긴 온도장 정보를 상세한 구조유한요소모델에 PAT기법을 이용해 보간하여 온도변화에 따른 열변형해석을 수행하였다. PAT로 보간된 온도분포의 정확도를 검증하였으며, 열변형해석결과로부터 열지향오차를 도출하였다.

• International Journal of Aeronautical and Space Sciences
• /
• 제4권1호
• /
• pp.75-87
• /
• 2003

The primary objective of this study is to demonstrate ground-based experiment for the attitude control of spacecraft. A two-axis rotational simulator with a flexible ann is constructed with on-off air thrusters as actuators. The simulator is also equipped with payload pointing capability by simultaneous thruster and DC servo motor actuation. The azimuth angle is controlled by on-off thruster command while the payload elevation angle is controlled by a servo-motor. A thruster modulation technique PWM(Pulse Width Modulation) employing a time-optimal switching function plus integral error control is proposed. An optical camera is used for the purpose of pointing as well as on-board rate sensor calibration. Attitude control performance based upon the new closed-loop control law is demonstrated by ground experiment. The modified switching function turns out to be effective with improved pointing performance under external disturbance. The rate sensor calibration technique by Kalman Filter algorithm led to reduction of attitude error caused by the bias in the rate sensor output.

• 천문학논총
• /
• 제14권1호
• /
• pp.47-56
• /
• 1999

We have improved the control and driving system of 16' reflector at Kwanak Observatory at Seoul National University, by completing encoder unit, and by developing programs for correction of errors resulting from hardware defects. The hardware defects of this telescope system are the large backlash and the nonuniform tracking and pointing. The telescope pointing accuracy for RA is improved to a few arc minutes, and that for DEC is several tens of arc minutes. The guiding error is improved to 0.7 arcsec/minute, allowing up to 3 minutes exposure for CCD imaging under typical seeing conditions at the Observatory.

• 한국군사과학기술학회지
• /
• 제1권1호
• /
• pp.65-81
• /
• 1998

Objective technology development has been carried out aiming performance improvement of the stabilized gun-pointing system for Type-4 tank. The full nonlinear simulation programs with gun bending modes and nonlinearities were developed to estimate, analyze and design the driving and stabilization system, and validated through the comparisons between simulations and test results of the existing Type-1 tank. The prototype is designed, fabricated, tested and evaluated on the test range as well as in the laboratory and followed by development and operational tests. The performance test results on stationary and on-the-move conditions are turned out to be superior to those of the advanced tanks developed in foreign countries.