• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.126-129
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• 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.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.1
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• pp.60-66
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• 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.

• Journal of Advanced Navigation Technology
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• v.20 no.6
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• pp.503-510
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• 2016

In recent years, owing to the growing user demand for the two-way internet service based on the move global broadband communications, a new type of satellite terminal has developed, known as earth station in motion (ESIM). This service was required by Resolution 158 (WRC-15) to study on the coexistence with the co-primary fixed service (FS) in 27.5-29.5 GHz as a FSS uplink. In this paper, four scenarios was introduced to account for the antenna pointing error and the azimuth for an analysis on the sharing between ESIM and FS. From analysis results, the required separation distance between two systems should be about 32~52 km according to the elevation angles of $20^{\circ}{\sim}40^{\circ}$ using thresholds of 5% and 10% outage probability. Therefore, it is necessary to control the azimuth angle due to a moving terminal as well as the pointing error of ESIM to minimize the required separation distance and to protect the co-primary FS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.11
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• pp.953-960
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• 2021

Korea Astronomy and Space Science Institute has been verifying the multipurpose laser tracking system with three functions of satellite laser tracking, adaptive optics and space debris laser tracking for not only scientific research but also national space missions. The system employs an optical telescope consisting of a 100 cm primary mirror and an altazimuth mount for fast and precise tracking. The precise pointing and tracking capability in a tracking mount is considered as one of important performance metrics in the fields of automatic tracking and precise application research. So it is required to analyze a mount model for investigating pointing error factors and compensating pointing error. In this study, we investigated various factors causing static pointing errors of tracking mount and analyzed the pointing accuracy of the tracking mount at Geochang observatory by estimating mount parameters based on the least square method.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.2
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• pp.157-178
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• 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.

• Journal of the Korean Society of Safety
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• v.24 no.3
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• pp.71-78
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• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.1
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• pp.80-87
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• 2016

In this work, we conduct a thermal pointing error analysis of the observation satellites considering seasonal and daily temperature variation with interpolated temperature based on prescribed average temperature (PAT) method. Maximum 200 degree temperature excursion is applied to the observation satellites during on-orbit operation, which cause the line of sight (LOS) to deviate from the designated pointing direction due to thermo-elastic deformation. To predict and adjust such deviation, the thermo-elastic deformation analysis with a fine structural finite element model is accomplished with interpolated thermal maps calculated from the results of on-station thermal analysis with a coarse thermal model. After verifying the interpolated temperatures by PAT with two benchmark problems, we evaluate the thermal pointing error.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.75-87
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• 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.

• Publications of The Korean Astronomical Society
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• v.14 no.1
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• pp.47-56
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• 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.

• Journal of the Korea Institute of Military Science and Technology
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• v.1 no.1
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• pp.65-81
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• 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.