• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.216-219
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• 2004

In this study, the concept and techniques to generate the level lA, lB and 2A image products have been reviewed. In particular, radiometric and geometric corrections and bands registration used to generate level lA, lB and 2A products have been focused in this study. Radiometric correction is performed to take into account radiometric gain and offset calculated by compensating the detector response non-uniformity. And, in order to compensate satellite altitude, attitude, skew effects, earth rotation and earth curvature, some geometric parameters for geometric corrections are computed and applied. Bands registration process using the matching function between a geometry, which is called 'reference geometry', and another one which is corresponds to the image to be registered is applied to images in case of multi-spectral imaging mode. In order to generate level-lA image products, a simple radiometric processing is applied to a level-0 image. Level-lB image has the same radiometry correction as a level-lA image, but is also issued from some geometric corrections in order to compensate skew effects, Earth rotation effects and spectral misregistration. Level-2A image is generated using some geo-referencing parameters computed by ephemeris data, orbit attitudes and sensor angles. Level lA image is tested by visual analysis. The difference between distances calculated level 1 B image and distances of real coordinate is tested. Level 2A image is tested Using checking points.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.512-514
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• 2004

The Electro-Optical Camera (EOC) is a high spatial resolution, visible imaging sensor which collects visible image data of the earth's sunlit surface and is the primary payload on KOMPSAT-l. The purpose of the EOC payload is to provide high resolution visible imagery data to support cartography of the Korean Peninsula. The EOC is a push broom-scanned sensor which incorporates a single nadir looking telescope. At the nominal altitude of 685Km with the spacecraft in a nadir pointing attitude, the EOC collects data with a ground sample distance of approximately 6.6 meters and a swath width of around 17Km. The EOC is designed to operate with a duty cycle of up to 2 minutes (contiguous) per orbit over the mission lifetime of 3 years with the functions of programmable gain/offset. The EOC has no pointing mechanism of its own. EOC pointing is accomplished by right and left rolling of the spacecraft, as needed. Under nominal operating conditions, the spacecraft can be rolled to an angle in the range from +/- 15 to 30 degrees to support the collection of stereo data. In this paper, the status of EOC such as temperature, dark calibration, cover operation and thermal control is checked and analyzed by continuously monitored state of health (SOH) data and image data during the mission life of 3 years. The aliveness of EOC and operation continuation beyond mission life is confirmed by the results of the analysis.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1867-1870
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• 2005

The celestial navigation is one of alternatives to GPS system and can be used as a backup of GPS. In the celestial navigation system using more than two star trackers, the vehicle's ground position can be solved based on the star trackers' attitude information if the vehicle's local vertical or horizontal angle is given. In order to determine accurate ground position of flight vehicle, the high accurate local vertical angle measurement is one of the most important factors for navigation performance. In this paper, the Earth geophysical deflection was analyzed in the assumption of using the modern electrolyte tilt sensor as a local vertical sensor for celestial navigation system. According to the tilt sensor principle, the sensor measures the tilt angle from gravity direction which depends on the Earth geoid surface at a given position. In order to determine the local vertical angle from tilt sensor measurement, the relationship between the direction of gravity and the direction of the Earth center should be analyzed. Using a precision orbit determination software which includes the JGM-3 Earth geoid model, the direction of the Earth center and the direction of gravity are extracted and analyzed. Appling vector inner product and cross product to the both extracted vectors, the magnitude and phase of deflection angle between the direction of gravity and the direction of the Earth center are achieved successfully. And the result shows that the angle differences vary as a function of latitude and altitude. The maximum 0.094$^{circ}$angle difference occurs at 45$^{circ}$latitude in case of 1000 Km altitude condition.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.1-6
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• 2013

A LEO satellite transmits recorded images to a ground station using an X-band antenna during contact. The X-band antenna points to the ground station according to a TPF (tracking parameter file) during communication time. A TPF generation software generates azimuth and elevation profile which make the antenna point to the ground station using satellite orbit and attitude information and mission information including recording and downlink operation. When the satellite passes above the ground station, azimuth velocity increases rapidly so that jitter may occur if the azimuth velocity is in specific range. In case of realtime mission in which the satellite perform recording and downlink simultaneously, azimuth velocity must be lower than specific value to prevent image blur due to jitter effect. The method to point one virtual ground station has limitation of azimuth velocity reduction. In this paper, we propose the azimuth fixing method to reduce azimuth velocity of X-band antenna. The experimental results show that azimuth velocity of the X-band antenna is remarkably reduced using proposed method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.228-239
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• 2016

CNUSAIL-1 is a 3U-sized cube satellite with $4m^2$ small solar sail which is currently being developed at the Chungnam National University. The primary purpose of the CNUSAIL-1 is successful sail deployment in LEO and its operation for investigating its effect on satellite orbit and attitude as well as performing de-orbiting using the sail membranes as drag sail at the final phase. The system design and mechanism of solar sail deployment is introduced, and optical and tensile tests are carried out for the material of membranes and booms for its safety and performance verification. The ground test is carried out to verify its performance for sail deployment and satellite through comparison between folding methods by determining its folding patterns, thickness of spiral spring and angular velocity measurement in a low-friction environment.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.359-365
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• 2008

This paper focused on generation of more accurate DEM and analysis of accuracy. For this, we applied suitable sensor modeling technique for each satellite image and automatic pyramid matching using image pyramid was applied. Matching algorithm based on epipolarity and scene geometry also was applied for stereo matching. IKONOS, Quickbird, SPOT-5, Kompsat-2 were used for experiments. In particular, we applied orbit-attitude sensor modeling technique for Kompsat-2 and performed DEM generation successfully. All DEM generated show good quality. Assessment was carried out using USGS DTED and we also compared between DEM generated in this research and DEM generated from common software. All DEM had $9m{\sim}12m$ Mean Absolute Error and $13m{\sim}16m$ RMS Error. Experimental results show that the DEMs of good performance which is similar to or better than result of DEMs generated from common software.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.9
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• pp.779-788
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• 2014

The satellite should generate electric power efficiently to perform the mission successfully within limited power. For this reason, the electrical power system of LEO satellites usually regulates the power which is generated from the solar cells using MPPT (Maximum Power Point Tracking) method. This paper proposes advanced MPPT algorithm based on the fuzzy logic applied to small CubeSat satellite. The simulation has been performed to confirm the validity of the proposed method by interlocking between MATLAB/Simulink and STK (Systems Tool Kit). The EBA(Energy Balance Analysis) has also been performed at two different pointing modes of KAUSAT-5 for solar irradiation according to the satellite orbit and attitude, and load capacity varied with operation modes by Simulink and STK. The performance of fuzzy logic-based MPPT algorithm was verified through the EBA. The validity of the proposed MPPT algorithm based on the fuzzy logic was also confirmed by comparing with P&O (Perturbation & Observation) algorithm that is general in the MPPT.

• Journal of Astronomy and Space Sciences
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• v.23 no.1
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• pp.29-38
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• 2006

This paper presents an Image Motion Compensation (IMC) algorithm for the Korea's Communication, Ocean, and Meteorological Satellite (COMS)-1. An IMC algorithm is a priority component of image registration in Image Navigation and Registration (INR) system to locate and register radiometric image data. Due to various perturbations, a satellite has orbit and attitude errors with respect to a reference motion. These errors cause depointing of the imager aiming direction, and in consequence cause image distortions. To correct the depointing of the imager aiming direction, a compensation algorithm is designed by adapting different equations from those used for the GOES satellites. The capability of the algorithm is compared with that of existing algorithm applied to the GOES's INR system. The algorithm developed in this paper improves pointing accuracy by 40%, and efficiently compensates the depointings of the imager aiming direction.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.97-101
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• 2012

The TC&R(Telemetry, Command & Ranging) antennas should have the hemispherical omni antenna patterns to make sure that the communication link between the satellite and the ground station can be established under whatever satellite attitude during after launch to on-orbit mission. The hemispherical omni-antennas are typically placed on the +z axis and -z axis of the satellite to provide the spherical omni patterns. The S-band qaudrifilar helix antennas having RHCP and LHCP hemispherical omni pattern are designed to meet the antenna gain and the axial ratio requirements. To investigate the omni-antenna pattern characteristics depending on four cases of antenna polarization combination placed on the +z axis and -z axis, the antenna pattern of each case is analyzed. Based on the result, after installing the designed RHCP and LHCP S-band omni-antennas on the +z axis and -z axis of the satellite, the combined antenna gain is obtained and finally analyzed in conjunction with the communication link influence.

• Korean Journal of Remote Sensing
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• v.25 no.4
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• pp.359-366
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• 2009

Research of accurate DEM generation using images of Kompsat-2 is not enough. This paper focused on generation of accurate Kompsat-2 DEM and comparison with DEM from common software like PCI Geomatica and ENVI. For Kompsat-2 DEM generation, we applied orbit-attitude sensor modeling technique and matching method based on epipolarity and image geometry. The comparison of performance with each commercial programs made a qualitative experiment through naked eyes and a quantitative experiment with USGS DTED. The accuracy was judged by the average absolute error and RMS error with DIED. The result of comparison experiment, we could confirm that the method used in the experiment showed much better performance than DEM made from other commercial programs in most of images.