• Journal of Astronomy and Space Sciences
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• v.37 no.2
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• pp.105-115
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• 2020

The Korean Institute of Technology Satellite (KITSAT-1) is the first satellite developed by the Satellite Technology Research Center and the University of Surrey. KITSAT-1 is orbiting the Earth's orbit as space debris with a 1,320 km altitude after the planned mission. Due to its relatively small size and altitude, tracking the KITSAT-1 was a difficult task. In this research, we analyzed the tracking results of KITSAT-1 for one year using the Midland Space Radar (MSR) in Texas and the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska operated by LeoLabs, Inc. The tracking results were analyzed on a weekly basis for MSR and PFISR. The observation was conducted by using both stations at an average frequency of 10 times per week. The overall corrected range measurements for MSR and PFISR by LeoLabs were under 50 m and 25 m, respectively. The ionospheric delay, the dominant error source, was confirmed with the International Reference of Ionosphere-16 model and Global Navigation Satellite System data. The weekly basis orbit determination results were compared with two-line element data. The comparison results were used to confirm the orbital consistency of the estimated orbits.

• Journal of Astronomy and Space Sciences
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• v.35 no.1
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• pp.31-37
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• 2018

Pc1 pulsations are geomagnetic fluctuations in the frequency range of 0.2 to 5 Hz. There have been several observations of Pc1 pulsations in low earth orbit by MAGSAT, DE-2, Viking, Freja, CHAMP, and SWARM satellites. However, there has been a clear limitation in resolving the spatial and temporal variations of the pulsation by using a single-point observation by a single satellite. To overcome such limitations of previous observations, a new space mission was recently initiated, using the concept of multi-satellites, named the Small scale magNetospheric and Ionospheric Plasma Experiments (SNIPE). The SNIPE mission consists of four nanosatellites (~10 kg), which will be launched into a polar orbit at an altitude of 600 km (TBD) in 2020. Four satellites will be deployed in orbit, and the distances between each satellite will be controlled from 10 to 1,000 km by a high-end formation-flying algorithm. One of the possible science targets of the SNIPE mission is observing electromagnetic ion cyclotron (EMIC) waves. In this paper, we report on examples of observations, showing the limitations of previous EMIC observations in low earth orbit, and suggest possibilities to overcome those limitations through a new mission.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.45-46
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• 2006

Usual LEO satellite for earth observation use a blowdown hydrazine monopropellant propulsion system for attitude hold and orbit maintenance. For precision control, thruster valve has very short closing time, but this can cause water hammering and pressure surge. Since water hammering and pressure surge can cause damage of propulsion system and ununiform thrust, Thruster valve closing is one of the special concern during satellite propulsion system design. In this paper, an analysis for propellant feed system is conducted using the method of characteristics. The results represent water hammer effect is negligible even at the worst case and pressure surge can be decreased effectively with a trim orifice.

• Proceedings of the KSRS Conference
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• v.2
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• pp.791-793
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• 2006

In the satellite camera, the incoming light source is converted to electronic analog signals by the electronic component for example CCD (Charge Coupled Device) detectors. The analog signals are amplified, biased and converted into digital signals (pixel data stream) in the video processor (A/Ds). The outputs of the A/Ds are digitally multiplexed and driven out using differential line drivers (two pairs of wires) for cross strap requirement. The MSC (Multi-Spectral Camera) in the KOMPSAT-2 which is a LEO spacecraft will be used to generate observation imagery data in two main channels. The MSC is to obtain data for high-resolution images by converting incoming light from the earth into digital stream of pixel data. The video data outputs are then MUXd, converted to 8 bit bytes, serialized and transmitted to the NUC (Non-Uniformity Correction) module by the Hotlink data transmitter. In this paper, the video data streams, the video data format, and the image data processing routine for satellite camera are described in terms of satellite camera control hardware. The advanced satellite with very high resolution requires faster and more complex image data chain than this algorithm. So, the effective change of the used image data chain and the fast video data transmission method are discussed in this paper

• Korean Journal of Remote Sensing
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• v.37 no.1
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• pp.169-176
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• 2021

The Global Space-based Inter-Calibration System (GSICS) is an international partnership sponsored by World Meteorological Organization (WMO) to continue and improve climate monitoring and to ensure consistent accuracy between observation data from meteorological satellites operating around the world. The objective for GSICS is to inter-calibration from pairs of satellites observations, which includes direct comparison of collocated Geostationary Earth Orbit (GEO)-Low Earth Orbit (LEO) observations. One of the GSICS inter-calibration methods, the Ray-matching technique, is a surrogate approach that uses matched, co-angled and co-located pixels to transfer the calibration from a well calibrated satellite sensor to another sensor. In Korea, the first GEO satellite, Communication Ocean and Meteorological Satellite (COMS), is used to participate in the GSICS program. The National Meteorological Satellite Center (NMSC), which operated COMS/MI, calculated the Radiative Transfer Model (RTM)-based GSICS coefficient coefficients. The L1P reproduced through GSICS correction coefficient showed lower RMSE and Bias than L1B without GSICS correction coefficient applied. The calculation cycles of the GSICS correction coefficients for COMS/MI visible channel are provided annual and diurnal (2, 5, 10, 14-day), but long-term evaluation according to these cycles was not performed. The purpose of this paper is to perform evaluation depending on the annual/diurnal cycles of COMS/MI GSICS correction coefficients based on the ray-matching technique using Suomi-NPP/Visible Infrared Imaging Radiometer Suite (VIIRS) data as reference data. As a result of evaluation, the diurnal cycle had a higher coincidence rate with the reference data than the annual cycle, and the 14-day diurnal cycle was the most suitable for use as the GSICS correction coefficient.

• Publications of The Korean Astronomical Society
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• v.19 no.1
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• pp.129-133
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• 2004

In the past, radio astronomers have sought isolation from man-made signals by placing their telescopes in remote locations. These measures may no longer safeguard scientific observations, since NGSO satellite systems, particularly low-Earth orbit (LEO) systems, are usually designed to provide global or wide regional coverage. Further, radio astronomers have historically made their observations in the frequency bands allocated for their use by the member countries of the International Telecommunication Union (ITU). The science of radio astronomy could be adversely impacted by the deployment of large constellations of new non-geostationary orbiting (NGSO) satellites for telecommunications, navigation and Earth observation, and the proliferation of new, high-power broadcasting and telecommunication satellites in geostationary (GSO) orbits. Radio telescopes are extremely sensitive, and, in certain situations, signals from satellites can overwhelm the signals from astronomical sources. This paper describes the problem in detail and identifies ways to mitigate it without adversely affecting the continued vigorous growth of commercial space-based telecommunications.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.357-366
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• 2015

By using the Optical Wide-field Patrol (OWL) network developed by the Korea Astronomy and Space Science Institute (KASI) we generated the right ascension and declination angle data from optical observation of Low Earth Orbit (LEO) satellites. We performed an analysis to verify the optimum number of observations needed per arc for successful estimation of orbit. The currently functioning OWL observatories are located in Daejeon (South Korea), Songino (Mongolia), and Oukaïmeden (Morocco). The Daejeon Observatory is functioning as a test bed. In this study, the observed targets were Gravity Probe B, COSMOS 1455, COSMOS 1726, COSMOS 2428, SEASAT 1, ATV-5, and CryoSat-2 (all in LEO). These satellites were observed from the test bed and the Songino Observatory of the OWL network during 21 nights in 2014 and 2015. After we estimated the orbit from systematically selected sets of observation points (20, 50, 100, and 150) for each pass, we compared the difference between the orbit estimates for each case, and the Two Line Element set (TLE) from the Joint Space Operation Center (JSpOC). Then, we determined the average of the difference and selected the optimal observation points by comparing the average values.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.442-444
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• 2007

How to observe the atmosphere is a subject of atmospheric research. The meteorological satellites and the ground states are used to do observation. However, both ways do not satisfy the requirement of scientists, especially the profiles of atmosphere on the ocean and the data for global atmosphere. Radio occultation (RO) technique, which has been used in planet science, is a method to solve the problem. In RO technique, the low Earth orbit (LEO) satellite receives the two frequency signal of Global Positioning System (GPS) satellite. The excess phase of the signal is calculated to retrieve the profiles of atmosphere parameters. In moist troposphere, the fluctuations appear in the phase of the signal and open loop (OL) is used to resolve it. The quality of the GPS signal generally deteriorates as the altitude decreases. In the procedure, the SNR of the GPS signal is used as the criterion. However, the SNR decreases with fluctuation which makes it difficult to locate the data of poor quality. In this paper, the phase of the signal will be used as part of the criterion.

• Journal of Astronomy and Space Sciences
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• v.36 no.4
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• pp.249-264
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• 2019

In this study, the precise orbit determination (POD) software is developed for optical observation. To improve the performance of the estimation algorithm, a nonlinear batch filter, based on the unscented transform (UT) that overcomes the disadvantages of the least-squares (LS) batch filter, is utilized. The LS and UT batch filter algorithms are verified through numerical simulation analysis using artificial optical measurements. We use the real optical observation data of a low Earth orbit (LEO) satellite, Cryosat-2, observed from optical wide-field patrol network (OWL-Net), to verify the performance of the POD software developed. The effects of light travel time, annual aberration, and diurnal aberration are considered as error models to correct OWL-Net data. As a result of POD, measurement residual and estimated state vector of the LS batch filter converge to the local minimum when the initial orbit error is large or the initial covariance matrix is smaller than the initial error level. However, UT batch filter converges to the global minimum, irrespective of the initial orbit error and the initial covariance matrix.

• Journal of Environmental Science International
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• v.26 no.5
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• pp.573-584
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• 2017

In order to simulate a typhoon precisely, the satellite observation data has been assimilated using WRF (Weather Research and Forecasting model) three-Dimensional Variational (3DVAR) data assimilation system. The observation data used in 3DVAR was GPS Radio Occultation (GPS-RO) data which is loaded on Low-Earth Orbit (LEO) satellite. The refractivity of Earth is deduced by temperature, pressure, and water vapor. GPS-RO data can be obtained with this refractivity when the satellite passes the limb position with respect to its original orbit. In this paper, two typhoon cases were simulated to examine the characteristics of data assimilation. One had been occurred in the Western Pacific from 16 to 25 October, 2015, and the other had affected Korean Peninsula from 22 to 29 August, 2012. In the simulation results, the typhoon track between background (BGR) and assimilation (3DV) run were significantly different when the track appeared to be rapidly change. The surface wind speed showed large difference for the long forecasting time because the GPS-RO data contained much information in the upper level, and it took a time to impact on the surface wind. Along with the modified typhoon track, the differences in the horizontal distribution of accumulated rain rate was remarkable with the range of -600~500 mm. During 7 days, we estimated the characteristics between daily assimilated simulation (3DV) and initial time assimilation (3DV_7). Because 3DV_7 demonstrated the accurate track of typhoon and its meteorological variables, the differences in two experiments have found to be insignificant. Using observed rain rate data at 79 surface observatories, the statistical analysis has been carried on for the evaluation of quantitative improvement. Although all experiments showed underestimated rain amount because of low model resolution (27 km), the reduced Mean Bias and Root-Mean-Square Error were found to be 2.92 mm and 4.53 mm, respectively.