• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.181-187
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• 2012

In satellite communication system, propagation characteristics analysis of the receiving environment is very important, because radio quality is changed by the receiving environment. Unlike Terrestrial wireless communications, satellite communication is affected by altitude and atmospheric environment. Therefore, there are many factors to consider for propagation characteristics analysis. In this paper, signal reception environment of geostationary earth orbit was analyzed on urban environment. In order to analyze the propagation simulation, virtual buildings was established and reception environment was changed. The results of this paper would help to design the satellite mobile communication systems in Ka-band.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.19-25
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• 2012

GEO-KOMPSAT2 shall provide higher quality of image than the COMS and uses star tracker instead of earth sensor, which requires precise onboard orbit information. This requires precise on-ground orbit determination. For COMS, orbit determination is performed using the ranging data obtained from tracking system located in DAEJON. For accurate orbit determination of GEO-KOMPSAT2, KARI is building a secondary tracking station in CHUUK Islands. In this paper, the achievable accuracy of table based onboard orbit parameter generator which interpolates orbit data obtained from on-ground orbit determination using tracking data collected from two ground stations. Two types of approaches have been applied; covariance analysis and numerical analysis. By combining two analysis results, total orbit error has been estimated.

• Proceedings of the KSRS Conference
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• v.1
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• pp.278-281
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• 2006

Korea Meteorological Administration(KMA) has issued the tropical storm(typhoon) warning or advisories when it was developed to tropical storm from tropical depression and a typhoon is expected to influence the Korean peninsula and adjacent seas. Typhoon information includes current typhoon position and intensity. KMA has used the Dvorak Technique to analyze the center of typhoon and it's intensity by using available geostationary satellites' images such as GMS, GOES-9 and MTSAT-1R since 2001. The Dvorak technique is so subjective that the analysis results could be variable according to analysts. To reduce the subjective errors, QuikSCAT seawind data have been used with various analysis data including sea surface temperature from geostationary meteorological satellites, polar orbit satellites, and other observation data. On the other hand, there is an advantage of using the Subjective Dvorak Technique(SDT). SDT can get information about intensity and center of typhoon by using only infrared images of geostationary meteorology satellites. However, there has been a limitation to use the SDT on operational purpose because of lack of observation and information from polar orbit satellites such as SSM/I. Therefore, KMA has established Advanced Objective Dvorak Technique(AODT) system developed by UW/CIMSS(University of Wisconsin-Madison/Cooperative Institude for Meteorological Satellite Studies) to improve current typhoon analysis technique, and the performance has been tested since 2005. We have developed statistical relationships to correct AODT CI numbers according to the SDT CI numbers that have been presumed as truths of typhoons occurred in northwestern pacific ocean by using linear, nonlinear regressions, and neural network principal component analysis. In conclusion, the neural network nonlinear principal component analysis has fitted best to the SDT, and shown Root Mean Square Error(RMSE) 0.42 and coefficient of determination($R^2$) 0.91 by using MTSAT-1R satellite images of 2005. KMA has operated typhoon intensity analysis using SDT and AODT since 2006 and keep trying to correct CI numbers.

• Aerospace Engineering and Technology
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• v.10 no.2
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• pp.87-93
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• 2011

FSSA(Fine Sun Sensor Assembly) is the important sensor for satellite attitude control. FSSA measures the direction of the sun's rays and determines whether the satellite is in the eclipse or not. FSSA for GEO Satellite is also used to acquire the attitude error information in the attitude control reference frame and acquire the Sun direction during transfer orbit or mission Process. This paper shows the configuration of Fine Sun Sensor for LEO and GEO Satellite and their principle of operation that angle measurement is obtained by using the transfer function which is the ratio of the difference between output currents of Solar Cell to the sum of all output currents.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.27.3-28
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• 2008

In this study, we report a new Monte Carlo ray tracing technique for estimating GOCI (Geostationary Ocean Color Instrument) radiative transfer characteristics and imaging performance simultaneously. First, a full scale GOCI optical model was constructed with measured characteristics at the component level and placed in the geostationary orbit. An optical model of approximated GOCI target area centered at the Korean penninsular was then built using the USGS coastal line data and representative land and sea surface reflectivity data. The light rays launched from a simulated sun model travel to the Earth surface, where they are reflected and scattered. Some of the light rays that are headed to the GOCI model in the orbit were selected and traced, as they have entered into the GOCI aperture. As they pass through each GOCI optical part, the ray path and intensity are adjusted according to the measured characteristics for reflection, transmission, refractive index and surface scattering. The ray-traced imaging and radiative transfer performance indicators confirm that the computer generated GOCI optical system with measured characteristics can be used for in-orbit operation simulation following the designed measurement sequence. The computational technique and its implications as a operation support tool are discussed.

• ETRI Journal
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• v.22 no.4
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• pp.32-39
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• 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.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.308-319
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• 1994

We can launch satellites only at a certain time which satisfies special conditions, since the current techniques cannot overcome these constraints. Launch window constraints are the eclipse duration, solar aspect angle, attitude control, launch site and the launch vehicle constraints, etc. In this paper, launch window is calculated that satisfies all these constraints. In calculating launch window, the basic concepts are relative locations of the sun-satellite-earth system and relative velocities of these, and these requires geometric consideration for each satellite. Launch window calculation was applied to Kitsat 2(low earth orbit) and Koreasat(geostationary orbit). The result is shown in the form of a graph that has dates on the X-axis and the corresponding times of the given day on the Y-axis.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.11-18
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• 2020

Satellite optical communication has gained significant attention owing to its many quality features (e.g., a larger bandwidth, license free spectrum, higher data rate, and better security) compared to satellite microwave communication. Various experiments have been performed during many space missions to demonstrate and characterize inter-satellite links, downlinks, and uplinks. Korea has also planned to establish an experimental communication system using a geostationary earth orbit (GEO) satellite and the Geochang station as an optical ground station for low Earth orbit (LEO)-to-ground optical relay links. In this study, the performance of inter-satellite communication links and downlinks was investigated for the new Korean experimental communication system in terms of link margin, bit error rate (BER), and channel capacity. In particular, the performance of the inter-satellite links was analyzed based on the receiving apertures and the transmitting power, while that of the downlink was analyzed in terms of atmospheric turbulence conditions and transmitting power. Finally, we discussed two system parameters of receiving aperture and transmitting power to meet the three criteria of link margin, BER, and channel capacity.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.3
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• pp.119-127
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• 2019

COsmicheskaya Sisteyama Poiska Avariynich Sudov Search and Rescue Satellite-Aided Tracking (COSPAS-SARSAT) is an international communication support program to perform search and rescue (SAR) operations in emergency situations by using satellite signals relayed from a beacon. The legacy COSPAS-SARSAT was originally composed of low altitude and geostationary Earth orbit satellites; thus, a limited number of directional dish antennas was sufficient to cover the limited number of visible satellites at the local user terminal. However, the second generation COSPAS-SARSAT newly added the medium Earth orbit satellites, e.g., Global Navigation Satellite Systems (GNSS) to the existing system, so that the number of visible satellites increase dramatically, and the system upgrade to cover all the visible satellites is foreseen. The additional use of planned Korea Positioning System (KPS) to existing GNSS is envisaged to provide a better performance of their SAR service. This paper presents the benefits of the additional use of KPS together with the phased array antennas at the local user terminal of the COSPAS-SARSAT. This is to effectively response to the increase of the number of visible satellites. Numerical simulation is included to evaluate the performance improvement of COSPAS-SARSAT in terms of the number of visible satellites, geometry between satellites and user, and position estimation accuracy.

• Journal of Advanced Navigation Technology
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• v.22 no.6
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• pp.514-521
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• 2018

COSPAS-SARSAT 406 MHz emergency beacons include ELTs for aviation, EPIRBs for maritime, and PLBs for individuals in distress. They are used to sending messages encoded on 406 MHzdistress frequency and sending alertsfor search and rescue in distress. C/S T.001 and T.018 are COSPAS-SARSAT technical documents. They include basic technical information needed for developing beacons, howmessages are constructed, and test methods for type approval. COSPAS-SARSAT systems that use existing low earth orbit (LEO) and geostationary earth orbit (GEO) satellites do not have a return link service (RLS). So, the survivors could not confirm whether the distress signal was sending or not. However, a new medium earth orbit (MEO)satellite system has been added to thissystem, allowing confirmation through the RLS function. This paper analyzed C/S T.001 and T.018 needed to develop navigation structuresthat incorporated improved PLB of 406 MHz, a homing signal generator of 121.5 MHz, and a VHF AM transmitter for aviation of 243 MHz.