• KIEAE Journal
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• v.12 no.1
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• pp.113-118
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• 2012

The photovoltaic is one of the most important sustainable technologies appliable to architectures. The power performance mainly depends on the installation conditions of them. This study aims to evaluate the power performance of photovoltaic system by the installation conditions, the tracking methods and reflecting mirrors. For the study, the Solar Pro computer simulations have been conducted on installation angles, solar azimuth and solar altitude. Also, the field mock-up tests are performed to of its application to verify the simulation results. Both the results of the experiment and the simulation have proved that the efficiency of 90-degree fixed angle method was higher than that of 30-degree fixed angle, the efficiency of altitude tracking was better than that of azimuth tracking method, and changing both the altitude and the azimuth together is more efficient rather than the shortened tracing way. In addition, the light-concentrating method in which the incidence angle of the sun is controlled by an adhered reflector has been analyzed to have better efficiency than the general method of tracing according to the orbit of the sun. Therefore, this thesis is expected to offer the basic data to set a more effective tracing-type of photovoltaic power generation system in the future. For this, more researches are to be conducted hereafter on a high efficiency drive motor and the establishment of an economic system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1306-1312
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• 2000

The quality loss of a X-band transmitter has been derived by means of MC simulation. The transmitter as a payload of LEO(Low Earth Orbit) satellite is capable of the down transmission the image data of hundreds Mbps generated from the Electro-Optical Instrument in real time. The parameters such as data asymmetry amplitude unbalance,phase unbalance, wave shaping and channel interference are included in the quality loss simulation Assuming that normally distributed gaussian noise is simply added to the channel, the quality loss of 0.7 dB has been obtained through this simulation based on a 95% confidence interval. The obtained quality loss can be applied to the link budgets as an additional loss item.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.1
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• pp.40-50
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• 1994

Through the low orbit GPS satellite a 3-dimensional real time position detection can be achieved anywhere. Utilizing the GPS satellite detection values an analysis of the varing characteristics of the iono- sphere can be achicved, and by calculating the correlation relationship of the position detection error and the ionospheric time delay characteristics, an advanced algorithm technique can be developed. Computer simulation of the developed algorithm for defining the correlation between the position detec- tion error and the varing ionospheric time delay characteristics has been proceeded. The results of simulation reveal the fact that the varing characteristics of the ionosphere nearly match the actual ionospheric time delay characteristics.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.34.3-34.3
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• 2008

Relative navigation system is presented using measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide real-time relative navigation results as well as absolute navigation results for two formation flying satellites separated about 1km in low earth orbit. To improve the performance, more accurate dynamic model and modified relative measurement model are developed. This modified method prevents non-linearity of the measurement model from degrading precision by applying linearization about the states from absolute navigation algorithm not about a priori states. Furthermore, absolute states are obtained using ion-free GRAPHIC pseudo-ranges and precise relative states are provided using double differential carrier-phase data based on Extended Kalman Filter. The software-based simulation is performed and achieved meter-level precision for absolute navigation and millimeter-level precision for relative navigation. The absolute and relative accuracies at steady state are about 0.77m and 4mm respectively (3D, r.m.s.). In addition, Integer ambiguity algorithm (LAMBDA method) improves simulation performances.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.103-109
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• 2006

In this paper, VDS(Vehicle Dynamics Simulator) and ACS(Attitude Control Simulator) are developed and are verified using PILS(Process In-the Loop Simulation) between VDS and ACS. VDS is including the AOCS(Attitude & Orbit Control Subsystem) hardware modeling of geosynchronous satellite and consists of modulation concept. ACS performs the attitude determination using sensor data and generates the attitude control commands. In order to transfer the data between VDS and PCDU(Power Control & Distribution Unit), data acquisition boards were mounted. VDS performance is verified using HILS(Hardware In-the Loop Simulation) between VDS and PCDU.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.4
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• pp.351-359
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• 2014

This paper introduces the lithium ion battery system for LEO(Low Earth Orbit) small satellites. This study proves the reliability of lithium ion batteries applying to the space application. The specifications for lithium ion battery unit are proposed to supply power to the satellite and the overall mechanical design including structural simulation to confirm the reliability of the lithium ion BMS(Battery Management System) under the space environment and launching conditions. The results of structural simulation, functional tests, and space environmental tests show the lithium ion battery system is space qualified. Space qualification of the small satellite battery system to secure reliability of BMS and lithium ion batteries lend credibility for using lithium ion batteries in space application.

• Journal of Astronomy and Space Sciences
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• v.26 no.1
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• pp.59-74
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• 2009

Relative navigation system is presented using GPS measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide the real-time inter-satellite relative positions as well as absolute positions for two formation flying satellites in low earth orbit. To improve the navigation performance, the absolute states are estimated using ion-free GRAPHIC (group and phase ionospheric correction) pseudo-ranges and the relative states are determined using double differential carrier-phase data and singled-differential C/A code data based on the extended Kalman filter and the unscented Kalman filter. Furthermore, pseudo-relative dynamic model and modified relative measurement model are developed. This modified EKF method prevents non-linearity of the measurement model from degrading precision by applying linearization about absolute navigation solutions not about the priori estimates. The LAMBDA method also has been used to improve the relative navigation performance by fixing ambiguities to integers for precise relative navigation. The software-based simulation has been performed and the steady state accuracies of 1 m and 6 mm ($1{\sigma}$ of 3-dimensional difference errors) are achieved for the absolute and relative navigation using EKF for a short baseline leader/follower formation. In addition, the navigation performances are compared for the EKF and the UKF for 10 hours simulation, and relative position errors are mm-level for the two filters showing the similar trends.

• Journal of The Korean Astronomical Society
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• v.41 no.1
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• pp.7-15
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• 2008

We carried out a set of simulations to reproduce the performance of wide-field NEO surveys based on the revised population model of Near Earth Objects (NEOs) constructed by Morbidelli (2006). This is the first time where the new model is carefully compared with discovery statistics, and with the exception of population model, the simulation is identical to the procedure described in Moon et al. (2008). Our simulations show rather large discrepancy between the number of NEO discoveries made by the actual and the simulated surveys. First of all, unlike Bottke et al. (2002)'s, Morbidelli (2006)'s population model overestimates the number of NEOs. However, the latter reproduces orbit distributions of the actual population better. Our analysis suggests that both models significantly underestimate Amors, while overestimating the number of Apollos. Our simulation result implies that substantial modifications of both models are needed for more accurate reproduction of survey observations. We also identify Hungaria region (HU) to be one of the most convincing candidates that supply a large fraction of asteroids to the inner Solar System.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.140-150
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• 2003

In this paper, we propose a novel code sharing method for downlink transmission of mobile satellite communication systems using a multibeam geosynchronous-orbit satellite. In the proposed system, spreading codes are shared among downlink beams in order to increase the system capacity. We also propose efficient radio resource and transmit power allocation schemes for the proposed system. Simplified analysis and simulation results on the system capacity show the capacity improvement by the proposed scheme. The simulation results show that the capacity of the proposed system is more than 2 times as large as that of a conventional multibeam satellite system. In the frequency-selective fading channel, the capacity improvement increases as the interference between orthogonal spreading codes decrease.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1148-1156
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• 2009

ETRI has developed GNSS digitized IF signal generator for providing test and evaluation environment for various software level application and navigation algorithm in Global Navigation Satellite System(GNSS). GNSS digitized IF signal generator provides two main capabilities, GPS and Galileo raw data generation and digitized IF signal generation. GNSS digitized IF signal generator consists of five main modules which are GNSS Satellite Orbit Simulation Module, Navigation Message Generation Module, Error Generation Module, GNSS IF Signal Generation Module, and Message & Signal Steering Module. We verified the signal generated by the GNSS signal generation algorithm using software receiver for generation of signal brother to real GNSS signal.